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MEMORANDUM <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION <br /> 3443 Router Road, Suite A Phone: (916)255-3000 <br /> Sacramento,CA 95827-3098 CALNET: 8-494-3000 <br /> TO: Wendy L. Cohen FROM: John D. Moody <br /> Senior Engineer Pro ct gineer <br /> 0 <br /> DATE: 10 April 1995 SIGNATURE: <br /> SUBJECT: COMMENTS ON WORK PLAN FOR PHASE III RE DIAL INVESTIGATION, <br /> PACIFIC GAS AND ELECTRIC COMPANY, LATHROP GAS DEHYDRATOR <br /> STATION, SAN JOAQUIN COUNTY <br /> I have reviewed the 10 March 1995 work plan entitled Work Plan for Ground Water Investigation, <br /> Lathrop Gas Dehydrator Station, San Joaquin County, California, prepared by Technical and Ecological <br /> Services (TES), a division of PG&E. The work plan proposes activites for additional remedial <br /> investigation at PG&E's Lathrop Gas Dehydrator Station. My comments on the work plan are included <br /> below. <br /> Background <br /> PG&E's Lathrop Gas Dehydrator Station is near the intersection of Undine and Willow Glen Roads about <br /> six miles northeast of Tracy in San Joaquin County. The site occupies approximately one-third of an acre <br /> and is surrounded by farmlands and orchards. The facility odorizes and removes natural gas fluids, <br /> including water and petroleum hydrocarbons. After the discovery of petroleum-contaminated soil near <br /> the facility's former reboiler unit, PG&E conducted a site assessment and initial investigation of the <br /> affected area in 1988, and a second phase remedial investigation in November 1992. The initial <br /> investigation included the removal of petroleum-contaminated soil, collecting condensate samples from <br /> the reboiler unit, and the installation of three soil borings near the reboiler unit, as shown in Attachment I: <br /> Site Map, to further assess the nature of the soil contamination. In 1992, TES installed nine additional <br /> soil borings, also shown in Attachment I, as part of the second phase investigation. The results of these <br /> previous investigations showed the presence of petroleum hydrocarbons in the soil and ground water, and <br /> glycol compounds in the reboiler unit condensate. These results are summarized, along with staff <br /> comments and a request for the subject third phase work plan, in a 5 December 1994 staff memorandum <br /> entitled Pacific Gas &Electric Company Lathrop Gas Dehydrator Station, San Joaquin. County, which <br /> is hereby incorporated by reference. <br /> Scope of Work Plan <br /> The work plan proposes the installation of five new monitoring wells approximate to the locations shown <br /> in Attachment I. The soil borings for the wells will be drilled using a hollow stem augur and cores will be <br /> obtained using a split spoon sampler or other feasible means. TES proposes to select the well locations <br /> based on the results of screening the borehole cuttings for hydrocarbons using a photoionization detector <br /> (PID). If hydrocarbons are detected in a boring, the boring would be abandoned and a new location <br /> selected approximately 50 feet outward from the abandoned boring. The well locations would be where <br /> no hydrocarbons are detected in the borehole cuttings. The wells will be completed to depths ranging <br /> from 20 to 25 feet below ground surface (bgs) and screened over the top 10 to 15 feet of the water table. <br /> Upon completion and development of the wells, TES plans to measure the ground water levels and <br />