During a recent landfill leak location survey a 2 to 3 mm diameter hole was found at a T extrusion weld on the edge of a patch. When shown the hole, and a much smaller pinhole close by, the installer commented that such a hole would not explain the leak flow rate of about 200 gpd. However, there was no argument about the caterpillar track holes at the toe of a slope in the adjacent cell!
For those who question leak flow rates through small holes, Table 1 (below) shows realistic numbers:
|
Water depth on top of the geomembrane, hw |
||||||
|
0 m |
0.003 m |
0.03 m |
0.3 m |
3 m |
> 10 m |
|
|
Coefficient of Migration, mg (m2/s)
|
0 |
9 x 10-20 |
9 x 10-18 |
9 x 10-16 |
9 x 10-14 |
3 x 10-13 |
|
Unitized leakage rate, qg |
–
|
–
|
–
|
–
|
–
|
–
|
|
(m/s)
|
0 |
9 x 10-17 |
9 x 10-15 |
9 x 10-13 |
9 x 10-11 |
3 x 10-10 |
Table 2 (below) shows water vapor diffusion rates through a 1 mm HDPE geomembrane without any physical holes:
|
Water depth on top of the geomembrane, hw |
||||||
|
Defect |
0.003 m |
0.03 m |
0.3 m |
3 m |
30 m |
|
|
Pinholes |
1 mm 0.3mm |
0.006 0.5 |
0.06 5 |
0.6 50 |
6 500 |
60 5,000 |
|
Holes |
2 mm 11.3 mm |
40 1,300 |
130 4,000 |
400 13,000 |
1,300 40,000 |
4,000 130,000
|
|
Values of leakage rate in liters/day (gallons/day) |
||||||
This clearly shows that zero leakage is not possible to achieve. Thus, a 2 mm hole will leak between 10 and 1,000 gpd as the hydrostatic head increase from 1 ft to 100 ft – quite significant numbers!
More can be found in Giroud and Bonaparte’s paper " Leakage Through Liners Constructed with Geomembranes – Part I. Geomembrane Liners." published in Geotextiles and Geomembranes, Volume 8, No. 2 pages 27-67, 1989.
