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I05 May 1997 AGE-NC Project No 95-0112 ' Page 12 of 14 ' estimated from historical local weather conditions An average hydraulic gradient was based on recent monitoring events Hydraulic conductivity was measured during slug tests detailed in the PAR prepared by GAS and outlined in section 2 5 above When all the mforrriation is entered, SESOIL provides a predicted mass loading to ground water for each year of the test The AT123D modeling program used the yearly predicted mass load to ground water from SESOIL and hydraulic properties of the aquifer to estimate the contaminant concentrations in ground water at a receptor well To obtain maximum ground water concentrations, the receptor well was placed at the down-gradient edge of the soil contaminant plume The maximum permitted running time of 100 years was used for this site 5 3 3 RESULTS OF SESOIL MODELING ' With all parameters entered, using the best available data, SESOIL predicted that no contaminants would impact ground water Appendix F includes SESOIL input data and the output graph ' The AT123D model predicts chemical concentrations in ground water at a down-gradient receptor well Since no hydrocarbons were predicted to reach ground water, this section of the modeling program was not used 1 6 0. CONCLUSIONS/SUMMARY ' Based upon data collected from the site AGE has the following for your consideration p g y • Field observations and analytical results of soil samples collected at the site indicate a significant reduction of petroleum hydrocarbon concentrations ' • Approximately 1,463 gallons of gasoline were estimated to be in soil prior to remediation, approximately 240 gallons of gasoline remain after remediation This represents a reduction of 83 6% of hydrocarbons in soil at the site • Benzene has not been detected in soil samples collected at the site since remediation began Toluene was detected in only two of 30 samples collected since remediation began Ethylbenzene and xylenes were detected in two of eleven samples analyzed from the -- --- February 1997' soil sampling event Therefare, the lighter-range volatile organic hydrocarbons, having greater migration potential, are not abundant at the site • Geotechnical analyses indicate a dense soil of low porosity beneath the site Although permeability calculations could not be made, dense soil with low porosity is generally