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24 March 1993 (GeoAudit 640-5) Page 2 of 5 results of soil samples from the tank removal or water samples from the well installation were present in the PHS/EHD files. PROCEDURES On 10 and 11 February 1993, a total of (5) soil borings were drilled at the site. Four of these borings were completed as groundwater monitoring wells. Boring #1 was advanced to a depth of �� 32 feet. Borings #2 through #5 were advanced to depths of 25 feet �"D 1 _7 5 /;IWJJ/ t a ` The borings were advanced using a truck mounted drilling rig equipped with 10-inch outside diameter hollow-stem augers. The CME- 55 drill rig and two man crew were supplied by West Hazmat Drilling. The auger returns were monitored for the presence of organic vapors using a photo-ionization; detector (PID: Thermo Environmental 580A, 10.0 eV, calibrated to isobutylene) . Discrete soil samples were collected ahead of the drill bit using a split-tube sampler loaded with three pre-clea�►ed 2 . 5 by 6 inch brass tubes. The samples were collected at five foot intervals. To avoid cross contamination, the sampling equipment was washed in a tri-sodium phosphate (TSP) solution and rinsed twice with water prior to each sampling run. For each sample, both ends of the lead/tube were then covered with aluminum sheets, capped and sealed with 'tape. The samples were stored on ice pending transmission to Alpha Analytical Laboratories in Ukiah. Selected soil samples were analyzed for total petroleum hydrocarbons (TPH as gasoline) and purgeable aromatics (BTE&X) in accordance with EPA methods 8015 modified and 8020, respectively. Auger returns and soil from the second brass tube were screened for the presence of organic vapors using a PID. The soil was then described in accordance with the Unified Soil Classification System (see Boring Logs) . Borings #2 through #5 were completed ias 4-inch groundwater ' monitoring wells (MW-1 through MW-4) . Each .well was completed using 0. 020 screen from 10 to 25 feet. The filter pack (#3 sand) was installed from 8 to 25 feet. Bentonite pellets were used from 6 to 8 feet and the well was backfilled to the surface with Portland Cement. On 24 February 1993, the water level in each well, including MW-5, was measured relative to the top of the casing. The relative piezometric levels and hydraulic gradient were determined from these data (Table 1 and Figure 3) . Monitoring well casing d elevations well surveyed relative to the bumper post at the southwest corner of the main building. The bumper post is assumed