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} <br /> I <br /> ARCADIS GERAGHTY&MILLER <br /> In the opinion of ARCADIS Geraghty & Miller, previous work by <br /> UNOCAL's consultants has resulted in delineation of the lateral extent of groundwater <br /> impact in the shallow zone. The scope of work proposed herein is designed to I <br /> delineate the vertical extent of site groundwater impacts and to finalize the database <br /> upon which a subsequent remedial strategy will be developed and a corrective action <br /> plan work plan written. <br /> i <br /> OBJECTIVES <br /> The objectives of the limited subsurface investigation are: <br /> 1. Vertically delineate the dissolved-phase petroleum hydrocarbon plume <br /> downgradient of wells with elevated concentrations of dissolved-phase i <br /> petroleum hydrocarbons; and <br /> 2. Evaluate the vertical groundwater gradient. <br /> Completion of.these objectives is expected to provide sufficient data to <br /> support completion of the delineation of the vertical and lateral extent of impact to <br /> groundwater and to form the basis for development of a corrective action plan. <br /> i <br /> SITE BACKGROUND AND SETTING <br /> The site is a vacant lot situated on the southwest corner of Pacific Avenue and + <br /> Walnut Avenue(Figure 1) in the City of Stockton,California. Land use in the vicinity i <br /> of the site includes retail stores, an elementary school, and private residences. The <br /> closest water-supply well was documented by Applied GeoSystetns, Inc. (AGS) to <br /> be 800 feet to the northeast of the site (December 1990). The site lies at an <br /> approximate elevation of 10 feet above 'mean sea level. The topography in the <br /> vicinity is essentially flat with a-gentle slope to the west toward the San Joaquin <br /> River, which is located 3 miles to the west of the site. <br /> I <br /> UNOCAL originally leased the site in January 1947. The station was <br /> completely remodeled in 1967. The station was demolished between February and <br /> April 1988. During station demolition, two 10,000-gallon underground gasoline <br /> tanks were removed from a common excavation along with a separate 550-gallon <br /> waste oil tank. The former tank locations, along with the product islands and station <br /> building, are shown on Figure 1. <br /> KleinfeIder, Inc. installed five soil borings (KB-1 through K13-5) at the site <br /> in January 1988 (Phase I Soil Investigation, Kleinfelder, March 3, 1988). These <br /> borings were installed around the tank complex, adjacent to the product islands, and <br /> Our ref.; Page: <br /> \\GM_SANTA_BARBARASAAMAPRO_SBOIUNOCAL\C_VALLEY\WPS_REWACWKP2A.DOC <br /> 2/11 <br />