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d <br /> .V <br /> w <br /> 1.0 Xntroduct.lon <br /> This report presents the results of a subsurface <br /> investigation for hydrocarbon contamination on the property <br /> located at 22 East Market; Strept in Stockton, California <br /> (Figure 1). The property is occupied by a City police <br /> station. The site has three underground (u/g) storage <br /> tanks which dispense regular and unleaded gasoline from two <br /> pumps (Figure 2). <br /> During precision testing at this site (May 1988) leakage was <br /> detected from the product line to Tank No. 2 (unleaded). <br /> Elevated levels of gasoline hydrocarbons were recorded in ' <br /> two of four soil samples collected June 9, 1988 from a <br /> trench located adjacent to the product lines at the site. <br /> Samples identified as #1,#2,#3 and #4, were collected from a <br /> � a depth of approximately sim feet below grade and which <br /> contained total petroleum hydrocarbon concentrations ranging <br /> from non-detectable to 800 ppm (Table. 2). A small hole:was; <br /> found in the unleaded, product line in the area of highest'. <br /> contam.lnaticn (Sample #2),' individual testing of the tanks <br /> at this site had indicated they were mathematically tight. <br /> - The unleaded product line was repaired and the tanks were <br /> certified tight again upon retesting. Based upon these <br /> positive leak indicators the San Joaquin County Public <br /> Health Services, Environmental Health Division required an <br /> ( + investigation to asses the extent of contamination. <br /> This investigation was conducted in accordance with <br /> ;_ ..J WaterWork's proposal dated April 20, 1989, which was <br /> submitted to the San Joaquin County Public Health Services, <br /> Environmental Health Division (SJCPHSEHD) for prior <br /> f approval. This proposal was drafted and the investigation <br /> x conducted in accordance with the Tri Regional Guidelines <br /> prepared by the Regional Water Quality Control Board. <br /> 2.0 Site Setting <br /> The site is situated on level terrain comprised of <br /> Quaternary-Recent alluvial sediments. Near surface <br /> W, materials consist of intercalated sands, silts, clays, and " <br /> gravels. As is .typical of alluvial environments, high <br /> permeability zones representing former stream channels may <br /> 4 occur as sinuous or lenticular features. Local groundwater <br /> gradients generally parallel the surface drainage_ trends. <br /> !^ , The water table- lies. at approximat®ly 38 " fBat' below grade' <br /> and west flus":.to:=the: southwest based on'San J6aqusi :Flcot3' <br /> ► ► Control and Conservation District data reference. The <br /> surface water bodies within or,-half mile of the site include <br /> Lake McLeod to ;,he northwest and ------- <br /> --� 3,� -south7souahwest. <br />