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1 <br /> 27 December 1996 <br /> AGE-NC Project No 95-0143 <br />' Page 19 of 19 <br />' been consistently detected in MW-6, MW-7 and MW-9 <br /> An in-situ method would be more effective in cost and in operation over a"pump and treat"method <br />' Both in-situ methods described in this CAP could be effective in remediating the site However, <br /> based upon limited regulatory acceptance and uncertain monitoring requirements, in-situ <br /> bioremediation of ground water may not be the most cost-effective remedial alternative for the site <br />' Remediation of impacted ground water should be conducted concurrently with soil remediation to <br /> prevent re-contamination of remediated soil In-situ air sparging/vapor extraction appears to be a <br />' viable alternative for remediation of both soil and ground water in the vicinity of the former UST <br /> location The system used for soil vapor extraction could also be used for the air sparging/extraction <br /> system Due to the large extent of impacted soil and water at the site, two extraction units may be <br />' a viable alternative to increase the rate of site remediation A sparging/ extraction system will also <br /> have a secondary effect of bioventing and increasing the natural degradation rate <br />' Combined with SVE,the TAS method mechanically strips hydrocarbons without the addition of any <br /> chemicals or microbe solution into the environment It is a better known and more widely accepted <br /> method of volatilizing hydrocarbons As IAS has few, if any, adverse environmental effects, it is <br /> likely to be more readily approved for implementation by regulatory agencies Based upon these <br /> considerations and the presence of relatively sandy soil in the impacted zone, we recommend the <br /> I installation of an IAS system for remediation of ground water An 18 to 24 month remediation <br /> period can be expected to reduce hydrocarbon concentrations to below State of California drinking <br /> water standards Ground water remediation alternatives, estimated durations and associated costs for <br /> the site are summarized on Table 5 <br /> A Remedial Action Work Plan detailing the proposed installation and operation of the SVE/TAS <br /> system should be prepared This work plan should include the installation of sparging points and <br /> extraction wells Air should be supplied to each of the IAS points via underground piping by a <br /> compressor or blower-driven IAS unit capable of approximately 10 to 15 psi to each sparging well <br /> at a rate of2to4scfm <br /> 9.0 LIMITATIONS <br />' Our professional 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 upon <br /> analytical results provided by an independent laboratory Evaluations of the geologic/hydrogeologic <br /> I conditions at the site for the purpose of this investigation are made from a limited number of <br /> available data points (i a monitoring wells, soil borings) and subsurface conditions may vary away <br /> from these data points No other warranty, expressed or implied, is made as to the professional <br /> recommendations contained in this report <br /> I <br />