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V 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 this work plan for 308 South El Dorado Street in Stockton, California. The work plan includes the advancement of seven soil borings for the collection of soil samples,the installation of ground water wells and the collection of ground water samples to confirm the lateral and vertical extent of dissolved hydrocarbons. The work will be conducted in two phases to expedite the assessment: Phase 1) on-site monitoring well installation work and Phase 2) City of Stockton permitting and off-site monitoring well installation work. The location of the site is illustrated on Figure 1. A plan of the site is illustrated on Figure 2. The San Joaquin County Environmental Health Department (EHD) required additional site assessment to define the vertical and lateral extent of hydrocarbon-impacted soil and ground water due to the presence of contaminants of concern beneath the USTs,in the monitoring wells and in the majority of samples collected during the CPT investigation conducted in November 2002.This work plan was prepared in response to the EHD letters dated 07 February and 06 July 2005, and was prepared in accordance with Central Valley Regional Water Quality Control Board(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 2005,the average depth to ground water at the site Advanced GeoEnvironmental,Inc. r