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an-off-site source, either to the west or north of the site, may be responsible for much of the impacted soil and groundwater at the site (see "Problem Assessment Report" prepared by GeoAudit, October 1993). After reviewing the data, the PHS/EHD Technical Review Committee (TRC) agreed that the source of hydrocarbon had not been identified. The TRC recommended that one additional monitoring well be installed on-site to confirm that ' impacted soil was removed from the old tank excavation, and that two monitoring wells be installed off-site, on the north side of Harding Way, to evaluate the possible existence of an ' off-site source. 3.0 PROCEDURES 31 Monitoring Well installation r, On March 24 and 25, 1994, three additional monitoring wells were installed at or near the site. Monitoring wells MW-6 and MW-7 were installed in the sidewalk along the north side of Harding Way. Monitoring well MW-8 was installed �,vithin the former UST cavity, near the southern portion of the property. The locations of the wells are illustrated on Figure 2. ' The borings were drilled using a truck-mounted, hollow stem auger drill rig. The BK-81 drill rig and two-man crew were provided by Turner Explorations of Rancho Cordova, California. Each boring was drilled to a depth of 58 feet. The wells were completed with 20 feet of 0.020 slotted PVC screen. The filter pack (#3 Monterey sand) extended from 35 to 58 feet and bentonite was used from 32 to 35 feet. The borings were then grouted to the surface. Soil samples were collected at five-foot intervals. Monitoring well MW-6 was continuously sampled from 35 to 42 feet. Samples were collected using a split spoon sampler loaded with three clean, 2 by 6-inch brass sleeves. The ends of the lead tube were covered with ' aluminum sheets, capped and sealed with tape. The samples were then placed in a chilled container pending transportation to a state-certified laboratory. All sampling equipment was washed and rinsed twice prior to each sampling run. Auger returns and sample duplicates were screened for the presence of organic vapors using ' a photo-ionization detector (PID) and logged in accordance with the Unified Soil Classification System. Boring logs are included in Appendix A. 3.2 Depth to Groundwater Groundwater depths were measured five times in each well between November 10, 1993 and ' April 13, 1994. A Solinst water meter was used to measure water depth in each well. Table 2 summarizes the groundwater depth data. CenbBal Audit S. ki For. 67,.g,QR-491lYt1bW Subenri.e ,