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amec <br /> problems, which are more costly to treat than VOCs. This is a major consideration for <br /> implementing bioaugmentation on a large scale where the aquifer system is directly used for <br /> industrial, agricultural and domestic purposes. Under this scenario, one groundwater problem <br /> would be traded for another that requires a more costly solution. For this reason, <br /> implementation of the bio-curtain does not appear to be feasible. <br /> The length of the bio-curtain would be almost one mile (4,500 feet; 0.85 mile). A system of this <br /> size would require access to a number of properties. Access agreements would need to be <br /> executed that allowed for the construction of monitoring wells, above ground infrastructure <br /> including system piping. This may also limit the implementability of bioaugmentation. <br /> 3.4 COST <br /> A feasibility level cost estimate has been developed for a bio-curtain adjacent to the Stanislaus <br /> River (Table B.2-1). The bio-curtain design utilizes recirculation well pairs to inject microbes <br /> and distribute soluble substrate within the aquifer pore space between the well pairs. It has <br /> been assumed that pulses of substrate would have to be injected on a weekly basis and <br /> recirculated for a period of six hours to maintain appropriate microbial conditions (consistent <br /> with Hyndman et al., 2000). Substrate mixing, injection, and recirculation would be controlled <br /> by a series of injection modules located along the bio-curtain alignment. The injection modules <br /> would consist of small buildings/sheds that would house supervisory control and data <br /> acquisition (SCADA), mixing tanks, pump controllers, flow instrumentation, and associated <br /> piping. It is assumed that each module would control ten recirculation well pairs (20 wells <br /> total). As shown in Table B.2-1, the total cost to implement a bio-curtain is estimated to be <br /> $47.3 million dollars. A major control on the cost of constructing the system is the number of <br /> recirculation well pairs and the number of injection modules. Supporting calculations for unit <br /> costs listed in Table B.2-1 are provided in Tables B.2-2 and B.2-3, based on the design basis <br /> described below. <br /> The design basis for the bio-curtain is based on the following assumptions: <br /> • The presumed location of the bio-curtain (based on existing monitoring data) is shown <br /> in Figures B.2-1; it is assumed that the length will be 4,500 feet and the target <br /> treatment interval will be from 120 to 135 feet bgs (this could change based on the <br /> results of the remedial investigation). <br /> • A remedial design investigation would be carried out along the alignment shown in <br /> Figure B.2-1 before the bio-curtain system is constructed. The investigation would <br /> include the installation, development and sampling of 45 multi-level wells (CMTTM <br /> wells) spaced 100 feet apart along the 4,500 feet alignment. Each CMT well would be <br /> installed to depth of 200 feet bgs and include seven sample ports (allowing for seven <br /> AMEC Geomatrix, Inc. <br /> \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTFS Assessment_Apx B_01 2711\Attachment B.2\Attach B-2.doc 132-9 <br />