SITE INFORMATION AND CORRESPONDENCE

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Tracie Billington, P.E. August 14, 1992 Page Two VOCs. The common factors among the proposed alternatives were extraction, a treatment process for VOCs, and re-injection. The proposed treatment alternatives are: . 1. No action/current Phase 1 interim remedial measure (IRM) : Extraction at 120 gallons per minute (gpm) with treatment by air stripping, disposal by injection wells. 2 . Designed IRM: Extraction at 340 gpm, treatment by air stripping and vapor-phase granular activated carbon (GAC) , disposal by injection wells. 3 . Extraction at 930 gpm: treatment via air stripping and GAC, disposal by injection wells. 4 . Extraction at 930 gpm: treatment by liquid phase GAC, disposal by injection wells. 5. Extraction at 930 gpm: treatment by ultraviolet/ozone oxidation, disposal by injection wells. 6. The same as system 3 with the addition of an oxygen and methane in situ bio-remediation process. 7. Extraction at 930 gpm: treatment by an above ground bio- remediation fixed film reactor, disposal by injection wells. The Proposed Plan selects the full scale treatment facility in alternative 3 . Aquifer cleanup goals are 2 .5 parts per billion (PPB) for TCE and 0. 7 PPB for PCE. These are aquifer cleanup standards proposed by the State of California and not enforceable at this time. However, the Department commends DDRW Tracy for instituting them now. Over the course of Tracy's remedial program this will reduce long term costs and minimize schedule changes. GENERAL COMMENTS FOR THE FS AND PROPOSED PLAN 1) The FS addresses VOCs as the principal contaminants of concern. This line of reasoning is supported by the following statements. a. VOCs have been the predominant contaminant detected during the investigation of OU # 1. This is true for both the number of positive sampling events and the concentrations measured.