EPSC 549
Hydrogeology
Winter 2005
Lab 7: Estimating aquifer properties from pumping test data
This lab is an introduction to the use of pumping test data to determine aquifer properties
such as T, K, and S. The analysis is performed on drawdown data collected at an
observation well in a completely confined aquifer. The derived aquifer parameters will
then be used to predict what the drawdown will be at a 3rd well (Farmer Bob’s stock well)
after 6 months of pumping. An image well is necessary to do this part of the problem.
Table 1 gives drawdown data measured at the observation well. Figure 1 shows the
relative location of the observation and pumping wells. Both wells are located in the
same completely confined aquifer. The pumping well was pumped at a constant
discharge of 200 gallons/minute for 400 minutes. From well logs, it is estimated that the
confined aquifer is 30 feet thick. The stock well is also completed in the same confined
aquifer.
Part 1. Use both the Theis and Jacob time vs. drawdown methods to calculate the
following aquifer properties:
a) transmissivity (ft2/day)
b) hydraulic conductivity (ft/day)
c) storativity (dimensionless)
Use the graph paper provided to plot the field data (by hand) and solve the calculations
using the Theis method. Use Excel for the Jacob method. Summarize your results in a
Table, and comment on the agreement between the two methods in your cover memo.
Look at your computed value of storativity .. is this value typical of confined or
unconfined aquifers?
Part 2. Use the aquifer properties you derived in Part 1 to estimate what the drawdown
will be at a Farmer Bob's well after 1 month (30 days) of continuous pumping at 200
gal/minute. Refer to Fig. 1 to see where is the relative location of the farmer's well and
the pumping well. Also on this sketch, notice the location of the Centennial Fault. This
is a vertical fault that juxtaposes alluvial sediments on the east against unweathered
granite bedrock on the west.
2a. Calculate the drawdown at farmer's well assuming no influence from the fault.
2b. If Farmer Bob had 15 feet of water in his well before the pumping began, will his
well go dry after 1 month of pumping?
2c. Repeat your calculation, but this time simulate the effect of the Granite Fault using an
image well. Refer to class notes on how to do this. Be sure to hand in the sketch map
showing where exactly you located your image well, and also show your calculations and
governing equations. Compare your results from 2a and 2b in your cover memo. Is the
farmer’s well going to go dry in the second (more realistic) scenario?
EPSC 549
Hydrogeology
Winter 2005
Table 1. Drawdown data:
elapsed time, min
1
1.5
2
3
4
5
6
8
10
15
20
drawdown, ft
0.06
0.159
0.285
0.51
0.78
0.93
1.14
1.5
1.74
2.25
2.55
elapsed time, min
30
40
50
60
80
100
150
200
300
400
drawdown, ft
3.15
3.6
3.9
4.2
4.5
4.95
5.4
6
6.6
7.2
Figure 1. Map of the field area
D
Observation
well
Centennial
Fault
Pumping
well
Farmer Bob’s
well
Centennial
Basin
Scale: 1” = 500 feet
N
U
Granite
Hills