Page 181 - Water and wastewater engineering

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used to estimate the drawdown. Estimates of the transmissivity and storage coefficient
are required to use the transient flow equations.
(1) Transmissivity
Transmissivity can be obtained from the pumping test data. The pumping test data given
in the example problem statement are plotted on semilog paper as shown in Figure 4-14 .
From the straight line portion of the curve, select two points and calculate the transmis-
sivity using Equation 4-5:

Q ⎛ t 2 ⎞
T ln ⎜ ⎟
4p( s 1 ) ⎝ t 1 ⎠
s
2
3
.
,
0035 m/s ⎛ 1 700 min ⎞ 3 2
T ln 2 818 10 m //s
.
4p( . ) ⎝ 100 min ⎠
5 90 310.

3
Note that Q is not the design pumping rate of 32 m /h. It is the pumping rate used in the
pumping test.
(2) Storage coefficient
Using the Michigan Department of Environmental Quality rules, the drawdown must be
estimated based on 100 days of pumping. Because only one pump is required to meet
the maximum day demand, only the drawdown for one operating pump is required. The
storage coefficient ( S ) is estimated as follows:
In Figure 4-14 , extrapolate the straight line portion of the graph to the virtual starting
elevation of 0.0 m to find the virtual time: t 0 4.2 min.
Use Equation 4-6 to estimate S.

0.0

1.0
= 4.2 min
t o
2.0
Drawdown, m 3.0

4.0

5.0
6.0

7.0
4.0 10.0 100.0 500 1,000 2,000 5,000
Time, min
FIGURE 4-14
Pumping test curve for Example 4-7.