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KLEINFELDER 1 EXECUTIVE SUMMARY This is a report of Kleinfelder's first quarter 2003 groundwater monitoring for the former Disco Facility located at 110 Filbert.Street in Stockton, California. On February 26, 2003, twenty monitoring wells and three piezometers were sounded for depth to groundwater. On March 4, 5, .and 6, 2003, twelve monitoring wells were sampled by Kleinfelder: The monitoring wells sampled were MW-DIS-1, MW-DIS-2, MW-DIS-I ls, MW- DIS-11d, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d, MW-DIS-15; and NPI-70'. NP1-80' and NPI-90'. The monitoring wells were sampled in accordance with the i "Groundwater Monitoring Frequency Decision Tree" developed by CH2M Hill. The depth to groundwater ranged from 43.33 feet below the top of the well casing (MW-DIS- 11s) to 52.53 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the monitoring wells ranged from —32.27 feet (MW-DIS-d) to —33.07. feet (MW-DIS-13). Groundwater flow direction at the site is estimated to be towards the east/southeast at approximately 0.0006 ft./ft. The 12 groundwater samples were analyzed for the following analysis: benzene, toluene, ethylbenzene, and total xylenes (BTEX), Total Petroleum Hydrocarbon as gasoline (TPH-g), 1,2- Dichloroethane (1,2-DCA), 1,2-Dibromoethane (EDB); and tert-Butyl Alcohol (TBA). Only one groundwater sample (MW-DIS-15) was additionally analyzed for the oxygenates Di-isopropyl Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert-Butyl Ether (MTBE), and tert-Amyl Methyl Ether (TAME). This was the first groundwater sampling event conducted, from MW- DIS-15 since it was installed in February 2003. TPH-g was detected in five samples collected from MW-DIS-1, MW-DIS-2, MW-DIS-14s, NPI- 70% NPI.-80' and NP1-90' with concentrations ranging from 770 ug/l (MW-DIS-2) to 160,000 ug/1 (NPI-80'). MW-DIS-2 is located northwest of the former service station footprint and NPI- 80' is located within the former service station footprint. BTEX compounds were detected in the same wells. Again, the lowest concentrations .were seen in MW-DIS-2 and the highest concentrations seen in NP1-80'. TPH-g or BTEX.compcunds were not detected in any other groundwater samples collected this quarter. 1,2-DCA was detected in eight of the twelve groundwater samples. The concentrations ranged from 0.57 ug/l (MW-DIS-2) to 2,100 ug/l (NPI-80'). It should be noted that 1,2-DCA was detected in the new monitoring.well MW-DIS-15 with a concentration of 10 ug/l. Only MW DIS-11d, MW-DIS-12, MW-DIS-13, and MW-DIS-14d had non-detectable concentrations of 1,2-DCA. The .detected concentrations of 1,2-DCA exceeded the Primary Maximum Contaminant Level (PMCL) for 1,2-DCA of 5 ug/1 in six of the eight.samples. I t 12280.MON/ST03R524 Page 1 of 12 0 2003,Kleinfelder,Inc May 6,2003