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r <br /> 1 <br /> rr <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 /> unpact in the shallow zone The scope of work proposed herein is designed to <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 /> ' OB TECTNES <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 <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 /> 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 <br /> of the site includes retail stores, an elementary school, and private residences The <br /> 1 closest water-supply well was documented by Applied GeoSystems, 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 /> 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 I <br /> ' Kleinfelder,Inc. installed five soil borings (KB-1 through KB-5) at the site <br /> in January 1988 (Phase 1 Soil Investigation, Klemfelder, March 3, 1988) These <br /> borings were installed around the tank complex,adjacent to the product islands,and <br /> 1 <br /> Page <br /> out Mr <br /> %%G <br /> ILGM CATAWRO sa0WNOMA C YMIEnVV'S RE ACMPMMOC 2/11 <br /> Sfâ–șNITA BARBARA <br />