Groundwater is the water beneath the ground surface. It is a vast freshwater reservoir often overlooked because invisible, yet 1000 times greater than all lakes and rivers. The Earth is blue for its oceans, but green for the freshwater under our feet. Half of the world’s population rely on groundwater for drinking. Inadequate access to safe freshwater contributes to social, economic and political instability. Human activities can affect the quality of underground freshwater. Storage tanks and sceptic systems can leak, old landfills can seep, road salts can infiltrate the ground.
This course describes the principles of transport in aquifers so that engineers can predict and plan the safe extraction of groundwater for private and public use. Engineers design the treatment of contaminated groundwater in situ or above ground; they understand how to isolate and treat a plume of using the principles of transport processes in porous media. In the United States, the Safe Drinking Water Act directs the Environmental Protection Agency to establish maximum contaminant-level goals (MCLGs) and maximum contaminant levels (MCLs) for drinking water.
How do we know how safe well-water is? How do different contaminants move through aquifers? How do we model contaminant plumes from landfills or other sources?
In this course, we will cover the following topics:
1) The Advection Dispersion Equation: The fluxes of dissolved contaminants are dictated by the mixing of water in the porous media by dispersion and its relocation by advection. We derive and describe these processes both conceptually and mathematically.
2) Methods of Solution: We describe a number of methods to help solve the differential Advection Dispersion Equation. Analytical solutions can help with heuristics, but often more practical numerical methods such as particle tracking and finite differences can help understand the behavior in more complicated, heterogenous formations.
3) Issues with Dimensions (and Boundaries): Unlike streams and channels, aquifers cannot be modeled with one dimensional equation. We focus on two dimensional schemes that treat aquifers as plane from a top view.
4) Notions of Reactive transport: Aquifers process nutrients and other contaminants. The fate of a chemical may be complex but is often described as a simple upscaled process. We describe the assumptions tied to the bulk behavior.
5) Applications: In this last topic, we provide examples of landfill and well contamination and walk through an example of a MODFLOW model