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5 May 1995 <br /> • AGE-NC-95-1036 <br /> Page 2of4 <br /> remaining wells indicated' only trace coltcecltrations of benzene and toluene. The Highest . <br /> Ile detected were 1.7 and 3.S b in MW-4 and MW-5, <br /> levels of benzene and tolue Pp <br /> respectively. Into contamination has been detected in samples from MSV-2 or MW-3. <br /> The depth to grodifd water at the site fluctuates between 37 and 41 feet below surface. The <br /> ground water.flow direction varied from nort1wlest in November of 1992 to northeast ill <br /> February of 1994. <br /> A single' soil boring was drilled by GeoAudit to a.depth of 45 feet approximately 7 feet <br /> north of monitoring well NIW-1 in July 1994. Three soil sitnlples,which where collected from <br /> depths of 35, 40 and 45 feet, did not indicate the detection of hydrocarbons. Therefore, it <br /> is likely that petroleum hydrbearbons detected III samples-frons 1\� W-1 in 1992 Have been <br /> naturally degraded to below detectable liirlits and/or the extent of impact is very limited. Tile' <br /> volume of hydrocarbons was calculated to be less than a teaspoon, if still present. Under <br /> these conditions, the reiitaining hydrocarbons do not appear to pose a significant risk to the . <br /> regional uotind water quality. <br /> . 3.0. SESOIL/A`C123D A10DELING PROGRAM <br /> 3.1.- OVERVIEW OF SESOIL/AT123D <br /> The American Petroleum Institute's (API) Risk/Exposure Assessment Decision Support <br /> System (DSS) is'a modeling program developed to estimate ltuntan elpostII-e and risk front <br /> contaminated sites. Several options are contained in DSS, including SESOIL and AT123D. <br /> SESOIL uses information obtained from the site assessment of c61Itatninants, <br /> hydrogeolooical .and'.Ineteorological information to estimate the mass of contaminants that <br /> Will reach groundwater over a given time frame. AT123D is used'to determine contaiilinallt <br /> concentratibrls in a receptol•Nvell located down-gradient from a contaminant source. AT123D <br /> can use-the information generated by SESO'IL as the input'data, or a specified Klass by <br /> contaminants and discharge rate may be entered. <br /> Chemical properties and health risk data for 26 chemicals of possible concern are sulaplied <br /> in the program including benzene, toluene, ettlylbenzene and.xylene. The collective lei-ill of <br /> toial'petroleum hydrocarbons (TPH) is not all individual chemical with definite pl.operties, <br /> and therefore is Ilot included oil the list of chemical choices. Output call be displayed ill <br /> several ways, illcludiner annual reports, tables and graphs. <br />