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5.4 No Action <br /> Based on McLaren/Hart's review of the August 1990 Tn-Regional Board Staff Recommendations <br /> for Preliminary Evaluation and Investigation of Underground Tank Sites, the "no action" <br /> alternative is not a feasible option for the Site. <br /> For the Site it has been determined that soil has been impacted at and below the seasonal high <br /> groundwater level The PHS/EHD has assumed the lead role with regard to requiring further <br /> investigation and potential remediation at the Site. Due to the presence of impacted soil beneath <br /> the former tank farm and throughout the Site at and below the reported seasonal high water level <br /> (approximately 25 feet below grade), the PHS/EHD has mandated that soil remediation be <br /> implemented at the site <br /> 6.0 PROPOSED REMEDIAL ALTERNATIVE <br /> i <br /> The recommended alternative for soil remediation at the Site is soil vapor extraction with GAC <br /> treatment of air emissions This alternative is considered the most practical and economical of <br /> those presented in Section S <br /> 6.1 System Design Considerations <br /> A description of the SVE pilot test is presented in Appendix III. Based on the observational data <br /> from this test, a general design of a SVE system for this site can be developed The key <br /> components would include <br /> • 8 to 9 SVE wells screened in the lower vadose zone, <br /> • Conveyance piping between the wells and the treatment system buned in subgrade <br /> trenches, <br /> A fenced treatment compound with the process blower and emissions control <br /> equipment, and <br /> • GAC vessels to control air emissions. <br /> This design is based on a conservative x - <br /> g extraction well radius-of-influence of 20 feet. This radius <br /> is based on the pilot test data, and will allow full coverage of the impacted soil, even if flow <br />' rates decrease over time. Each SVE well would be individually valved to allow tuning of the <br /> system over time The 8 to 9 wells would be spaced such that the trailing edges of the off-site <br /> plumes could also be remediated <br /> Twoears of operation are included in <br /> y pe the system budget estimate Actual duration of operation <br /> will depend on site vadose zone response to SVE, and the clean-up goals agreed upon with the <br /> PHS/EHD <br /> i»oiW3 18 <br />