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1 <br /> 28 July 1995 <br /> AGE-NC-95-0134 <br /> Page 4 of 6 <br />' 3 3 SESOIL MODELING PROGRAM <br />' 3 3 1 Overview of SESOIL <br /> The American Petroleum institute's (API) Risk/Exposure Assessment Decision Support System <br />' (DSS) is a modeling program developed to estimate human exposure and risk from contaminated <br /> sates Several modeling options are contained in DSS, including SESOIL and AT123D SESOIL uses <br /> information obtained from the site assessment of contaminants, hydrogeological, and meteorological <br />' information to estimate the mass of contaminants that will reach ground water over a given time <br /> frame AT123D can be used to determine contaminant concentrations in a receptor well located <br /> down-gradient from a contaminant source AT123D can use the information generated by SESOIL <br />' as the input data <br /> Chemical properties and health risk data for 26 chemicals of possible concern are supplied in the <br />' program including benzene, toluene, ethylbenzene and xylenes Total petroleum hydrocarbons (TPH) <br /> is not an individual chemical with definite properties, and therefore is not included on the list of <br /> chemical choices Output can be displayed in several way, including annual reports, tables and graphs <br /> 3 3 2 Site Specific Conditions <br /> The area of concern was divided into four layers The top layer consists of non-impacted silts from <br /> surface grade to 6 meters (20 feet), the second layer is non-impacted sands from 6 meters to 9 25 <br /> I meters (20 to 30 feet), the third layer is the impacted silts from 9 25 meters to 12 25 meters (30 to <br /> 40 feet), and the fourth layer is the non-impacted sands from 12 25 meters to 15 25 meters (40 to 50 <br /> feet) The lateral extent of impacted soil was assumed as 15 meters Figure 4 depicts a cross section <br /> of the impacted soil prepared in June 1994 by GeoAudit <br /> The highest concentrations of hydrocarbons were detected in sample CB 1-35 These concentrations <br /> I were assumed to extend throughout the impacted zone to provide a worse case scenario The method <br /> detections limits were used for the hydrocarbon concentrations in the non-impacted zones The <br /> masses of toluene, ethylbenzene and xylenes were then calculated for each layer No benzene was <br /> detected in any of the soil samples analyzed Therefore, benzene was not used in the modeling Soil <br /> characteristics were estimated from borings CB-1 and CB-2 drilled by Geoaudit in June 1994 at the <br /> site Climatic parameters were estimated from historical local weather conditions <br /> When all the information is entered, SESOIL provides a predicted mass loading to ground water for <br /> each year of the test The AT 123D modeling program used the yearly predicted mass load to ground <br /> water from SESOIL and hydraulic properties of the aquifer to estimate the contaminant <br /> 1 concentrations in ground water at a receptor well The maximum permitted running time of 100 years <br /> I <br />