Treatability Study in Support of Monitored Natural Attenuation at Landfill 3 (Site LF-03), F. E. Warren Air Force Base, Cheyenne, Wyoming

This report presents the results of a treatability study (TS) conducted to evaluate the use of natural attenuation for remediation of chlorinated aliphatic hydrocarbon (CAM) - contaminated groundwater at Site LF-03, F. E. Warren AFB, Wyoming. The numerical models MODFLOW and MT3D were used in conjunction with site-specific geologic, hydrologic, and laboratory analytical data to simulate the migration and biodegradation of trichloroethene (TCE) dissolved in groundwater. It is likely that contaminants were first introduced into groundwater at this site shortly after the opening of LF-03 around 1960. Solvents, fuels, and other liquid wastes may have been spilled or dumped, or have leaked from containers in the landfill. Contaminants dissolved in leachate are assumed to have entered groundwater over relatively large areas (i.e., the landfill), through point sources due to spills or dumping, or through contact between groundwater and residual non-aqueous phase liquid (NAPL) at or below the water table. Contaminants observed in groundwater at LF-03 at concentrations greater than US Environmental Protection Agency (USEPA) maximum contaminant levels (MCLs) include TCE and cis-1,2-dichloroethene (cis-1,2-DCE). The dissolved CAM plume - appears to have migrated approximately 1,500 feet northeast from the source area at LF-03. Comparison of TCE plumes delineated in 1993 and 1999 indicate that the TCE plume is stable, although TCE concentrations have increased at several locations within the plume.