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w .. <br /> 1..0 Introduction <br /> `7 This report presents the results of a subsurface <br /> investigation for hydrocarbon contamination on the property <br /> located at 2500 Navy Drive in Stockton, California <br /> (Figures 1 and 2) . The property is occupied by the City of <br /> Stockton Regional Waste Water Control Plant. The site <br /> previously had an underground (u/g) fuel storage tank used <br /> to service facility vehicles and equipment. <br /> A 5000 gallon diesel tank was removed from this facility in <br /> n August 1987 (Figure 3). Free product was noted floating on <br /> groundwater within the tank pit. A water sample collected <br /> " from the tank pit at, approximately 6 feet below grade <br /> recorded 18 parts per billion (ppb) xylene and 65000 pp:-) <br /> total petroleum hydrocarbons as diesel. Based these <br /> positive leak indicators, the San Joaquin County Public <br /> Health Services, Environmental Health Division (SJCPHSEHD) <br /> required an investigation to assess the extent of <br /> contamination. <br /> .. This investigation was conducted in accordance with <br /> WaterWork's proposal dated April 20, 1989 and an addendum <br /> dated September 19, 1989 which were submitted to the <br /> SJCPHSEHD for prior approval. The proposals were drafted <br /> ` and the investigation conducted in accordance with the Tri <br /> Regional Guidelines prepared by the Regional Water Quality <br /> f , <br /> Control Board. <br /> i � 2.0 Site Setting <br /> The project site is situated on level terrain comprised of <br /> iA Quaternary-Recent alluvial sediments. The site is bounded <br /> on the south and west sides by the northwesterly flowing San <br /> ?' Joaquin River (Figure 2). Groundwater .flow is currently <br /> ix north to northeast, away from the river, although seasonal <br /> reversals are likely to occur. Due to the proximity of the <br /> river the water table is relatively shallow, approximately <br /> 10 feet below grade. Near surface materials in the area <br /> consist of intercalated sands, silts, clays, and gravels. <br /> ;a <br /> As is typical of alluvial environments, higher permeability <br /> zones representing former stream channels occur as sinuous <br /> or lenticular features. Locations of wells within one mile <br /> of the project site provided by the Department of Water <br /> E ' Resources (DWR) are plotted on Figure 4. The closest wells <br /> to the former tank location are located to the north and <br /> east at distances exceeding 2600 feet. <br /> k1 <br /> 1111 ME MINI'MM, 11111M NOR 0119M, <br /> i <br /> 1 <br />