ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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O&M costs are estimated to be $3.2 million per year, and the NPV for 30 years (7% discount rate) is estimated to be $39.1 million. • Other important O&M assumptions include: o Sparge wells are assumed to operate for six (6) hours per day in a pulsed manner. o Air injection flow rates for the entire system are estimated to be 15,000 CFM (time-averaged to account for the pulsed operation, with 75% of the sparging wells idle). o Annual system operating time is assumed to be 8,400 hours per year for 30 years. o The performance monitoring system will consist of 90 multi-level wells spaced at 100-feet centers along two transects, with 45 wells in the upgradient monitoring well transect, and 45 wells in the downgradient monitoring well transect. o Performance monitoring will be performed in the upgradient and downgradient transects on a quarterly basis for 30 years. Supporting calculations for unit costs listed in Table B.1-1 are provided in Tables B.1-2 and B.1-3. The total cost of in situ treatment by biosparging greatly outweighs the costs for wellhead treatment and water replacement (the current strategy). Furthermore, as discussed in Section 3.2, the IAS system is unlikely to be effective at completely treating and containing COC-affected groundwater in the vicinity of the WWTP. For these reasons alone, biosparging is not considered to be a cost effective alternative for groundwater treatment in the WWTP area. 3.5 ENERGY REQUIREMENTS The amount of power required to inject air with up to 175 feet of hydrostatic pressure at approximately 3,000 locations (Table B.1-2) is substantially larger than most remediation system requirements and is estimated to be 22,567 mega-watt hours (MWh) per year of operation (Table B.1-1). This energy is the calculated amount required to operate 120 air compressors rated at 30 horsepower each to sustain the pulsed air injection across the 4,500 feet long alignment. Annual energy costs are estimated to be greater than $2.2 million. This energy consumption would require substantial infrastructure along the Stanislaus River. The greenhouse gas emissions associated with this energy use has an environmental cost that also needs to be considered. Using a carbon dioxide (CO2) electricity equivalent factor of 878.71 pounds of CO2/MWh, for California, as reported in the California Climate Action AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.1\Attach B1.doc 131-9