NCD980602163_19961001_Warren County PCB Landfill_SERB C_Re Pressure head and leakage rate through a geomembrane liner-OCR

State of North Carolina
Department of Environment,
Health and Natural Resources
Division of Waste Management
James B. Hunt, Jr., Governor
Jonathan B. Howes, Secretary
William L. Meyer, Director
AVA
DEHNR
October 1, 1996
RE: Pressure head and leakage rate through a geomembrane liner
Pressure head difference on geomembrane liner:
Assuming the effective pressure from the soil on the landfill liner remains constant, the difference in
pressure on the liner due to 13 feet of head change is 809.2 pounds per square foot ofliner. Pressure
on the liner from 1 centimeter head of water is 2.05 pounds per square foot ofliner and 811.2 pounds
per square foot of liner from a water head of 13 feet. This is a ratio of 396 to 1.
Leakage rate through a geomembrane liner:
-The movement of water through a geomembrane occurs both through diffusion of moisture
through the polymer and from flow through defects.
-Leakage rates due to permeation through the geomembrane is generally negligible when
compared to leakage rates due to flow through defects or holes in the geomembrane.
Therefore, consider leakage through geomembrane defects:
Q=2.66ah112 Where: Q=flowrate (m3/secJ
Assume a 1 cm2 (lxl0-4 m2) defect:
For h=13 feet (3 .96m)
a=area of defect (m)
h=head on geomembrane(m)
Q= 2.66(lxl0-4 m2)(3 .96m/12 = 5.96 x 10-4 m3/sec x 2.26368 x 107 gpd/ m3/sec z 12000gpd
For h=lcm (.Olm)
Q= 2.66(1x10-4 m2)(.0lm)112 = 2.66 x 10-5 m3/sec x 2.26368 x 107 gpd/ m3/sec z 600gpd
12000gpd + 600gpd = 20 times more infiltration per day with a head of 13 feet (h=l3)
Reference: Giroud, J.P. and Bonaparte, R. "Leakage through liners constructed with
Geomembranes, Part I -Geomembrane liners", Geotextiles and Geomembranes 8(1)
1989a pp 27-67.
Therefore, the limiting factor is the permeability of the soils or the flow rate (infiltration rate).
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