Synthetic Wellhead Protection Model

A small community pumps groundwater from a confined sandstone aquifer for their drinking water supply (see figure).  A recent monitoring study, however, shows that the aquifer is contaminated by a TCE plume near an industrial site upgradient of the community well. Although the well water is currently not contaminated, the citizens are concerned since groundwater is their exclusive source of water supply. The fact that groundwater is invisible make them particularly anxious. They need to know:

1. Under the suggested pumping rate of 500 GPM, will the community pumping affect the plume migration?

2. Under the suggested pumping rate, will the advancing plume hit the community well?

• If yes, how long will it take for the plume to reach the well?
• If no, increase the pumping rate (e.g. double it), and estimate how long it would take the plume to reach the well

3. What is the safe yield of the community wells? (The safe yield is defined as the maximum pumping rate that can be used without attracting contaminants).

4. What is the area of contribution (recharge area) of the community well for the case of safe yield? 

Suppose you are hired as a consultant by the local citizens, develop a quantitative analysis for the situation. Develop a 2D model of the groundwater flow using MAGNET to support your analysis.

Additional information/instructions:

• Suggested initial pumping rate of the community well, Q = 500 GPM
• Hydraulic conductivity of the aquifer: 100 ft/day
• Aquifer thickness: 100 ft
• Effective porosity: 0.2
• Both the river and stream are fully connected with the aquifer
• Top elevation of the aquifer: - 10 ft
• Bottom elevation of the aquifer: -110 ft
• Plume dimensions: 460 ft by 1045 ft
• Use particles to represent the plume, and a large number of grid cells (NX=100) in your model
• Make sure the ‘no-flow’ side boundaries are sufficiently far away so that they are outside the area of influence under maximum pumping conditions.
• Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.