Page 100 - Materials Chemistry, Second Edition

Plume Migration in Aquifer and Soil 83

• Aquifer thickness = 30 ft
• Pumping rate = 40 gpm
• Steady-state drawdown in the well = 11.3 ft

Solution:
(a) First let us determine the specific capacity. Use Equation (3.12):
Q 40
Specific capacity = = = 3.54 gpm/ft
s w 11.3
(b) The transmissivity of the aquifer can be estimated as:
T = (3.54)(2,000) = 7,080 gpd/ft
(c) The hydraulic conductivity of the aquifer can be estimated as:

K = T/b = 7,080/30 = 236 gpd/ft 2
Discussion:
The calculated hydraulic conductivity (236 gpd/ft ) from this exercise
2
is not much different from the value specified in Example 3.7 (200
gpd/ft ).
2

3.3.2 Steady-State Flow in an Unconfined Aquifer
The equation describing steady-state flow of an unconfined aquifer (water-
table aquifer) from a fully penetrating well may be written as follows:

Kh( 2 − h )
2
2
Q = 1 (AmericanPractical Units)
rr/)
1,055 log( 2 1
2
2
1.366 Kh( 2 − h )
= 1 (SIUnits) (3.13)
rr/)
log( 2 1
All the terms are as defined for Equation (3.10).
Equation (3.13) can be easily modified to calculate the hydraulic conductiv-
ity of an unconfined aquifer if data of two steady-state drawdowns and flow
rate are available.

1,055 r r/)
K = Qlog( 2 1 (AmericanPractical Units)
2
h −
2
( 2 h )
1
r r/)
= Qlog( 2 1 2 (SIUnits) (3.14)
2
h −
1.366 ( 2 h )
1