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SITE DESCRIPTION The Thornton Gas Dehydrator Station occupies an area of about one-eighth acre and is located at an elevation of approximately 10 feet MSL on a relatively flat, rectangular-shaped lot. The surface of the dehydrator station is covered with about 6 inches of J-inch crushed rock. Land use in the near vicinity is primarily agricultural. The facility is underlain by younger alluvium which is characterized by unconsolidated clay, silt, sand and gravel. Although the depth to groundwater is unknown, it is believed to be fairly shallow due to the site's proximity to the Mokelumne River. The Mokelumne River is located approximately 500 feet to the north and east of the site. The major process equipment and underground utilities are shown relative to the site boundaries on the Site Plan, Figure 2. A glycol reboiler, along with two interconnected sumps, and a dehydrator unit are located in northern portion of the site. A former dehydrator and two above-ground production fluids tanks are present in the southern end of the facility. The glycol reboiler includes a still for condensing production fluid vapors which presently drain to the above-ground tanks. Buried gas supply and triethylene glycol (glycol) lines connect the dehydrator unit to the glycol reboiler. The glycol lines transport wet glycol from the dehydrator to the reboiler and dry glycol from the reboiler back to the dehydrator (Figure 2). According to PG&E employees, a surface spill of production fluids occurred at the facility on July 28, 1992. The amount of fluid spilled was estimated to be 300 gallons of water which may have contained a small quantity of petroleum hydrocarbons. cca/9-23-92/8809a/JAWP12 3