SITE INFORMATION AND CORRESPONDENCE

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A� y groundwater in the area is approximately 10 feet. The regional groundwater gradient is towards the west or southwest. x 3.0 PROCEDURES 3.1 Drilling and Sampling On November 17, 1993, one soil boring was drilled at the site. At the suggestion of the PHS/EHD and Central Valley Regional Water Quality Control Board (CVRWQCB), the boring was drilled immediately east of the excavation, thereby placing the boring between the excavation and the on-site domestic water well. The chosen location for MW-1 is up- gradient of the tank cavity, according to the San Joaquin County Flood Control Map (1990). The boring was advanced to a depth of 25 feet and completed as groundwater monitoring well MW-1. Auger returns were placed on plastic sheeting and stored on-site. The monitoring well location is illustrated on Figure 2. The boring was drilled using a truck-mounted CME-75 drill rig. The drill rig and two-man - crew were supplied by Mitchell Drilling Environmental Corporation. During drilling, 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-cleaned 2-inch by 6-inch brass sleeves. The samples were collected at five-foot intervals, using a 140 pound hammer to advance the sampler 18 inches. The number of blows required to advance the sampler in 6-inch increments was recorded on the boring logs. 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 covered with aluminum sheets, capped and sealed with tape. The samples were then stored on ice and transported under chain-of- custody to McCampbeil Analytical Inc. in Pacheco, California. 3.2 Logging Soil was extruded from the second brass tube and screened for the presence of organic vapors, using a PID, and the readings were recorded on the boring logs. The soil was then described in accordance with the Unified Soil Classification System (see Boring Log, Appendix A). 3.3 Well Completion The boring was completed as groundwater monitoring well MW-1 using 2-inch diameter PVC casing with 0.020 screen from 25 to 5 feet. The filter pack (#3 Lonestar sand) was installed from 25 to 3.5 feet. Bentonite chips were used to make a plug and the well was 6w1eeiwl Audit Serv:a.Ino Revd Pr po ty/12-1693 ]&S