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Subsurface Drainage

Collected groundwater is pumped to treatment system.

Cross Section

Cross Section

Contaminated Groundwater Plume

FIG. 9.17.5 Interceptor drains downgradient of the plume of contamination. (Reprinted from U.S. Environmental Protection Agency, 1985, Leachateplume management, EPA/540/2-85/004, Washington, D.C.: U.S. EPA.)

Contaminated Groundwater Plume

FIG. 9.17.5 Interceptor drains downgradient of the plume of contamination. (Reprinted from U.S. Environmental Protection Agency, 1985, Leachateplume management, EPA/540/2-85/004, Washington, D.C.: U.S. EPA.)

the drains, (3) the pipe diameter and slope, and (4) the envelope and filter materials around the pipe.

An interceptor drain should be installed perpendicular to the groundwater flow direction and downgradient from the plume of contamination. The drain should be installed on top of a layer of low hydraulic permeability to prevent underflow beneath the drain. The location of the drain should be selected so that the upgradient and downgradi-ent influences of the drain completely capture the contamination plume. The upgradient and downgradient influences of an interceptor drain can be calculated using the following equations described by Van Hoorn and Vandemolen (1974) and Kuffs (1983):

where:

effective distance of drawdown upgradient, ft m, = saturated thickness of aquifer not affected by drainage, ft I = hydraulic gradient Dd = downgradient influence, ft K = hydraulic conductivity, ft/day Q = drainage coefficient, ft/day

Map View

(a) The conventional subsurface drain receives recharges from the stream as well as the leachate plume resulting in larger collection and treatment requirements.
FIG. 9.17.6 Interceptor drains in conjunction with a barrier wall. (Reprinted from U.S. Environmental Protection Agency, 1985, Leachate plume management, EPA/540/285/004, Washington, D.C.: U.S. EPA.)

Collection Sump

FIG. 9.17.7 Interceptor drains connected to a header. (Reprinted from U.S. Environmental Protection Agency, 1985, Leachate plume management, EPA/540/2-85/004, Washington, D.C.: U.S. EPA.)

Collection Sump

FIG. 9.17.7 Interceptor drains connected to a header. (Reprinted from U.S. Environmental Protection Agency, 1985, Leachate plume management, EPA/540/2-85/004, Washington, D.C.: U.S. EPA.)

depth of drain, ft depth of drawdown, ft distance from ground surface to water table prior to drainage at the distance Dd downgradient from the drain, ft

The spacing between two parallel relief drains should be selected so that their combined drawdown is adequate to lower the water table beneath the waste. The minimum spacing, however, is often imposed by the boundaries of the waste material. The drain spacing depends on the hydraulic conductivity of the aquifer, the depth of the impermeable layer beneath the drain, the cross-sectional area of the drain, the water level in the drain, and precipitation and other sources of recharge. The spacing between two parallel drains resting on an impermeable barrier can be calculated with the use of the Wasseling (1973) equation as

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