Design Considerations

The design of a well system involves determining the number of wells needed, placing and spacing the wells, and determining the pumping cycles and rates of the wells. The number and spacing of the wells should completely capture the plume of contamination and produce as little un-contaminated water as possible to reduce treatment costs. In addition, the well's capture zones should intersect each other to prevent dead spots where contaminants stay stagnant or routes where the contaminant can escape the zone of capture. Environmental engineers determine the zone of capture by plotting the drawdowns within the radius of influence of each well on the potentiometric surface map of the site and calculating the cumulative drawdowns. The radius of influence of each well is determined by pumping test analysis as discussed in Section 9.8 or estimated from the following formulas when pumping test data are lacking (Kuffs et al. 1983): Equilibrium:

Nonequilibrium:

where:

R0 = radius of influence, ft

K = permeability, gpd/ft2

FIG. 9.17.1 Suction lift and a series of point wells. (Reprinted from S. Sommer and J.F. Kichens, 1980, Engineering and development support of general decon technology for the DARCOM installation and restoration program, Task 1: Literature review on groundwater containment and diversion barriers, Draft report by Atlantic Research Corp. to U.S. Army Hazardous Materials Agency, Contract No. DAK 11-80-C-0026, [October], Aberdeen Proving Ground.)

FIG. 9.17.1 Suction lift and a series of point wells. (Reprinted from S. Sommer and J.F. Kichens, 1980, Engineering and development support of general decon technology for the DARCOM installation and restoration program, Task 1: Literature review on groundwater containment and diversion barriers, Draft report by Atlantic Research Corp. to U.S. Army Hazardous Materials Agency, Contract No. DAK 11-80-C-0026, [October], Aberdeen Proving Ground.)

FIG. 9.17.2 Dual pumping wells. (Reprinted from E.K. Nyer, 1992, Groundwater treatment technology, 2d ed., New York: Van Nostrand Reinhold.)

T = transmissivity, gpd/ft t = time, min

S = storage coefficient, dimensionless

0 0

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