A well extracting water from a confined aquifer will lower the piezometric head and create a cone of depression. In steady state, if the distance r to the point where the drawdown is wanted is smaller than the radius of influence R, then the drawdown s of a well pumping at rate 
in a confined aquifer of transmissivity T is
in a confined aquifer of transmissivity T is 
If the distance r is greater than the radius of influence, then the drawdown is zero. If multiple wells are pumping, the drawdown at the requested point is the sum of the drawdowns from the individual wells.
Boundaries, such as no-flow and constant-head boundaries, can be modeled using the method of images, as described in Cody Problem 57497. Each real well will have a corresponding image, and the drawdown will be the sum of the drawdowns from all wells—real and image. Recall from the previous problem that for no-flow boundaries, the image wells pump in the same sense as the real wells, whereas for constant-head boundaries, the image wells pump in the opposite sense as the real wells.
Write a function to compute steady-state drawdown in a confined aquifer. Input to the function will be the x- and y-coordinates of the points where drawdown is requested, the x- and y-coordinates of the real wells, the pumping rates and radii of influence of the wells, and the transmissivity of the aquifer. If a boundary is present, it will be specified by two pairs of x- and y-coordinates as well as a character string (‘NF’ for no-flow, ‘CH’ for constant-head).
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My results in test 5 are s = 0.5558 0.8738 -0.2454. Also, in test 8 my results for case 3 are very slightly outside of the 1e-3 tolerance from the test values.
OK, I will check. I computed test 8 by hand, and that matched the results from my code. I might loosen the tolerance there.
Did you see that I corrected the description to mention that if r > R, the drawdown is zero? I assume you did because the other tests seem to be working for you.
No, I didn't see the correction to the description, and that was apparently the reason for the differences. My results now all agree, including the tolerance issue on the last problem. I will submet my solution after I clean it up a bit. Thanks for the tip!