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PROBLEM ASSESSMENT REPORT Moreland Court Shelf 7700 Moreland Court, Stockton, California Delta Project No 40-88-146 ' Page 15 ' The monitoring well was constructed with 4-inch-diameter, Schedule 40 PVC blank casing and 0 020 inch slot screen The annular space was filled with #3 Clementtna sand from 3 5 feet above the screened interval (about 22 5 feet below grade) to 40 5 feet below grade A 2-foot-thick bentonite seal was installed above the sand Above the bentonite seal, from 1 foot below grade to approximately 20 5 feet below grade, the ' annular space was filled with cement grout containing 5 percent bentontte The top of the casing was completed with an internal locking cap and protected with a traffic-rated watertight cover(12-inch-diameter) ' that is flush with the ground surface A 36- by 36- by 4-inch concrete pad was installed around the traffic-bearing lid for additional support Monitoring well construction details are provided in Figure 7 ' Monitoring well field measurements collected on August 2 and 10, 1990, indicated that the well was dry ' 4 0 DISCUSSION OF INVESTIGATION RESULTS The extent of petroleum hydrocarbons in soils and ground water beneath the site is discussed below 4.1 Distribution of Petroleum Hydrocarbon Constituents in Soils ' Field screening of 24 soil samples collected from six soil borings (B-1 through B-6, Figure 2) advanced at the site on April 4, 1988, prior to tank removal work,did not detect the presence of petroleum hydrocarbons One of seven soil samples collected from the bottom of the former underground storage tank excavation on December 27, 1988, contained petroleum hydrocarbons The concentration of TPH in that sample (sample ' TS-2, Table 3, Figure 3) was 1,030 ppm Two of six soil samples collected from the bottom of the former product line trenches on January 3, 1989, contained petroleum hydrocarbons The concentrations of TPH ' in those samples (samples PL-5 and PL-6, Table 4, Figure 3) were 1,130 and 117 ppm, respectively ' To evaluate the horizontal and vertical extent of petroleum hydrocarbons identified in soil at the site during tank removal work, five soil borings (SB-7 through SB-10, and MW-1, Figure 3) were advanced to depths ' ranging from 40 to 70 feet below the site surface Tables 6 and 7 summarize the sample depths and laboratory analytical results on 11 soil samples collected from these borings Concentrations of TPH were less than the laboratory analytical method detection limit, and concentrations of benzene ranged from less than the detection limit to 0 0073 ppm T