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4491 Durham Ferry Road Page 4 <br /> The feasibility testing summary indicated that the radius of the soil contamination <br /> was 50 feet rather than the 70 feet which was used to calculate the mass of <br /> hydrocarbons. The only method evaluated for free product removal from MW1 <br /> was groundwater extraction, with another recovery well required. Passive <br /> skimmers have been very successful to remove the volumes of free product which <br /> have been typically observed, i.e. .03 feet. In this section of the report, SP1 rather <br /> than SP2, was reportedly used for sparging. This conflicts with other information <br /> in the report. <br /> Remedial Action Plan <br /> PHS/EHD concurs with the concept to use air sparging with vapor extraction. <br /> PHS/EHD recognizes the potential problems with regard to the possible migration of <br /> free product. However, PHS/EHD does not agree that a two recovery well <br /> extraction system is necessary to remove the relatively small volumes of free <br /> product which are observed in MW1 . As such, PHS/EHD will refrain from <br /> comment on the conceptual remedial design which was included in the report. An <br /> alternate conceptualized design plan should be submitted. <br /> Please submit by August 15, 1996 an addendum which addresses PHS/EHD <br /> comments. Quarterly sampling should continue and results included in the <br /> addendum. Please re-sample the domestic well, under PHS/EHD inspection and <br /> analyze the sample for BTEX, TPH-gas and MTBE. <br /> PHS/EHD attempted to schedule a meeting with you to discuss the report and to <br /> provide further regulatory directions so that the site can be remediated to <br /> acceptable regulatory limits and site closure issued. PHS/EHD still believes that <br /> such a meeting will be of benefit. Please contact me at (209) 468-0337 if you <br /> wish to discuss issues raised within this letter, to further clarify the revisions which <br /> are required or to schedule a meeting. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> Mary Meays, Senior REHS MargatVt Lagorio, REHS <br /> Site Mitigation Unit Lead Senior <br /> MM14491 DURH <br /> c: Elizabeth Thayer, CVRWQCB c: George Lockwood, SWRCB <br /> c: Brook Birkie, Neumiller and Beardslee c: Marcus Niebanck, Clearwater <br />