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T I I 1.0 INTRODUCTION t This report presents the results of a subsurface drilling investigation conducted on Au ,ust 24, 1999 at 1282 Shaw,Road in Stockton, California (Figure I)- The property is own(d by the Stockton Terminal & Eastern Railroad (ST&E) and is operated as a diesel locomc Live maintenance and fueling house. The investigation was undertaken by Upgradient Environmental Consultants under contract#99027.2 at the request of the San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD). The purr ose of the investigation was to determine whether operation of an underground diesel fuel storage tank at the site has resulted in soil and/or groundwater contamination beneath the property, and if so, to determine the extent of the contamination. 2.0 BACKGROUND In November 1998, one underground diesel storage tank was removed from the locorr otive shop area by Bowen Construction. During the tank removal, contaminated soil was obs,:rved at the base of the tank excavation, and diesel hydrocarbons were detected in samples toll acted from the excavated soil.'The tank was disposed of at Erickson, Inc_ in Richmond, Calif,nnia, and the excavated soil was subsequently returned to the excavation and covered with vise uine. Additional imported soil was placed on top of the visquine to bring the excavation i.p to surface grade, and a thin:ilayer of crushed rock(railroad ballast) was poured over the surd.--e to match the surrounding area. No evidence of leakage from the tank was observed, but it is our understanding from S T&E personnel that leakage was observed around a corroded coupling in the piping bet,vee i the tank and the dispenser. 1Two samples were collected from beneath the tank at a dep h of approximately 14 feet, and 5 samples were collected from the excavated soil. Four c f the stockpile samples were composited 2:1 before analysis. The samples were analyzed by EPA methods 8015m for Total Petroleum Hydrocarbons as diesel, and 8020 for benzene. tol iene, ethylbenzene, and xylene,(BTEX). Diesel was reported in all of the samples, ranging fron.200 to 4900 mg/kg (parts per million). Benzene was not detected in any of the samples, not was ethylbenzene. Toluene and xylene were detected at low concentrations, mainly in the stockpile (Table 1). At the request of PHS/EHD, Upgradient Environmental conducted a sensitive receptor si irvey in the vicinity of the site in June 1999. The results of that survey were reported in the Jul& 25 N work plan for assessment that Upgradient prepared on behalf of ST&E. The survey ider,rified ten private wells within a 2,000-foot radius of the site, the nearest one being owned by S''&E. This well is located at the west (front) end of the locomotive service building, approxin ately 300 feet west of the underground tank site. l7 h i 1 `