GROUNDWATER - Water Quality Engineering in Natural Systems - page 189

boundary of capture zone

extraction well

2Q
KbJ

3Q
KbJ

3

2Q
πKbJ

Q
πKbJ

regional ow

(b)

(a)

Figure 5.23. multiple extraction wells in uniform flow. (a) Two extraction wells. (b) Three extraction wells.

wells, the maximum spacing, Δ 2,max , between the two
wells such that groundwater will not pass between
the wells is

y

property line

60 m

Q
KbJ

(5.113)

∆ 2,max =

30 m

π

x

regional ow

50 m plume

and with this spacing, the maximum width of the capture
zone, W 2,max , is given by

extraction well(s)

Q
KbJ

2

Figure 5.24. Contaminated groundwater on industrial

(5.114)

W

,max =

property.

2

which is twice as wide as the maximum capture zone for
a single extraction well, as given by Equation (5.112).
For the case of three extraction wells, the maximum well
spacing, Δ 3,max , and the maximum width of the capture
zone, W 3,max , are given by

zone. Corresponding to Equation (5.117), the maximum
width of the capture zone in the case of n wells at their
optimal separation, W n,max , is given by

nQ
KbJ

W

n,max =

(5.118)

3 2

Q
KbJ

(5.115)

∆ 3

,max =

π

In general, Equations (5.117) and (5.118) are applied
such that the capture zone corresponding to the number
of wells deployed encompasses the contaminant con-
centration contour line corresponding to the maximum
acceptable contaminant concentration in the aquifer.
The allowable drawdown in the aquifer is a constraint
in determining the number, locations, and pumping
rates of the extraction wells.

Q
KbJ

3

(5.116)

W

,max = 3

In the case of n wells spaced at their maximum sepa-
ration (not to allow flow between them), the boundary
of the capture zone is given by

n

EXAMPLE 5.21

Q
KbJ

1

∑

y = n − φ (5.117)

i

2 π

i = 1

A plume of contaminated groundwater is discovered on
an industrial property as shown in Figure 5.24. The
plume is 60 m long and 30 m wide, and penetrates
the entire aquifer depth of 28 m. Existing buildings on

where ϕ i is the angle between the horizontal line through
the i ith well and a point on the boundary of the capture