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' 05 May 1997 <br /> AGE-NC Project No 95-0112 <br /> Page 11 of 14 <br /> ' period is 28 6 gallons This brings the total volume of hydrocarbons removed from the soil since <br /> initiation of the SVE system up to approximately 1,651 gallons The mass calculations for the <br /> culTent quarter are attached in Appendix D A summary of the mass removed during each month is <br /> tabulated on Table 4 <br /> 5 3 MODELING OF REMAINING HYDROCARBON-IMPACTED SOIL <br /> 5 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 contaminatcd <br /> ' sites Several modeling options are contained in DSS,including SESOIL and ATI 23D SESOIL uses <br /> information obtained from the site assessment of contaminants,hydrogeologic.al, and meteorological <br /> information to estimate the mass of contaminants that will reach ground water over a given time <br /> frame AT 123D can be used to determine contaminant concentrations in a receptor well located <br /> dorm-gradient from a contaminant source ATI23D can use the information generated by SESOIL <br /> lieas the input data <br /> Chemical properties and health risk data for 26 chemicals of possible concern are supplied in the <br /> ' prograrn including benzene,toluene,ethylbenzene and xylenes Total petrolcum 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 <br /> ' graphs <br /> 5 3 2 SITE SPECIFIC CONDITIONS <br /> The area of concern was divided into four layers The top layer consists of non-impacted salt from <br /> ' surface grade to 3 meters (10 feet), the second layer is impacted sand from 3 to 7 6 meters (10 to 25 <br /> feet), the third layer is non-impacted sand from 7 6 to 10 6 meters (25 to 35 feet), and the fourth <br /> layer is the impacted silt from 10 6 to 16 7 meters (35 to 55 feet) The lateral extent of impacted soil <br /> was defined as 6 75 meters to yield the approximate horizontal cross-sectional area of the <br /> contaminant plume A vertical cross section of the impacted soil plume after remediation is depicted <br /> ' in Figure 4 - - - - -­ - - - , - - -- - - - - <br /> The mass of TPH-g in each section of the contaminant plume was calculated in Section 5 12 below <br /> ' General site stratigraphy was defined fiom numerous soil borings advanced at the site Two samples <br /> from probing P4 were analyzed for porosity, soil density and fraction organic carbon Conservative <br /> permeability values were estimated from general soil characteristics Climatic parameters were <br /> 1 <br />