Geomembrane-Leachate Compatibility for the U.S. Department of Energy CERCLA Waste Disposal Facilities

This paper presents a review of available information on leachates from several U.S. Department of Energy (DOE) Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) waste disposal facilities (WDFs) in order to characterize radioactivity doses and chemical exposures for high-density polyethylene (HDPE) geomembrane liners used in them. This exposure information is compared to the results of studies performed to evaluate the effects of radiation and chemical exposure on the physical and mechanical properties of HDPE materials. Case study data from laboratory geomembrane-leachate compatibility testing programs performed for several CERCLA WDFs and other relevant projects are also presented and discussed. From this information, it is concluded that the radiological doses to which HDPE geomembrane liners will be exposed in CERCLA WDFs are well below the threshold doses likely to induce geomembrane physical and mechanical property changes. Consistent with this finding, the physical and mechanical properties of HDPE geomembrane liners were not measurably degraded in the CERCLA WDF leachate compatibility testing programs described in the paper. In addition to radionuclides, the paper also reviews information on pH levels, trace metal concentrations, and volatile organic compound concentrations in CERCLA WDF leachates. The conclusion is reached that the service life for HDPE geomembrane liners in these facilities should be well in excess of the 200-year minimum facility performance period of DOE Order 458.1 and may approach the DOE performance-period goal of 1,000 years “to the extent reasonably achievable.” To maximize service life, it is recommended that relatively thick geomembranes (e.g., 2.0-mm thick) be used in CERCLA WDF applications. Lastly, the paper briefly discusses the implications of this long geomembrane service life in the context of the design philosophy for CERCLA WDFs and provides suggestions for further studies.