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1`1 <br /> HYDRO <br /> ENVIRONMENTAL <br /> TEGINOLOGES,INC. <br /> 1.2 Background <br /> In March 1990, four underground storage tanks (USTO were removed from the site. <br /> Soil samples collected from beneath the former USTs and the former dispenser <br /> islands contained detectable concentrations of petroleum hydrocarbons. Based on <br /> these results, the San Joaquin County Public Health Services Environmental Health <br /> Division required a preliminary site assessment to be performed <br /> In August 1991, Nachant Environmental, Inc (NEI) supervised the drilling of three <br /> soil borings (B-1, B-2 and B-3) to depths between 40 and 50 feet below grade. <br /> Detectable concentrations of petroleum hydrocarbons were present in all borings, <br /> but highest in the soil samples collected from boring B-1, located in the center of the <br /> former UST area. Detailed results are presented in the Preliminary Site Assessment <br /> Report by NEI, dated November 22, 1991. <br /> In July 1992, Tank Protect Engineering (TPE) supervised the drilling of five soil <br /> borings and the installation of five monitoring wells (MW-1, MW-2, MW-3, MW-4 <br /> and MW-5), each to a depth of approximately 90 feet below grade Detectable <br /> concentrations of petroleum hydrocarbons were present in soil and ground water <br /> samples collected from all monitoring wells, except from MW-5 Depth to ground <br /> water beneath the site is approximately 81 feet below grade, and flows in a southerly <br /> direction with a gradient of 0 0004 feet/feet. Detailed results are presented in the <br /> . Preliminary Site Assessment Report by TPE, dated September 3, 1992. <br /> 2.0 FIELD ACTIVITIES <br /> All drilling, well construction, and sampling during this recent phase of <br /> investigation was performed in accordance with state and local agency guidelines A <br /> copy of HETI's standard field protocols is attached as Appendix A <br /> 2.1 Soil Borehole Drilling and Soil Sampling <br /> A safety briefing was conducted prior to drilling on December 1, 2, and 3, 1993, with <br /> B & F Drilling personnel of Rancho Cordova, California At the end of the briefing, <br /> all personnel reviewed and signed the Site Safety Plan prepared for this site <br /> (Appendix B) Prior to drilling, HETI obtained off-site access for drilling on adjacent <br /> private properties Well installation permits were obtained from the San Joaquin <br /> County Public Health Services Environmental Health Division (Appendix C) <br /> B & F Drilling used a Mobile B-61 drill rig to drill three 8-inch diameter soil borings, <br /> designated MW-6, MW-7 and MW-8, each to a total depth of 90 feet below grade A <br /> California-modified split spoon sampler, lined with brass tubes, was used to collect <br /> soil samples at five foot intervals The soil samples were labeled, documented on a <br /> chain-of-custody form, and placed in a cooler for transport to Trace Analysis <br /> 2 <br />