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2.2 Site Specific Conditions The volume of petroleum hydrocarbons remaining in the soil on and off-site was estimated in the Closure Summary Report (CSR), prepared by GeoAudit, dated August 30, 1994. An ' addendum to the CSR, dated October 4, 1994, discussed the methods for the calculations. The data from the CSR and addendum was input into the SESOIL modeling program. All ' data was converted to metric units for input to SESOIL. The area of concern was divided into four layers. The top layer consists of non-impacted ' silts and sands from surface grade to 2 meters; the second layer is the impacted silts and sands from 2 to 5 meters; the third layer is the impacted clays and silts from 5 to 12 meters; and the fourth is the non-impacted clays and silts from 12 to 15 meters (groundwater). tFigure 3 is a cross section of the impacted soil. The mass of ethylbenzene, toluene and xylene was calculated from the known data and input ' into SESOIL. No benzene has been detected at the site. Therefore, benzene was not used in the modeling. Soil characteristics were estimated from borings drilled on and off-site. Climatic parameters were estimated from historical local weather conditions. When all information is entered, SESOIL provides a predicted mass loading to groundwater for each year of the test. The AT123D modeling program uses the yearly predicted mass ' load to groundwater from SESOIL and hydraulic properties of the aquifer to estimate the contaminant concentrations in groundwater at a receptor well. For this model (site), the receptor well was placed at the down-gradient edge of the hydrocarbon impacted soil to obtain maximum influence. The hydraulic gradient was calculated from groundwater monitoring conducted at the site. Other parameters were estimated from the soil types. The maximum permitted running time of 100 years was used for this site. ' 2.3 Results ' When all parameters were entered using the best available data, SESOIL predicted no contaminants reaching groundwater (Appendix A). Appendix A includes three pages of input data, SESOIL and AT123D output files with annual reports, receptor point summary ' sheets and graphs, and chemical intake evaluation tables. The modeling program was run again with various data. For the second, third and forth runs, the mass of total petroleum hydrocarbons (TPH) in soil was substituted for the mass of toluene, ethylbenzene and xylene and then increased by 10 percent. The effective porosity ' and intrinsic permeability were also significantly increased and the area of contamination was decreased to provide a worse possible estimate for impacting the groundwater. Again, SESOIL predicted no contaminants reaching groundwater (Appendix B). Oeabgorl A"I Se ki I- 4 YatloW g.Mnsiee SE50[L 1.95