Page 244 - Materials Chemistry, Second Edition

Groundwater Remediation 227

2. Do not specify the y values beyond the values of ±Q/2Bu. As
discussed, ±Q/2Bu are the asymptotic values of the capture zone
curve (x = ∞).

Example 6.6: Determine the Downstream and Sidestream
Distances of a Capture Zone
A groundwater extraction well is installed in an aquifer (hydraulic conduc-
tivity = 1,000 gpd/ft , hydraulic gradient = 0.015, and aquifer thickness = 80 ft).
2
The design pumping rate is 50 gpm. Delineate the capture zone of this
recovery well by specifying the following characteristic distances of the
capture zone:

(a) The sidestream distance from the well to the envelope of the capture
zone at the line of the pumping well
(b) The downstream distance from the well to stagnation point of the
envelope
(c) The sidestream distance of the envelope far upstream of the pum-
ping well

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
(b) Determine the sidestream distance from the well to the envelope
of the capture zone at the line of the pumping well:
3
Q = (50gal/min)(1 ft /7.48 gal) = 15.0 ft
−3
4Bu (4)(80ft)(1.39 × 10 ft/min)
(c) Determine the downstream distance from the well to stagnation
point of the envelope:

3
Q = (50gal/min)(1 ft /7.48 gal) = 9.6 ft
−3
2 πBu (2)( π)(80ft)(1.39 × 10 ft/min)
(d) Determine the sidestream distance of the envelope far upstream
of the pumping well:

3
Q (50gal/min)(1 ft /7.48 gal)
−3
2Bu = (2)(80ft)(1.39 × 10 ft/min) = 30.0 ft