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Section 1 INTRODUCTION PURPOSE This workplan addresses site assessment activities designed to determine the lateral extent of petroleum hydrocarbons in subsurface soils and the uppermost water-bearing zone beneath PG&E's Lathrop Gas Dehydrator Station in San Joaquin County, California(Figure 1). The scope of work is presented in response to a request by the Central Valley Regional Water Quality Control Board (letter dated December 5, 1994) requiring further lateral definition of the soil and groundwater contamination at the site. t This workplan is based on the results of prior site activities, and will focus on characterizing petroleum I hydrocarbons residues in subsurface soils and groundwater around the facility. This workplan includes a t description of previous site activities, the regional and local geologic and hydrogeologic setting, and a 1 description of the methods which will be used during all proposed field activities. A site specific Health and Safety Plan (Appendix A) is also included for the protection of on-site workers and the neighboring public. JBACKGROUND In the spring of 1988, during the construction of a foundation pad for a new reboiler unit at the Lathrop Gas Dehydrator Station, PG&E personnel reported the presence of petroleum hydrocarbon odors in excavated soil removed from the area surrounding the reboiler water collection sump and associated discharge line. As a result, PG&E removed approximately 100 cu yds of soil from around the affected area. The soil was subsequently manifested and hauled to the Class I disposal facility in Kettleman Hills. On March 11, 1988, Twining Laboratories collected three soil samples (S-1, S-2, and S-3) from the excavation and one condensate sample (S-4) from the reboiler discharge line(Figure 2). These samples were analyzed by Twining Laboratories for total petroleum hydrocarbons (TPH), and benzene, toluene and Jxylenes. The water sample was also analyzed at PG&E chemical laboratory in San Ramon for glycol 1 compounds. The results of these analyses are presented in Table 1. The chemical analyses of the samples indicated that petroleum hydrocarbons were present in the three soil samples and the condensate sample collected from the site. Benzene, toluene and xylenes were not detected cca/03/10/95 08:19 AM(0688brpt.doc/ntw12) 1-1