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A S S O C I A T E S I N C 3.2 Hydrology ' During this subsurface investigation, groundwater was encountered at a depth of 5 feet bgs in the boring located inside the building Groundwater was generally encountered at depths ranging from approximately 10 to 19 feet below grade in the remaining borings on site ' 4.0 RESULTS ANALYTICAL C SU S ' 4.1 Soil Analytical Results ' Petroleum hydrocarbon constituents including TPHg, TPHd, benzene, ethyl benzene and xylenes were detected in boring SB 11 at 5 feet bgs and in boring SB 14 at depths of 8 and 20 feet bgs Concentrations of petroleum hydrocarbons in boring SB 14 generally attenuated rapidly with ' depth Bonngs SB 12, SB 13 and SB 15 did not contain detectable concentrations of TPHg, TPHd, or BTEX No oxygenate fuel additives, including 1,2-DCA and EDB were detected in any of the soil samples above laboratory method detection limits ' Analytical results for soil are summarized in Table 1 The extent of petroleum hydrocarbons in soil is shown on Figure 3 Laboratory data sheets and chain of custody documentation are included as Appendix B 4.2 Groundwater Analytical Results ' Dissolved petroleum hydrocarbon constituents were detected at moderate to elevated concentrations in the groundwater at borings SB 13 and SB 14, located near well MW2 where free product has been detected The groundwater sample from boring SDI I contained relatively low concentrations of TPHg, TPHd, benzene and ethylbenzene Borings SB 12 and SB 15 did not contain detectable concentrations of TPHg, TPHd or BTEX No oxygenate fuel additives, tincluding 1,2-DCA and EDB were detected in any of the groundwater samples above laboratory method detection limits ' Analytical results for groundwater are summarized in Table 2 The extent of petroleum hydrocarbons in groundwater is shown on Figure 4 Laboratory data sheets and chain of custody ' documentation are included as Appendix B 4.3 Mass Balance Calculations - Soil ' Using the analytical results from the subsurface investigations presented in Table 1, ATC estimated the lateral extent of petroleum hydrocarbons in the unsaturated zone beneath the site as depicted on Figure 3 The isoconcentration shown on Figure 3 was then used by ATC to perform mass balance calculations to estimate the mass of residual soil contamination The total mass of TPHg remaining in the soil is estimated to be approximately 963 pounds or 437 kilograms The ' total mass of BTEX remaining in the soil is estimated to be approximately 2 98 pounds or 1 35 ' w Iwordpro1258031Sub_tnv doc 4