ARCHIVED REPORTS_XR0009519 - Laserfiche WebLink

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1 ' 1.0 SITE LOCATION AND DESCRIPTION The subject property is located at the intersection of Fremont and Stockton Streets in Stockton, ' California (see Figure 1). The subject property is a former display manufacturing business. The property consists of a commercial building situated on several parcels totaling approximately 114 acre. A single, 500-gallon underground fuel storage tank had apparently been used to store leaded gasoline for use in the company vehicles. The tank was located at the northeast rear of the building (see Figure 2). 1 2.0 PROJECT HISTORY In February 1988, the underground fuel storage tank was removed. Evidence of soil contamination as gasoline was noted during tank removal. Soil sample analysis confirmed the presence of total petroleum hydrocarbons as gasoline (TPH-g) in the soil to a depth of at least 16 feet. The San Joaquin County Public Health District (San Joaquin County) subsequently issued a directive to assess the extent of soil and groundwater contamination. ' In March 1994, three groundwater monitoring wells (MW-1, MW-2 and MW-3) were installed at the site in the vicinity of the former tank (see figure 2). The wells were installed to depths of ' approximately 30 feet each, and screened over depths of approximately 15 to 30 feet. During installation of the wells, soil contamination was noted to be present in well borehole MW-2 to a depth of approximately 20 feet. This depth equated to the approximate top of the water table. Groundwater contamination was also detected in this well. No soil contamination was apparently detected in well boreholes MW-1 and MW-3. ' In December 1994, overexcavation of contaminated soil in the vicinity of the former underground tank was conducted. Approximately 108 cubic yards of contaminated soil was overexcavated in the vicinity of the former tank. ' In November 1995 and January 1996, a total of eleven soilp robe holes were advanced in the vicinity of, and down-gradient of, the former tank. Soil and groundwater samples were collected to define the lateral extent of soil and groundwater contamination. The results were presented in the February 1996 report by Wm. J. Hunter & Associates titled Interim Report Covering Results of Soil & Groundwater Investigation. In May 1996, a fourth groundwater monitoring well (MW-4) was installed down-gradient of the site (see Figure 2). The well was installed to a depth of approximately 25 feet, and screened ' over a depth of approximately 5 to 25 feet. Quarterly groundwater monitoring and sampling of the four wells has continued since. ' 3.0 MONITORING WELL INSTALLATION 3.1 Purpose of Investigation . The purpose of this phase of investigation was to install one groundwater monitoring well adjacent to MW-2, and collect soils and ground-water samples. Due to rising groundwater levels, monitoring well MW-2 is no longer screened across the top of the water table. 1 JJW GEOSCIENCFS Inc.