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ERI 205503.W01 Unocal Service Station 5886,Stockton, California March 28, 1997 <br /> Collect soil samples from the borings to evaluate soil stratigraphy and for submittal to the <br /> laboratory. <br /> • Develop newly installed wells, purge newly installed wells, and collect groundwater samples <br /> from existing and newly installed monitoring wells. <br /> • Submit soil and groundwater samples to Sequoia Analytical Laboratories (Hazardous Waste <br /> Certification No. 1210) for analysis of MTBE using EPA Method 5030/8020. Detection <br /> limits for the test requested and concentrations present will be stated on the laboratory <br /> reports. <br /> Task 3: Data Interpretation/Report <br /> • Interpret field and laboratory data to evaluate the integrity of the existing system, the source <br /> of MTBE, and soil and groundwater conditions. <br /> • Prepare a report describing subsurface conditions at the site and vicinity as observed in <br /> borings and wells, summarizing findings, and presenting conclusions. <br /> Evaluation of System Integrity <br /> To evaluate the integrity of the existing product storage and distribution system, 76 Products <br /> Company has completed an inspection of the existing facilities. Further work will include obtaining <br /> data from the laboratory regarding the absence or presence of MTBE in groundwater collected from <br /> the 21 geoprobe locations prior to placement of the existing tanks and lines, and obtaining inventory <br /> reconciliation records from the site. These data will allow evaluation of whether.MTBE detected in <br /> groundwater originated prior to placement of existing tanks and lines and/or whether a release of <br /> petroleum hydrocarbons may have potentially occurred at the site. <br /> Soil Borings/Monitoring Wells <br /> Locations of the proposed soil borings and monitoring wells are shown on Plate 2. The locations <br /> were chosen to evaluate MTBE concentrations downgradient of potential source areas, at property <br /> boundaries in the inferred crossgradient and downgradient directions of groundwater flow, and near <br /> the upgradient property boundary. Monitoring wells constructed in these locations will further help to <br /> 3 <br />