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18 November 1996 <br /> AGE-NC-Project No 95-0134 <br /> Page 5 of 8 <br /> impacted soil before remediation in 1988 and in June 1994 after vapor extraction, respectively <br /> Using the analytical results from CB-1 and CB-2,the volume of remaining gasoline was calculated <br /> to be approximately 186 gallons The calculation work sheet is attached as Appendix A This <br /> represents a 93 8%reduction compared to the calculated original volume Although more generalize, <br /> results of PID readings yield similar results The soil boring installations and estimated of remaining <br /> hydrocarbons were described by GeoAudit in a quarterly report, dated July 1994 <br /> 2 5 2 GROUND WATER INVESTIGATION <br /> A ground water sample was collected from EW-I by GeoAudit on 10 August 1993 Xylenes were <br /> detected at a concentration of 0 98 ppb No other petroleum hydrocarbons were detected in this <br /> sample <br />' Ground water monitoring was conducted on six occasions between June 1994 and September 1995 <br /> by GeoAudit and subsequently by AGE The ground water gradient ranged from 0 00048 ft/ft to <br /> 0 0040 ft/ft The flow direction ranged from N 84° E to N 56° E on five occasions An anomalous <br /> flow direction of due south was observed in September 1994 The depth to ground water in EW-1 <br /> varied from 64 12 feet bsg in September 1994 to 58 53 feet in September 1995 Depth to ground <br /> water data is summarized on Table 1 Ground water flow direction and gradient data is summarized <br /> on Table 2 <br /> Toluene and xylenes were detected in the sample from MW-9 at concentrations of 0 52 and 2 9 ppb, <br /> respectively in June 1994 Petroleum hydrocarbons were not detected in any other samples collected <br /> during the five quarterly monitoring events Procedures and findings weie summarized in various <br /> quarterly reports from July 1994 to September 1995 <br /> 26 SESOIL MODELING PROGRAM <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 /> sites Several modeling options are available including SESOIL, for leaching potential from soil to <br /> ground water, and AT1231), for estimating concentrations in ground water at a receptor well An <br /> overview and description of API/DSS was included in the Quarterly Report - September 1995 <br /> prepared by AGE <br /> IEight models were run using data obtained during the installation of borings CB-1 and CB-2 <br /> Climatic parameters were estimated from historical local weather conditions Four models were <br />