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ODOR CONTROL STUDY ( Figure 20 ) reduces the areas the next most. However, the 1 ppbv isopleth still extends a significant distance from the plant site . When both RSF Scrubber emissions and Anoxic Tank emissions are reduced ( Figures 21 and 22 ) , the potential area of off-site odor impacts reduce significantly. Figure 23 shows that the area reduces even further if the control efficiency for the RSF Scrubber and Anoxic Tank is increased to 95 % . This increased efficiency should be achieved , with proper design and operation of the improved scrubbers . 5 . 0 Cost Benefit Analysis The air dispersion model indicates that controlling the three major odor sources can greatly reduce off-site odor impacts and help make the Central WWTF a "community- friendly facility" . As indicated above , the three most important odor sources , in order of importance , are : • Regional Sludge Facility Scrubber • Anoxic Tank • Sludge and Septage Storage Tank Fugitive Emissions Several options were developed for controlling odorous emissions from these sources . To calculate which option is most cost effective , a cost/benefit analysis was performed . The estimated capital and operating costs for each option were divided by the total amount of sulfur removed . The cost/benefit analysis is shown in Table 7 . A present worth cost estimate is also presented for each option , assuming annual costs are prorated at 8 % interest over 20 years ( PWF = 9 . 6 ) . As can be seen in Table 7 , the costs per pound of sulfur are lowest for Options 1 and 4 . However, if only these improvements are made , there will still be considerable off-site odor impacts under the second worst hour criteria . The greatest amount of sulfur removed involves improving the existing RSF Scrubber system . If the RSF Scrubber improvements are added to Options 1 and 4 , the off-site odor impacts are reduced considerably , as shown on Figure 21 . The costs for installing covers and controlling emissions from the Anoxic Tank (Option 5 ) are significantly higher than any other option , but are expected to greatly reduce off- site odors . Since the Anoxic Tank emissions and costs are independent of the RSF emissions and costs , the total capital and incremental increase in operating costs for the RSF odor control improvements are approximately $270 , 000 and $ 30 , 000 to $45 , 000 per year, respectively . Since the RSF dewaters about 13 , 000 wet tons of septage and sludge per year, these costs equate to approximately $4 . 50 to $ 5 . 75 per wet ton of sludge . Based on our experience , these costs probably represent less than 10 % increase in sludge dewatering and disposal costs and are relatively minor compared to costs to relocate the RSF or employ an alternative sludge disposal technology. 26 Indian River County, Central Wastewater Treatment Facility 1 PBS&J #071230, February 2003