HW#5 - Well Equations

1. A 12 inch diameter well was installed in a thick layer of sand. The water table was at elevation 2039 ft before pumping of the well began. The well was then pumped at a rate of 30 gallons per minute and the water level in the well dropped to 2014 ft after a steady-state condition was reached. The radius of well influence is 2000 ft. The elevation of the bottom of the sand layer = 2000 ft.

a. Calculate the permeability of the sand assuming the aquifer is confined and D = 10 ft.

b. Calculate the permeability of the sand assuming the aquifer is unconfined.

2. Click here to download a modified copy of the spreadsheet we developed in class for a well in an unconfined aquifer. Follow the instructions on the spreadsheet to add a drawdown correction term.

3. Two wells are installed a distance of 60 feet apart in an unconfined aquifer 40 feet thick. The water table is 5 feet below the ground surface. The hydraulic conductivity of the aquifer is 0.02 ft/min. The following information is also known for the wells:

Radius of well influence: 3000 ft
Diameter of well: 6 inches
Pumping rate per well: 35 gallons per minute per well

Compute and plot the drawdown surface produced by pumping the two wells under steady state conditions. Use a cross-section which passes through both wells. Do not use the "a" term to correct the drawdown. Set up your tables such that there is a column for h1 (head for well 1 assuming it is pumping independently), a column for h2 (head for well 2 assuming it is pumping independently), and a column for h1,2 (head resulting from two wells pumping simultaneously). Include all three curves on your plot. Make the x values in your table/plot vary from x=-250 to x=+250 with increments of 10 ft assuming x=0 exactly halfway between the wells. Your chart should look something like this (plus labels on the vertical axis):

NOTE: Some of your locations may coincide with the well locations. At these points, the radial distance r will be zero and you will get a divide by zero error on your formula. Change your formula at these locations to use rw instead of z for r. I.e., do not let the radial distance drop below the well radius.

Submittal Instructions

Put your solutions into a single spreadsheet or put your spreadsheets into a single zip archive. Upload your spreadsheet via Learning Suite.