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1 <br /> 15 August 1997 <br /> AGE-NC Project No 96-0254 <br />' Page 6 of 7 <br />' line TPH-g concentrations in ground water decrease eastward of the former fuel tanks, in <br /> the area of boring 131 The estimate lateral extent of dissolved benzene concentrations above <br /> 20,000 ppb and TPH-g concentrations above 100,000 ppb is depicted in Figure 4 -Dissolved <br />' Hydi ocarbon Concenti ations <br /> • The lateral extent of the dissolved phase plume has not been determined in any direction, <br />' although boring B i appears to be near the eastern margin of the plume <br />' 6.0. RECOMMENDATIONS <br /> Based on the results of this investigation, AGE recommends the following <br />' • If determination of the lateral extent of the dissolved hydrocarbons and the monitoring of <br />' hydrocarbon plume stability is required, the installation of ground water monitoring wells <br /> will be necessary <br /> • The collection and field screening of grab ground water samples should be performed prior <br /> to installation of any monitoring wells to more completely define the lateral extent of the <br /> dissolved phase plume Additional well locations should be determined based upon new field <br /> observations and/or analysis of previously collected grab ground water samples and the <br />' concurrence of the PHS-EHD Information obtained from the initial soil boring program and <br /> any additional grab water sampling studies will allow optimization of well placements, <br /> resulting in the minimal number of well installations <br /> • Quarterly monitoring at the site should be initiated upon the installation of monetoiing wells <br />' • TPH-d concentrations should be part of the monitoring program <br /> • If remediation of soil and/or ground water is necessary at the site, a Conecteve Action Plan <br />' (CAP) should be prepared The CAP should include remediation feasibility studies (e g in- <br /> situ air sparging pilot test, soil vapor extraction, soil excavation and bio-enhanced <br /> remediation or attenuation) to determine appropriate remedial options for the site <br /> 7 0. LIMITATIONS <br /> Ourr fe <br /> p o ssaonal services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or similar localities The findings were based mainly <br /> upon analytical results provided by an independent laboratory Evaluations of the <br /> . geologic/hydrogeologic conditions at the site for the purpose of this investigation are made from a <br /> I <br /> Adti anted GeoEnvironmental Inc <br />