GAS INDUSTRY GROUNDWATER RESEARCH PROGRAM

The objective of the research described in this report was to provide data and insights that will enable the natural gas industry to (1) significantly improve the assessment of subsurface glycol-related contamination at sites where it is known or suspected to have occurred and (2) make scientifically valid decisions concerning the management and/or remediation of that contamination. The described research was focused on subsurface transport and fate issues related to triethylene glycol (TEG), diethylene glycol (DEG), and ethylene glycol (EG). TEG and DEG were selected for examination because they are used in a vast majority of gas dehydration units, and EG was chosen because it is currently under regulatory scrutiny as a drinking water pollutant. Because benzene, toluene, ethylbenzene, and xylenes (collectively referred to as BTEX) compounds are often very closely associated with glycols used in dehydration processes, the research necessarily included assessing cocontaminant effects on waste mobility and biodegradation. BTEX hydrocarbons are relatively water-soluble and, because of their toxicity, are of regulatory concern. Although numerous studies have investigated the fate of BTEX, and significant evidence exists to indicate the potential biodegradability of BTEX in both aerobic and anaerobic environments (Kazumi and others, 1997; Krumholz and others, 1996; Lovely and others, 1995; Gibson and Subramanian, 1984), relatively few investigations have convincingly demonstrated in situ biodegradation of these hydrocarbons (Gieg and others, 1999), and less work has been done on investigating the fate of BTEX species in combination with miscible glycols. To achieve the research objectives, laboratory studies were conducted to (1) characterize glycol related dehydration wastes, with emphasis on identification and quantitation of coconstituent organics associated with TEG and EG wastes obtained from dehydration units located in the United States and Canada, (2) evaluate the biodegradability of TEG and DEG under conditions relevant to subsurface environments and representative of natural attenuation processes, and (3) examine the possibility that high concentrations of glycol may act as a cosolvent for BTEX compounds, thereby enhancing their subsurface mobility. To encompass a wide variety of potential wastes representative of different natural gas streams and dehydration processes, raw, rich, and lean glycol solutions were collected from 12 dehydration units at eight different gas-processing facilities located at sites in Texas, Louisiana, New Mexico, Oklahoma, and Alberta. To generate widely applicable environmental fate data, biodegradation and mobility experiments were performed using four distinctly different soils: three obtained from three gas-producing areas of North America (New Mexico, Louisiana, and Alberta), and one obtained from a North Dakota wetland to represent a soil with high organic matter content