Page 239 - Materials Chemistry, Second Edition

222 Practical Design Calculations for Groundwater and Soil Remediation

To determine the drawdown in the pumping well, set r at the
pum ping well = well radius = (2/12) ft = 0.051 m, and use
Equation (6.2):

2
(200)( 2 h 2 − 35 )
40 = → h 2 = 29.2 ft
1,055 log[(2/12)/10]
or
2
1.366 [(200)(0.0410)]( 2 h 2 − 10.7 )
[(0.15)(1440)] = → h 2 = 9.0 m
log(0.051/3.0)
So the drawdown in the extraction well = 40 − 29.2 = 10.8 ft (or
= 12.2 − 9.0 = 3.2 m)
(b) To determine the radius of influence of the pumping well, set r at
the radius of influence (r ) at the location where the drawdown
RI
is equal to zero. We can use the drawdown information of the
pumping well as:

2
(200)(29.2 2 − 40 )
40 = → RI r = 580 ft
1,055 log[(2/12)/ RI r ]
or
2
1.366 [(200)(0.0410)](9.0 2 − 12.2 )
[(0.15)(1440)] = → RI r = 168 m
log(0.051/ RI r )
Similar results can also be derived from using the drawdown
information of the observation well as:

2
(200)(35 2 − 40 )
40 = → RI r = 598 ft
1,055 log[10/ RI r ]
or
2
1.366[(200)(0.0410)](10.7 2 − 12.2 )
[(0.15)(1440)] = → RI r = 181 m
log(3/ RI r )
Discussion:
1. As discussed in Example 6.2, the h –h term in Equation (6.1) (for
1
2
confined aquifers) can be replaced by s –s . However, no anal-
1
2
ogy can be made here, that is, h –h in Equation (6.2) cannot be
2
2
1
2
replaced by s –s .
2
2
1
2
2. The differences in the calculated r values in part (b) come
RI
mainly from the unit conversions and data truncations.