ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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amec�9 system would have limited near-term effect on groundwater impacts located outside of the proposed treatment area. Therefore, the effectiveness of groundwater recirculation towards minimizing the risk to downgradient receptors is low because COC-affected groundwater exists beyond the alignment of the proposed recirculation system. Intrinsic remediation would be required to manage the risk of COC impacts to receptors downgradient of the barrier. 3.3 IMPLEMENTABILITY The overall size of the proposed system represents a substantial implementation challenge. The total alignment length for the proposed system is 12,000 feet (2.3 miles). Due to the length of the alignment (2.3 miles) and the total treatment flow rate (2.88 MGD), the system could potentially require multiple treatment compounds located at different locations along the alignment as opposed to one centralized treatment compound. The large total flow rate for the system (2.88 MGD) is due primarily to the amount of recharge in the proposed treatment area from the WWTF lagoons (approaching 2 MGD). The re-injection of 2.88 MGD of treated groundwater would present a substantial operation and maintenance burden and rapid clogging of the injection well screens could seriously interfere with the operation such that the system cannot perform as designed. Therefore, the proposed system does not appear to be implementable. 3.4 COST A feasibility level cost estimate for the groundwater recirculation system described above is included in Table B.3-1. Supporting calculations and assumptions for the unit costs in Table B.3-1 are provided in Table B.3-2. Several of the unit costs for this cost estimate were obtained from the Remedial Action Cost Engineering and Requirements software program (RACER). As shown in Table B.3-1, the total cost to construct the groundwater recirculation system would be approximately $4.4 million. The annual operation and maintenance (O&M) costs are estimated to be $4.3 million for a 30 year net present value of$53.7 million (note that the non- discounted O&M costs amount to $130 million). The total cost for installation of the P&T system and 30 years of discounted O&M costs is $58.8 million. The design basis for the P&T system is based on the following assumptions: • The presumed location of the P&T alignment (based on existing monitoring data) is shown in Figures B.3-1; it is assumed that the length of the alignment will be approximately 12,000 feet to a total depth of 135 feet bgs. • Pre-construction costs include engineering design and legal/permitting costs, which are assumed to be 8% and 5% of capital costs respectively. Pre-construction costs are estimated to be $543,700. AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.3\Attach B-3.docx 133-3