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s A S S O C I A T E S I N C 5.1.4 Pre-Remediation Mass Balance Calculations- Soil ' Using the analytical results from the subsurface investigations described in Section 2 0, ATC estimated the lateral extent of TPHg and benzene concentrations in the unsaturated zone beneath the site as depicted on Figure 5 The isoconcentratton shown on Figure 5 was then used by ATC ' to perform mass balance calculations to estimate the mass of residual soil contamination prior to remediation of the site The total mass of TPHg in the soil was estimated to be approximately 1,468 pounds or 665 kilograms The total mass of benzene in the soil was estimated to be approximately less than one pound or 0 19 kilograms Mass balance calculations are included in Appendix C 5.1,5 Pre-Remediation Mass Balance Calculations-Groundwater Using groundwater analytical results presented in Table 3, the most recent data available, ATC estimated the lateral extent of dissolved TPHd, TPHg, and benzene concentrations beneath the site as depicted on Figures 6, 7 and 8, respectively Figures 7 and 8 were then used by ATC to ' perform mass balance calculations to estimate the mass of residual contamination in the site's saturated zone The total mass of dissolved TPHg present in the saturated zone is estimated to be 9 7 pounds or 4 4 kilograms The total mass of benzene present in the groundwater is estimated to be 2 3 pounds or 1 0 kilograms Mass balance calculations are included in Appendix C 5.1.6 Estimated Length of Operation and Final Constituent Concentrations ' The total mass of TPHg in the soil was estimated to be approximately 1,468 pounds while the total mass of dissolved TPHg present in the saturated zone is estimated to be 9 7 pounds The tremoval rate from one vapor extraction well was calculated at approximately one pound per day This is expected to increase with the addition of air sparging By using up to four extractions wells and one air sparge well during the first few months of operation, extraction rates of up to 10 ' pounds per day can be expected Removal rates typically reduce over time Rotation of air sparge wells and vapor extraction wells will provide for the maximum removal rate over time It ' is anticipated that up to 75% of the petroleum hydrocarbons will be removed during the first nine months of operation Actual removal rates will vary depending on subsurface geologic conditions, the extent and distribution of hydrocarbons in soil and groundwater, the effect of ' concurrently operating the AS system, and site-specific operating conditions of the VES The effectiveness of the remediation system will be continually evaluated but it is anticipated that after one to one and a half years of operation, the site will be remediated to near nondetectable levels or it will no longer be efficient to operate the system 5.2 Design Specifications 5.2.1 Vapor Extraction System The proposed VES will utilize existing vapor extraction wells VW-1, VW-3, and VW-5s, a vacuum blower, and vapor phase carbon to address the hydrocarbon impacted soil Due to the increase in the W 162574 01\CAP report doc 7 1