Assessment of Municipal Solid-Waste Landfill Liner Performance

The leachate collection system (LCS) and leak detection system (LDS) flow rate data from 240 cells (or a combination of cells) at 54 municipal solid-waste landfills (located in seven US states) with double-liner systems were analyzed to assess the performance of the primary liner system. The average LCS leachate collection rates for the study sites ranged from 380 L ha^-1 day^-1 (40.7 gal. acre^-1 day^-1) to 22,400 L ha^-1 day^-1 (2,390 gal. acre^-1 day^-1) on a sitewide basis, and the average LDS leachate collection rates ranged from 1.8 L ha^-1 day^-1 (0.2 gal. acre^-1 day^-1) to 577 L ha^-1 day^-1 (61.7 gal. acre^-1 day^-1) on a sitewide basis. Assuming all leachate generated is collected either by the LCS or LDS, the data suggest that the primary liner systems' aggregated efficiency is over 98%. The collection efficiency at sites that used a composite liner (geomembrane underlain by a geosynthetic clay liner or a compacted clay liner) system was not statistically different from the sites that used only a geomembrane as the primary liner (geomembrane underlain by a permeable layer) (median of 99% for both types). Leakage rates were compared with those estimated from the equations used by the hydrologic evaluation of landfill performance (HELP) model. The comparison suggests that the equations used by the HELP model to estimate leakage through the liner overestimate the leakage rate through geomembrane primary liners but underestimate the leakage rate through composite primary liners based on the HELP-model-default defect size and suggested defect frequency. It is also possible that groundwater intrusion could contribute to a portion of the leachate collected from the LDS because leachate quality data collected from a few sites indicated the LCS leachate had a higher concentration of most constituents than the leachate collected from LDS.