ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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infeasible. As shown in Table B.1-1, the total cost to implement a biosparging barrier is estimated to be $86.5 million dollars. A major control on the cost of constructing the system is the number of sparge wells required — 374 locations with eight wells per location (based on previously referenced design guidance), amounting to 441,320 feet in drilling and well materials (total cost for the sparge wells is estimated at $32.8 million; the cost for drilling and well materials is estimated at $74.4/foot). Operation and maintenance (O&M) costs also comprise a major portion of the costs, amounting to $3.15 million/year, or a net present value (NPV) of$39.1 million dollars (based on the EPA-recommended 30 year O&M duration and 7% NPV rate). Additional details on the derivation of these costs are provided below: The design for the biobarrier is based on the following assumptions (Table B.1-1) • The presumed location of the barrier (based on existing monitoring data) is shown in Figures B.1-1; it is assumed that the length will be 4,500 feet and depth will be 200 feet bgs (this could change based on the results of the remedial investigation). • A remedial design investigation will be carried out along the alignment shown in Figures B.1-1 before the biosparging system is constructed. The investigation includes the installation, development and sampling of 45 multi-level wells (CMT TM wells) spaced 100 feet apart along the 4,500 feet alignment. Each CMT well will be installed to depth of 200 feet bgs and will be constructed with seven sample ports (allowing for seven discrete sampling depths). The estimated cost for this investigation is $1.2 million. • Pre-construction costs include engineering design and legal/permitting costs, which are assumed to be 6% and 5% of capital costs, respectively, for total cost of$4.2 million. • Contractor and Equipment Costs include 374 biosparge well clusters spaced at 12 feet centers, based on a recommended ZOI of 15-feet (USACE, 2008; ESTCP 2002; NAVFAC, 2001) and an overlap factor of 1.3 (for a total of 374 biosparge well clusters). Eight sparge wells will comprise each cluster, with injection depths spaced at 15-feet vertical offsets between 75 feet bgs and 200 feet bgs. Equipment costs (power connections, support facilities, compressors, manifolds, etc.) are also included in construction costs. The total construction cost is estimated to be $38.1 million. • Supervision/Labor costs include construction and project management, which are combined to amount to 10% of capital costs, respectively. Well development and sampling are very minor components of this task. The total cost for supervision and labor is estimated to be $3.9 million. • O&M costs include electricity costs (approximately $2.3 million per year), maintenance, and quarterly performance monitoring (approximately $303,000 per year). Total annual AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.1\Attach B1.doc 131-8