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December 2007 Georgetown – Final Alternatives Analysis Report <br />page 5 <br />5.0 Cost Comparison <br />An engineer’s opinion of probable cost was developed for each alternative. The following assumptions <br />were made: <br />x Alternative 1 assumes a 4-foot by 4-foot square cast iron slide gate and trashrack, operated with a <br />submerged hydraulic cylinder, and concrete removal by diamond wire cutting in the dry using a <br />half-pipe temporary bulkhead. <br />x Alternative 2 assumes a 48-inch diameter by-pass pipe with an upstream bulkhead gate and <br />trashrack, a downstream regulating gate valve with electric operators, and installation of the <br />upstream gate in the dry using a half-pipe temporary bulkhead. <br />x Alternative 3 assumes a concrete intake structure, a 54-inch diameter by-pass pipe with an <br />upstream bulkhead gate and a downstream regulating gate valve with electric operators, trenching <br />in the road, and dredging an inlet channel after completing construction of the intake tower in the <br />dry. <br />x Costs of general construction were estimated using the Means catalog and by obtaining vendor <br />quotes. <br />x Since this is a small project Engineering / Design costs were estimated as 30%. <br />x Permitting and Legal costs (“Owner’s Costs”) were estimated as 10% for all alternatives. <br />x Mobilization was estimated at 5%. <br />x Alternatives 1 and 2 include a 35% contingency due to the non-traditional construction practices <br />required. Since Alternative 3 utilizes traditional construction practices, a contingency of 25% was <br />included. <br />6.0 Comparative Analysis of Alternatives <br />The relevant advantages and disadvantages of each spillway modification alternative are provided in the <br />table below: <br />Table1: Alternative Advantages and Disadvantages <br />Alternative Advantages Disadvantages <br />Alternative 1 <br />Slide Gate <br />x Operation and Maintenance <br />x SEO acceptance <br />x Least Expensive <br />x Underwater construction <br />x Operator in flow path, or <br />x Expensive submerged <br />operation <br />x Non-traditional construction <br />techniques <br />Alternative 2 <br />Bypass Pipe through dam <br />x Operation and Maintenance <br />x Potential siphon removal <br />x Slightly more expensive than <br />Alternative 1 <br />x Underwater construction <br />x Structure stability during <br />construction <br />x Seepage potential along pipe <br />x Non-traditional construction <br />techniques <br />Alternative 3 <br />Bypass Pipe around dam <br />x Simple Operation <br />x Potential for limited regulatory <br />involvement <br />x Potential for siphon removal <br />x Traditional construction <br />techniques <br />x Pipe route through road and <br />under sewer pipe (may <br />require sewer pipe relocation) <br />x Cost (most expensive option)