ARCHIVED REPORTS_XR0013116 - Laserfiche WebLink

Home Browse Search

6.0 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 6.1 SUMMARY The following subsections provide a summary of the investigation activities conducted at the Site. In addition, a summary of analytical results generated from the sampling conducted during the RI/SSI are provided. The information generated from these activities/results was used in the development of the conclusions and recommendations provided in subsequent subsections. 6.1.1 Investigation Activities The following is a summary of two phases of investigation activities conducted at the Site during the RI/SSI: • Advanced 15 on-site soil borings to a maximum depth of 25 feet bgs to delineate impacts identified during previous investigations. Collected samples at depths of 1-, 3-, 5- or 6-, and 8-feet bgs at all locations. Collected additional soil samples at 10- and 15-feet bgs in two borings (E3-1 and E3-2), and at 10-, 15-, 20- and 25-feet bgs in one boring (A3-2) that was subsequently converted to monitoring well TW-5; • Installed 22 soil gas probes at 5 feet bgs to characterize soil gas impacts across the entire Site. Of the 22 soil gas probes installed, 15 were advanced on 100 foot centers for an unbiased characterization of the Site, and the remaining seven were installed to delineate impacts identified in two of the initial 15 locations; • Installed one new groundwater monitoring well (TW-5), in the vicinity of the former gasoline UST, to investigate potential remaining impacts after the removal and closure of the UST by the RWQCB and SJCDEH; • Collected one grab groundwater sample (E3-2GW) from Boring E3-2 to investigate potentially impacted groundwater that may have resulted from elevated TPH detections observed in Boring E3-1; • Installed five background soil borings to a depth of 0.5-feet bgs and collected samples for analysis; • Analyzed 83 on-site soil samples, including duplicates, for the following MGP-related constituents: PAHs, TPH, and metals. Analyzed 11 select soil samples, including duplicates, for VOCs; • Analyzed 27 on-site soil gas samples, including duplicates, for VOCs including naphthalene and the leak detection compound (isobutane during Phase 1 and helium during Phase 2); • Analyzed eight on-site groundwater samples, including duplicates, from monitoring wells TW-1 through TW-5 for PAHs, TPH, metals and VOCs; • Analyzed one on-site grab groundwater sample for PAHs and TPH; and • Analyzed five background soil samples from locations surrounding the Former Tracy MGP Site for PAHs, TPH and metals. PARSONS 45 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010