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332 Waste Management Practices: Municipal, Hazardous, and Industrial

TABLE 10.16
Runoff Coefficients for Various Slopes and Soil Permeabilities

Surface Slope Runoff Coefficient
Grass, sandy soil 0–2% 0.05–0.10
2–7% 0.10–0.15
7% 0.15–0.20
Grass, heavy soil 0–2% 0.13–0.17
2–7% 0.17–0.25
7% 0.25–0.35
Source: Fenn, D. G., U.S. EPA, 1975.

runoff from the site is 10%. There is no run-on of surface water; similarly, there is no underflow of
groundwater into the cell (i.e., R 0 and U 0).
on

SOLUTION

For these calculations it is necessary to convert the depth of precipitation to a volume. This is eas-
ily accomplished because the depth of water is received over a known area (units of 1 ha). The pre-
cipitation depth is thus converted into 1.07 h m. The quantity of leachate is then calculated using
the equation

L P E R
off
L 1.07 ha m (0.55)(1.07 ha m) (0.10)(1.07 ha m)
L 0.37 ha m
3
2
3750 m (1 ha 10,000 m )
6
3.75 10 L or 990,645 gal
10.4.23.2 The Leachate Collection and Removal System
A leachate collection and removal (LCR) system is designed to collect leachate and convey it out
of the landfill for eventual treatment. The LCR system is constructed so that less than 30 cm of
leachate (the amount of leachate the liner is designed to maintain according to Subtitle D) accu-
mulates above the composite liner. When designing and constructing a LCR system, the following
components must be considered (U.S. EPA, 1994):

● Area collector — the drain that covers the liner and collects leachate
● Collection laterals – the pipe network that drains the area collector
● Sump – the low point where the leachate exits the landfill
● Stormwater and leachate separation system

10.4.23.3 Area Collector

The area collector, also known as the blanket drain, covers the entire surface of the geomembrane
liner and collects the leachate. The area collector system is typically constructed with at least a
30 cm (12 in.) layer of sand having a hydraulic conductivity greater than 10 2 cm/sec. An alterna-
tive type of blanket drain can be constructed using geosynthetic drainage nets (geonets), porous
synthetic materials applied over the geomembrane liner. A brief discussion of geosynthetic materi-
als for landfill construction follows.