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c � <br /> PROBLEM ASSESSMENT REPORT St1 �Mtna �i-� <br /> 6131 Pacific Ave Stockton, CA. <br /> Aegis Project No 90-020 <br /> Page 1 l/N Iq <br /> 1.0 INTRODUCTION <br /> Aegis Environmental , Inc. (Aegis) is hereby submitting the results of <br /> monitoring well and vapor extraction well installations at the Shell <br /> retail service station located at 6131 Pacific Street, Stockton, San <br /> Joaquin County, California (Figure 1) . This is the second phase of a <br /> continuing problem assessment at the site resulting from an <br /> unauthorized release of petroleum hydrocarbons in soil . <br /> 1.1 Purpose <br /> The purpose of the subsurface investigation included the following: <br /> Io Characterize the site subsurface and hydrogeologic conditions. <br /> o Assess the presence of petroleum hydrocarbons in the soils and <br /> ground water beneath the site. <br /> o Evaluate the need for further assessment and/or mitigation of <br /> petroleum constituents in soil and ground water beneath the site. <br /> C 1.2 Scope <br /> 11 The subsurface investigation scope of work is summarized below. <br /> Methods used in the investigation are included in Appendix A. <br /> o On March 26-29, 1990, a preliminary subsurface investigation was <br /> completed. The investigation included a total of fourteen soil <br /> borings and the collection and analysis of 28 soil samples (Aegis <br /> 6/12/90) . <br /> I o On June 7, 1990, three underground fuel storage tanks and the <br /> associated underground piping were excavated. Soil samples were <br /> collected from beneath the underground fuel tanks and product <br /> line trenches. Additionally, a horizontal vapor extraction piping <br /> system was installed below the product line trenches (Aegis <br /> 612/90) . The resulting tank excavation was backfilled with the <br /> original fill material and was brought to grade with imported <br /> fill. <br /> l <br /> o On July 12-13 , 1989 a total of five soil borings were advanced <br /> using hollow-stem auger techniques. Three of the soil borings <br /> were drilled 65 feet below grade. The remaining two soil borings <br /> were drilled to 20 feet and 46 feet below grade in the area of <br /> the original underground fuel-storage-tanks, and adjacent <br /> locations. <br />