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-gi mg <br /> f51 <br /> 1.0 INTRODUCTION <br /> This report presents the results of a subsurface <br /> y investigation for hydrocarbon contamination on the Linden <br /> Unified School District property located at Highway 26 and <br /> Duncan Road in Linden, California (Figure I). The <br /> is occupied by the Linden Unified School Disnc busy <br /> triP <br /> garage. The site has four underground (u/g) storage tanks• <br /> including: 10,000 gallon diesel. tank, 6000 and 1,000 gallon <br /> ! ' gasoline tank and a waste oil -tank of unknown size (Figure <br /> 2). This investigation is being conducted in response to <br /> ( 1 pressure tests conducted on the 10,000 gallon diesel: tank on <br /> 4 July 10, August 26, September 3 and 8th, 1906which <br /> indicated a leaking system. As a result the tank was lined <br /> is with fiberglass and testing conducted January 14, 1987 <br /> indicated a tight system. Subsequent testing in July 1987, <br /> December 1988 and February 1989 indicated this tank to be <br /> mathematically tight. <br /> ► � This investigation was initiated in response to a direction <br /> issued by the San Joaquin County Public Health Services <br /> Environmental Health Division <br /> (SJCPHSEHD) to assess <br /> subsurface conditions beneath the ug <br /> diesel s tank. Te <br /> investigation was conducted in accordance with 1WaterWorkhs <br /> proposal dated October 25, 1989, which was submitted to the <br /> SJCPHSEHD for prior approval. <br /> E�Fr` 1 2.0 INVESTIGATION PROCEDURES <br /> On December 6, 1989, a total of three angles soil borings <br /> f:a rrpre drilled to an de'pt'h`of 27.feet..: (24, feet,-bellow.,grade). <br /> g Permits and inspection of the boring seal wens approved <br /> "'by <br /> the SJCPHSEHD. Drilling was conducted with a Tom Cat 28M <br /> rig using 7.5-inch (P.D.) hollow-stem augers. The drilling. <br /> was. performed under the direction of a field geologist who <br /> maintained a continuous log of the material encountered <br /> using the Unified Soil Classification System (Appendix I). <br /> i Vertical soil borings ASB-1 through ASB-3 were drilled to <br /> confirm that contamination had not resulted from <br /> leakage beneath the 10,00o product <br /> gallon diesel tank. These angle a <br /> a borings, drilled at 30° to vertical, were advanced to an <br /> auger depth of 27 fee;. to access soil conditions directl <br /> beneath each end andthe middle of the 10,000 gallon tank. <br /> The actual sample depth from grade is 24 feet as depicted on <br /> Figure 3. The location of the borings is presented on V <br /> Figure 2. All of the soil borings were abandoned by placing <br /> a 2-foot thick bentonite bottom plug within. sach boringand <br /> backfilling with the sand/cement slurry to grade. ' <br /> Grab samples of cuttings were logged continuously during <br /> t drilling for identification of-stratigraphy-.-and-detection-of <br /> - _ - - -- ydrocarbon aontamiriaton. Discreet samples were taken <br /> from the bottom of each boring. These samples were collected <br /> { <br /> in 2-inch-diameter brass tubes using a California modified <br /> f <br />