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REQUEST FOR SITE CLOSURE REPORT . Former Beacon Station #610 3300 Waterloo Road, Stockton, California AMV Project No 19042 04 r -3- below grade (T1 1 -K) Concentrations of TPHd in soil samples collected on October 18, 1993, ranged from less than 1.0 to 9,900 mg/kg in soil sample T11 -K. Analytical results from soil samples collected during UST removal activities in October 1993 are compiled in Table 2. A cumulative total of approximately 900 cubic yards of soil was removed from the site in October 1993. Soil sample analytical results (Table 2, Figure 4) indicated that soil containing concentrations of TPHg and TPHd greater than 100 mg/kg was limited to soil beneath the southwest end of the former UST basin (soil samples collected from 16 to 33 feet below grade) 2.2 Initial Distribution of Petroleum Constituents in Ground Water Seven ground water monitoring wells have been installed at the site to monitor the presence of petroleum constituents in the ground water Separate -phase petroleum product has not been detected on the water table beneath the site Only the ground water sample collected from monitoring well MW -4 reported a benzene concentration above the method detection limit at 1.2 parts per billion (ppb) The initial distribution of dissolved benzene inferred from ground water samples collected on April 13, 1987, is illustrated on Figure 5 Historic ground water sample analytical results are compiled in Table 4. g 8 �a 'ti s9 SW l�9 `t %y j,sJc rJiVW 2.3 Hydrogeology h r s�• Ground water elevations have decreased significantly since the installation of monitoring wells MW -1 through MW -4 in 1987 (ground water was encountered at approximately 40 feet below grade during the installation of these wells) The reported direction of ground water flow was toward the southwest in 1987. Ground water is currently present at approximately 73 5 feet below grade The current direction of ground water flow, interpreted from data collected from monitoring wells MW -5 through MW -7 on October 13, 1994, is toward the north-northwest (Figure 6) The ground water gradient on October 13, 1994, was less than 0 01 foot per foot Table 3 summarizes historical ground water elevation data collected at the site Soil underlying the site consists of silt, silty sand, silty clay, sandy silt, and sand with minor gravel In general, soil grain size increases with increasing depth beneath the site In soil boring SB -3, for example, silt is present to a depth of 9 feet below grade The silt is underlain f— by silty clay between 9 and 33 feet below grade Sand underlies the silty clay to a depth of 60 feet (the total depth of this boring) '3Q01 1-523 ,pt114 mJ