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ATTACHMENT III <br /> FEASIBILITY STUDY <br /> EPA COMMENTS ON <br /> DDRW-TRACY'S <br /> DRAFT LETTER REPORT OF 10/30/91 <br /> GENERAL COMMENTS <br /> 1. Response No. 6 <br /> It is recognized that the remedial action is intended to prevent <br /> further migration of the plume. However, an FS is expected to <br /> discuss the expected ability of the proposed remedy to accomplish <br /> this, e.g. , experiences elsewhere, favorable and unfavorable <br /> conditions, etc. <br /> SPECIFIC COMMENTS <br /> 1. Response No. 5 <br /> The 10 pore volume "rule of thumb" referred to needs to be <br /> supported. If it has a literature source, state it. In any <br /> case, simple contaminant fate-transport modeling will show that <br /> theoretically the number of pore volumes can vary over a wide <br /> range depending upon such factors as initial contaminant <br /> concentration, contaminant adsorption factor (Kd) , quantity of <br /> carbon in the soil, heterogeneity of the soil, etc. <br /> 2 . Response No. 49 <br /> The safeguards mentioned -- granular-activated carbon (GAC) unit <br /> and flow switches -- are confusing. The objective is to prevent <br /> reinjection of contaminated water due to treatment system <br /> malfunction. To accomplish this, you need a way to measure <br /> effluent quality and prevent reinjection from occurring if <br /> quality is not satisfactory. This can be done by testing full <br /> storage tanks before releasing them for reinjection (batch <br /> method) , or using an in-line device to measure trichloroethene <br /> (TCE) concentration and automatically shut off reinjection <br /> operations if readings are unsatisfactory. State how a GAC unit <br /> and flow switches would work to accomplish this. <br /> IZI-1 <br />