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1.0 INTRODUCTION <br />This report is being submitted in response to a request by the San <br />Joaquin County Public Health Services, Environmental Health <br />Division (PHS/EHD) for investigation of soil and groundwater <br />impaction at the Corrigan property located at 620 San Juan Avenue, <br />Stockton, California (Figure 1). <br />On May 25, 1991, WaterWork supervised the drilling of five soil <br />borings, three of which were completed as groundwater monitoring <br />wells (CPMW1, CPMW2, and CPMW3). Drilling was initiated to further <br />assess the lateral and vertical extent of soil and groundwater <br />impaction, as requested by San Joaquin County Public Health <br />Services in correspondence dated March 16, 1988. This report <br />details the results of that investigation. <br />2.0 PREVIOUS WORK <br />On May 27, 1986, hydrocarbon impaction of soil was noted during the <br />removal of two steel underground fuel tanks at the project site <br />(Figure 2). Both tanks were 1,000 -gallon in capacity. One tank <br />contained regular gasoline and the other diesel fuel. <br />Soil and groundwater samples were collected from the bottom of the <br />tank pit during tank removal. Laboratory analyses determined that <br />both soil samples contained detectable concentrations of total <br />petroleum hydrocarbons as gasoline (TPHG), 75 mg/kg and 960 mg/kg, <br />respectively. Also, groundwater samples contained benzene <br />concentrations below the California Primary Maximum Contaminant <br />Level (MCL) of 1 pg/l. Laboratory reports are included as Appendix <br />I. <br />3.0 HYDROLOGY/GEOLOGY <br />The site is situated on level terrain composed of Quaternary to <br />Recent alluvial sediments. Depth to water is approximately 8 to 10 <br />feet below grade based on the presence of water in the tank pit <br />during removal of the underground storage tanks. The closest <br />surface water body is the San Joaquin River which is approximately <br />200 feet from the former tank location. <br />The proximity of private, municipal, and irrigation wells located <br />within a one-half mile radius of the site is shown on Figure 3. <br />The closest well is located approximately 800 feet east of the <br />site. <br />The soils encountered during drilling activities consist primarily <br />of silty clays (CL/MH) to a total depth of approximately 26 feet <br />below grade. The northwest portion of the site contained a fine -to <br />i <br />Corrigan Property - 381 <br />90691 TLP 1 <br />