Page 237 - Materials Chemistry, Second Edition

220 Practical Design Calculations for Groundwater and Soil Remediation

(b) To determine the radius of influence of the pumping well, set the
radius of influence (r ) at the location where the drawdown is
RI
equal to zero and use the drawdown information of the extrac-
tion well:
(200)(30)(68.7 − 80)
40 = → RI r = 270 ft
528 log[(2/12)/]r RI
or
2.73 [(200)(0.041)](9.1)(21.0 − 24.4)
[(0.15)(1, 440)] = → RI r = 82 m
log(0.051/ RI r )
Similar results can also be derived from using the drawdown
information of the observation well (r = 10 ft = 3 m) as:
−
(200)(30)(75 80)
40 = → r RI = 263 ft
528 log[10/]
r RI
or
−
2.73 [(200)(0.0410)](9.1)(22.9 24.4)
[(0.15)(1, 440)] = → h 2 = 78 m
r )
log(3/ RI
Discussion:
1. In parts (a) and (b), 0.041 is the conversion factor to convert the
hydraulic conductivity from gpd/ft to m/day. The factor was
2
taken from Table 3.1.
2. Calculations in part (a) have demonstrated that the results would
be the same by using two different systems of units.
3. The h -h term can be replaced by s -s , where s and s are the
1
2
1
2
2
1
drawdown values at r and r , respectively.
1
2
4. The differences in the calculated r values in part (b) come
RI
mainly from the unit conversions and data truncations.
Example 6.2: Estimate the Groundwater Extraction Rate from a Confined
Aquifer Using the Steady-State Drawdown Data
Use the following information to estimate the groundwater extraction rate of
a fully penetrating well in a confined aquifer:
• Aquifer thickness = 30.0-ft (9.1-m) thick
• Well diameter = 4-in. (0.1-m) diameter
• Well perforation depth = fully penetrating