Page 246 - Materials Chemistry, Second Edition

Groundwater Remediation 229

TABLE 6.1
Characteristic Distances of the Capture Zone of a Network of Pumping Wells
No. of Optimal Distance Distance between Distance between the
Extraction between Each Pair the Streamlines at Streamlines at Far
Wells of Extraction Wells the Line of the Wells Upstream from the Wells
1 … 0.5(Q/Bu) (Q/Bu)
2 0.32(Q/Bu) (Q/Bu) 2(Q/Bu)
3 0.40(Q/Bu) 1.5(Q/Bu) 3(Q/Bu)
4 0.38(Q/Bu) 2(Q/Bu) 4(Q/Bu)
Source: Modified from [1].

n is the number of the pumping wells. This distance is twice the distance
between the streamlines at the line of the wells.
The downstream distance of a network of wells is very similar to that of
one pumping well, which is equal to Q/2πBu.

Example 6.7: Determine the Downstream and Sidestream Distances
of the Capture Zone of a Network of Wells
Two groundwater extraction wells are to be installed in an aquifer (hydraulic
conductivity = 1,000 gpd/ft , hydraulic gradient = 0.015, and aquifer thick-
2
ness = 80 ft).
The design pumping rate of each well is 50 gpm. Determine the optimal
distance between these two wells and delineate the capture zone of these
extraction wells by specifying the following characteristic distances of the
capture zone (see Figure 6.4):

(a) The sidestream distance from the wells to the envelope of the cap-
ture zone at the line of the pumping wells
(b) The downstream distance from the wells to stagnation points of the
envelope
(c) The sidestream distance of the envelope far upstream of the pump-
ing wells

Solution:
(a) Determine the groundwater velocity, u:
u = (K)(i) = [(1,000 gal/d/ft )(1 d/1,440 min)(1 ft /7.48 gal)](0.015)
2
3
= 1.39 × 10 ft/min
-3