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k" KLEINFEL©ER 1 EXECUTIVE SUMMARY i This report presents the Fourth Quarter 2005 groundwater monitoring results and a summary of the remediation activities at the former Disco Facility at 110 North Filbert Street in Stockton, California. The site is a former gasoline service station. The underground storage tanks were removed in 1985, site investigation began in 1991, and site remediation began in 1995. Nineteen groundwater monitoring wells have been installed at the site. The primary constituents of concern at the site are total petroleum hydrocarbons as gasoline, benzene and 1,2-DCA. Remediation of the impacted groundwater to the south of the site is performed with an ozone air sparging system. Remediation of the impacted soil and groundwater at the former source area is performed with an air sparging/vapor extraction system. GROUNDWATER MONITORING RESULTS On December 8, 2005, the depth to groundwater was measured in all of the wells at the site, and groundwater samples were collected from seven down gradient monitoring wells (MW-DIS-11S, MW-DIS-11D, MW-DIS-12, MW-DIS-13, MW-DIS-14S, MW-DIS-14D, and MW-DIS-15). The monitoring wells sampled were selected in accordance with the "Groundwater Monitoring Frequency Decision Tree" developed by CH2M Hill for this site. I The depth to groundwater ranged from 44.60 feet below the top of the well casing (MW- DIS-11S) to 53..82 feet below the top of the well casing (MW-DIS-15). Groundwater elevations in the wells ranged from —32.79 feet (SVE-N) referenced to Mean Sea Level (MSL) to —34.38 feet MSL (MW-DIS-13). During the Fourth Quarter 2005 the groundwater gradient was calculated to be 0.0006 feet/foot towards the east/southeast. The groundwater elevations recorded at the site have shown fluctuations over time from season to season with a general increasing trend recorded from 1991 to 2000 followed j by a general decreasing trend from 2000 to 2004. Over the past year the groundwater elevations at the site have increased. The seven 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). MW-DIS-15 was additionally analyzed for Di-isopropyl Ether (DIPE), Ethyl t- Butyl Ether (ETBE), Methyl tert-Butyl Ether (MTBE), and tent-Amyl Methyl Ether (TAME). i 1,2-DCA was the only constituent detected during the Fourth Quarter 2005 monitoring well sampling. TPH purgeable, BTEX, TBA and EDB were not detected above laboratory reporting limits in the groundwater samples. 1,2-DCA was detected in four { of the seven groundwater monitoring wells sampled (MW-DIS-11S. at 22 ug/L, MW- DIS-12 at 1.4 ug/L, MW-DIS-14S at 1.0 ug/L, and MW-DIS-15 at 1.0 ug/L). w 12280.M0N/ST06R070/CD:Iv Page 1 of 14 ©2006 Kleinfelder, Inc. February 16,2006