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S E C 0 R 3017 Kilgore Road Suite 100 Rancho Cordova CA 95670 916-861-0400 rex 91 686 1-0430 FAx on wells MW-11R, MW-2R, and VW-1 for 92 hours Vapor extraction flow rates ranged between 10 90 scfm (standard cubic feet per minute) to 42 86 scfm, and vacuums ranged from 14 to 25 Inches of mercury, and at groundwater extraction flow rates ranging from 0 01 gallons per minute (gpm) to 6 2 gpm During DPE testing, an estimated 8 11 pounds of TPHg, 0 17 pounds of benzene, and 5 26 pounds of MtBE were removed from beneath the site, and approximately 26,210 gallons of impacted groundwater were extracted and transported off-site for disposal Based on the results of DPE testing, this technology was determined to be Ineffective based on the low soil vapor extraction radius of Influence calculated for simultaneous application of DPE (24 feet), the large quantity of extracted groundwater, and low estimated mass removal quantities (SECOR, 2002) J SENSITIVE RECEPTORS In 1999 Cambria conducted a sensitive receptor survey for the Site The survey identified an unnamed levee restricted slough approximately 2000 feet south of the Site and a man-made lake 1,500 feet southwest of the Site The survey also identified a destroyed irrigation wells owned by California Department of Transportation approximately 315 feet west of the Site No other water supply wells were identified MONITORING AND SAMPLING Groundwater monitoring and sampling was initiated In 1992 Currently, 11 wells are monitored and sampled quarterly Samples are analyzed for TPHg, BTEX and fuel oxygenates Depth to groundwater at the site as ranged from 11 to 18 feet bgs REMEDIAL STATUS �v In August 2000, an Interim migration control plan at the site was Initiated to reduce the amount of petroleum hydrocarbons and MtBE beneath the site, and to prevent further off-site migration of the dissolved plume The plan consisted of the periodic extraction of approximately 5,000 gallons of Impacted groundwater from wells historically containing the highest concentrations of petroleum hydrocarbons and MtBE (MW-IR, MW-2R, and VW-1) An ozone sparge remediation system began operation in May, 2004 Batch extraction was discontinued in June, 2004 l CHARACTERIZATION STATUS Contamination in soil Is adequately delineated Historical data indicated the highest levels of gasoline range hydrocarbons are localized near the northern dispenser Island The highest concentrations of MtBE were detected in the vicinity of the UST pit during removal and replacement of the fuel systems Contaminant concentrations In samples from soil borings and monitoring wells were low to non-detectable Contamination in groundwater is not fully delineated In the absence of the effects of batch extraction, local groundwater Is predominantly to the south Downgradient well MW-6 has consistently contained detectable TPHg and/or MtBE since this well was installed in 1994 RECENT SUBMITTALSICORRSPONDENCE March 29, 2004 — Addendum to Revised Remedial Action Work Plan and Work Plan for Ozone Sparge Well Installation and Additional Off-Site Assessment submitted to San Joaquin County Environmental Health Division Proposed two cone penetrometer borings and HydroPunch groundwater sampling to identify deeper water bearing zones and delineate vertical extent of dissolved contamination