Limestone - User contributions [en]

Model concepts

2023-06-12T11:58:38Z

Klmos:

{| class="side1"
!Highlights
|-
|
* Overview of model concepts for fractured limestone
|}

{| class="body1"
|
== Model concepts ==
Model concepts of different complexity can be used for the modeling of flow and transport in fractured porous media. Here is an overview of some major groups.
The model concepts are discussed for their applicability in the chapter [[Model output | '''Recommendations for modeling fractured limestone aquifers and comparison of model concepts''']].

[[File:EPM_square.png|x200px|Equivalent porous medium approach.|frameless|right|Equivalent porous medium approach.]]
=== Equivalent porous-medium model (EPM) ===

The equivalent porous medium model is a standard model concept for porous media with parameters averaged over control volumes (e.g. hydraulic conductivity, porosity).
Usually, a flow model and a transport model are solved.
The flow field can be computed based on Darcy's law.
The contaminant transport is described by the advection-dispersion equation, where different processes like sorption and degradation can be included.

Due to its simplicity and its low computational effort, the EPM model is widely used, also for fractured geologies.
Fractures, however, are not explicitly modeled.
Instead, bulk hydraulic conductivities and effective diffusion or dispersion coefficients are used.
This has as consequence that flow and transport in fractures and the exchange with the matrix cannot be correctly reproduced, leading to poor predictions for transport in dual-continuum aquifers.
<br clear=all>

[[File:DualContinuumSchematics.png|x180px|Dual continuum approach.|frameless|right|Dual continuum modeling approach.]]
=== Dual-continuum model ===
The dual-continuum model, often also called dual-porosity model, uses two continua, the matrix and the fracture continuum.
Balance equations for flow and transport are formulated for each continuum, and the two continua have the same dimensionality (e.g. 3D fracture continuum and 3D matrix continuum).
The continua are coupled via exchange fluxes using the source and sink terms in the balance equations, allowing for exchange of water and substances between fractures and matrix.
For that purpose, exchange coefficients have to be specified, which determine the exchange fluxes between fracture and matrix continuum.
The exchange coefficients are usually used as fitting parameters.
The basic concept is described in Gerke and Van Genuchten (1993) <ref>Gerke and Van Genuchten (1993). ''A Dual-Porosity Model for Simulating the Preferential Movement of Water and Solutes in Structured Porous Media'', Water Resources Research, 29, 305-319.</ref>.
Different parameters are used in the two continua, f.e. porosities and conductivities specific for the fractures and for the matrix.
Concepts with more than two coupled continua have also been developed, f.e. the Multiple INteracting Continua approach (MINC).
<br clear=all>

[[File:DFM.png|Discrete-fracture approach.|x180px|frameless|right|Discrete-fracture approach.]]
=== Discrete-fracture model (DFM) ===
The discrete-fracture model (DFM) is the most detailed approach for fracture flow and transport modeling.
The (major) fractures are explicitly discretized and embedded in the porous matrix.
Fractures and matrix are coupled at the fracture-matrix interface by flux continuity and continuity of the primary variables (hydraulic head, concentration).
This is the most physically-based approach and the exchange fluxes between fractures and matrix are calculated by the model.
However, the numerical efforts are also highest for this model, especially for complex fracture networks with many fractures.
For good simulation results, a very fine grid resolution at the fracture-matrix interface is essential, particularly when the contrast between fracture and matrix conductivity is strong.

Usually, the fractures are resolved with one dimension less than the matrix (e.g. matrix is a 3D volume while the fractures are 2D planes).
The geometric properties of the fractures have to be specified by properties like aperture, length, spacing and main orientation.
The cubic law (based on the parallel-plate model) is often used to determine the fracture hydraulic conductivity based on the hydraulic aperture.
In combination with Darcy's law and the hydraulic gradient, it is used to compute the flux and the velocity in fractures.
The cubic law scales the fracture flux with the aperture cubed, hence large-aperture fractures contribute significantly stronger to the total flux than fractures with smaller apertures.

[[File:Plume DFM 8yrs highKcontrast-50ug.png|x200px|none|thumb|Example of a transport simulation with a DFM showing PCE concentrations.]]



=== Random-walk methods ===
Continuous-time random walk methods (CTRW).

{{Return}}
|}
[[Category:Modeling]]

Content

2023-06-12T11:50:40Z

Klmos:

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Sustain and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Contributors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf] (main author), [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://sustain.dtu.dk/ DTU Sustain] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ Example: Akacievej |(example: Akacievej, Hedehusene)]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Content

2021-01-18T13:52:04Z

Klmos:

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Contributors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf] (main author), [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ Example: Akacievej |(example: Akacievej, Hedehusene)]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Content

2021-01-18T13:14:29Z

Klmos:

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Contributors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf (main author)], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ Example: Akacievej |(example: Akacievej, Hedehusene)]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Example: Akacievej

2019-07-05T09:57:39Z

Klmos: /* Example: Setup and application of models for a field site (Akacievej, Hedehusene) */

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.1: Coupled 3D source-zone model and 2D plume-scale model.]]
Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of new field tests and in the update of the conceptual model of the contaminated site, starting from a simple model and adding complexity, when new field data was available.

The field data included information on spill history, hydraulic head data, well data (location, screen depth etc.), distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores were combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test was conducted at the site to determine flow and transport parameters of the fractures and matrix and depth-specific contaminant sampling allowed to characterize the contaminant distribution in the aquifer.
For the planning and interpretation of the pumping and tracer test models of different complexity were applied.
This is described in detail in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

In 2018, the the hydraulic heads were again measured in the plume area, which showed that the flow conditions were fairly constant since the hydraulic head leveling campaign in spring 2015.
The picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
To reduce the numerical effort and to simulate the plume propagation on a larger scale, a 3D source-zone model coupled to a 2D plume-scale model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE in the monitoring wells at the Akacievej site.
The source-zone model was calibrated to the long-term pumping and tracer test and then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model (Figure 1).

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

[[File:mapcoupled2D-3Dmodel.png|500px|thumb|Fig.2: Map of the coupled 3D source-zone model and 2D plume-scale model.]]

Since the depth-discrete contaminant sampling showed that a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), the crushed limestone was included in the model setup as a separate layer with different properties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone, and no distinct horizontal fractures as in the fractured limestone could be identified.
Detailed investigations of the properties were very difficult for the crushed limestone, because due to its crushed state it is very unstable and core material was mostly lost.
The characterization of the hydraulic properties was based on slug tests in wells that have a screen mostly in the crushed limestone and by evaluating the drawdown caused by the remediation pump installed at the Akacievej, which is also mostly located in the crushed limestone.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.

Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive (immobile) areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a uniform conductivity was used.
To still account for the contaminant mass exchange with the immobile areas, the sorption coefficient was increased.
This is further explained in the report linked above.



{{Return}}
[[Category:Modeling]]

Example: Akacievej

2019-07-04T16:05:26Z

Klmos: /* Example: Setup and application of models for a field site (Akacievej, Hedehusene) */

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.1: Coupled 3D source-zone model and 2D plume-scale model.]]
Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of new field tests and in the update of the conceptual model of the contaminated site, starting from a simple model and adding complexity, when new field data was available.

The field data included information on spill history, well data (location, screen depth etc.), distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores were combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test was conducted at the site to determine flow and transport parameters of the fractures and matrix and depth-specific contaminant sampling allowed to characterize the contaminant distribution in the aquifer.
For the planning and interpretation of the pumping and tracer test models of different complexity were applied.
This is described in detail in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

In 2018, the the hydraulic heads were measured in the plume area, which showed that the flow conditions were fairly constant.
The picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
To reduce the numerical effort and to simulate the plume propagation on a larger scale, a 3D source-zone model coupled to a 2D plume-scale model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE in the monitoring wells at the Akacievej site.
The source-zone model was calibrated to the long-term pumping and tracer test and then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model (Figure 1).

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

[[File:mapcoupled2D-3Dmodel.png|500px|thumb|Fig.2: Map of the coupled 3D source-zone model and 2D plume-scale model.]]

Since the depth-discrete contaminant sampling showed that a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), the crushed limestone was included in the model setup as a separate layer with different proporties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone, and no distinct horizontal fractures as in the fractured limestone could be identified.
Detailed investigations of the properties were very difficult for the crushed limestone, because due to its crushed state it is very unstable and core material was mostly lost.
The characterization of the hydraulic properties was based on slug tests in wells that have a screen mostly in the crushed limestone and by evaluating the drawedown caused by the remediation pump installed at the Akacievej, which is also mostly located in the crushed limestone.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.

Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a unifrom conductivity was used.
To still account for the immobile areas with storage of contaminant, the sorption coefficient was modified.



{{Return}}
[[Category:Modeling]]

Content

2019-07-04T08:52:02Z

Klmos: /* Modeling contaminant transport in limestone */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ Example: Akacievej |(example: Akacievej, Hedehusene)]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Conceptual modeling

2019-07-04T08:50:54Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the [[The Akacievej field site|Akacievej field site]] based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report and in [[ Example: Akacievej | this chapter ]].
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Example: Akacievej

2019-07-04T08:38:49Z

Klmos:

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.1: Coupled 3D source-zone model and 2D plume-scale model.]]
Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of new field tests and in the update of the conceptual model of the contaminated site, starting from a simple model and adding complexity, when new field data was available.

The field data included information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores were combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test was conducted at the site to determine flow and transport parameters of the fractures and matrix and depth-specific contaminant sampling allowed to characterize the contaminant distribution in the aquifer.
For the planning and interpretation of the pumping and tracer test models of different complexity were applied.
This is described in detail in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

In 2018, the the hydraulic heads were measured in the plume area, which showed that the flow conditions were fairly constant.
The picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
To reduce the numerical effort and to simulate the plume propagation on a larger scale, a 3D source-zone model coupled to a 2D plume-scale model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE in the monitoring wells at the Akacievej site.
The source-zone model was calibrated to the long-term pumping and tracer test and then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model (Figure 1).

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

[[File:mapcoupled2D-3Dmodel.png|500px|thumb|Fig.2: Map of the coupled 3D source-zone model and 2D plume-scale model.]]

Since the depth-discrete contaminant sampling showed that a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), the crushed limestone was included in the model setup as a separate layer with different proporties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone, and no distinct horizontal fractures as in the fractured limestone could be identified.
Detailed investigations of the properties were very difficult for the crushed limestone, because due to its crushed state it is very unstable and core material was mostly lost.
The characterization of the hydraulic properties was based on slug tests in wells that have a screen mostly in the crushed limestone and by evaluating the drawedown caused by the remediation pump installed at the Akacievej, which is also mostly located in the crushed limestone.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.

Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a unifrom conductivity was used.
To still account for the immobile areas with storage of contaminant, the sorption coefficient was modified.



{{Return}}
[[Category:Modeling]]

File:Mapcoupled2D-3Dmodel.png

2019-07-04T08:26:17Z

Klmos: Overview map showing the extend of the 3D model domain (blue) and the 2D cross section model.

Overview map showing the extend of the 3D model domain (blue) and the 2D cross section model.

Example: Akacievej

2019-07-04T08:25:02Z

Klmos:

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model of the contaminated site, starting with a simple model and adding complexity, when new field data was available.

The field data included information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores were combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test was conducted at the site to determine flow and transport parameters of the fractures and matrix and depth-specific contaminant sampling allowed to characterize the contaminant distribution in the aquifer.
For the planning and interpretation of the pumping and tracer test models of different complexity were applied.
This is described in detail in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.1: Coupled 3D source-zone model and 2D plume-scale model.]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a 3D source-zone model coupled to a 2D plume-scale model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE in the monitoring wells at the Akacievej site.
The source-zone model was calibrated to the long-term pumping and tracer test and then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model (Figure 1).

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

Since a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), it was included in the model setup.
The crushed limestone has different hydraulic properties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone.
No distinct horizontal fractures as in the fractured limestone could be identified.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.
Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a unifrom conductivity was used.
To still account for the immobile areas with storage of contaminant, the sorption coefficient was modified.

[[File:mapcoupled2D-3Dmodel.png|500px|thumb|Fig.2: Map of the coupled 3D source-zone model and 2D plume-scale model.]]



{{Return}}
[[Category:Modeling]]

Content

2019-07-04T08:23:31Z

Klmos: /* Modeling contaminant transport in limestone */ Added link to Example: Akacievej

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ Example: Akacievej |(example: Akacievej, Hedehusene) ]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Conceptual modeling

2019-07-04T08:22:36Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the [[The Akacievej field site|Akacievej field site]] based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Content

2019-07-04T08:22:06Z

Klmos: /* Modeling contaminant transport in limestone */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] [[ The Akacievej field site |(example: Akacievej, Hedehusene) ]]<br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

File:Coupled2D-3Dmodel.png

2019-07-04T08:20:43Z

Klmos: Klmos uploaded a new version of File:Coupled2D-3Dmodel.png

Detailed 3D modeling of the source zone coupled to a 2D cross section model of the plume.

File:Coupled2D-3Dmodel.png

2019-07-04T08:19:50Z

Klmos: Klmos uploaded a new version of File:Coupled2D-3Dmodel.png

Detailed 3D modeling of the source zone coupled to a 2D cross section model of the plume.

Example: Akacievej

2019-07-04T08:07:13Z

Klmos: /* Example: Setup and application of models for a field site (Akacievej, Hedehusene) */

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model of the contaminated site, starting with a simple model and adding complexity, when new field data was available.

The field data included information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores were combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test was conducted at the site to determine flow and transport parameters of the fractures and matrix and depth-specific contaminant sampling allowed to characterize the contaminant distribution in the aquifer.
For the planning and interpretation of the pumping and tracer test models of different complexity were applied.
This is described in detail in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a 3D source-zone model coupled to a 2D plume-scale model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE in the monitoring wells at the Akacievej site.
The source-zone model was calibrated to the long-term pumping and tracer test and then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model (Figure 1).

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.1: Coupled 3D source-zone model and 2D plume-scale model.]]

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

Since a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), it was included in the model setup.
The crushed limestone has different hydraulic properties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone.
No distinct horizontal fractures as in the fractured limestone could be identified.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.
Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a unifrom conductivity was used.
To still account for the immobile areas with storage of contaminant, the sorption coefficient was modified.



{{Return}}
[[Category:Modeling]]

Example: Akacievej

2019-07-03T15:26:19Z

Klmos: Added sorption and crushed limestone

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

Several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model of the contaminated site, starting with a simple model and adding complexity, when new field data was available.

The field data included information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores was combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test with depth-specific contaminant sampling was conducted at the site to determine flow and transport parameters of the fractures and matrix and to quantify the contaminant distribution in the aquifer.
Different models were used for the planning and interpretation of the pumping and tracer test.
This is described in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a coupled 2D plume-scale and 3D source-zone model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE.
The source-zone model is then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model.

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system]]

Since a great part of the PCE contamination is located in the crushed limestone (upper 3-5 m), it was included in the model setup.
The crushed limestone has different hydraulic properties as the fractured limestone.
The bulk hydraulic conductivity was slightly lower than in the fractured limestone.
No distinct horizontal fractures as in the fractured limestone could be identified.
Most likely, the fractured limestone contains many more small fractures, small cavities and some larger intact limestone chunks.
Then, most of the advective transport happens in the conductive areas with a diffusive exchange with lower conductive areas.
This could be described by a dual-porosity model.
However, there was only limited knowledge of the hydraulic properties in the high- and low-conductive areas and the exchange between them.
Instead, a homogeneous unit with a unifrom conductivity was used.
To still account for the immobile areas with storage of contaminant, the sorption coefficient was modified.



{{Return}}
[[Category:Modeling]]

Example: Akacievej

2019-07-03T15:00:00Z

Klmos:

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

First, several models were compared for the [[The Akacievej field site|'''Akacievej site''']], where a plume of dissolved PCE had spread in a fractured limestone aquifer and where a remediation system was in the process of re-evaluation.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model of the contaminated site.
Field data includes information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores was combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test with depth-specific contaminant sampling was conducted at the site to determine flow and transport parameters of the fractures and matrix and to quantify the contaminant distribution in the aquifer.
Different models were used for the planning and interpretation of the pumping and tracer test.
This is described in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a coupled 2D plume-scale and 3D source-zone model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE.
The source-zone model is then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model.

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of ther remediation system]]



{{Return}}
[[Category:Modeling]]

Data acquisition

2019-07-03T14:58:05Z

Klmos: /* Fracture characterization */

{| class="side1"
!Highlights
|-
|
* Methods to describe geology and hydrogeology
* Aquifer tests to obtain parameters
* Fracture characterization
|}

{| class="body1"
|
== Geology and hydrogeology ==

[[File:BoreholeCores.png|thumb|200px|Fig. 1: Borehole cores from the Akacievej site.]]
Knowledge about geology and hydrogeology of a contaminated site is usually limited and not easily obtainable.
This page gives a description of some useful methods to determine relevant aquifer parameters and to characterize the fracture system.
Information about the geology and hydrogeology at a site is primarily obtained from locations that provide access to the subsurface, such as outcrops, excavations and boreholes, and from geophysical measurements.
The Danish national well database ([http://www.geus.dk/UK/data-maps/jupiter/Pages/default.aspx Jupiter]) contains very useful borehole information, such as the location of boreholes, the geology in the boreholes, groundwater analyses, and information about water supply wells.
This can be combined with information from geologic maps and interpretations, as, for example, provided by the [http://www.geus.dk Geological Survey of Denmark and Greenland].

=== Borehole cores and borehole tests ===
[[File:Geo4-17.jpg|thumb|200px|Fig. 2: Borehole core with substantial core loss.]]
A common method to obtain knowledge about the local geology is to drill boreholes, collect borehole cores (Figure 1) and perform (geophysical) borehole tests.
However, one has to bear in mind that cores only represent the geology at the location of the borehole and that the geology can have a strong spatial variability.
The information obtained from cores from different boreholes can be spatially interpreted and combined with geologic knowledge from maps to build up a geologic model.

Collected borehole cores can be analyzed (e.g. determination of porosity and hydraulic conductivity) and the depth-discrete stratigraphy at the location of the borehole can be determined.
With a microfossil analysis, the age and the type of limestone can be further characterized.
However, in limestone geologies with flint layers and a strongly varying hardness with depth, core losses may be significant (Figure 2), and thereby alternative borehole and aquifer tests needed to characterize these areas.

At the Akacievej site, several borehole cores were extracted, and microfossil analyses were conducted to determine the limestone type.
The limestone had a strongly varying hardness.
Thus, losses of especially the crushed material were considerable, despite the use of wireline drilling, which is a good coring method in limestone as the geology is only little disturbed by the drilling.
Especially when drilling through flint inclusions, substantial core losses were observed (Figure 2), because the cooling water flushed out soft material.
The boreholes, where no cores were extracted, were drilled with different methods: dry drilling (tørboring), symmetrix and DTH drilling.

The borehole tests at the Akacievej site included:
* induction probes (electrical conductivity measurement)
* caliper probes (minimal local borehole diameter)
* porosity probes (gamma-gamma probes for relative porosity)
* density probes
* temperature probes
* fluid resistivity probes
* impeller flow logs

== Aquifer tests ==

=== Pumping tests ===
Pumping tests are very useful to characterize the local hydrogeology at a contaminated site.
Usually, a well is pumped and the drawdown behavior (hydraulic head changes) in the pumping well and (if available) in neighboring observation wells are measured.
This can be done with manual head measurements, if the hydraulic head changes happen relatively slow.
Fractured aquifers, however, often exhibit a high hydraulic conductivity and the drawdown happens quickly, which makes it difficult to manually measure the drawdown caused by the pumping.
In this case, the head changes can be monitored with programmable pressure transducers (divers), which measure the hydraulic heads at a high measurement frequency.
Two measurements per seconds or even more are recommended for fracture-flow dominated aquifers or aquifers with a high hydraulic conductivity.

The drawdown curves can be interpreted with a suitable tool (e.g. [http://www.aqtesolv.com/ Aqtesolv]), which allows the determination of aquifer parameters like the hydraulic conductivity.
In fractured aquifers, long-term pumping tests with a high pumping rate can potentially reveal information about the hydraulic conditions in both fractures and matrix.
Drawdown curves from long-term pumping tests in fractured limestone aquifers exhibit different stages - first, pumped water is mainly withdrawn from the fractures, followed by a stage with fracture-matrix interflow, and in the last stage, the water is mainly abstracted from the matrix.
At the Akacievej site, the full drawdown had developed within a time period of about 10 days.
For the interpretation of such drawdown curves, specialized dual-continuum solution schemes (e.g. the dual-porosity solution presented in Moench, 1984 <ref>Moench, A.F. (1984), ''Double-porosity models for a fissured groundwater aquifer with fractures skin'', Water resources research, Vol.20, 831-846.</ref> or Barker, 1988 <ref>Barker, J.A. (1988), ''A generalized radial flow model for hydraulic tests in fractured rock'', Water resources research, Vol.24, 1796-1804.</ref>) can be employed.

However, it has to be kept in mind that the obtained values only describe the area affected by the pumping test and an extrapolation has to be done with care, especially if the aquifer is very heterogeneous.
A higher pumping rate can potentially enlarge the affected area.
Further, in screened wells, the (vertical) location of the screen is important, since water is mainly pumped from the part of the aquifer at the depth of the screen (or in case of an open borehole, of the open section of the borehole).
Packers can be installed to separate sections of the aquifer and to determine hydraulic conductivities (or transmissivities) for these sections.

[[File:PumpTracerTest-images.png|thumb|center|800px| Fig.3: Photos from the pumping test and the tracer tests at Akacievej (spring 2016). From left to right: Pumping well, preparation of tracer injection system, mixing of fluorescein into 1000 L tanks with groundwater, tracer sampling on sampling carousel.]]

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf|Pumping and tracer test in a limestone aquifer and model interpretation (PDF)]]

=== Slug tests ===
[[File:SlugTest.jpg|thumb|Fig. 4: Example of a vacuum slug test at the Akacievej site.]]
Slug tests are relatively cheap and easy single-borehole aquifer tests, where the water table in a borehole is abruptly changed, for example, by releasing a slug of water into the borehole while monitoring the pressure response, when the water table changes back to its original state again.
They can be used to obtain approximate values of the hydraulic conductivities at the location of a borehole.
Therefore, the hydraulic head has to be measured with a high frequency.
In low conductivity aquifers, this can be done with manual measurements using common dip-meters.
In highly conductive aquifers, the water table responds quickly, and automated measurements with pressure transducers should be chosen.
These pressure transducers should be set to a sufficiently small time interval (ideally several measurements per second).

There are different types of slug tests.
A main distinction can be made between rising-head slug tests and falling-head slug tests.

* '''Rising-head slug test'''
To perform a rising-head slug test, water is removed from the borehole and the recovery of the hydraulic head in the borehole is recorded.
This can be a good choice for aquifers with moderate flow velocities but can be problematic for highly conductive aquifers.

* '''Falling-head slug test'''
For a falling-head slug test, the water level in the borehole is abruptly increased.
This can be done on different ways.
A slug of water can be added into the borehole and the head change monitored.
For aquifers with a high hydraulic conductivity, a different method is recommended:
A vacuum is applied on the borehole to pull the water table up at the borehole (Figure 4).
The raised water table is then released and the equilibration of the water table measured with pressure transducers with a short measurement interval (several measurements per second).
This method was particularly useful for slug tests in the highly conductive fractured limestone at the Akacievej site.

The interpretation of slug tests with standard aquifer test software like [http://www.aqtesolv.com/ Aqtesolv] allows for obtaining information about the local hydraulic conductivity.
For fractured aquifers, a solution scheme that is accounting for the fractures and the dual-porosity aquifers like the Barker-Black (1983) solution can be chosen.
In very conductive aquifers, an oscillating water table caused by inertia can occur when the slug is released.
There are specialized solution schemes (f.e. the solution by Springer and Gelhar (1991)<ref>Springer, R. and Gelhar, L. (1991), ''Characterization of large-scale aquifer heterogeneity in glacial outwash by analysis of slug tests with oscillatory response'', Report, U.S. Geological Survey.</ref>), which can be applied then.

Note that slug tests are very local measurements, because they usually affect only a small volume around a borehole and an extrapolation of the determined parameters should be done with care.
Furthermore, the slug test results can be influenced by the borehole filling (gravel or sand pack around the well screens).
If several boreholes are close by or if there are boreholes with several well screens at different depth, slug tests can yield information about the local variability of the hydraulic conductivity.
Slug tests at different depths can yield hydraulic parameters for different geologic units.

=== Additional information from water works data and remediation systems ===
Waterworks can provide a cheap and simple way for getting additional pumping test data.
Waterworks are operating one or several wells, where often automated loggers are installed, which monitor the hydraulic heads in the pumped wells.
When the pumps are switched on and off, drawdown and recovery curves can be obtained, which can be analyzed with standard aquifer test software (e.g. Aqtesolv) like usual pumping tests.
To obtain data useful for interpretation, a high measurement frequency should be set for the hydraulic head logging in the wells, particularly for aquifers with a high hydraulic conductivity.
For highly conductive aquifers like the one at Akacievej, a good choice of the measurement interval is 1 second or less.

The Fløng waterworks close to the Akacievej site operates an alternating pumping scheme in four drinking water wells, where the individual wells are automatically switched on and off according to the water demand.
This creates a sequence of pumping-test like events, which were evaluated to obtain the hydraulic conductivity at the wells of the water works.
Note that the wells used by the water works have often long screens, and that the measurements represent average values over the screen length or borehole length (in case of an open borehole).

Furthermore, head measurements from a remediation system can be interpreted to obtain hydraulic parameters at the location of the remediation system.
At the Akacievej site, the remediation system was turned on and off several times, and the hydraulic heads in the remediation well and in observation wells next to it were measured.
This information was used to calibrate a flow model to the observed drawdown and to get more information about the crushed limestone, where most of the screen of the remediation well is located in.

== Fracture characterization ==
[[File:OTVexample.jpg|thumb|600px|Fig. 5: Example of an optical televiewer measurement in Geo18 showing a fracture (dark) at 35.5 m bgs. This is also reflected on the caliper log (left) and the flow log (right). Courtesy of Geo.]]
In fractured limestone aquifers, the fractures are the primary travel pathways for substances, and their characterization is important for risk assessment and remedial planning.
Information about the fracture geometry and location is, however, generally scarce and the determination of appropriate parameters may be challenging.
Fractures are generally described by their aperture, spacing, distribution, length, height and their main orientation.
The flow and transport in fractures is furthermore controlled by the fracture connectivity.

The following measurements are useful to determine fracture parameters:
* slug tests and pumping tests to obtain hydraulic conductivity and storativity values
* flow logs in boreholes to identify high-flow zones
* temperature logs in boreholes and induced temperature gradients to identify high flow zones
* tracer tests to obtain information about solute transport in parts of the aquifer
* fracture mapping at analogue sites like outcrops and excavations
* borehole cores
* geophysical measurements
* open-borehole methods like flexible liners ([http://www.flut.com/ FLUTe]) or televiewers

[[File:FlowLogs Fractures.png|thumb|500px|Fig. 6: Flow logs in boreholes to identify horizontal fractures and high-flow zones. The green lines indicate high-flow zones.]]
Flow logs in boreholes can be very useful to identify highly conductive zones (Figure 6).
Therefore, a propeller probe is lowered in the borehole and the speed of the propeller rotation is recorded while pumping the borehole.
The propeller probe is slowly moved up- or downwards.
High-flow zones will lead to a change of the propeller rotation speed and high-flow zones can be identified from the logs.
For this method, even borehole walls are beneficial.
Holes or gaps in the borehole walls can lead to disturbances in the flow logs due to local turbulences and backflow of water.
When the propeller probe is used without pumping, some information about vertical flows in the boreholes can be obtained.

When open boreholes (without well screen) are available, [http://www.flut.com/ FLUTe] liners can be used to identify high-flow zones.
Moreover, optical and acoustical televiewers can be used to take images of the borehole walls.
With vertical boreholes, mainly horizontal fractures and flint layers can be identified by this method.
For the determination of vertical fractures, diagonal boreholes can be beneficial, because they increases the likelihood that vertical fractures intersect with the borehole.
A sample image from a vertical borehole at the Akacievej site (Geo18d) is shown in Figure 5.
The dark area at a depth of 35.4 m below ground surface is a significant horizontal fracture.
This is reflected in the flow log in the right part of Figure 5.
At the same depth as the dark area, a strong change in the flow log can be observed.
This is an indication for a high-flow zone.

{{Return}}
|}
[[Category:Field methods]] [[Category:Geology]]

Data acquisition

2019-07-03T14:54:26Z

Klmos: /* Pumping tests */

{| class="side1"
!Highlights
|-
|
* Methods to describe geology and hydrogeology
* Aquifer tests to obtain parameters
* Fracture characterization
|}

{| class="body1"
|
== Geology and hydrogeology ==

[[File:BoreholeCores.png|thumb|200px|Fig. 1: Borehole cores from the Akacievej site.]]
Knowledge about geology and hydrogeology of a contaminated site is usually limited and not easily obtainable.
This page gives a description of some useful methods to determine relevant aquifer parameters and to characterize the fracture system.
Information about the geology and hydrogeology at a site is primarily obtained from locations that provide access to the subsurface, such as outcrops, excavations and boreholes, and from geophysical measurements.
The Danish national well database ([http://www.geus.dk/UK/data-maps/jupiter/Pages/default.aspx Jupiter]) contains very useful borehole information, such as the location of boreholes, the geology in the boreholes, groundwater analyses, and information about water supply wells.
This can be combined with information from geologic maps and interpretations, as, for example, provided by the [http://www.geus.dk Geological Survey of Denmark and Greenland].

=== Borehole cores and borehole tests ===
[[File:Geo4-17.jpg|thumb|200px|Fig. 2: Borehole core with substantial core loss.]]
A common method to obtain knowledge about the local geology is to drill boreholes, collect borehole cores (Figure 1) and perform (geophysical) borehole tests.
However, one has to bear in mind that cores only represent the geology at the location of the borehole and that the geology can have a strong spatial variability.
The information obtained from cores from different boreholes can be spatially interpreted and combined with geologic knowledge from maps to build up a geologic model.

Collected borehole cores can be analyzed (e.g. determination of porosity and hydraulic conductivity) and the depth-discrete stratigraphy at the location of the borehole can be determined.
With a microfossil analysis, the age and the type of limestone can be further characterized.
However, in limestone geologies with flint layers and a strongly varying hardness with depth, core losses may be significant (Figure 2), and thereby alternative borehole and aquifer tests needed to characterize these areas.

At the Akacievej site, several borehole cores were extracted, and microfossil analyses were conducted to determine the limestone type.
The limestone had a strongly varying hardness.
Thus, losses of especially the crushed material were considerable, despite the use of wireline drilling, which is a good coring method in limestone as the geology is only little disturbed by the drilling.
Especially when drilling through flint inclusions, substantial core losses were observed (Figure 2), because the cooling water flushed out soft material.
The boreholes, where no cores were extracted, were drilled with different methods: dry drilling (tørboring), symmetrix and DTH drilling.

The borehole tests at the Akacievej site included:
* induction probes (electrical conductivity measurement)
* caliper probes (minimal local borehole diameter)
* porosity probes (gamma-gamma probes for relative porosity)
* density probes
* temperature probes
* fluid resistivity probes
* impeller flow logs

== Aquifer tests ==

=== Pumping tests ===
Pumping tests are very useful to characterize the local hydrogeology at a contaminated site.
Usually, a well is pumped and the drawdown behavior (hydraulic head changes) in the pumping well and (if available) in neighboring observation wells are measured.
This can be done with manual head measurements, if the hydraulic head changes happen relatively slow.
Fractured aquifers, however, often exhibit a high hydraulic conductivity and the drawdown happens quickly, which makes it difficult to manually measure the drawdown caused by the pumping.
In this case, the head changes can be monitored with programmable pressure transducers (divers), which measure the hydraulic heads at a high measurement frequency.
Two measurements per seconds or even more are recommended for fracture-flow dominated aquifers or aquifers with a high hydraulic conductivity.

The drawdown curves can be interpreted with a suitable tool (e.g. [http://www.aqtesolv.com/ Aqtesolv]), which allows the determination of aquifer parameters like the hydraulic conductivity.
In fractured aquifers, long-term pumping tests with a high pumping rate can potentially reveal information about the hydraulic conditions in both fractures and matrix.
Drawdown curves from long-term pumping tests in fractured limestone aquifers exhibit different stages - first, pumped water is mainly withdrawn from the fractures, followed by a stage with fracture-matrix interflow, and in the last stage, the water is mainly abstracted from the matrix.
At the Akacievej site, the full drawdown had developed within a time period of about 10 days.
For the interpretation of such drawdown curves, specialized dual-continuum solution schemes (e.g. the dual-porosity solution presented in Moench, 1984 <ref>Moench, A.F. (1984), ''Double-porosity models for a fissured groundwater aquifer with fractures skin'', Water resources research, Vol.20, 831-846.</ref> or Barker, 1988 <ref>Barker, J.A. (1988), ''A generalized radial flow model for hydraulic tests in fractured rock'', Water resources research, Vol.24, 1796-1804.</ref>) can be employed.

However, it has to be kept in mind that the obtained values only describe the area affected by the pumping test and an extrapolation has to be done with care, especially if the aquifer is very heterogeneous.
A higher pumping rate can potentially enlarge the affected area.
Further, in screened wells, the (vertical) location of the screen is important, since water is mainly pumped from the part of the aquifer at the depth of the screen (or in case of an open borehole, of the open section of the borehole).
Packers can be installed to separate sections of the aquifer and to determine hydraulic conductivities (or transmissivities) for these sections.

[[File:PumpTracerTest-images.png|thumb|center|800px| Fig.3: Photos from the pumping test and the tracer tests at Akacievej (spring 2016). From left to right: Pumping well, preparation of tracer injection system, mixing of fluorescein into 1000 L tanks with groundwater, tracer sampling on sampling carousel.]]

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf|Pumping and tracer test in a limestone aquifer and model interpretation (PDF)]]

=== Slug tests ===
[[File:SlugTest.jpg|thumb|Fig. 4: Example of a vacuum slug test at the Akacievej site.]]
Slug tests are relatively cheap and easy single-borehole aquifer tests, where the water table in a borehole is abruptly changed, for example, by releasing a slug of water into the borehole while monitoring the pressure response, when the water table changes back to its original state again.
They can be used to obtain approximate values of the hydraulic conductivities at the location of a borehole.
Therefore, the hydraulic head has to be measured with a high frequency.
In low conductivity aquifers, this can be done with manual measurements using common dip-meters.
In highly conductive aquifers, the water table responds quickly, and automated measurements with pressure transducers should be chosen.
These pressure transducers should be set to a sufficiently small time interval (ideally several measurements per second).

There are different types of slug tests.
A main distinction can be made between rising-head slug tests and falling-head slug tests.

* '''Rising-head slug test'''
To perform a rising-head slug test, water is removed from the borehole and the recovery of the hydraulic head in the borehole is recorded.
This can be a good choice for aquifers with moderate flow velocities but can be problematic for highly conductive aquifers.

* '''Falling-head slug test'''
For a falling-head slug test, the water level in the borehole is abruptly increased.
This can be done on different ways.
A slug of water can be added into the borehole and the head change monitored.
For aquifers with a high hydraulic conductivity, a different method is recommended:
A vacuum is applied on the borehole to pull the water table up at the borehole (Figure 4).
The raised water table is then released and the equilibration of the water table measured with pressure transducers with a short measurement interval (several measurements per second).
This method was particularly useful for slug tests in the highly conductive fractured limestone at the Akacievej site.

The interpretation of slug tests with standard aquifer test software like [http://www.aqtesolv.com/ Aqtesolv] allows for obtaining information about the local hydraulic conductivity.
For fractured aquifers, a solution scheme that is accounting for the fractures and the dual-porosity aquifers like the Barker-Black (1983) solution can be chosen.
In very conductive aquifers, an oscillating water table caused by inertia can occur when the slug is released.
There are specialized solution schemes (f.e. the solution by Springer and Gelhar (1991)<ref>Springer, R. and Gelhar, L. (1991), ''Characterization of large-scale aquifer heterogeneity in glacial outwash by analysis of slug tests with oscillatory response'', Report, U.S. Geological Survey.</ref>), which can be applied then.

Note that slug tests are very local measurements, because they usually affect only a small volume around a borehole and an extrapolation of the determined parameters should be done with care.
Furthermore, the slug test results can be influenced by the borehole filling (gravel or sand pack around the well screens).
If several boreholes are close by or if there are boreholes with several well screens at different depth, slug tests can yield information about the local variability of the hydraulic conductivity.
Slug tests at different depths can yield hydraulic parameters for different geologic units.

=== Additional information from water works data and remediation systems ===
Waterworks can provide a cheap and simple way for getting additional pumping test data.
Waterworks are operating one or several wells, where often automated loggers are installed, which monitor the hydraulic heads in the pumped wells.
When the pumps are switched on and off, drawdown and recovery curves can be obtained, which can be analyzed with standard aquifer test software (e.g. Aqtesolv) like usual pumping tests.
To obtain data useful for interpretation, a high measurement frequency should be set for the hydraulic head logging in the wells, particularly for aquifers with a high hydraulic conductivity.
For highly conductive aquifers like the one at Akacievej, a good choice of the measurement interval is 1 second or less.

The Fløng waterworks close to the Akacievej site operates an alternating pumping scheme in four drinking water wells, where the individual wells are automatically switched on and off according to the water demand.
This creates a sequence of pumping-test like events, which were evaluated to obtain the hydraulic conductivity at the wells of the water works.
Note that the wells used by the water works have often long screens, and that the measurements represent average values over the screen length or borehole length (in case of an open borehole).

Furthermore, head measurements from a remediation system can be interpreted to obtain hydraulic parameters at the location of the remediation system.
At the Akacievej site, the remediation system was turned on and off several times, and the hydraulic heads in the remediation well and in observation wells next to it were measured.
This information was used to calibrate a flow model to the observed drawdown and to get more information about the crushed limestone, where most of the screen of the remediation well is located in.

== Fracture characterization ==
[[File:OTVexample.jpg|thumb|600px|Fig. 5: Example of an optical televiewer measurement in Geo18 showing a fracture (dark) at 35.5 m bgs. Courtesy of Geo.]]
In fractured limestone aquifers, the fractures are the primary travel pathways for substances, and their characterization is important for risk assessment and remedial planning.
Information about the fracture geometry and location is, however, generally scarce and the determination of appropriate parameters may be challenging.
Fractures are generally described by their aperture, spacing, distribution, length, height and their main orientation.
The flow and transport in fractures is furthermore controlled by the fracture connectivity.

The following measurements are useful to determine fracture parameters:
* slug tests and pumping tests to obtain hydraulic conductivity and storativity values
* flow logs in boreholes to identify high-flow zones
* temperature logs in boreholes and induced temperature gradients to identify high flow zones
* tracer tests to obtain information about solute transport in parts of the aquifer
* fracture mapping at analogue sites like outcrops and excavations
* borehole cores
* geophysical measurements
* open-borehole methods like flexible liners ([http://www.flut.com/ FLUTe]) or televiewers

[[File:FlowLogs Fractures.png|thumb|500px|Fig. 6: Flow logs in boreholes to identify horizontal fractures and high-flow zones. The green lines indicate high-flow zones.]]
Flow logs in boreholes can be very useful to identify highly conductive zones (Figure 6).
Therefore, a propeller probe is lowered in the borehole and the speed of the propeller rotation is recorded while pumping the borehole.
The propeller probe is slowly moved up- or downwards.
High-flow zones will lead to a change of the propeller rotation speed and high-flow zones can be identified from the logs.
For this method, even borehole walls are beneficial.
Holes or gaps in the borehole walls can lead to disturbances in the flow logs due to local turbulences and backflow of water.
When the propeller probe is used without pumping, some information about vertical flows in the boreholes can be obtained.

When open boreholes (without well screen) are available, [http://www.flut.com/ FLUTe] liners can be used to identify high-flow zones.
Moreover, optical and acoustical televiewers can be used to take images of the borehole walls.
With vertical boreholes, mainly horizontal fractures and flint layers can be identified by this method.
For the determination of vertical fractures, diagonal boreholes can be beneficial, because they increases the likelihood that vertical fractures intersect with the borehole.
A sample image from a vertical borehole at the Akacievej site (Geo18d) is shown in Figure 5.
The dark area at a depth of 35.4 m below ground surface is a significant horizontal fracture.
This is reflected in the flow log in the right part of Figure 5.
At the same depth as the dark area, a strong change in the flow log can be observed.
This is an indication for a high-flow zone.

{{Return}}
|}
[[Category:Field methods]] [[Category:Geology]]

Example: Akacievej

2019-07-03T14:44:53Z

Klmos:

== Example: Setup and application of models for a field site (Akacievej, Hedehusene) ==

First, several models were compared for a contaminated site in Denmark, where a plume of dissolved PCE has migrated through a fractured limestone aquifer.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model.
Field data includes information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores was combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test with depth-specific contaminant sampling was conducted at the site to determine flow and transport parameters of the fractures and matrix and to quantify the contaminant distribution in the aquifer.
Different models were used for the planning and interpretation of the pumping and tracer test.
This is described in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a coupled 2D plume-scale and 3D source-zone model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE.
The source-zone model is then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model.

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of ther remediation system]]



{{Return}}
[[Category:Modeling]]

Example: Akacievej

2019-07-03T14:44:21Z

Klmos: Started to add a description of the coupled 3D-2D model

== Example: Setup of models for a field site (Akacievej, Hedehusene) ==

First, several models were compared for a contaminated site in Denmark, where a plume of dissolved PCE has migrated through a fractured limestone aquifer.
Numerical modeling was integrated in the planning of field tests and in the update of the conceptual model.
Field data includes information on spill history, distribution of the contaminant (multilevel sampling), geology and hydrogeology.
To describe the geology and fracture system, data from borehole logs, packer tests, optical televiewers and cores was combined with an analysis of local heterogeneities and data from analogue sites.
A pumping and tracer test with depth-specific contaminant sampling was conducted at the site to determine flow and transport parameters of the fractures and matrix and to quantify the contaminant distribution in the aquifer.
Different models were used for the planning and interpretation of the pumping and tracer test.
This is described in the following report:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To reduce the numerical effort and to simulate the plume propagation on a larger scale, a coupled 2D plume-scale and 3D source-zone model was developed.
The 3D model resolves flow and transport in the source zone.
Therefore, an initial contaminant distribution in the source zone was implemented, which is based on depth-specific measurements of PCE.
The source-zone model is then used to compute the contaminant input fluxes for the 2D model, which starts at the downstream end of the source zone model.

The following report (in Danish) shows the setup and application of this coupled 3D source-zone and 2D plume-scale model, which supported the re-evaluation of the remediation system at the Akacievej site:
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of ther remediation system]]



{{Return}}
[[Category:Modeling]]

Conceptual modeling

2019-07-03T13:24:04Z

Klmos: /* Contaminant distribution and dynamics */ Integrated 2D-3D coupled model

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the [[The Akacievej field site|Akacievej field site]] based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.4: Coupled 3D source zone model and 2D plume model.]]

This served as input for combined 2D and 3D modeling of the plume dynamics (see Fig. 4), which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

File:Coupled2D-3Dmodel.png

2019-07-03T13:21:56Z

Klmos: Detailed 3D modeling of the source zone coupled to a 2D cross section model of the plume.

Detailed 3D modeling of the source zone coupled to a 2D cross section model of the plume.

Conceptual modeling

2019-07-03T13:19:23Z

Klmos: /* Conceptual model development */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the [[The Akacievej field site|Akacievej field site]] based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

[[File:coupled2D-3Dmodel.png|500px|thumb|Fig.4: Coupled 3D source zone model and 2D plume model.]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Geology and properties of limestone

2019-07-03T13:09:37Z

Klmos: /* Properties of the limestone at Akacievej (Hedehusene, Denmark) */

{| class="side1"
!Highlights
|-
|
* Description of limestone geology
* Properties of limestone aquifers
|}

[[File:GeologicSequenceGEUS2014.png|thumb|25em|Fig. 1: Geologic sequence in eastern Denmark. From: Galsgaard et al. (2014)<ref name="GeoGeus2014" />.]]
[[File:BoreholeCores.png|thumb|25em|Fig. 2: Borehole cores from the Akacievej field site with flint inclusions and fractures. Note that some of the fractures and crushing that can be seen in Figure 2 are caused by the drilling.]]

{| class="body1"
|
== Geology and hydrogeology ==
In eastern Denmark, glacial Quaternary deposits (clayey till, sand) are usually on top of limestone aquifers.
The uppermost limestone layer is typically a calcarenitic limestone (also called Københavns Kalk), followed by bryozoan limestone.
The calcarenitic limestone is rather evenly and horizontally layered and may contain flint layers and nodules.
The bryozoan limestone typically shows bank structures and few to no flint inclusions.
A good description of the geologic stratification in the greater Copenhagen area is given in the Report by GEO and GEUS <ref name="GeoGeus2014"> Galsgaard et al. (2014), ''[[:Media:Stroemning_og_stoftransport_i_kalklagene_pa_den_koebenhavnske_vestegn.pdf| Strømning og stoftransport i kalklagene på den københavnske vestegn]]'' (in Danish).</ref>.
Figure 1 shows the typical krono-, bio- and lithostratigraphy in eastern Zealand (Denmark) and in the Øresundsregion.

Limestone geologies are often heavily fractured and especially the calcarenitic limestone includes almost impermeable chert layers and nodules.
The chert layers can stretch over distances of tens to hundreds of meters or they can occur as loose inclusions embedded in the limestone.
Figure 2 shows some borehole cores from the Akacievej site, which illustrate the heterogeneity of the limestone with chert, crushed material and fractures.
The upper part of the limestone aquifer may be crushed due to glacial activity.
At the Akacievej site, a crushed layer with a thickness of 3-5 m was observed.
It has different hydraulic properties than the fractured limestone, f.e. the bulk hydraulic conductivity was lower than in the fractured limestone below.

Limestone aquifers are often very heterogeneous and the hydraulic parameters can span over wide ranges and have a strong spatial variation.
As with many other geologic materials, limestone aquifers are typically anisotropic, which means that their horizontal hydraulic conductivity is about 2 to 10 times as high as in the vertical direction.
Major horizontal fractures can intensify the observed degree of anisotropy.
The intact limestone matrix has a very low hydraulic conductivity.
When fractures are present, their conductivity is often orders of magnitude higher than the matrix and flow occurs predominantly in the fractures.

Different kinds of fractures can be distinguished: horizontal fractures, which are often caused by decompression (related to glacial activity), and vertical/subvertical fractures, typically caused by tectonic activities.
Fractures can influence the anisotropic behavior of limestone aquifers, because the groundwater flow is guided through the fractures.
Due to that, it is possible that the main flow direction differs from the overall hydraulic head gradient, and the direction of the major fractures has to be considered.
The orientation of the vertical fractures is, as a rule of thumb, often aligned with major faults in the area <ref name="GeoGeus2014" />.
Limestone has a relatively high matrix porosity (between 7 and 46 Vol.-% were observed at the Akacievej site <ref name="Broholm2016"> Broholm et al. (2016a), ''[[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf|Sammenligning af niveauspecifikke prøvetagningsmetoder for vurdering af koncentrationsfordeling i kalkmagasin]]'' (in Danish). Technical University of Denmark, DTU Environment</ref>). The porosity of the fracture system (volume fraction of the fractures), where groundwater flow and advective transport often mainly take place, is comparably low (0.5 to 2 Vol.-%).

== Properties of the limestone at Akacievej (Hedehusene, Denmark)==
The local geology at the Akacievej site in Hedehusene (eastern Denmark) is described [[The Akacievej field site|here]].
Based on a set of different measurements and modeling interpretations, hydraulic parameters and transport parameters were determined for the Akacievej site.
The employed field methods are described in the Chapters [[ Data acquisition | '''Data acquisition and field methods''' ]] and [[ Transport parameters and contaminant data | '''Determination of transport parameters and contaminant data''']].
Table 1 gives an overview of values that were determined at the Akacievej site.

{| class="wikitable"
|+ Tab. 1: Overview of parameters determined at the Akacievej site or for comparable limestone sites.
|-
! Parameter !! Value !! Comment !! Determination method
|-
| <math> K_\text{crushed} </math> || <math> 5\cdot 10^{-4}\ \text{m/s} </math>|| crushed limestone (bulk) conductivity || slug tests, data from remedial well
|-
| <math> K_\text{matrix} </math> || <math> 10^{-6} - 5\cdot 10^{-11}\ \text{m/s} </math> || matrix conductivity || permeameter tests on subcores, pumping test
|-
| <math> K_\text{fractures} </math> || <math> 0.6 - 5.4\ \text{m/s} </math> || fracture conductivity || determined from hydraulic fracture aperture with the cubic law
|-
| <math> Ap </math> || <math> 1 - 3\ \text{mm} </math> || typical hydraulic aperture of major horizontal fracture || pumping test, packer test
|-
| <math> n_\text{matrix} </math> || <math> 0.07 - 0.46 </math> || matrix porosity || porosimeter tests on subcores, pumping test
|-
| <math> B </math> || <math> 20 - 25\ \text{m} </math> || aquifer thickness || flow logs
|-
| <math> D_\text{m} </math> || <math> 7.5\cdot 10^{-7} \text{m}^2/\text{s} </math> || (augmented) effective diffusivity of bromide || modeling of tracer test, includes effect of neglected fractures and stagnant flow zones
|-
| <math> k_\text{d} </math> || <math> 0.5-1.0\ \text{L/kg} </math> || sorption coefficient for PCE on limestone || sorption tests in lab <ref name="Salzer2013" />
|}

The sorption behavior for chlorinated solvents on limestone was examined in Salzer (2013) <ref name="Salzer2013"> Salzer, J.P. (2013), ''Sorption capacity and governing parameters for transport of chlorinated solvents in chalk aquifers'', Master Thesis, DTU. </ref>.
For chlorinated solvents like PCE, sorption to limestone can be strong ($k_d$ values of $0.5-1 \ \text{L/kg}$ were measured in lab tests).

{{Return}}
|}
[[Category:Introduction]] [[Category:Geology]]

Geology and properties of limestone

2019-07-03T13:07:55Z

Klmos: /* Geology and hydrogeology */

{| class="side1"
!Highlights
|-
|
* Description of limestone geology
* Properties of limestone aquifers
|}

[[File:GeologicSequenceGEUS2014.png|thumb|25em|Fig. 1: Geologic sequence in eastern Denmark. From: Galsgaard et al. (2014)<ref name="GeoGeus2014" />.]]
[[File:BoreholeCores.png|thumb|25em|Fig. 2: Borehole cores from the Akacievej field site with flint inclusions and fractures. Note that some of the fractures and crushing that can be seen in Figure 2 are caused by the drilling.]]

{| class="body1"
|
== Geology and hydrogeology ==
In eastern Denmark, glacial Quaternary deposits (clayey till, sand) are usually on top of limestone aquifers.
The uppermost limestone layer is typically a calcarenitic limestone (also called Københavns Kalk), followed by bryozoan limestone.
The calcarenitic limestone is rather evenly and horizontally layered and may contain flint layers and nodules.
The bryozoan limestone typically shows bank structures and few to no flint inclusions.
A good description of the geologic stratification in the greater Copenhagen area is given in the Report by GEO and GEUS <ref name="GeoGeus2014"> Galsgaard et al. (2014), ''[[:Media:Stroemning_og_stoftransport_i_kalklagene_pa_den_koebenhavnske_vestegn.pdf| Strømning og stoftransport i kalklagene på den københavnske vestegn]]'' (in Danish).</ref>.
Figure 1 shows the typical krono-, bio- and lithostratigraphy in eastern Zealand (Denmark) and in the Øresundsregion.

Limestone geologies are often heavily fractured and especially the calcarenitic limestone includes almost impermeable chert layers and nodules.
The chert layers can stretch over distances of tens to hundreds of meters or they can occur as loose inclusions embedded in the limestone.
Figure 2 shows some borehole cores from the Akacievej site, which illustrate the heterogeneity of the limestone with chert, crushed material and fractures.
The upper part of the limestone aquifer may be crushed due to glacial activity.
At the Akacievej site, a crushed layer with a thickness of 3-5 m was observed.
It has different hydraulic properties than the fractured limestone, f.e. the bulk hydraulic conductivity was lower than in the fractured limestone below.

Limestone aquifers are often very heterogeneous and the hydraulic parameters can span over wide ranges and have a strong spatial variation.
As with many other geologic materials, limestone aquifers are typically anisotropic, which means that their horizontal hydraulic conductivity is about 2 to 10 times as high as in the vertical direction.
Major horizontal fractures can intensify the observed degree of anisotropy.
The intact limestone matrix has a very low hydraulic conductivity.
When fractures are present, their conductivity is often orders of magnitude higher than the matrix and flow occurs predominantly in the fractures.

Different kinds of fractures can be distinguished: horizontal fractures, which are often caused by decompression (related to glacial activity), and vertical/subvertical fractures, typically caused by tectonic activities.
Fractures can influence the anisotropic behavior of limestone aquifers, because the groundwater flow is guided through the fractures.
Due to that, it is possible that the main flow direction differs from the overall hydraulic head gradient, and the direction of the major fractures has to be considered.
The orientation of the vertical fractures is, as a rule of thumb, often aligned with major faults in the area <ref name="GeoGeus2014" />.
Limestone has a relatively high matrix porosity (between 7 and 46 Vol.-% were observed at the Akacievej site <ref name="Broholm2016"> Broholm et al. (2016a), ''[[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf|Sammenligning af niveauspecifikke prøvetagningsmetoder for vurdering af koncentrationsfordeling i kalkmagasin]]'' (in Danish). Technical University of Denmark, DTU Environment</ref>). The porosity of the fracture system (volume fraction of the fractures), where groundwater flow and advective transport often mainly take place, is comparably low (0.5 to 2 Vol.-%).

== Properties of the limestone at Akacievej (Hedehusene, Denmark)==
The local geology at the Akacievej site in Hedehusene (eastern Denmark) is described [[The Akacievej field site|here]].
Based on a set of different measurements and modeling interpretations, hydraulic parameters and transport parameters were determined for the Akacievej site.
The employed field methods are described in the Chapters [[ Data acquisition | '''Data acquisition and field methods''' ]] and [[ Transport parameters and contaminant data | '''Determination of transport parameters and contaminant data''']].
Table 1 gives an overview of values that were determined at the Akacievej site.

{| class="wikitable"
|+ Tab. 1: Overview of parameters determined at the Akacievej site or for comparable limestone sites.
|-
! Parameter !! Value !! Comment !! Determination method
|-
| <math> K_\text{crushed} </math> || <math> 5\cdot 10^{-4}\ \text{m/s} </math>|| crushed limestone (bulk) conductivity || slug tests, data from remedial well
|-
| <math> K_\text{matrix} </math> || <math> 10^{-6} - 5\cdot 10^{-11}\ \text{m/s} </math> || matrix conductivity || permeameter tests on subcores, pumping test
|-
| <math> K_\text{fractures} </math> || <math> 0.6 - 5.4\ \text{m/s} </math> || fracture conductivity || determined from hydraulic fracture aperture with the cubic law
|-
| <math> Ap </math> || <math> 1 - 3\ \text{mm} </math> || typical hydraulic aperture of major horizontal fracture || pumping test, packer test
|-
| <math> n_\text{matrix} </math> || <math> 0.07 - 0.46 </math> || matrix porosity || porosimeter tests on subcores, pumping test
|-
| <math> B </math> || <math> 20 - 25\ \text{m} </math> || aquifer thickness || flow logs
|-
| <math> D_\text{m} </math> || <math> 7.5\cdot 10^{-7} \text{m}^2/\text{s} </math> || effective diffusivity of bromide || modeling of tracer test, includes effect of neglected fractures and stagnant flow zones
|-
| <math> k_\text{d} </math> || <math> 0.5-1.0\ \text{L/kg} </math> || sorption coefficient for PCE on limestone || sorption tests in lab <ref name="Salzer2013" />
|}

The sorption behavior for chlorinated solvents on limestone was examined in Salzer (2013) <ref name="Salzer2013"> Salzer, J.P. (2013), ''Sorption capacity and governing parameters for transport of chlorinated solvents in chalk aquifers'', Master Thesis, DTU. </ref>.
For chlorinated solvents like PCE, sorption to limestone can be strong ($k_d$ values of $0.5-1 \ \text{L/kg}$ were measured in lab tests).

{{Return}}
|}
[[Category:Introduction]] [[Category:Geology]]

Modeling tools

2019-07-03T12:50:48Z

Klmos: /* TOUGH */

{| class="side1"
!Highlights
|-
|
* Overview of modeling tools and software
* Useful little tools and helpers
* Spreadsheet tool for flow field under pumped conditions
|}

{| class="body1"
|
== Modeling tools ==

The following list shows some selected modeling tools that can be used for the simulation of fracture flow and transport.


=== COMSOL Multiphysics ===

[https://www.comsol.com COMSOL Multiphysics®] is a comprehensive and flexible modeling suite that can be used to simulate various kinds of physics.
It is well suited for computing flow and transport in limestone aquifers.
It provides predefined physics-based interfaces (e.g. a module for subsurface flow) and allows equation-based modeling, where arbitrary partial differential equations can be solved.
Different physics can be coupled, e.g., a flow model can be coupled with a transport model.
The toolbox provides tools for geometry and mesh generation, a user interface for the simulation setup, several direct and indirectsolvers, and visualization and post-processing tools.
It uses the finite-element method and includes higher-order discretization schemes.

For the modeling of flow and transport in porous media, there are predefined physics interface available.
Fractures can be included as additional discrete features.

Another option is to use the PDE interface of COMSOL.
The flow and transport equations are implemented as partial differential equations and the fracture flow and transport can be added using a feature called "Weak contributions".
Here is an instruction file which describes how to setup a 2-dimensional flow and transport model including fracture flow and transport in COMSOL Multiphysics using the PDE interface.
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT!]]

=== FEFlow ===
[http://www.mikepoweredbydhi.com/products/feflow FEFlow] is a finite-element simulator focused on groundwater flow and transport of contaminants, groundwater age and heat in porous media.
It comprises mesh generators, solvers and post-processing tools for visualization and result evaluation.
It facilitates the computation of porous medium flow and transport in 2D and 3D aquifers, which can be confined, semi-confined or unconfined.
Unsaturated flow can also be modeled with based on the Richards model.
(Hydro-)geologic data can be easily imported and discrete fractures can be included.

=== TOUGH ===
* [https://tough.lbl.gov/ TOUGH]

=== DuMuX ===
* [http://dumux.org/ DuMuX] (free and open source)

=== Hydrogeosphere ===
* [http://www.aquanty.com/hydrogeosphere HydroGeoSphere]

=== Petrel ===
* [https://www.software.slb.com/products/petrel/petrel-geology-and-modeling Petrel]

=== FRACGEN and NFFLOW ===
* [https://edx.netl.doe.gov/dataset/fracgen-and-nfflow-version-14-9 FRACGEN and NFFLOW]

=== FRACMAN ===
* [http://fracman.golder.com/ FRACMAN]



== Useful helpers ==
Besides the comprehensive models, there are several small tools available that can be helpful when dealing with contaminant transport in limestone aquifers.
Some of them will be described in the following.

[[File:CaptureZones_Akacievej.png |thumb| Example of capture zone calculations for the wells around the Akacievej site in Hedehusene. The blue lines are calculated streamlines and the green lines are simulated isopotentials.]]

=== Capture zone delineation of extraction wells (Matlab model) ===
Contaminated sites often pose a threat to drinking water wells.
Christ and Goltz <ref name="christ2002">[http://dx.doi.org/10.1016/S0022-1694(02)00026-4 Christ and Goltz (2002)], J. Hydrology, p. 224-244 </ref> have developed a semi-analytical algorithm that allows estimating the capture zones of extraction wells.

Following parameters are required to set up and run the model:
* Estimate of the bulk hydraulic conductivity
* Average hydraulic gradient of the natural groundwater flow
* Reference head at one point in the domain
* Direction of the natural groundwater flow
* Aquifer thickness
* Location of wells
* Pumping rates of the wells in the study area

The model computes streamlines and isopotential lines for the specified set of parameters.

This tool can be very useful to get a quick estimate of well capture zones to check, for example, if a contaminant is likely to flow towards a drinking water well.
It does, however, not consider fracture flow and is based on several simplifying assumptions.
When a background map of the study area is specified, the streamlines and isopotential lines can be directly plotted on the map, as shown in the example below.

A Matlab model was developed based on the solution from Christ and Goltz (2002) <ref name="christ2002" />.
An example file for the larger Akacievej area can be seen here:
* [[ Matlab model Christ and Goltz | Matlab model for capture zone calculation]]

The example including the background map shown above can be downloaded as zipfile here:
* [[:File:CaptureZones_MATLAB.zip|Download Matlab model]]


=== Spreadsheet tool for fracture transport based on the semi-analytical solution from West (2004) ===
* [http://www.aktor.dk/software/simfracflow SimFracFlow]

[[File:Slugtest_GEO19s_KGS_Aqtesolv.png |thumb|Example for the evaluation of a slug test at the Akacievej site using the KGS model.]]
=== Hydraulic parameters from aquifer tests using Aqtesolv ===
[http://www.aqtesolv.com/ Aqtesolv] is an easy-to-use tool for the design and interpretation of aquifer tests like pumping tests and slug tests.
It provides a variety of conventional solution methods for aquifer tests in confined, leaky and unconfined aquifers and several advanced methods, e.g. for fractured aquifers or oscillating water tables.
A comprehensive description of the capabilities and a free demo version is available on the software's webpage.
The software tool contains a comprehensive help menu that provides explanations of the different solution methods and the required parameters.

=== Geologic modeling with GeoScene3D ===
[http://www.geoscene3d.com/ GeoScene3D] is a tool to import and work with borehole data to create a geologic model.
It is possible to directly import data from the Danish borehole database [https://www.geus.dk/produkter-ydelser-og-faciliteter/data-og-kort/national-boringsdatabase-jupiter/ Jupiter] and to interpolate borehole data, for example to obtain the surface of the top of the limestone.

<references />
{{Return}}
|}
[[Category:Modeling]]

Modeling tools

2019-07-03T12:47:17Z

Klmos: /* Modeling tools */

{| class="side1"
!Highlights
|-
|
* Overview of modeling tools and software
* Useful little tools and helpers
* Spreadsheet tool for flow field under pumped conditions
|}

{| class="body1"
|
== Modeling tools ==

The following list shows some selected modeling tools that can be used for the simulation of fracture flow and transport.


=== COMSOL Multiphysics ===

[https://www.comsol.com COMSOL Multiphysics®] is a comprehensive and flexible modeling suite that can be used to simulate various kinds of physics.
It is well suited for computing flow and transport in limestone aquifers.
It provides predefined physics-based interfaces (e.g. a module for subsurface flow) and allows equation-based modeling, where arbitrary partial differential equations can be solved.
Different physics can be coupled, e.g., a flow model can be coupled with a transport model.
The toolbox provides tools for geometry and mesh generation, a user interface for the simulation setup, several direct and indirectsolvers, and visualization and post-processing tools.
It uses the finite-element method and includes higher-order discretization schemes.

For the modeling of flow and transport in porous media, there are predefined physics interface available.
Fractures can be included as additional discrete features.

Another option is to use the PDE interface of COMSOL.
The flow and transport equations are implemented as partial differential equations and the fracture flow and transport can be added using a feature called "Weak contributions".
Here is an instruction file which describes how to setup a 2-dimensional flow and transport model including fracture flow and transport in COMSOL Multiphysics using the PDE interface.
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT!]]

=== FEFlow ===
[http://www.mikepoweredbydhi.com/products/feflow FEFlow] is a finite-element simulator focused on groundwater flow and transport of contaminants, groundwater age and heat in porous media.
It comprises mesh generators, solvers and post-processing tools for visualization and result evaluation.
It facilitates the computation of porous medium flow and transport in 2D and 3D aquifers, which can be confined, semi-confined or unconfined.
Unsaturated flow can also be modeled with based on the Richards model.
(Hydro-)geologic data can be easily imported and discrete fractures can be included.

=== TOUGH ===
* [http://esd1.lbl.gov/research/projects/tough/ TOUGH]

=== DuMuX ===
* [http://dumux.org/ DuMuX] (free and open source)

=== Hydrogeosphere ===
* [http://www.aquanty.com/hydrogeosphere HydroGeoSphere]

=== Petrel ===
* [https://www.software.slb.com/products/petrel/petrel-geology-and-modeling Petrel]

=== FRACGEN and NFFLOW ===
* [https://edx.netl.doe.gov/dataset/fracgen-and-nfflow-version-14-9 FRACGEN and NFFLOW]

=== FRACMAN ===
* [http://fracman.golder.com/ FRACMAN]



== Useful helpers ==
Besides the comprehensive models, there are several small tools available that can be helpful when dealing with contaminant transport in limestone aquifers.
Some of them will be described in the following.

[[File:CaptureZones_Akacievej.png |thumb| Example of capture zone calculations for the wells around the Akacievej site in Hedehusene. The blue lines are calculated streamlines and the green lines are simulated isopotentials.]]

=== Capture zone delineation of extraction wells (Matlab model) ===
Contaminated sites often pose a threat to drinking water wells.
Christ and Goltz <ref name="christ2002">[http://dx.doi.org/10.1016/S0022-1694(02)00026-4 Christ and Goltz (2002)], J. Hydrology, p. 224-244 </ref> have developed a semi-analytical algorithm that allows estimating the capture zones of extraction wells.

Following parameters are required to set up and run the model:
* Estimate of the bulk hydraulic conductivity
* Average hydraulic gradient of the natural groundwater flow
* Reference head at one point in the domain
* Direction of the natural groundwater flow
* Aquifer thickness
* Location of wells
* Pumping rates of the wells in the study area

The model computes streamlines and isopotential lines for the specified set of parameters.

This tool can be very useful to get a quick estimate of well capture zones to check, for example, if a contaminant is likely to flow towards a drinking water well.
It does, however, not consider fracture flow and is based on several simplifying assumptions.
When a background map of the study area is specified, the streamlines and isopotential lines can be directly plotted on the map, as shown in the example below.

A Matlab model was developed based on the solution from Christ and Goltz (2002) <ref name="christ2002" />.
An example file for the larger Akacievej area can be seen here:
* [[ Matlab model Christ and Goltz | Matlab model for capture zone calculation]]

The example including the background map shown above can be downloaded as zipfile here:
* [[:File:CaptureZones_MATLAB.zip|Download Matlab model]]


=== Spreadsheet tool for fracture transport based on the semi-analytical solution from West (2004) ===
* [http://www.aktor.dk/software/simfracflow SimFracFlow]

[[File:Slugtest_GEO19s_KGS_Aqtesolv.png |thumb|Example for the evaluation of a slug test at the Akacievej site using the KGS model.]]
=== Hydraulic parameters from aquifer tests using Aqtesolv ===
[http://www.aqtesolv.com/ Aqtesolv] is an easy-to-use tool for the design and interpretation of aquifer tests like pumping tests and slug tests.
It provides a variety of conventional solution methods for aquifer tests in confined, leaky and unconfined aquifers and several advanced methods, e.g. for fractured aquifers or oscillating water tables.
A comprehensive description of the capabilities and a free demo version is available on the software's webpage.
The software tool contains a comprehensive help menu that provides explanations of the different solution methods and the required parameters.

=== Geologic modeling with GeoScene3D ===
[http://www.geoscene3d.com/ GeoScene3D] is a tool to import and work with borehole data to create a geologic model.
It is possible to directly import data from the Danish borehole database [https://www.geus.dk/produkter-ydelser-og-faciliteter/data-og-kort/national-boringsdatabase-jupiter/ Jupiter] and to interpolate borehole data, for example to obtain the surface of the top of the limestone.

<references />
{{Return}}
|}
[[Category:Modeling]]

Modeling tools

2019-07-03T12:46:45Z

Klmos: /* Geologic modeling with GeoScene3D */

{| class="side1"
!Highlights
|-
|
* Overview of modeling tools and software
* Useful little tools and helpers
* Spreadsheet tool for flow field under pumped conditions
|}

{| class="body1"
|
== Modeling tools ==

The following list shows some selected modeling tools that can be used for the simulation of fracture flow and transport.


=== COMSOL Multiphysics ===

[https://www.comsol.com COMSOL Multiphysics®] is a comprehensive and flexible modeling suite that can be used to simulate various kinds of physics.
It is well suited for computing flow and transport in limestone aquifers.
It provides predefined physics-based interfaces (e.g. a module for subsurface flow) and allows equation-based modeling, where arbitrary partial differential equations can be solved.
Different physics can be coupled, e.g., a flow model can be coupled with a transport model.
The toolbox provides tools for geometry and mesh generation, a user interface for the simulation setup, several direct and indirectsolvers, and visualization and post-processing tools.
It uses the finite-element method and includes higher-order discretization schemes.

For the modeling of flow and transport in porous media, there are predefined physics interface available.
Fractures can be included as additional discrete features.

Another option is to use the PDE interface of COMSOL.
The flow and transport equations are implemented as partial differential equations and the fracture flow and transport can be added using a feature called "Weak contributions".
Here is an instruction file which describes how to setup a 2-dimensional flow and transport model including fracture flow and transport in COMSOL Multiphysics using the PDE interface.
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT!]]

=== FEFlow ===
[http://www.mikepoweredbydhi.com/products/feflow FEFlow] is a finite-element simulator focused on groundwater flow and transport of contaminants, groundwater age and heat in porous media.
It comprises mesh generators, solvers and post-processing tools for visualization and result evaluation.
It facilitates the computation of porous medium flow and transport in 2D and 3D aquifers, which can be confined, semi-confined or unconfined.
Unsaturated flow can also be modeled with based on the Richards model.
(Hydro-)geologic data can be easily imported and discrete fractures can be included.

=== TOUGH ===
* [http://esd1.lbl.gov/research/projects/tough/ TOUGH]

=== DuMuX ===
* [http://dumux.org/ DuMuX] (free and open source)

=== Hydrogeosphere ===
* [http://www.aquanty.com/hydrogeosphere HydroGeoSphere]

=== Petrel ===
* [https://www.software.slb.com/products/petrel/petrel-geology-and-modeling Petrel]

=== FRACGEN and NFFLOW ===
* [https://edx.netl.doe.gov/dataset/fracgen-and-nfflow-version-14-9 FRACGEN and NFFLOW]

=== FRACMAN ===
* [http://fracman.golder.com/ FRACMAN]

[[ Comparison of capabilities ]] - ''will come soon''

== Useful helpers ==
Besides the comprehensive models, there are several small tools available that can be helpful when dealing with contaminant transport in limestone aquifers.
Some of them will be described in the following.

[[File:CaptureZones_Akacievej.png |thumb| Example of capture zone calculations for the wells around the Akacievej site in Hedehusene. The blue lines are calculated streamlines and the green lines are simulated isopotentials.]]

=== Capture zone delineation of extraction wells (Matlab model) ===
Contaminated sites often pose a threat to drinking water wells.
Christ and Goltz <ref name="christ2002">[http://dx.doi.org/10.1016/S0022-1694(02)00026-4 Christ and Goltz (2002)], J. Hydrology, p. 224-244 </ref> have developed a semi-analytical algorithm that allows estimating the capture zones of extraction wells.

Following parameters are required to set up and run the model:
* Estimate of the bulk hydraulic conductivity
* Average hydraulic gradient of the natural groundwater flow
* Reference head at one point in the domain
* Direction of the natural groundwater flow
* Aquifer thickness
* Location of wells
* Pumping rates of the wells in the study area

The model computes streamlines and isopotential lines for the specified set of parameters.

This tool can be very useful to get a quick estimate of well capture zones to check, for example, if a contaminant is likely to flow towards a drinking water well.
It does, however, not consider fracture flow and is based on several simplifying assumptions.
When a background map of the study area is specified, the streamlines and isopotential lines can be directly plotted on the map, as shown in the example below.

A Matlab model was developed based on the solution from Christ and Goltz (2002) <ref name="christ2002" />.
An example file for the larger Akacievej area can be seen here:
* [[ Matlab model Christ and Goltz | Matlab model for capture zone calculation]]

The example including the background map shown above can be downloaded as zipfile here:
* [[:File:CaptureZones_MATLAB.zip|Download Matlab model]]


=== Spreadsheet tool for fracture transport based on the semi-analytical solution from West (2004) ===
* [http://www.aktor.dk/software/simfracflow SimFracFlow]

[[File:Slugtest_GEO19s_KGS_Aqtesolv.png |thumb|Example for the evaluation of a slug test at the Akacievej site using the KGS model.]]
=== Hydraulic parameters from aquifer tests using Aqtesolv ===
[http://www.aqtesolv.com/ Aqtesolv] is an easy-to-use tool for the design and interpretation of aquifer tests like pumping tests and slug tests.
It provides a variety of conventional solution methods for aquifer tests in confined, leaky and unconfined aquifers and several advanced methods, e.g. for fractured aquifers or oscillating water tables.
A comprehensive description of the capabilities and a free demo version is available on the software's webpage.
The software tool contains a comprehensive help menu that provides explanations of the different solution methods and the required parameters.

=== Geologic modeling with GeoScene3D ===
[http://www.geoscene3d.com/ GeoScene3D] is a tool to import and work with borehole data to create a geologic model.
It is possible to directly import data from the Danish borehole database [https://www.geus.dk/produkter-ydelser-og-faciliteter/data-og-kort/national-boringsdatabase-jupiter/ Jupiter] and to interpolate borehole data, for example to obtain the surface of the top of the limestone.

<references />
{{Return}}
|}
[[Category:Modeling]]

Content

2019-07-03T12:44:44Z

Klmos: /* Modeling contaminant transport in limestone */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer]] <br>

[[ Model output | Comparison of model concepts and recommendations for modeling fractured limestone aquifers]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Content

2019-07-03T12:43:38Z

Klmos: /* Modeling contaminant transport in limestone */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers ]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Steps to setup an advanced model for fracture flow and transport in a limestone aquifer ]] <br>

[[ Model output | Recommendations for modeling fractured limestone aquifers and comparison of model concepts ]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Content

2019-07-03T12:16:28Z

Klmos: /* Modeling contaminant transport in limestone */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers ]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Setup of an advanced model for fracture flow and transport in a limestone aquifer ]] <br>

[[ Model output | Recommendations for modeling fractured limestone aquifers and comparison of model concepts ]]
</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Model setup

2019-07-03T12:07:12Z

Klmos: /* Mesh generation */

{| class="side1"
!Highlights
|-
|
* Setup of a model for a fractured limestone aquifer
* Modeling objectives
* Typical steps of setting up a model for limestone aquifers
|}

{| class="body1"
|
== Steps to setup a model for flow and transport in fractured limestone aquifers ==
This chapter gives an overview of the recommended steps to setup a model for the simulation of flow and transport in a fractured limestone aquifer.
The following list shows the typical steps to setup a model for contaminant transport in a fractured limestone aquifer.
Expand an item (button on the right) to get more information about it.

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Formulation of the modeling objectives ===
<div class="mw-collapsible-content">
Before setting up a model, it is important to define the specific modeling objective(s).
The choice of the model concept, model extent, modeling scale and included details should be closely linked to these objectives.
One should aim at including the most relevant features in the model, while keeping it as simple as possible to address the modeling objective(s).

The following list gives some examples for modeling objectives:
* Delineate the capture zone of a well
* Improve risk assessment, e.g. for a contaminant threatening a drinking water well, in order to assess future actions
* Analyze the distribution and potential spreading of a contaminant plume in an aquifer
* Test hypotheses related to the origin of a contaminant
* Interpret observed / measured field data
* Analyze the influence of transient hydraulic conditions (annual variations, pumping in the area) on plume propagation
* Develop and optimize a remediation strategy for the source zone of a contaminated site
* Optimize a remediation strategy for a contaminant plume
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Conceptualization and setup of a conceptual model including geology and hydrogeology ===
<div class="mw-collapsible-content">
[[File:SE-NO_profil.jpg |thumb|550px|Example geologic profile of a Geoscene3D model.]]
==== Geologic modeling ====
Borehole data, outcrops, geophysical measurements etc. can give valuable information about the [[ Geology and properties of limestone | geology ]] at a site.
Bits of geologic knowledge can be connected to establish a geologic model, that shows different geologic layers and relevant geologic features (like inclusions or lenses).
Typically, these layers are characterized by different hydrogeologic properties.
The geometry can be stored as a CAD interpolation of the surfaces, that delineate the geologic layers.
Tools like GeoScene3D can be very useful to manage borehole data and to create interpolation surfaces.
The surfaces can be imported into the numerical model later on.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Definition of the model scope ===
<div class="mw-collapsible-content">
The scale also depends on the modeling objectives.
The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) and for the planning of source zone remedial actions (local scale).
An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells.
The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest.
It should be chosen based on physically meaningful boundaries (f.e. known head isolines or no-flow boundaries).

The modeling of source zone remediation requires a different scale than the risk assessment of a contaminant plume for water works.
The following scales can be distinguished:
* well or borehole scale
* source zone scale
* intermediate scale for e.g. pumping tests
* plume scale

Based on available data and modeling objectives, the model complexity has to be chosen.
A very complex and detailed model is not appropriate if only little field data is available.
Then, a simple model can be applied, which can be improved as soon as new data is measured.

Modeling was an integral part in the limestone project and already done at an early stage of the project.
Initially, a rough model based on first measurements and available data was setup.
It was used for the planning of further field work and measurements.
It also helps to identify further data requirements and to plan measurements that support the modeling.
These additional measurements and data can then be incorporated in the model.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model) ===
<div class="mw-collapsible-content">
See Chapters [[Data acquisition]] and [[Transport parameters and contaminant data]].
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous) ===
<div class="mw-collapsible-content">
Based on available data and the chosen model, parameter distributions have to be defined.
For a steady-state flow simulation, the hydraulic conductivity (or permeability) is required.
For transport, parameters like porosity, (effective) diffusion coefficients, dispersivities and sorption parameters are required.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Choice of boundary conditions and sources/sinks ===
<div class="mw-collapsible-content">
Boundary conditions should be chosen according to known or delineated boundaries, such as geologic boundaries, known hydraulic head isolines, known flowlines (can be used as no-flow condition perpendicular to them, if the flow field is stable).
The most common boundary conditions are
* Dirichlet conditions (or first-type boundary conditions), where the primary variable is fixed to a value (e.g. fixed hydraulic head or fixed concentration).
* Neumann conditions (or second-type boundary conditions), where the gradient of the primary variable is specified (e.g. flux across the boundary, often no-flow boundaries)
* Cauchy conditions (or third-type boundary conditions), which sets a condition to the primary variable and its derivative (used f.e. for the infiltration flux through a river bed).
The proper choice of boundary conditions is a very important step and determines the calculated results.

Sources and sinks can be added in the model domain to include e.g. withdrawal/injection at wells or groundwater recharge due to precipitation.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== For transient models: definition of initial conditions ===
<div class="mw-collapsible-content">
Steady-state models do not require the definition of initial conditions.
Transient problems, however, require to specify the initial value of the primary variables (e.g. concentrations at each location of the model domain.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Mesh generation ===
<div class="mw-collapsible-content">
[[File:MeshExample.png |thumb|right|500px|Example a mesh used for discrete-fracture simulations of the Akacievej tracer tests. The mesh is refined at the horizontal fractures and at the wells.]]
When working with complex models it is useful to start with a coarse mesh to test the model and the setup with limited computational efforts.
When the model is properly setup, a finer grid can be employed.

Modern grid generators allow a local mesh refinement at specific locations in the model domain.
Locations, where strong gradients of the primary variables (head, concentration) occur, should be resolved at a high resolution, while for the parts of the model domain with only small changes, a coarser mesh resolution may be sufficient.
Especially at heterogeneities and fractures, at wells and at concentration fronts, the mesh should be sufficiently fine to resolve the local gradients (e.g. of concentration or head gradients) appropriately.

If the applied mesh is sufficiently fine can be tested by a grid refinement study, where the mesh is gradually refined and the model results are compared.
When the results do not significantly change with a further grid refinement, the grid resolution is sufficient.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Simulation ===
<div class="mw-collapsible-content">
After setting up the geometry, boundary conditions, initial conditions, material parameters and simulation parameters (simulation time, solver settings), the actual simulation can be run.
It is always a good idea to start with a test run, f.e. with a coarse mesh and a short duration, to test if everything is set as desired.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Critical evaluation of the modeling results ===
<div class="mw-collapsible-content">
Modeling results should always be critically evaluated and the model should be properly tested.
It is, for example, helpful, to check the mass balance of a model, i.e. to balance all inflows and outflows and the storage in the model domain.
It is also important to visually inspect the results, f.e. by visualizing the hydraulic heads and concentrations in the domain and in special areas of interest.
Then, it should be checked, if the results look reasonable and as expected, if the boundary conditions are fulfilled and if there are any disturbances like oscillations in the model domain.
Oscillations can be an indication for a too coarse mesh.
It is also a good idea to test for grid convergence, i.e. to test if the model results change, when the numerical grid is refined.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model calibration and validation ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model reporting ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

== Example: Setup of a COMSOL Multiphysics model for a contaminated site with a fractured limestone aquifer (Akacievej, Hedehusene) ==
The setup of a discrete-fracture model in 2D in COMSOL Multiphysics using Coefficient Form PDEs is described in the following document:
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT]]
[https://www.comsol.com/ COMSOL] provides also the possibility to include fracture flow in the Darcy's Law interface, while fracture transport can be included in the Transport of Diluted Species in Porous Media interface.
We refer to the product documentation for more details.
[https://www.mikepoweredbydhi.com/products/feflow FEFlow] provides a tutorial, that describes the steps of setting up a flow and transport model and how to include discrete fractures.

DRAFT: The typical workflow for modeling a contaminated site will be demonstrated using an example field site close to Copenhagen.
[[ Example: Akacievej | Example: Setup of models for a field site (Akacievej, Hedehusene) ]]

{{Return}}
|}
[[Category:Modeling]]

Model setup

2019-07-03T12:04:51Z

Klmos: /* For transient models: definition of initial conditions */

{| class="side1"
!Highlights
|-
|
* Setup of a model for a fractured limestone aquifer
* Modeling objectives
* Typical steps of setting up a model for limestone aquifers
|}

{| class="body1"
|
== Steps to setup a model for flow and transport in fractured limestone aquifers ==
This chapter gives an overview of the recommended steps to setup a model for the simulation of flow and transport in a fractured limestone aquifer.
The following list shows the typical steps to setup a model for contaminant transport in a fractured limestone aquifer.
Expand an item (button on the right) to get more information about it.

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Formulation of the modeling objectives ===
<div class="mw-collapsible-content">
Before setting up a model, it is important to define the specific modeling objective(s).
The choice of the model concept, model extent, modeling scale and included details should be closely linked to these objectives.
One should aim at including the most relevant features in the model, while keeping it as simple as possible to address the modeling objective(s).

The following list gives some examples for modeling objectives:
* Delineate the capture zone of a well
* Improve risk assessment, e.g. for a contaminant threatening a drinking water well, in order to assess future actions
* Analyze the distribution and potential spreading of a contaminant plume in an aquifer
* Test hypotheses related to the origin of a contaminant
* Interpret observed / measured field data
* Analyze the influence of transient hydraulic conditions (annual variations, pumping in the area) on plume propagation
* Develop and optimize a remediation strategy for the source zone of a contaminated site
* Optimize a remediation strategy for a contaminant plume
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Conceptualization and setup of a conceptual model including geology and hydrogeology ===
<div class="mw-collapsible-content">
[[File:SE-NO_profil.jpg |thumb|550px|Example geologic profile of a Geoscene3D model.]]
==== Geologic modeling ====
Borehole data, outcrops, geophysical measurements etc. can give valuable information about the [[ Geology and properties of limestone | geology ]] at a site.
Bits of geologic knowledge can be connected to establish a geologic model, that shows different geologic layers and relevant geologic features (like inclusions or lenses).
Typically, these layers are characterized by different hydrogeologic properties.
The geometry can be stored as a CAD interpolation of the surfaces, that delineate the geologic layers.
Tools like GeoScene3D can be very useful to manage borehole data and to create interpolation surfaces.
The surfaces can be imported into the numerical model later on.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Definition of the model scope ===
<div class="mw-collapsible-content">
The scale also depends on the modeling objectives.
The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) and for the planning of source zone remedial actions (local scale).
An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells.
The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest.
It should be chosen based on physically meaningful boundaries (f.e. known head isolines or no-flow boundaries).

The modeling of source zone remediation requires a different scale than the risk assessment of a contaminant plume for water works.
The following scales can be distinguished:
* well or borehole scale
* source zone scale
* intermediate scale for e.g. pumping tests
* plume scale

Based on available data and modeling objectives, the model complexity has to be chosen.
A very complex and detailed model is not appropriate if only little field data is available.
Then, a simple model can be applied, which can be improved as soon as new data is measured.

Modeling was an integral part in the limestone project and already done at an early stage of the project.
Initially, a rough model based on first measurements and available data was setup.
It was used for the planning of further field work and measurements.
It also helps to identify further data requirements and to plan measurements that support the modeling.
These additional measurements and data can then be incorporated in the model.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model) ===
<div class="mw-collapsible-content">
See Chapters [[Data acquisition]] and [[Transport parameters and contaminant data]].
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous) ===
<div class="mw-collapsible-content">
Based on available data and the chosen model, parameter distributions have to be defined.
For a steady-state flow simulation, the hydraulic conductivity (or permeability) is required.
For transport, parameters like porosity, (effective) diffusion coefficients, dispersivities and sorption parameters are required.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Choice of boundary conditions and sources/sinks ===
<div class="mw-collapsible-content">
Boundary conditions should be chosen according to known or delineated boundaries, such as geologic boundaries, known hydraulic head isolines, known flowlines (can be used as no-flow condition perpendicular to them, if the flow field is stable).
The most common boundary conditions are
* Dirichlet conditions (or first-type boundary conditions), where the primary variable is fixed to a value (e.g. fixed hydraulic head or fixed concentration).
* Neumann conditions (or second-type boundary conditions), where the gradient of the primary variable is specified (e.g. flux across the boundary, often no-flow boundaries)
* Cauchy conditions (or third-type boundary conditions), which sets a condition to the primary variable and its derivative (used f.e. for the infiltration flux through a river bed).
The proper choice of boundary conditions is a very important step and determines the calculated results.

Sources and sinks can be added in the model domain to include e.g. withdrawal/injection at wells or groundwater recharge due to precipitation.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== For transient models: definition of initial conditions ===
<div class="mw-collapsible-content">
Steady-state models do not require the definition of initial conditions.
Transient problems, however, require to specify the initial value of the primary variables (e.g. concentrations at each location of the model domain.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Mesh generation ===
<div class="mw-collapsible-content">
[[File:MeshExample.png |thumb|right|500px|Example a mesh used for discrete-fracture simulations of the Akacievej tracer tests. The mesh is refined at the horizontal fractures and at the wells.]]
When working with complex models it is useful to start with a coarse mesh to test the model and the setup with limited time efforts.
When everything is properly setup, a finer grid can be employed.

Modern grid generators allow a local mesh refinement at specific parts of the mesh.
Especially at heterogeneities and fractures, at wells and at concentration fronts, the mesh should be sufficiently fine to resolve the local gradients (e.g. of concentration or head gradients) appropriately.
Locations, where strong gradients of the primary variables (head, concentration) occur, should be resolved at a high resolution, while for the parts of the model domain with only small changes, a coarser mesh resolution may be sufficient.

If the applied mesh is sufficiently fine can be tested by a grid refinement study, where the mesh is gradually refined and the results are compared.
When the solution does not significantly change with a further grid refinement, the grid resolution is sufficient.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Simulation ===
<div class="mw-collapsible-content">
After setting up the geometry, boundary conditions, initial conditions, material parameters and simulation parameters (simulation time, solver settings), the actual simulation can be run.
It is always a good idea to start with a test run, f.e. with a coarse mesh and a short duration, to test if everything is set as desired.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Critical evaluation of the modeling results ===
<div class="mw-collapsible-content">
Modeling results should always be critically evaluated and the model should be properly tested.
It is, for example, helpful, to check the mass balance of a model, i.e. to balance all inflows and outflows and the storage in the model domain.
It is also important to visually inspect the results, f.e. by visualizing the hydraulic heads and concentrations in the domain and in special areas of interest.
Then, it should be checked, if the results look reasonable and as expected, if the boundary conditions are fulfilled and if there are any disturbances like oscillations in the model domain.
Oscillations can be an indication for a too coarse mesh.
It is also a good idea to test for grid convergence, i.e. to test if the model results change, when the numerical grid is refined.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model calibration and validation ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model reporting ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

== Example: Setup of a COMSOL Multiphysics model for a contaminated site with a fractured limestone aquifer (Akacievej, Hedehusene) ==
The setup of a discrete-fracture model in 2D in COMSOL Multiphysics using Coefficient Form PDEs is described in the following document:
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT]]
[https://www.comsol.com/ COMSOL] provides also the possibility to include fracture flow in the Darcy's Law interface, while fracture transport can be included in the Transport of Diluted Species in Porous Media interface.
We refer to the product documentation for more details.
[https://www.mikepoweredbydhi.com/products/feflow FEFlow] provides a tutorial, that describes the steps of setting up a flow and transport model and how to include discrete fractures.

DRAFT: The typical workflow for modeling a contaminated site will be demonstrated using an example field site close to Copenhagen.
[[ Example: Akacievej | Example: Setup of models for a field site (Akacievej, Hedehusene) ]]

{{Return}}
|}
[[Category:Modeling]]

Model setup

2019-07-03T12:03:42Z

Klmos: /* Choice of boundary conditions and sources/sinks */

{| class="side1"
!Highlights
|-
|
* Setup of a model for a fractured limestone aquifer
* Modeling objectives
* Typical steps of setting up a model for limestone aquifers
|}

{| class="body1"
|
== Steps to setup a model for flow and transport in fractured limestone aquifers ==
This chapter gives an overview of the recommended steps to setup a model for the simulation of flow and transport in a fractured limestone aquifer.
The following list shows the typical steps to setup a model for contaminant transport in a fractured limestone aquifer.
Expand an item (button on the right) to get more information about it.

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Formulation of the modeling objectives ===
<div class="mw-collapsible-content">
Before setting up a model, it is important to define the specific modeling objective(s).
The choice of the model concept, model extent, modeling scale and included details should be closely linked to these objectives.
One should aim at including the most relevant features in the model, while keeping it as simple as possible to address the modeling objective(s).

The following list gives some examples for modeling objectives:
* Delineate the capture zone of a well
* Improve risk assessment, e.g. for a contaminant threatening a drinking water well, in order to assess future actions
* Analyze the distribution and potential spreading of a contaminant plume in an aquifer
* Test hypotheses related to the origin of a contaminant
* Interpret observed / measured field data
* Analyze the influence of transient hydraulic conditions (annual variations, pumping in the area) on plume propagation
* Develop and optimize a remediation strategy for the source zone of a contaminated site
* Optimize a remediation strategy for a contaminant plume
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Conceptualization and setup of a conceptual model including geology and hydrogeology ===
<div class="mw-collapsible-content">
[[File:SE-NO_profil.jpg |thumb|550px|Example geologic profile of a Geoscene3D model.]]
==== Geologic modeling ====
Borehole data, outcrops, geophysical measurements etc. can give valuable information about the [[ Geology and properties of limestone | geology ]] at a site.
Bits of geologic knowledge can be connected to establish a geologic model, that shows different geologic layers and relevant geologic features (like inclusions or lenses).
Typically, these layers are characterized by different hydrogeologic properties.
The geometry can be stored as a CAD interpolation of the surfaces, that delineate the geologic layers.
Tools like GeoScene3D can be very useful to manage borehole data and to create interpolation surfaces.
The surfaces can be imported into the numerical model later on.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Definition of the model scope ===
<div class="mw-collapsible-content">
The scale also depends on the modeling objectives.
The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) and for the planning of source zone remedial actions (local scale).
An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells.
The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest.
It should be chosen based on physically meaningful boundaries (f.e. known head isolines or no-flow boundaries).

The modeling of source zone remediation requires a different scale than the risk assessment of a contaminant plume for water works.
The following scales can be distinguished:
* well or borehole scale
* source zone scale
* intermediate scale for e.g. pumping tests
* plume scale

Based on available data and modeling objectives, the model complexity has to be chosen.
A very complex and detailed model is not appropriate if only little field data is available.
Then, a simple model can be applied, which can be improved as soon as new data is measured.

Modeling was an integral part in the limestone project and already done at an early stage of the project.
Initially, a rough model based on first measurements and available data was setup.
It was used for the planning of further field work and measurements.
It also helps to identify further data requirements and to plan measurements that support the modeling.
These additional measurements and data can then be incorporated in the model.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model) ===
<div class="mw-collapsible-content">
See Chapters [[Data acquisition]] and [[Transport parameters and contaminant data]].
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous) ===
<div class="mw-collapsible-content">
Based on available data and the chosen model, parameter distributions have to be defined.
For a steady-state flow simulation, the hydraulic conductivity (or permeability) is required.
For transport, parameters like porosity, (effective) diffusion coefficients, dispersivities and sorption parameters are required.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Choice of boundary conditions and sources/sinks ===
<div class="mw-collapsible-content">
Boundary conditions should be chosen according to known or delineated boundaries, such as geologic boundaries, known hydraulic head isolines, known flowlines (can be used as no-flow condition perpendicular to them, if the flow field is stable).
The most common boundary conditions are
* Dirichlet conditions (or first-type boundary conditions), where the primary variable is fixed to a value (e.g. fixed hydraulic head or fixed concentration).
* Neumann conditions (or second-type boundary conditions), where the gradient of the primary variable is specified (e.g. flux across the boundary, often no-flow boundaries)
* Cauchy conditions (or third-type boundary conditions), which sets a condition to the primary variable and its derivative (used f.e. for the infiltration flux through a river bed).
The proper choice of boundary conditions is a very important step and determines the calculated results.

Sources and sinks can be added in the model domain to include e.g. withdrawal/injection at wells or groundwater recharge due to precipitation.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== For transient models: definition of initial conditions ===
<div class="mw-collapsible-content">
Steady-state models do not require the definition of initial conditions.
Transient problems, however, require to specify the initial value of the primary variables at each location of the model domain.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Mesh generation ===
<div class="mw-collapsible-content">
[[File:MeshExample.png |thumb|right|500px|Example a mesh used for discrete-fracture simulations of the Akacievej tracer tests. The mesh is refined at the horizontal fractures and at the wells.]]
When working with complex models it is useful to start with a coarse mesh to test the model and the setup with limited time efforts.
When everything is properly setup, a finer grid can be employed.

Modern grid generators allow a local mesh refinement at specific parts of the mesh.
Especially at heterogeneities and fractures, at wells and at concentration fronts, the mesh should be sufficiently fine to resolve the local gradients (e.g. of concentration or head gradients) appropriately.
Locations, where strong gradients of the primary variables (head, concentration) occur, should be resolved at a high resolution, while for the parts of the model domain with only small changes, a coarser mesh resolution may be sufficient.

If the applied mesh is sufficiently fine can be tested by a grid refinement study, where the mesh is gradually refined and the results are compared.
When the solution does not significantly change with a further grid refinement, the grid resolution is sufficient.
<br clear=all>
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Simulation ===
<div class="mw-collapsible-content">
After setting up the geometry, boundary conditions, initial conditions, material parameters and simulation parameters (simulation time, solver settings), the actual simulation can be run.
It is always a good idea to start with a test run, f.e. with a coarse mesh and a short duration, to test if everything is set as desired.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">
=== Critical evaluation of the modeling results ===
<div class="mw-collapsible-content">
Modeling results should always be critically evaluated and the model should be properly tested.
It is, for example, helpful, to check the mass balance of a model, i.e. to balance all inflows and outflows and the storage in the model domain.
It is also important to visually inspect the results, f.e. by visualizing the hydraulic heads and concentrations in the domain and in special areas of interest.
Then, it should be checked, if the results look reasonable and as expected, if the boundary conditions are fulfilled and if there are any disturbances like oscillations in the model domain.
Oscillations can be an indication for a too coarse mesh.
It is also a good idea to test for grid convergence, i.e. to test if the model results change, when the numerical grid is refined.
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model calibration and validation ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

<div class="collapsiblebar mw-collapsible mw-collapsed">

=== Model reporting ===
<div class="mw-collapsible-content">
more information will be included soon
</div>
</div>

== Example: Setup of a COMSOL Multiphysics model for a contaminated site with a fractured limestone aquifer (Akacievej, Hedehusene) ==
The setup of a discrete-fracture model in 2D in COMSOL Multiphysics using Coefficient Form PDEs is described in the following document:
* [[:File:WeakFormulation_toolbox.pdf |Instructions for setting up a discrete-fracture model in COMSOL Multiphysics (PDF) - DRAFT]]
[https://www.comsol.com/ COMSOL] provides also the possibility to include fracture flow in the Darcy's Law interface, while fracture transport can be included in the Transport of Diluted Species in Porous Media interface.
We refer to the product documentation for more details.
[https://www.mikepoweredbydhi.com/products/feflow FEFlow] provides a tutorial, that describes the steps of setting up a flow and transport model and how to include discrete fractures.

DRAFT: The typical workflow for modeling a contaminated site will be demonstrated using an example field site close to Copenhagen.
[[ Example: Akacievej | Example: Setup of models for a field site (Akacievej, Hedehusene) ]]

{{Return}}
|}
[[Category:Modeling]]

Literature and links

2019-07-03T10:55:25Z

Klmos: /* Reports */

== Literature ==
* Christ, J. and Goltz, M. (2002), ''Hydraulic containment: analytical and semi-analytical models for capture zone curve delineation.'' Journal of Hydrology 262 (2002), 224-244 [http://dx.doi.org/10.1016/S0022-1694(02)00026-4].
* Gerke, H.H. and van Genuchten, M.T. (1993), ''A dual-porosity model for simulating the preferential movement of water and solutes in structured porous media.'' Water Resources Research 29 (1993), [http://dx.doi.org/10.1029/92WR02339].
* Broholm, M.M. et al. (2016). ''Characterization of Chlorinated Solvent Contamination in Limestone Using Innovative FLUTe Technologies in Combination with Other Methods in a Line of Evidence Approach.'' Journal of Contaminant Hydrology 189 (2016), 68–85, [http://dx.doi.org/10.1016/j.jconhyd.2016.03.007].
* Mosthaf, K. et al. (2018). ''Conceptualization of flow and transport in a limestone aquifer by multiple dedicated hydraulic and tracer tests.'' Journal of Hydrology 561 (2018), 532-546, [https://doi.org/10.1016/j.jhydrol.2018.04.011].

== Reports ==
* [[:Media:Overview_reports_and_publications_limestone_project.pdf|Overview of reports and publications related to the limestone project (updated Feb 2017)]] (PDF)
* Galsgaard et al. (2014), [[:Media:Stroemning_og_stoftransport_i_kalklagene_pa_den_koebenhavnske_vestegn.pdf| Strømning og stoftransport i kalklagene på den københavnske vestegn]] (PDF)

* Mosthaf et al. (2016), [[:Media:Pumping_and_tracer_test_report.pdf|Pumping and tracer test in a limestone aquifer and modeling interpretation]] (PDF)

* Broholm et al. (2016), [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf|Sammenligning af niveauspecifikke prøvetagningsmetoder for vurdering af koncentrationsfordeling i kalkmagasin]] (PDF, in Danish)
* Thalund-Hansen et al. (2019), [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- og modelgrundlag for revurdering af afværgeanlæg]] (PDF, in Danish)

== Links ==
* [http://www.sara.env.dtu.dk/Samarbejdsprojekter/Kalk Kalk: Risikovurdering og oprensning (www.sara.env.dtu.dk)]

* [http://www.geus.dk/produkter-ydelser-og-faciliteter/data-og-kort/national-boringsdatabase-jupiter/ JUPITER database]

* [https://www.mikepoweredbydhi.com/products/feflow FEFlow]

* [https://www.comsol.dk COMSOL Multiphysics]

* [https://www.enviro.wiki/index.php?title=Main_Page Environmental restoration Wiki]

{{Return}}

Content

2019-07-03T10:53:51Z

Klmos: /* Field methods and conceptual model development */

__INDEX__
__NOTOC__
== Wiki: Investigation of contaminant transport in fractured limestone aquifers ==
[[Image:RegionH logo.png|right|180px|link=https://www.regionh.dk/]]
This is a Wiki about the fate of contaminants in fractured limestone aquifers. It is part of a collaboration project between DTU Environment and the [https://www.regionh.dk/ Capital Region of Denmark].<br />
The content is subject to changes and the Wiki is being further extended.<br />
''Authors:'' [https://www.dtu.dk/english/service/phonebook/person?id=93506 Klaus Mosthaf], [https://www.dtu.dk/english/service/phonebook/person?id=14939&cpid=39328 Annika S. Fjordbøge], [https://www.dtu.dk/english/service/phonebook/person?id=77203 Rasmus Thalund-Hansen], [https://www.dtu.dk/english/service/phonebook/person?id=277 Mette M. Broholm], [https://www.dtu.dk/english/service/phonebook/person?id=206 Poul L. Bjerg], [https://www.dtu.dk/english/service/phonebook/person?id=23688 Philip J. Binning] ([https://www.env.dtu.dk/ DTU Environment] )

<div class="content1">

<div class="toccolours mw-collapsible">
=== Introduction, geology and physical processes ===
<div class="mw-collapsible-content">
[[ Introduction and background ]] <br>
[[ Structure of the Wiki ]] <br>
[[ Geology and properties of limestone ]] <br>
[[ Physical processes and governing equations ]]
</div>
</div>


<div class="toccolours mw-collapsible">
=== Field methods and conceptual model development ===
<div class="mw-collapsible-content">
[[ Data acquisition | Data acquisition and methods to determine hydraulic parameters ]] <br>
[[ Transport parameters and contaminant data | Determination of transport parameters and contaminant distribution ]] <br>
[[ Conceptual modeling | Conceptual model development for a contaminated limestone site]] [[ The Akacievej field site |(based on example: Akacievej, Hedehusene) ]]
</div>
</div>


<div class="toccolours mw-collapsible">

=== Modeling contaminant transport in limestone ===
<div class="mw-collapsible-content">
[[ Model concepts | Model types for flow and transport in fractured aquifers ]] <br>
[[ Modeling tools | Modeling tools and useful helpers]] <br>
[[ Model setup | Setup of an advanced model for fracture flow and transport in a limestone aquifer ]] <br>
[[ Field data and model calibration | Model calibration with field data ]] <br>
[[ Model output | Recommendations for modeling fractured limestone aquifers and comparison of model concepts ]]

</div>
</div>

----

[[File:Outcrop small.jpg|border|right|550px|Limestone outcrop]]

[[ Literature and links|Literature, reports and links ]]

[[ Glossary ]]

[[ Involved people and impressum ]]
</div>

Conceptual modeling

2019-07-03T09:59:35Z

Klmos: /* Conceptual model development */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the [[The Akacievej field site|Akacievej field site]] based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Model output

2019-07-03T09:45:28Z

Klmos: /* Discussion of model concepts */ Revised chapter

{| class="side1"
!Highlights
|-
|
* Flow and advective transport mainly in fractures
* Standard equivalent porous medium model neglects interplay between fractures and matrix
* Mapping of well capture zones in fractured limestone difficult
* Plume migration in fractured limestone slows down with time due to matrix diffusion
* Predictions of different model types differ considerably
|}

{| class="body1"
|
== Discussion of model concepts ==
=== Equivalent porous medium (EPM) model ===
[[File:EPM_square.png|x200px|Equivalent porous medium approach.|frameless|right|Equivalent porous medium approach.]]
The EPM model is the simplest of the considered models and is widely used in practice.
Compared to the dual-continuum model or the discrete-fracture model, it has low computational costs.
It is well-established for porous media systems without fractures.
However, for fractured aquifers, it should only be used for a rough approximation and with care, particularly for solute transport.
It cannot reproduce the interactions between fractures and matrix (diffusive mass exchange, storage in matrix).
Particularly for long-term simulations, where matrix diffusion usually plays an important role, an EPM model will lead to incorrect results.

That the EPM model fails in fractured limestone aquifers becomes obvious when trying to simulate the tracer tests, which were performed at the Akacievej site.
A homogeneous EPM model could only reproduce the fast arrival observed in the tracer tests by lowering the (effective) porosity to very low values (below 1 %, in the order of the fracture porosity).
Then, however, the simulated peak concentrations were higher than the observed ones, because diffusive exchange of tracer with the matrix is neglected by the model.
Hence, the simulated tracer breakthrough concentration decreased early, and the tailing observed in the field tests could not be reproduced.
An application of the EPM model calibrated to one tracer test to another one with different flow conditions or at a different location lead to poor results and required a recalibration of the model.

It is possible to obtain a tailing in the simulated breakthrough curve if a heterogeneous parameter distribution in the porous medium is included (Figure 6.9), introducing very conductive structures and less conductive structures that are less penetrated by flow <ref>Pedretti et al. (2013), ''On the formation of breakthrough curves tailing during convergent flow tracer tests in three-dimensional heterogeneous aquifers'', Water Resources Research, 49, 4157-4173.</ref>.
However, the variation of the hydraulic conductivity has to be of a similar order of magnitude as the contrast between fracture and matrix conductivity and it has to have a similar connectivity of the highly conductive zones (fractures).
Note that a different vertical placement of the screens for injection and extraction can also lead to a tailing in the breakthrough curves.

The use of an EPM model for the simulation of the fate of a contaminant in a fractured limestone aquifer is not recommended, because exchange processes between fractures and matrix are generally neglected and model results may be misleading for risk assessment or remedial planning.
For example, remediation times can be greatly underestimated because the effect of back-diffusion from the matrix cannot be reproduced.
It is preferable to include fractures in a model as discrete features in order to better reproduce the actual physics.
<br clear=all>

=== Dual-continuum model (DCM) ===
[[File:DualContinuumSchematics.png|x180px|Dual continuum approach.|frameless|right|Dual continuum modeling approach.]]
The dual-continuum model matches the observed tracer breakthrough curves from the Akacievej tracer tests better than the EPM model.
The fractures and the matrix are each represented as a continuum and the coupling of the two continua allows for an exchange of substances between fractures and matrix.
With a DCM, the breakthrough behavior can be reproduced by choosing appropriate fracture and matrix porosities and conductivities, and by fitting the parameters controlling the exchange between fractures and matrix (Dpm, α, a).
However, this concept has many degrees of freedom, and it is not clear how to determine the required parameters governing the fracture-matrix exchange experimentally.
The DFM is also reported in the literature to be a “black-box” model <ref name="Riley" />.
The computational effort required to run this model type is usually moderate.
It has been reported in the literature that the dual-continuum model has to be recalibrated, when it is used with different flow conditions or at different scales.
<br clear=all>

=== Discrete-fracture model (DFM) ===
[[File:DFM.png|Discrete-fracture approach.|x180px|frameless|right|Discrete-fracture approach.]]
The discrete-fracture model aims at representing the actual physics in a fractured limestone aquifer and yields the best results.
Drawbacks are the often limited knowledge of the fracture parameters and geometry, the complexity of the model and the high computational costs.
The inclusion of fractures requires a very high grid resolution next to them to correctly resolve concentration gradients, and the computational effort usually limits the number of fractures that can be included in a model.

When setting up the model for the tracer tests at the Akacievej site, it was sufficient to include major horizontal fractures to provide preferential flow paths for the tracer transport to obtain a fast tracer arrival and the tailing caused by the matrix diffusion.
However, this has to be based on the observed fracture pattern.
The horizontal fractures were placed at locations where high-flow zones were seen on flow logs in the boreholes (indicating horizontal fractures), see Chapter [[Data acquisition]] for more information.

However, at the Akacievej site, the limestone is likely to have many more fractures at different scales, providing a bigger specific surface area for the exchange between fractures and matrix and leading to more matrix diffusion.
The neglected fractures can be accounted for by adjusting the effective matrix diffusion coefficient, which also controls the exchange fluxes between fractures and matrix.
Since the major horizontal fractures were resolved in the model and neglected fractures were mostly subvertical and vertical ones, only the vertical components of the effective diffusion coefficient were increased.
This is described further in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]
Moreover, increasing the effective diffusion coefficient can also help to account for stagnant flow zones, small-scale turbulences and channeling within fractures with varying aperture <ref name="Riley">Riley et al. (2001), ''Converging flow tracer tests in fissured limestone'', Quarterly Journal of Engineering Geology and Hydrogeology, 34, 283-297.</ref> <ref>DeDreuzy et al.(2013), ''Multi-Rate Mass Transfer (MRMT) models for general diffusive porosity structures'', Advances in Water Resources, 76, 146-156.</ref>.
However, the increased effective diffusion coefficient may have to be adjusted when a different spatial or temporal scale is simulated.
In the simulations of the tracer tests at the Akacievej site, the effective diffusion coefficient had to be increased by a factor of 100 to 1000 in order to fit the observed breakthrough behavior.
<br clear=all>

== Comparison ==
[[File:HeadsAroundGeo17.png|Head distribution around a pumped well. First figure: no pumping. Second figure: simulated heads while pumping and using a DFM Third picture: heads simulated with an EPM model that does not include fractures. Clear differences of the hydraulic head distributions can be observed for the two different models.|frameless|right|Dual continuum modeling approach.]]
The tracer tests and model applications have clearly shown that a crucial aspect of the transport of a substance in fractured limestone cannot be reproduced with a simple equivalent porous medium model: the diffusion and back-diffusion of a substance between fractures with strong flow and low-conductive matrix.
In a fractured aquifer, this should be accounted for, or the propagation of a substance will not be realistically simulated.
Hence, the use of a traditional equivalent porous medium model is not recommended for fractured limestone aquifers.

The dual-continuum model can describe the exchange between fractures and matrix while keeping computational efforts low.
However, the specification of the exchange terms between fracture and matrix continuum has a crucial influence on the modeling results and a physically-based choice is often challenging.
It is not clear how to determine the exchange parameters by measurements.
Further, it is questionable if a model, once calibrated, can be employed at a different scale without modifying the used parameters.
A requirement for the use of a dual-continuum model is a fracture network with many connected fractures with a relatively uniform distribution, since the fractures are represented as averaged quantities in the fracture continuum.

The use of a discrete-fracture model comes with the cost of being the most complex and numerically demanding model described here.
However, it represents the actual physics best and can, depending on the knowledge of the fracture system, yields the best results.
Usually, only few details about the fracture network are available, which restricts the setup of a detailed model.
In this study, the information provided by flow logs could successfully be used to setup a representative network containing the major horizontal flow paths.
But such a model does not contain smaller fractures and to compensate for that the diffusion coefficient governing the exchange between fractures and matrix had to be greatly increased.
With that, the measured breakthrough curves from the tracer tests could be reproduced.
The tracer test in Geo18s before pumping clearly shows that the discrete-fracture model best reproduced the observed data.

Since matrix and fractures are both included in the model and the exchange between the two happens naturally (continuity of fluxes, concentrations and heads at the fracture-matrix interface), the discrete-fracture model is the recommended approach in cases where fractures dominate the transport behavior and matrix diffusion occur.
Even a simple analytical tool (such as Chambon et al. 2011 <ref name="Chambon">Chambon et al. (2011), ''A risk assessment tool for contaminated sites in low-permeability fractured media'', Journal of Contaminant Hydrology, 124, 82-98.</ref>) or a dual-continuum model should be preferred to an equivalent porous medium model, which completely neglects the influence of the fractures.

== Recommendations for modeling flow and transport in fractured limestone aquifers ==
[[File:IntegratedModelingApproach.png|thumb|right|Integrated modeling approach: combination of modeling, collection of data and field work and update of the conceptual model.]]
* Modeling should be included at an early stage of a project based on the available data. This can be used to plan further measurements and investigations.
* Traditional contaminant transport models fail at reproducing important processes in fractured aquifers (diffusion into matrix and back, slowing down of plume migration speed with time, extent of capture zones) and are not recommended for for fractured limestone geologies similar to the Akacievej site.
* It is better to use a simple analytical model (as f.e. presented in Chambon, 2011<ref name="Chambon" />) for the modeling than to use an equivalent porous medium model, which neglects the presence of fractures.
* In general, it is a good idea to start with a simple model and to increase complexity. If the results look strange, try to simplify the system.
* Always be critical with modeling results.
* When a discrete-fracture model is used, the mesh resolution has to be high in the vicinity of the fractures in order to properly approximate the gradients of primary variables there.
* A too coarse grid resolution can lead to oscillations in the solution and a bad convergence behavior.
* The mesh resolution is fine enough, when the results do not change when the mesh is further refined. This should be tested to avoid a mesh-dependency of the modeling results.

{{Return}}
|}
[[Category:Modeling]]

Conceptual modeling

2019-06-26T13:02:21Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site (separation pumping, bladder pump, snap samplers, diffusion cells) are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T13:01:35Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques (separation pumping, bladder pump, snap samplers, diffusion cells).

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T12:59:38Z

Klmos: /* Conceptual model development */ Small updates in the flow field section

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous hydraulic head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine the potential migration pathways of contaminants, it is important to have knowledge of the local groundwater flow field.
A good indication is given by the hydraulic head distribution in the area and an isopotential map.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site in 2015, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.
A new isopotential map was created in 2018.
It showed only minor changes of the flow field since the sounding round in 2015, indicating stable flow conditions.
The groundwater table was about 50 cm higher than in 2018, but this was relatively uniformly distributed in the investigated area.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T12:45:29Z

Klmos: /* Conceptual model development */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine, where contaminants may migrate, it is important to have knowledge about the local flow field.
This can be approximated by the hydraulic head distribution in the area.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation (winter 2014). The vertical PCE distribution along a central flow line through the plume is shown.]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T12:32:00Z

Klmos: /* Contaminant distribution and dynamics */ Included re-evaluation of Akacievej report and added some info about it

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine, where contaminants may migrate, it is important to have knowledge about the local flow field.
This can be approximated by the hydraulic head distribution in the area.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T12:27:37Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine, where contaminants may migrate, it is important to have knowledge about the local flow field.
This can be approximated by the hydraulic head distribution in the area.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- and modeling basis for the re-evaluation of the remediation system(PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}

[[Category:Modeling]] [[Category:Field methods]]

Conceptual modeling

2019-06-26T12:23:18Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine, where contaminants may migrate, it is important to have knowledge about the local flow field.
This can be approximated by the hydraulic head distribution in the area.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.

In 2018, the picture of the PCE distribution was updated by depth-specific measurements in the source- and plume area using a bladder pump.
An updated map of the contaminant distribution was made and documented in the following report (in Danish):
* [[:Media:Akacievej-Data-og_modelgrundlag_for_revudering_af_afværgeanlæg.pdf|Akacievej - Data- og modelgrundlag for revurdering af afværgeanlæg (PDF)]]

This served as input for combined 2D and 3D modeling of the plume dynamics, which are further described in the report.
The detailed 3D model of the source zone, that was previously calibrated to the tracer tests, was employed to simulate the evolution of the contamination distribution and to estimate the contaminant flux out of the source zone.
This contaminant flux was used as input for a plume-scale 2D model to investigate the long-term effects of the remediation system on the plume propagation.
The model results showed possible effects of different remediation strategies and contributed to the re-evaluation of the remedial system at the Akacievej site.



{{Return}}
|}
[[Category:Modeling]] [[Category:Field methods]]

Physical processes and governing equations

2019-05-29T14:32:22Z

Klmos: /* Governing equations */

{| class="side1"
!Highlights
|-
|
* Description of major physical processes in limestone aquifers
* Governing equations for flow and transport in limestone
|}

{| class="body1"
|
== Physical processes ==
Flow in fractured limestone can be very complex, because strongly contrasting flow conditions between fractures and matrix can prevail.
The flow in the fractures can be very fast, whereas it is usually very slow in the limestone matrix.
The hydraulic conductivity in the matrix can be orders of magnitude lower than the fracture hydraulic conductivity.
The combined hydraulic conductivity of fractures and matrix is called bulk hydraulic conductivity.

Transport of substances in porous media can be subdivided in advective transport (due to the groundwater flow) and diffusive/dispersive transport (related to concentration gradients).
The fate of contaminants in fractured limestone aquifer is determined by both, transport in fractures and the matrix.
The fractures are the primary transport pathways for contaminants, where mainly '''advective transport''' dominates.
The hydraulic conductivity of the fractures is mainly depending on their aperture (width).
For an estimation of the flow velocity in fractures, the cubic law is often used as approximation.
With that, the water flux scales with the third power of the fracture aperture.
Hence, fractures with a big aperture are far more important as small fractures, since the total water flow and the flow velocity velocity are greater in them.
The connectivity of the fractures is another very important parameter for the spreading of a substance in the aquifer.

While being transported through the fractures, the contaminant '''diffuses''' into the surrounding matrix, which provides usually a high porosity and can store substantial amounts of contaminants.
As a consequence, the concentration in the fracture decreases.
The continuous diffusion from the fractures into the matrix slows the propagation speed of the plume more and more down.
Once diffused into the matrix, it is difficult to remove the contaminant again.
Due to the extremely low flow velocities in the limestone matrix, the removal of contaminants from the matrix with a pump-and-treat remediation happens mainly due to back-diffusion from the matrix into the fractures, which can take very long.

Part of the contaminant can be '''sorbed''' to the surface of the limestone matrix (and the fracture walls), which has a retarding effect on plume propagation.
The sorption behavior is often quantified by sorption coefficients or retardation coefficients.
Furthermore, contaminants can be '''degraded''' by microbial activity, if the proper microbes are present and the conditions are favorable (for PCE: anaerobic conditions).

== Governing equations ==
The basic equations for flow and transport in fractured porous media are shown below.
For more details, be referred to standard literature like e.g. Bear, J. (1972) <ref> Bear, J. (1972), ''Dynamic of fluids in porous media''</ref> or Fetter, C.W. (2008) <ref>Fetter, C.W. (2008), ''Contaminant hydrogeology''</ref>.

=== Flow ===
Groundwater flow in porous media is usually described by Darcy's law, giving a relation between hydraulic head gradient and groundwater flow, with the hydraulic conductivity as proportionality factor.
The flow field is calculated by solving the mass balance for incompressible fluid flow in combination with Darcy's law.

''Mass balance equation'' for incompressible fluid flow: <br>
<math> S_\text{s} \frac{\partial h}{\partial t} - \nabla \cdot (\mathbf{K} \nabla h) = q_\text{w} </math>

''Darcy's law'' (also used in the fractures with the fracture hydraulic conductivity $k_f$) relates water fluxes to hydraulic head gradients: <br>
<math> q_\text{darcy} = -\mathbf{K} \nabla h </math>

The hydraulic conductivities in the fractures can be several orders of magnitude higher than the conductivity of the limestone matrix.
The fracture conductivity is usually calculated via the hydraulic fracture aperture using the '''cubic law'''<ref name="witherspoon1980">Witherspoon et al. (1980), ''Water Resources Research'', Vol. 16, p. 1016-1024 </ref>, which gives a relation between fracture aperture and fracture conductivity.
The cubic law considers the fracture flow as flow between parallel plates with no roughness.

With the ''Cubic law'', the fracture conductivity can be estimated as: <br>
<math> K_\text{f} = \frac{(2b)^2 \rho_\text{w} g}{12 \mu_\text{w}} </math>

{| class="wikitable"
|-
! Variable !! Name !! Unit
|-
| <math> S_\text{s} </math> || specific storage || <math> \text{1/m} </math>
|-
| <math> t </math> || time || <math> \text{s} </math>
|-
| <math> \mathbf{K} </math> || hydraulic conductivity || $\text{m/s}$
|-
| <math> q_\text{w} </math> || water sources/sinks || <math> \text{m}^3\text{/m}^3 </math>
|-
| <math> q_\text{darcy} </math> || Darcy flux || <math> \text{m}^3/\text{(m}^2 \text{s)} </math>
|-
| <math> K_\text{f} </math> || fracture conductivity || <math> \text{m/s} </math>
|-
| <math> 2b </math> || hydraulic fracture aperture || <math> \text{m} </math>
|-
| <math> \rho_\text{w} </math> || density of water || <math> \text{kg/m}^3 </math>
|-
| <math> \mu_\text{w} </math> || dynamic viscosity of water || <math> \text{Pa} \cdot \text{s} </math>
|-
| <math> g </math> || gravity constant || <math> \text{m/s}^2 </math>
|}

=== Contaminant transport ===
The advection-dispersion equation (ADE) can be used to describe the transport of a solute in a porous medium.

''Transport equation'' for a dissolved species: <br>
<math>(n + \rho_\text{b} k_\text{d}) \frac{\partial c}{\partial t} + \nabla \cdot (n \mathbf{v} c) - \nabla \cdot (n \mathbf{D}_\text{m} \nabla c) = q_\text{m}</math>

The first term describes the storage (here including retardation due to linear sorption), the second and third terms describe advective and dispersive transport of a solute.
Degradation can be accounted for as additional source/sink term.

''Transport in fractures'': <br>
<math> 2b R_\text{f} \frac{\partial c_\text{f}}{\partial t} + \nabla \cdot (2b \mathbf{v}_\text{f} c_\text{f}) - \nabla \cdot (2b D_\text{f} \nabla_\text{T} c_\text{f}) = q_\text{f}</math>

Variables are:

{| class="wikitable"
|-
! Variable !! Name !! Unit
|-
| <math> n </math> || porosity || $ - $
|-
| <math> q_\text{m}\text{,} q_\text{f} </math> || mass sources and sinks, also degradation || $ \text{kg/(m}^3 \text{s)} $
|-
| <math> c_\text{f} </math> || concentration in the fractures || $ \text{kg/m}^3 $
|-
| <math> \rho_\text{b} </math> || bulk density || $ \text{kg/m}^3 $
|-
| <math> k_\text{d} </math> || sorption coefficient || $ \text{m}^3\text{/kg} $
|-
| <math> c </math> || concentration || $ \text{kg/m}^3 $
|-
| <math> \mathbf{v} </math> || flow velocity in the matrix || $ \text{m/s} $
|-
| <math> \mathbf{v}_\text{f} </math> || flow velocity in the fractures || $ \text{m/s} $
|-
| <math> R_\text{f} </math> || retardation factor accounting for sorption to the fracture walls || $ 1 $
|-
| <math> \mathbf{D}_\text{m}\text{,} D_\text{f} </math> || hydrodynamic dispersion tensor and coefficient|| $ \text{m}^2\text{/s} $
|-
| <math> \nabla_\text{T} </math> || tangential gradient || $ \text{1/m} $
|}

=== Coupling of flow and transport between fractures and matrix ===
The fracture and the matrix system are coupled by the continuity of water fluxes and solute fluxes at the fracture-matrix interface.
Furthermore, the hydraulic head and the solute concentration are continuous at the interface between fractures and matrix.

{{Return}}
[[Category:Introduction]]

Conceptual modeling

2019-04-24T15:57:54Z

Klmos: /* Contaminant distribution and dynamics */

{| class="side1"
!Highlights
|-
|
* Development of a conceptual model
* Geologic modeling
* Flow field determination
|}

{| class="body1"
|
== Conceptual model development ==
This chapter describes the development of a conceptual model for the Akacievej field site based on a set of field measurements and modeling.

[[File:Geology_Akacievej_GEO_extended.png|thumb|500px|Fig.1: Geology at the Akacievej site.]]
=== Geologic model ===
Data from boreholes (drilling reports), borehole cores, geophysical measurements, larger-scale geologic maps and expert knowledge were combined to setup a 3D geologic model using the software GeoScene3D.
The top of the limestone layer, the transition from crushed to fractured limestone and the transition from the København's kalk to bryozoan limestone were determined in an array of boreholes and the data was spatially interpolated to obtain 3D surfaces that can be used in a numerical flow and transport model.
A cross section of the geologic model at the Akacievej site is shown in Figure 1 and described in the Chapter [[Geology and properties of limestone]].

[[File:Heads_Akacievej_2015.png|500px|thumb|Fig.2: Flow field at Akacievej determined by a synchronous head leveling campaign in spring 2015.]]
=== Flow field and isopotential map ===
To determine, where contaminants may migrate, it is important to have knowledge about the local flow field.
This can be approximated by the hydraulic head distribution in the area.
At the Akacievej site, several synchronous hydraulic head measurement campaigns were done to determine the hydraulic head distribution in the larger plume area and to assess the temporal variation of the flow field.
Therefore, the hydraulic heads in the boreholes in a larger area around the Akacievej site were sounded on the same day using dipmeters.

For the head measurements at the Akacievej site, the remediation system at the site and the wells of the Fløng waterworks were switched off in advance before measuring the heads.
The measured heads were included in a geographic information system (GIS) and an isopotential map was created.
It can be beneficial to include wells in an area larger than the area of immediate interest (e.g. plume), to get a good picture of the regional groundwater flow and to allow the choice of a model domain with little influence of the boundaries on the flow field in the area of interest.
Figure 2 shows the isopotential map that was created for the area around the Akacievej field site in 2015.

=== Determination of aquifer parameters ===
A combination of methods was tested and used to determine aquifer parameters at the Akacievej site.
The hydraulic conditions were investigated with a long-term pumping test, short-term pumping tests, packer tests and vacuum slug tests.
This was complemented by head measurements at the remediation well and at the wells of neighboring waterworks during operation and while the pumps were switched off.
Additional measurements included geophysical borehole logging with flow logs, gamma logs, caliper probes, density and porosity measurements and temperature probes.

The remediation system was turned off and on several times while monitoring the head changes in the remediation well and in observation wells in the area with pressure transducers.
Groundwater flow fields could be determined with and without remedial pumping.
The pumping-test like event of switching the remediation well on and off yielded drawdown- and recovery curves and allowed to determine the hydraulic conductivity around the remediation well.

The following report contains a detailed description of a long-term pumping test that was conducted at the Akacievej site in combination with six tracer tests and PCE measurements:
* [[:Media:Pumping_and_tracer_test_report.pdf |Report about the pumping and tracer tests at Akacievej, Hedehusene (PDF)]]

To investigate the transport behavior in the aquifer, six tracer tests were completed in combination with the long-term pumping test at Akacievej in spring 2016.
Model simulations guided the design of the tracer tests.
Tracer was injected at four different screened wells, which have wells screens at different depths and in different geologic aquifer units.


[[File:PCE_distribution_wRemediation.png|500px|thumb|Fig.3: PCE distribution at Akacievej during remediation]]

=== Contaminant distribution and dynamics ===
The PCE concentrations at the Akacievej site were monitored in the pumped water from the remediation well (PB) since the installation of the remediation system.
Additionally, several sampling rounds were done in the period from 2014-2016 and 2018 using different sampling techniques.

The wells were also sampled under different conditions:
* No pumping at the site
* Remediation system running
* Before, during and after the long-term pumping test
This showed strong dynamics of the PCE distribution in the aquifer - the pumping had a strong influence on the observed concentrations in the wells at Akacievej.

The different depth-discrete sampling methods that were used at the Akacievej site are described in detail in the following report (in Danish):
* [[:Media:Sammenligning_af_niveauspecifikke_prøvetagningsmetoder.pdf |Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)]]

To improve the understanding of the contaminant dynamics in the greater source zone under different pumping conditions, a detailed 3D flow and transport model was setup in COMSOL Multiphysics.
A discrete-fracture model was used to account for the interactions between major horizontal fractures and matrix.
The horizontal fractures had been identified from flow logs in some of the wells in the area.
A stationary flow model was setup and compared to the drawdown measurements from the remediation system and from the long-term pumping test.
The fracture aperture and the hydraulic conductivity of the crushed limestone (where fractures were not resolved) were varied to match the observed drawdown in the wells.
The hydraulic conductivity of the limestone matrix in the fractured limestone was obtained from hydraulic tests on subcores from the intact limestone matrix.
The steady-state flow model served as basis for the transport models.

The tracer tests allowed to estimate the limestone porosity and an effective diffusivity (the diffusivity had to be increased to account for neglected small fractures).
Porosity and hydraulic conductivity measurements on limestone probes from borehole cores were done with steady-state gas permeameter and porosimeter (PoroPerm) tests.
They were used for the hydraulic properties of the limestone matrix in the discrete-fracture model.
To analyze the origin of PCE that was observed in the wells at the Akacievej site, the transport model was run on the inverse flow field.
This method can be employed to analyze the volume, where substances are coming from to the different observation boreholes under pumped and non-pumped conditions.



{{Return}}
|}
[[Category:Modeling]] [[Category:Field methods]]