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WfiS .f. E: R \ C 1: (3L0GIC f2irS0UItC EN . I .NC rs+ p . L,Marinaro/i Apr 1989 3 and 3,500 gallons. A subsurface investigation conducted by Gettler-Ryan, Inc. of Hayward and Emcon Associates of San Jose, California, which included the installation of ten onsite monitoring wells, 2 off-site wells, and an onsite recovery well. About 600 gallons of free porduct were initially removed from the recovery well. Results of groundwater sampling conducted by Emcon in October 1985 indicated that five of the wells contained free product. The remaining on- and Off-site wells contained dissolved gasoline up to 80,000 ppb and benzene up to 8,000 ppb. In April 1987, Western Geo-Engineers of Woodland, California, conducted a soil vapor survey. The results indicated that volatile hydrocarbons- y were present in high concentrations particularly on the south half of the site to a depth of about 10 ft. In January 1988, Brown and Cald;:ill Consulting Engineers (B&C) of Sacramento, California installed 4 additional off site monitoring wells along Plymouth Road and Benjamin holt Drive. The estimated direction of groundwater flow was to the northeast. - Results of groundwater sampling conducted by B&C in November 1988 indicated that benzene was present, in all but one well sampled, including well PR-I at 6.4 ppb, located at the northeast corner -of B. Holt Drive and Plymouth Road. Well BHD-1 located in the sidewalk along B. Holt Drive and adjacent to the Chevron site contained 1,870 ppb benzene and well E- 10 across the street on the Arco site contained 2,78u ppb benzene. When the recovery well was operating at a rate of about 15 gpm, the northeast direction of groundwater flow on the north side of the site was reversed to a direction approximately to the southwest and southeast. The information concerning the Arco site was obtained from reports on file at . the San Joaquin Local Health District. �a in August 1988, Applied Geosystems conducted a subsurface investigation at the Shell service station to the west of the Chevron site. The results of the investigation were submitted to Shell Oil Company in a report dated 16 September 1988.. Four monitoring wells were installed. Fuel hydrocarbons were not detected in soil or groundwater samples. The estimated direction of groundwater flow was to the northeast. L.. SOIL BORINGS AND HYDROGEOLOGY Soil borings B-1 through 8-5 were drilled on the site (Figure 2) with hollow-stem augers by PC Exploration of Roseville, California, between 27 Februa„y and 2 March 1989. Boreholes were continuously logged by WGR geologist Mike Edmonson. Soil samples were collected at approximately 5 ft intervals. Twenty-three selected samples were sent under chain-of-,..ustody to Central Coast Analytical Services (CCAS) of San Luis Obispo, California, for analysis by EPA Method 524.2. The WGR standard operating procedure for soil sampling is included as Attachment moi_ tier .A�, l