SITE INFORMATION AND CORRESPONDENCE

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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 255-3000 Sacramento, CA 95827-3098 CALNET: 8-494-3000 TO: Wendy L. Cohen'ur`y' FROM: John D. Moody Senior Engineer Pro t Engine DATE: 5 December 1994 SIGNATURE: SUBJECT: PACIFIC GAS AND ELECTRIC COMPANY, LATHROP GAS DEHYDRATOR STATION, TRACY, SAN JOAQUIN COUNTY I have reviewed the August 1993 report entitled Report of Subsurface Investigation, PG&E's Lathrop Gas Dehydrator Station, San Joaquin County, California, prepared by Technical and Ecological Services (TES). PG&E submitted the report in September 1994. The results of this review are summarized below. Background PG&E's Lathrop Gas Dehydrator Station is near the intersection of Undine and Willow Glen Roads about six miles northeast of Tracy in San Joaquin County. The site occupies approximately one- third of an acre and is surrounded by farmlands and orchards. The unstaffed facility odorizes and removes natural gas fluids, including water and petroleum hydrocarbons. Petroleum contaminated soil was discovered at the site during the installation of a foundation pad for a new reboiler unit, which was being constructed to replace an existing reboiler unit which has been out of operation since 1969 (See Attachment I: Site Map). The site assessment was then conducted for the San Joaquin County Public Health Services (PHS) to determine the nature and extent of contamination. Initial Investigation An initial investigation of the area was conducted in March 1988. The reboiler unit included a water collection sump and a discharge line, from which area approximately 100 cubic yards of petroleum-contaminated soil were removed and hauled to an offsite landfill (Kettleman Hills). Laboratory analysis of soil samples taken from the excavation contained total petroleum hydrocarbons (TPH) at levels up to 12,000 mg/kg. An effluent sample taken from the discharge line contained 6,330 mg/l diethylene glycol, 11,110 mg/1 triethylene glycol, and 7,230 mg/1 tetraethylene glycol. Groundwater Technology, Inc. subsequently installed three soil borings near the reboiler unit in May 1988. The results are shown in Table 1. The results showed up to 1,400 mg/kg TPH, 1,800 mg/kg TPH as gasoline (TPHg), and low levels of benzene toluene, ethylbenzene, and xylene (BTEX). None of the boring samples contained Benzene. One sample contained triethylene glycol up to 12,000 mg/kg. The soil samples did not contain polychlorinated biphenyls, volatile organic compounds (VOCs), or semi-volatile organic compounds (semi-VOCs).