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INTRODUCTION This work plan addresses site assessment activities designed to supplement the data collected during previous investigations at PG&E's Lathrop Gas Dehydrator Station in San Joaquin County, California (Figure 1). The purpose of this proposed investigation is to further define the vertical and lateral extent of petroleum hydrocarbons in the subsurface soils at the site and to determine if groundwater in the uppermost water-bearing unit has been impacted. This work plan includes a brief description of previous site activities, the regional geologic and hydrogeologic setting, and a description of the methods which will be used during all proposed field activities. A site specific Health and Safety Plan is also included for the protection of on- site workers and the neighboring public. This work plan has been prepared at the request of Mr. E. Lee of PG&E's Gas Production and Storage Department. BACKGROUND 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 cubic yards 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 water sample (S-4) from the reboiler discharge line (Figure 2). These samples were analyzed by Twining Laboratories for total petroleum hydrocarbons, and benzene,toluene and xylenes. The water sample was also analyzed at PG&E's chemical laboratory in San Ramon for glycol 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 water sample collected from the site. The water sample (S-4) also contained levels of diethylene glycol, triethylene glycol and tetraethylene glycol; however, these glycol compounds are not regulated per Chapter 11, Title 22 of the California Code of Regulations. Benzene, toluene, and ethylbenzene were not detected in samples S-1 and S-4. On May 19, 1988, Groundwater Technology Inc. performed three exploratory soil borings in the immediate vicinity of the reboiler discharge line (Figure 2). The purpose of this study was to evaluate the vertical extent of petroleum hydrocarbons in the soils and to determine the feasibility of using in-situ bioremediation techniques to remediate the affected soils. Selected soil samples from each borehole were analyzed for total cca/9-30-92/8913a/JAWP13 1