Wednesday, April 2, 2008 : 8:20 a.m.

Geochemical and Hydrologic Characterization to Identify the Source of Low Level Benzene Concentrations in Groundwater Samples

Henry B. Kerfoot, GeoSyntec Consultants, Warren D. Brady, Geosyntec Consultants, Mark A. Allendorf, Allied Waste Industries, Inc. and William H. Schramm, Louisiana Department of Environmental Quality

An investigation to evaluate the source of benzene in groundwater samples at a landfill was performed. The samples were from a major drinking water supply aquifer in Southwestern Louisiana. Because dissolved methane was detected along with the benzene, an evaluation of the source of the benzene was performed. Two potential sources of benzene were evaluated: the landfill (either gas or leachate) and deep petroliferous deposits (i.e., natural gas). The evaluation was based on assessment of evidence of the fluid that transported the benzene to the groundwater. The 3H content of water was used to evaluate landfill leachate (water) as the transporting fluid. The 14C content of dissolved methane, dissolved CO2 concentrations, and the 13C / 2H content of dissolved methane were used to evaluate landfill gas as the transporting fluid. The 14C and 13C / 2H contents of methane and concentrations of dissolved ethane were used to evaluate natural gas as the transporting fluid. Background groundwater and groundwater in wells with benzene detections had 3H levels below 1 Tritium unit (TU), while the leachate had 2,649 TU. Landfill gas methane had delta-13C and delta -2H values consistent with fermentation methane and literature values for landfill gas. However, the dissolved methane in groundwater samples from wells with benzene detections had delta -13C and delta-2H values consistent with literature values for thermogenic (natural gas) methane. The methane in the landfill gas had a 14C level of 116 percent Modern Carbon (pMC), while dissolved methane in a monitoring well with benzene detected had a 14C level of 2.3 pMC, inconsistent with the landfill as the methane source. All of these results and others were consistent with natural gas as the source of the benzene and inconsistent with a landfill source

Henry B. Kerfoot, GeoSyntec Consultants Henry Kerfoot is a Senior Chemist with Geosyntec Consultants in Huntington Beach, California. He has over 25 years experience in site characterization and landfill geochemistry.

Warren D. Brady, Geosyntec Consultants Mr. Brady is a senior geochemist in Geosyntec's Baton Rouge office. He specializes in the the development and application of innovative groundwater assessment and remediation at project sites based on geochemistry.

Mark A. Allendorf, Allied Waste Industries, Inc. Mark Allendorf is a Hydrogeology Manager in the Engineering Department of Allied Waste focusing on the management of technical and environmental issues at company solid waste, hazardous waste, and superfund sites. He has over 20 years experience in applied hydrogeology.

William H. Schramm, Louisiana Department of Environmental Quality William Schramm is a Geologist III with the Environmental Technology Division of the LDEQ. He has over 17 years of regulatory experience in the investigation and remediation of unpermitted releases in Louisiana. He is also an instructor in the Geology Department at the University of Louisiana at Lafayette. Mr. Schramm has served as President and Director of the Baton Rouge Geological Society and currently represents those members of BRGS as Delegate to the American Association of Petroleum Geologists.


2008 Ground Water Summit