NCD980602163_19961007_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 .AVA James B. Hunt, Jr., Governor
Jonathan B. Howes, Secretary
William L. Meyer, Director October 7, 1996 DEHNR
RE: Pressure head and leakage rate through a geomembrane liner
The following model assumes a geomembrane liner with a pin hole ( 1 mm2) leaking into a sandy soil
from a water reservoir contained on the liner. This assumes no leakage restriction from a clay layer
below the geomembrane and no leakage restriction from the low permeable soils within the landfill.
Pressure head difference on geomembrane liner:
From the Solid Waste Section monthly water level records from 1991 through 1996, the greatest
water level depth is 15 .17 feet ( see water level data on following page). Assuming the effective
pressure from the soil on the landfill liner remains constant and a water weight of 62.4 pounds per
cubic foot, the difference in pressure on the liner due to 15 .14 feet of head change is 944. 7 4 pounds
per square foot ofliner. Pressure on the liner from 1 centimeter head of water is 2.05 pounds per
square foot of liner and 946.6 pounds per square foot ofliner from a water head of 15.17 feet. This
is a ratio of 462 to 1.
Leakage rate through a geomembrane liner:
-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 leaka~e through geomembrane defects:
Q=2.66ah 2 Where: Q=flowrate (m3/secJ
a=area of defect (m)
Assume a 1 mm2 ( 1 x 10-6 m2) defect:
h=head on geomembrane(m)
For h=l5. l 7 feet (4.62m)
Q= 2.66(lx10-6 m2)(4.62m)112 = 5.72 x 10-6 m3/sec x 2.26368 x 107 gpd/ m3/sec ~ 130 gpd
For h=lcm (.Olm)
Q= 2.66(lxl0-6 m2)(.0lm)112 = 2.66 x 10-7 m3/sec x 2.26368 x 107 gpd/ m3/sec ~ 6 gpd
130gpd + 6gpd = 22 times more leakage per mm2 of defect per day with a head of 15.17 feet
(h=l5.17)
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.
The limiting factor is the permeability of the soils or the infiltration rate into clay layer.
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From the Solid Waste Section monthly water level records from 1991 through 1996 the measured
water level in the Warren County PCB Landfill fluctuates from a depth of 15.17 feet on 16 September
1996 to 12.89 feet on 27 June 1991 at the sloped sump pipe measuring point. The Water level depth
at the air vent monitoring well fluctuates from 12.06 feet on 16 September 1996 to 10.88 on 29
March 1996.
Annual water level fluctuations at the sump pipe are:
1.25 feet in 1991
1.38 feet in 1992
1. 16 feet in 1993
1.25 feet in 1994
1.35 feet in 1995
1.19 feet in 1996
Annual water level fluctuations at the air vent monitoring well since 1995 are:
0.68 foot in 1995
1.18 feet in 1996
The mean annual fluctuation in water level in the Warren County PCB Landfill is 1.18 feet. This
fluctuation appears to be caused by a seasonal weather change.