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� v <br /> A S S O C I A T E S I N C <br /> kilograms The total mass of TPHd remaining in the soil is estimated to be approximately 3,874 <br /> pounds or 1,757 kilograms Mass balance calculations are included in Appendix C <br />' 4.4 Mass Balance Calculations - Groundwater <br />' Using groundwater analytical results presented in Table 2, the most recent data available, ATC <br /> estimated the lateral extent of dissolved petroleum hydrocarbons beneath the site as depicted on <br /> Figure 4 Figure 4 was then used by ATC to perform mass balance calculations to estimate the <br /> mass of residual contamination in the site's saturated zone The total mass of dissolved TPHg <br /> present in the saturated zone is estimated to be 104 1 pounds or 47 3 kilograms The total mass <br />' of BTEX present in the groundwater is estimated to be 8 pounds or 3 6 kilograms The total <br /> mass of TPHd present in the groundwater is estimated to be 2,364 pounds or 1,072 kilograms <br /> Mass balance calculations are included in Appendix C <br />' 5.0 DISCUSSION/RECOMMENDATIONS <br />' The soil borings advanced during this phase of work address the concerns raised by the PHS/EHD <br /> to further establish vertical and horizontal definition of the petroleum hydrocarbon plume at the <br /> site The additional soil boring SB 15, where no detectable concentrations of petroleum <br /> hydrocarbons were found, addresses the extent of petroleum hydrocarbons in soil and <br /> groundwater west of well MW3 Borings SB 13 and SB 14 address the vertical extent of <br /> petroleum hydrocarbons in the vicinity of the former tank pit and well MW2, the location where <br />' free phase petroleum hydrocarbons have historically been encountered Borings SB 11 and SB 12 <br /> address the lateral extent of the hydrocarbon plume <br />' Results of this investigation and previous investigations show that the lateral extent of petroleum <br /> hydrocarbons in soil and groundwater has been defined as shown on Figures 3 and 4, respectively <br />' As shown, the hydrocarbons plume is essentially limited to the site boundaries Elevated <br /> concentrations of TPHd remain in the soil and groundwater but appear to be confined laterally to <br /> within 50 feet north of the former tank pit (the vicinity of well MW2 and boring SB 14) The <br /> vertical extent of petroleum appears to be limited to a depth of approximately 20 feet or less as <br /> exhibited by soil analytical results and FID readings in boring SB 14 which attenuate rapidly with <br /> depth <br /> ATC recommends no further subsurface investigation at the site <br />' w Iwordpru1258031.Sub_uiv doc 5 <br />