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19 October 2012 <br /> AGE-NC Project No. 97-0312 <br /> Page 8 of 22 <br /> 3.0. ASSESSMENT OF HYDROCARBON-IMPACTED SOIL <br /> 4 <br /> Between May 1990 and September 1999, soil sampling was performed at forty-two soil <br /> borings (131 through B29, P-1 through P-13), six shallow tank excavation samples (T-1 <br /> through T-6) and six groundwater monitoring well pilot borings (UST-1 through UST-6) as <br /> part of a subsurface petroleum hydrocarbon investigation. <br /> Petroleum hydrocarbons were not detected in soil samples collected from borings B3, B4, <br /> B5, B6, B12, B16, B23, B25, B28, B29, UST-2 and UST-3, delineating the maximum <br /> potential lateral extent of impacted soil. Low concentrations of BTEX were detected in <br /> borings B8, B13, B22, B27 and UST-4. Borings UST-1 through UST-5, B14 through B19 <br /> and B21 through B29 were advanced to depths below the vertical extent of impacted soil, <br /> defining the vertical extent of impacted soil at these locations.The greatest concentrations <br /> of hydrocarbons were detected beneath the former UST locations. Higher concentrations <br /> were also detected in the shallow piping samples and in borings UST-1 and UST-5: The <br /> plume of impacted soil at the site has an estimated northeast-southwest diameter of <br /> approximately 180 feet, a northwest-southeast diameter of approximately 70 feet and <br /> appears to extend vertically more than 80 feet bsg. The calculated volume of rT rG <br /> hydrocarbon-impacted soil is approximately 10,000 cubic yards as presented in the AGE <br /> prepared Problem Assessment Report,dated 16 August 2001.The approximate lateral and <br /> vertical extent of impacted soil were included in the PAR. Figures and tables which <br /> illustrate impacted soil and analytical results at the site are provided in Appendix C. <br /> 3.1. FATE AND TRANSPORT MODELING OF HYDROCARBON-IMPACTED SOIL <br /> In 1999,to assess the current potential for vadose zone adsorbed petroleum hydrocarbons <br /> �.., to impact groundwater AGE modeled site conditions and performed computer analyses of <br /> the likelihood of such impacts. The fate and transport model was presented in the AGE <br /> prepared Quarterly Report - Fourth Quarter 1999, dated 10 March 2000. <br /> 3.1.1 Overview of Sesoil <br /> The American Petroleum Institute's (API) Risk/Exposure Assessment Decision Support <br /> System(DSS)is a modeling program developed to estimate human exposure and risk from <br /> contaminated sites.Several modeling options are contained in DSS, including SESOIL and <br /> AT123D. SESOIL uses information obtained from the site assessment of contaminants, <br /> hydrogeological,and meteorological information to estimate the mass of contaminants that <br /> will reach groundwater over a given period of time. AT123D can be used to determine <br /> contaminant concentrations in a receptor well located down-gradient from a contaminant <br /> source. AT123D can use the information generated by SESOIL as the input data. <br /> Advanced GeoEnvironmental,Inc. <br /> v <br />