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EKLEINFELDER I EXECUTIVE SUMMARY I This is a report of Kleinfelder's Fourth Quarter 2004 groundwater monitoring for the former Disco Facility located at 110 North Filbert Street in Stockton, California. MONITORING EVENT RESULTS On December 20, 2004, twenty (20) monitoring wells and three (3) piezometers were sounded for depth to groundwater. On December 20, 21, and 22, 2004, seven (7) monitoring wells were sampled by Kleinfelder. The wells included MW-DIS-11s, MW-DIS-Ild, MW-DIS-12, MW- DIS-13, MW-DIS-14s, MW-DIS-14d and MW-DIS-15. The monitoring wells were sampled in accordance with the "Groundwater Monitoring Frequency Decision Tree" developed by CH2M Hill for this project. The depth to groundwater ranged from 46.54 feet below the top of the well casing (MW-DIS- lls) to 57.68 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the monitoring wells ranged from —35.72 feet (MW-DIS-6) to —38.00 feet (MW-DIS-15). Groundwater flow direction at the site is estimated to be generally towards the east/northeast with a relatively flat gradient of approximately 0.0005 ft./ft. This flow direction is a shift from previous south and southeast flow directions. The 7 groundwater samples were analyzed for the following: Total Petroleum Hydrocarbon as gasoline (TPH-g), benzene, toluene, ethylbenzene, and total xylenes (BTEX), Tert-Butyl Alcohol (TBA), 1,2-Dichloroethane (1,2-DCA), 1,2-Dibromoethane (EDB). Only MW-DIS-15 was additionally analyzed for Di-isopropyl Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert- } Butyl Ether (MTBE), and tert-Amyl Methyl Ether(TAME). ` The seven downgradient well samples (MW=DIS-11s, MW-DIS-I ld, MW-DIS-12, MW-DIS-13, # MW-DIS-14s, MW-DIS-14d and MW-DIS-15) all showed non-detectable concentrations of TPH-g, BTEX, TBA, and EDB. Concentrations of 1,2-DCA were detected in MW-DIS-IIs, MW-DIS-14s, and MW-DIS-15. The 1,2-DCA concentration in MW-DIS-Ils decreased approximately 60% from the previous quarterly results (down to 73 ug/1). MW-DIS-14s continued to show a decreasing trend during the 2004 monitoring period (down to 1.8 ug/l from 3.2 ug/l, the lowest since monitoring began). It should be noted that the concentration of 1,2- DCA reported for MW-DIS-15 was the lowest since monitoring began (1.9 ug/1).at this location. The additional oxygenates MTBE, DIPE, ETBE, and TAME (MW-DIS-15 was the only well analyzed for these constituents) were non-detectable at or above the laboratory reporting limits. GROUNDWATER TREATMENT SYSTEM OPERATION The soil vapor extraction system installed by CH2M Hill was replaced by Kleinfelder during 2003 with an air sparging (AS)/high vacuum soil vapor extraction (SVE)/ozone injection system. 12280.M0N/ST05R173/JZ:Iv Page 1 of 11 S @ 2005,Kleinfelder,Inc. February 11,2005