Introduction and background

Introduction and background

The understanding of the fate and transport behavior of contaminant plumes from contaminated sites in limestone aquifers is important because these aquifers are often a major drinking water resource. This is challenging because limestone aquifers may be heavily fractured and contain chert layers and nodules, resulting in a complex flow and transport behavior. Standard field methods may give poor or misleading results and more advanced techniques, which can give information about processes and conditions in the fractures and in the limestone matrix are required. Different field methods have been developed in the past to better characterize the flow field and transport behavior in such aquifers. Moreover, specialized methods for determining aquifer parameters and estimating the contaminant distribution in fractured aquifers have been shown to be useful.

This wiki gives an overview of some useful methods for the assessment of contaminant plumes in fractured limestone aquifers and evaluates their effectiveness. Modeling can help with the interpretation of measurements and is a viable tool for the prediction of the contaminant behavior in the aquifer. It is, however, important to select an appropriate model, which does not oversimplify the studied system. Then, it can be used as a tool to advance the conceptual understanding and aid with decision support for risk assessment and remedial site management.

Fracture flow and transport models with different complexity are available for the modeling of contaminant transport. This wiki aims at giving an overview of modeling tools that can be used for the interpretation and prediction of flow and transport processes in fractured limestone aquifers. The focus is on dissolved chlorinated solvents (PCE, TCE etc.) as contaminants.

An overview of different model concepts are presented in the chapter Model concepts. The features and limitations of the models are discussed. The models will be compared for their suitability to simulate field data and to represent typical features of fracture flow and transport based on a field example (Example: Akacievej). Furthermore, it will be exemplified how to establish a conceptual model for a contaminated site. The steps how to build up a suitable numerical model will be described and recommendations for a good approach will be made.

Physical processes

Advection, diffusion and dispersion, fracture flow, sorption and retardation

Governing equations

Flow

Groundwater flow in porous media is usually described by Darcy's law, giving a relation between hydraulic head gradient and groundwater flow. Flow equation.

Contaminant transport

Transport equation

Properties of limestone

Borehole cores from the Akacievej field site.

Low conductive matrix - can be heavily fractured - chert layers and nodules - sorption behavior for chlorinated solvents

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