Introduction: In this week’s lab we will examine a groundwater pollution source problem in the Madison-Bouckville outwash plain. The nature and details of the problem have been changed slightly because of proprietary information, but the substance of the circumstance is real. We will use our basic understanding of groundwater flow and apply two relatively simple modeling programs to analyze a domestic well pollution situation.

This lab will make use of the data and results from Lab #5, so please be sure to bring those data files with you – in particular you will find it useful to have the water table contour map (done in Surfer).

The Problem: The attached map illustrates the area of interest. The wells of Client 1 and Client 2 have both shown elevated levels of nitrate, which is a fairly common problem in this area. The area shown as ‘nitrate source’ was used as a storage area for bulk fertilizer (potassium chloride, potassium nitrate) by a major agricultural products supplier. The two clients have sued the supplier to recover costs and damages. The history of the clients’ wells and use of the storage area is summarized below:

1954-62: Fertilizer unloaded from railroad siding and carried to open storage piles.

1962-1977: Storage barns built and used for storage.

1977: Storage area abandoned.

1981: Storage areas cleaned; barns torn down.

Client #1 Well: (77 gpm)

May, 1971: Nitrate level of 36 mg/l detected in tap water sample

August, 1971: Nitrate level - 4 mg/l

June, 1993: Nitrate level - 44 mg/l

May, 1994: Nitrate level – 40 mg/l

August, 1994: Nitrate level - 6 mg/l

May, 1995: Nitrate level 39 mg/l – Well abandoned for domestic use

Client #2 Well: (34 gpm)

May 1971: Nitrate level – 4 mg/l

June 1993: Nitrate level – 37 mg/l

August 1993: Nitrate – 39 mg/l

May 1994: Nitrate level - 44 mg/l

August 1994: Nitrate level 44 mg/l – Well abandoned for domestic use

The clients claim that the fertilizer supplier is responsible for nitrate pollution in their wells. Does the hydrogeology of this site support the contention of either or both clients?

Your analysis should include the following:

1. A map illustrating the water table contours. This can be drawn directly from lab #5, but note that conclusions based on this map may not be accurate because of the wide spacing of data points.

2. A cross-section illustrating the subsurface geology of the site based on the well data set. Note that this cross-section should be drawn carefully with horizontal and vertical scales given, and geological and hydrologic contacts shown. When you have constructed the cross-section, examine the representative samples of the different aquifer materials and using the table in Heath, assign appropriate hydraulic conductivity (K) values to each stratigraphic unit. Define the aquifer, and determine a representative saturated thickness in the cross-section.

3. A determination of the direction and magnitude of the gradient of the water table in the area of interest. You may wish to use the method outlined on page10-11 in Heath to determine the gradient.

4. Calculation of seepage velocity in the aquifer. You may wish to review your class notes and page 25 in Heath.

5. A Quickflow model of the site that illustrates in map view the pathlines, sources and sinks in the area of interest. We will review this in lab.

6. A FlownetD model which illustrates the flow pattern in cross-section. We will review this in lab.

Discussion: Based on the analysis above, does either client have a case? Explain your reasoning clearly, and use additional maps or graphics to illustrate your argument.