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.�, Ceob9io t reChn1cs lac. 1101 7",Street Modesto,California 95354 (209)522-4119/Fax(209)522-4227 REPORT Additional Site Characterization Vt Quarter 2004 Groundwater Monitoring George's Service 1600 Durham Ferry Road Tracy, California Project No. 425.2 March 22, 2004 1.0 INTRODUCTION The site, located at the intersection of Highway 33 and Durham Ferry Road, has been ' owned and operated by George and Mei Teranishi since the 1940's as an automobile repair facility and market. Gasoline was sold at the site until 1990, when the tanks were removed. ` The site has been undergoing site characterization work commencing 1995 by Del Tech Geotechnical Support Services (Del-Tech). Three monitoring wells were installed in early 1995 and elevated levels of petroleum hydrocarbons were detected on the northern and +- western sides of the property. In January of 1997, Geological Technics Inc. (GTI) contracted with Mr. and Mrs. Teranishi to provide additional site characterization work regarding the definition of the lateral and vertical extent of petroleum hydrocarbons in the soil and groundwater. In early April 1997, GTI installed five new water-table monitoring wells and one intermediate depth, discretely screened, monitoring well. In mid 1998, GTI installed two additional intermediate depths, discretely screened, monitoring wells and one deep discretely screened, monitoring well. Quarterly groundwater monitoring reports have been submitted throughout the project. ,.. In late July of 2001, GTI and Del-Tech performed a limited soil excavation at the site and removed approximately 500 cubic yards of contaminated soil. Analytical data show that approximately 4,900 pounds of TPH-G were removed from the site. At the end of October 2001, the stockpiled soil was transported and disposed of at Forward Landfill. GTI submitted a report on the soil excavation activities on January 28, 2002. During the backfill of the excavation, the County inspector reviewed the work in progress '-' and discussed the issue of the residual contamination left under the building, around the monitoring wells, and under Durham Ferry Road. It was concluded that piping should be installed for use in a bio-venting project that could extract at a slow rate the vapors emitted from the residual contamination. Subsequently, two pipes were installed to allow for the operation of a low flow bio-venting/vapor extraction system in and around the excavation.