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c� <br /> ppb TPH and MW-1 (ND) and SB-5 (320,000 TPH-d, 93,000 TPH-g) and MW- <br /> 3 <br /> W3 (55 ppb TPH-g, ND TPH-d) may indicate that the wells are not providing <br /> accurate data. PHS/EHD recommends that additional wells be constructed with <br /> short screen intervals. <br /> An EPA Method 8260 confirmation of the detection of MTBE by EPA method 602 <br /> and 8020 was not performed. PHSIEHD recommends that future analyses for <br /> MTBE be confirmed by an 8260. Currently there are six other oxygenate <br /> compounds that you are required to analyze for using EPA method 8260. These <br /> compounds are Methanol, Ethanol, Tertiary butanol, Di-isopropyl ether (DIPE), <br /> Ethyl tertiary butyl ether (ETRE), and Tertiary amyl methyl ether (TAME). <br /> In the recommendation section of the report Twining recommends remediation <br /> and additional assessment to determine the rate of biodegradation which may be <br /> occurring at this site. PHSIEHD recommends that in addition to natural <br /> attenuation the feasibility of at least two active remedial alternatives such as air <br /> sparge/vapor extraction be evaluated. PHSIEHD also recommends additional <br /> assessment to determine the full extent of the plume in soil and groundwater, the <br /> lithology which underlays the site, and a receptor survey. The completed <br /> assessment and the feasibility study should be included in a Corrective Action <br /> Plan (CAP) which will be submitted to PHS/EHD for evaluation. <br /> Please submit a workplan which will describe a method to complete the <br /> assessment and a method to evaluate the feasibility of at least two active <br /> remedial alternatives in addition to remediation by natural attenuation by October <br /> 1, 1997. <br /> Please contact Steven Sasson, Senior REHS, at (209) 468-3459 for additional <br /> information. <br /> Donna Heran, REHS, Director <br /> Envir nmental Health Division <br /> Ste a as o & REHS ar Mar9 La9 orio, R S <br /> LOP/Site Mitigation Unit IV Supervisor <br /> c: RWQCB, Central Valley Region - Elizabeth Thayer <br /> C' SWRCB, Mel Jacobo <br /> c: The Twining Labs, Inc.- Kenneth Clark, RG, CEG <br />