Transport parameters and contaminant data

Transport parameters

Advective transport happens mainly with the groundwater flow. However, to describe the transport of a substance in a fractured limestone aquifer properly, additional parameters are required. Important transport parameters that influence the migration of a substance are

• diffusion coefficient of the substance in the limestone (often estimated as molecular diffusion coefficient times the tortuosity or porosity of the limestone
• sorption coefficient
• limestone porosity

Tracer tests are very useful to analyze the transport behavior in a limestone aquifer. Different types of tracer tests can be distinguished

• push-pull tracer tests, where a tracer is injected and monitored in the same borehole
• tracer tests with an injection well and one or several observation wells
• forced-gradient (with pumping) or natural gradient tracer tests

In the limestone project, a forced-gradient tracer test with several injection wells and a central pumping well for tracer monitoring was conducted. Details are described in the report LINK TO REPORT.

Furthermore, measurements from core material can be used to determine the porosity and hydraulic conductivity of a limestone sample (poroperm tests).

Contaminant data

Different sampling and monitoring techniques to determine the depth-discrete contaminant distribution in boreholes have been developed. Depth-discrete sampling is important, since due to a very heterogeneous nature of the aquifer, the concentration can vary strongly over depth. For the planning of a site remediation it is important to know the vertical extent of the contamination, so the remediation system can be planned targeted on the high concentration zones.

The following list gives an overview of some useful sampling methods in wells in limestone aquifers:

• Snap samplers
• Diffusion cells
• Bladder pump
• Separation pumping with a heat pulse probe

The following ones require open (unscreened) boreholes:

• NAPL-FLUTe
• FACT-FLUTe
• Passive flux meters for fractured aquifers
• etc.

The following report gives a comparison of different sampling methods.

• Comparison of depth-discrete sampling methods and contaminant measurements at Akacievej (PDF)

Integral pump tests can be used to quantify the contaminant mass discharge through a control plane.

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