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' S9po Aclk5 T?ff5 <br /> CVVZ <br /> A S S O C I A T E S I N C <br /> Sol] bonng/well construction logs from previous reports are contained in Appendix B Cross <br /> sections depicting the site stratigraphy are included on Figure 5 and the location of the cross <br /> ' sections are shown on Figure 4 <br /> ' 4 12 Petroleum Hydrocarbons in Soil <br /> A review of historical soil analytical data and field measurements indicate TPHg and BTEX are <br /> ' generally present in soil samples collected beneath the site and in soil samples collected from <br /> borings located in a hydrologically downgradient direction, to the west-southwest of the site <br /> Petroleum hydrocarbons were generally present at the highest concentrations in soil borings <br /> ' advanced on the northeastern portion of the site, near the former 5,000-gallon UST locations <br /> where TPHg and benzene were detected at concentrations up to 5,900 and 33 mg/kg, <br /> respectively, in soil samples collected at depths ranging from 10 to 20 feet bgs Laboratory <br /> ' analytical data from soil samples collected in soil borings located off site and in slant borings <br /> advanced beneath the on-site building indicate that TPHg and BTEX was not detected in soil <br /> samples collected at depths of 6 to 13 feet The lateral extent of shallow TPHg and BTEX <br /> ' impacted soils appears to be limited to the area adjacent to the former UST locations at the <br /> northern portion of the site, north of the on-site building Figure 6 shows a TPHg isocontour <br /> map of the vadose zone <br /> 4 Petroleum hydrocarbons were only detected in soil samples collected at depths of 20 feet or `fft <br /> greater in soil borings located off site The lateral extent of petroleum hydrocarbon impacted <br /> ' soils at depths of greater than 20 feet bgs appears to be confined to the areal extent of the site to <br /> the north, east, and south of the site and extend to at least 145 feet to the west-southwest of the <br /> site in a hydrologically downgradient direction Fluctuating groundwater elevations at the site <br /> ' has submerged a significant portion of contaminated soil below the groundwater table and <br /> capillary fringe It appears that hydrocarbons have been transported by groundwater to <br /> ' downgradient locations and adsorbed to the soil as a result of fluctuating groundwater <br /> elevations <br /> ' 4 1 3 Mass Balance Calculations - Soil <br /> ATC reviewed historical soil data collected at the site and performed mass balance calculations <br /> ' using soil data from 1990 to 2003 ATC estimated that residual soil contamination was present <br /> from approximately 10 to 30 feet bgs ATC calculated areas of impacted soil at five foot <br /> intervals (10, 15, 20, 25, and 30 feet bgs) and then performed mass balance calculations <br /> 1 Vapor extraction and groundwater extraction systems have been operational at the site <br /> intermittently since 1996 and an unknown amount of petroleum hydrocarbons have been <br /> ' remediated from the soil In addition, an unknown amount of soil contamination present beneath rt"'k..J <br /> the water table, approximately 16 to 18 feet bgs, is likely to have dissolved into the groundwater <br /> These factors make this calculation conservative ATC calculated that there is approximately <br /> 271,604 cubic feet of hydrocarbon impacted soil beneath the site The calculated total petroleum. <br /> faraoo J�3 1 <br /> w 1271421reportslelosure doc 12 <br /> 1 <br /> I <br />