Figure 1: (top) Approximate area of interest and (bottom) conceptual cross section. Note that the initial head is assumed to be constant in the area of interest.
Background
A dispute has arisen between two farmers after one of the farmers installed a 500 GPM irrigation well 2000 ft from the small domestic water supply well of the other farmer (see above). After the irrigation well had been operating for 3 months it was observed that the water level in the domestic well had declined over 30 feet. The owner of the domestic well claims that the decline in water level in his well is due to pumping from the irrigation well and is trying to restrict that pumping. The owner of the irrigation well claims that the decline is related to the recent drought; he has been advised that the "radius of influence" of his well is at most 500 feet.
You are asked to determine whether it is possible for the water level decline in the domestic well to be produced by pumping from the irrigation well. It is known that both wells produce from the same completely confined aquifer. A prior well pumping test on the irrigation well indicates that the confined aquifer has a transmissivity of 1350 ft2/day and a storativity of 10-4.
Problem 1: Solve the problem analytically.
Problem 2: Solve the problem numerically and compare the result to your analytical solution.
Hints/Suggestions:
- Assume the initial head is zero and spatially-constant. (‘Initial’ refers to the instant the irrigation well is installed but has not yet started pumping).
- Assume a top elevation for the confined aquifer of -50 ft.
- Make sure the ‘no-flow’ side boundaries are sufficiently far away so that they are outside the area of influence under maximum pumping conditions. (Make the domain size at least twice as large as the area of interest).
- Use a very large grid size (NX=150).
- Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.