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k`■ KLEINFELDER 1 EXECUTIVE SUMMARY This is a report of Kleinfelder's Third Quarter 2002 groundwater monitoring for the former Disco Facility located at 110 Filbert Street in Stockton, California. On August 12, 2002, twelve (12) monitoring wells were sampled by Del-Tech Geotechnical Support Services. The monitoring wells(NP-1-70', NP-1-80', NP-1-90', MW-DIS-1, MW-DIS- 2, MW-DIS-9, MW-DIS-11s, MW-DIS-Lld, MW-DIS-12, MW-DIS-13, MW-DIS-14s, and MW-DIS-14d) were sounded for depth to groundwater and sampled. The monitoring wells were sampled in accordance with the "Groundwater Monitoring Frequency Decision Tree" developed by CH2M Hill. ` The depth to groundwater ranged from 43.53 feet below the top of the well casing (MW-DIS- I ls) to 52.97 feet below the top of the well casing (MW-DIS-14d). Groundwater elevations for the monitoring wells ranged from —32.67 feet (MW-DIS-5) to —33.16 feet (MW-DIS-14d). Groundwater flow direction at the site is estimated to be towards the south at approximately 0.0002 ft./ft. The 12 groundwater samples were analyzed for the following analysis: benzene, toluene, ethylbenzene, xylene, Total Petroleum Hydrocarbon as gasoline (TPH-g), 1,2-Dichloroethane (1,2-DCA), 1,2-Dibromoethane (EDB), tert-Butyl Alcohol (TBA), and the oxygenates Di- isopropyl Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert-Butyl Ether (MTBE), and tert- Amyl Methyl Ether(TAME). TPH-g was detected in five of the groundwater samples collected. The detected concentrations of TPH-g detected ranged from 100 ug/l to 170,000 ug/l. TPH-g was not detected in monitoring wells previously noted as not having TPH-g. Benzene was also detected in five groundwater samples with concentrations ranging from 0.50 ug/l to 25,000 ug/l. The remaining seven groundwater samples showed non-detect concentrations of benzene above the laboratory reporting limit (ND < 0.50 ug/1). The Primary Maximum Contaminant Level (PMCL) for benzene is 1 ug/l. The laboratory reporting limit for benzene (0.50 [to) is below the PMCL for benzene in water in one groundwater sample collected from monitoring well MW-DIS-1 Is, however, exceeds the PMCL for benzene in MW- DIS-1,NP-1-70', 80', and 90'. Toluene was detected in four groundwater samples with a range of 1,000 ug/1 to 44,000 ug/l. The remaining eight groundwater samples showed non-detect concentrations above the laboratory reporting limit of 0.50 ug/l. The PMCL for toluene is 150 ug/l. i ' I 12280-MON/ST02R519 Page I of 14 0 2002,Kleinfelder,Inc September 19,2002