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r' `00, �1 Additional Site Assessment Work Plan DEN'S AUTO REPAIR 308 South El Dorado Street, Stockton, California 1.0. INTRODUCTION At the request of Mr. Den Ueda of Den's Auto Repair,Advanced GeoEnvironmental, Inc. (AGE) has prepared the enclosed additional site assessment work plan for 308 South El Dorado Street in Stockton, California. The work plan includes the advancement of four paired, cone penetrometer testing (CPT) soil borings for the collection of soil and ground water samples and the installation of two ground water wells. The location of the site is illustrated on Figure 1. A plan of the site is illustrated on Figure 2. The EHD required additional site assessment of the vertical and lateral extent of hydrocarbon impacted soil and ground water due to the presence of dissolved MTBE beneath the USTs and in monitoring well MW-1 at the western edge of the site. This work plan was prepared at the request of the San Joaquin County Environmental Health Department (EHD) by letter dated 21 May 2002, and was prepared in accordance with California Regional Water Quality Control Board - Central Valley Region (CVRWQCB) guidelines for the investigation of underground storage tank (UST) sites. 2.0. BACKGROUND The site is located in an commercial/industrial area of south Stockton at the southeast corner of the intersection of South El Dorado Street and East Lafayette Street.A single structure is located on the property and is currently occupied by an auto repair facility(Figure 2). 2.1. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The site is located in an area of low topographic relief. According to Geologic Map of California, published in 1966 by the California Department of Conservation Division of Mines and Geology, the site area is shown to be within the Great Valley Geomorphic Province (GVGP) of California, a large, elongate, northwest trending structural trough. The GVGP is subdivided into two major divisions designated the Sacramento and San Joaquin Valleys, which have been filled to the present elevation with thick sequences of sediment ranging in age from Jurassic to Recent, creating a nearly flat-lying alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively. Based on data collected from the site in February 2002 the average depth to groundwater at the site is approximately 25 feet below surface grade(bsg). The ground water in February 2002 was inferred to be flowing toward the north-northeast under a gradient of 0.008 ft/ft. Advanced GeoEnvironmental,Inc.