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2. PREVIOUS INVESTIGATIONS 2.1 TANK REMOVAL AND SOIL SAMPLING The tanks were excavated from the site in January 1987 (BTS 1987), and closure samples were collected for analysis by Blaine Tech Services. Several samples were collected at the locations shown in Figure 3. Except for samples 119 and 414 (these are at locations 1 and 4 at depths of 19 and 14 feet),all of the samples were analyzed by Thermo-Analytical Inc, (Flay 1987a,b) for benzene, toluene, xylenes, and total petroleum hydrocarbons. The results of these analyses are given in Table 1. In addition to those components,the sample taken from the waste oil tank pit (client ID#4,Table 1)was analyzed for polychlorinated biphenyls(PCB) and for 25 halogenated volatile hydrocarbons. None of these compounds were detected(Flay 1987x). On 3 June 1987, soil samples were taken approximately five feet below the surface of the stock- pile of excavated soil with a hand auger. The samples were collected at six points from the pile and composited for two analyses. The samples(3062 and 3063) were analyzed by Environmen- tal Laboratories for benzene, toluene, xylenes,ethylbenzene, and total aromatic hydrocarbons. The results are in Table 1. 2.2 INSTALLATION OF MONITORING WELLS On,18 March 1987'Groundwater Technology, Inc. installed three monitoring wells (MW1, MW2,4W3)surrounding the area of the former tank field (Figure 4). Well logs are in Appen- dix A. Soil samples were taken for chemical analysis at 26 and 36 feet from MWl,30 feet from MW2, and 34 feet from MW3. On 19,March 1987 groundwater from these wells was sampled and analyzed. All of the soil and groundwater samples were analyzed for benzene, toluene, ethylbenzene,xylenes, and total petroleum hydrocarbons by E,tivironmon.ital Laboratories. Ana- lytical results are presented in Table 2(soil)and Table 3(water). 2.3 DOMESTIC WELL SEARCH AND SAMPLI14G On 20 August 1987,EA conducted an investigation into the presence of hydrocarbons in water supply wells in the vicinity of the site. Four domestic wells (sample numbers 1-4,Table 4) hydrologically downgradient of the site and one well (sample number 5) upgradient of the site were sampled. H. Knoll (personal communication 1987) of the San Joaquin County Health Services was consulted on the sampling sites and agreed that they were appropriate. At a location as close to the wellhead as possible,and ahead of any storage tank, a water sample - was taken from the existing pipes.-Prior to the sampling, the water line was run for 5 to 10 minutes to allow the plumbing to flush. The samples were sent to Brown and Caldwell Analyti- cal Laboratories and analyzed for benzene, toluene, xylenes, and total fuel hydrocarbons. c67/97780/tx 2