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, I I' ,.' '/ co C\J ''1' (\J t..:) C;o .' ~, :;-~: Evaluations of the technical risks for use of Lower Virgin River Unit water vs. secondary sewage effluent showed that the plant design and operating un- certainties were about equal In magnitude If water quality for the sources were predictable. .) The total levellzed cost comparisons, based on appraisal-level accuracy and economic factors suppl ied by Nevada Power Company, are shown on the following bar graph. The comparisons show that Option I Is approximately equal to the base case Option V, that Option II Is approximately $3.2 mil I Ion higher than the base case, and that Option I I I Is approximately $5.5 mil I Ion higher than the base case. Option IV, which uses brine concentrator product water rather than softened cool ing tower ,blowdown for FGD system makeup, is $450,000 less expensive than the base case Option V. ,~ . ,j.. (;." Economic sensitivity analysis, which examined the effects of varying chemical cost, power cost and evaporation pond cost, showed that chemical cost was the most slglnflcant economic variable. Of the five options, Option I and Option IV were the least sensitive to chemical cost. While the sensitivity analyses did not directly evaluate the Impact of variations of Lower Virgin River Unit water quality on total level Ized cost, It Is apparent that total cost Is quite sensitive to the predictability of water quality. ~; .;.~( :.., , , ';>;1 '.. The in-plant cost of salt removal from the Colorado River system was deter-' mined from the difference In levelized costs of Options I, II and III compared to the base case, and the rate of Lower Virgin River water use. The levelized cost of salt removal was $9 per ton per year for Option I, $66 dollars per ton per year for Option I I, and $115 per ton per year for Option I I I. These In- plant costs must be added to the levellzed costs of collecting and transport- ing Lower Virgin River water to the Harry Allen site to determine the total level Ized cost of salt removal. Collection and transportation costs have been estimated separately by Reclamation. , ,,', ;;:.," t:~~ The overal I results of the Task 4 study show that the Lower Virgin River Unit water source Is a viable water supply for the Harry Allen Station, provided the quality and quantity of the water supply are confirmed by additional wells and monitoring. The evaluation of saline water use technologies and water treatment process options showed that both emerging and commercially proven power plant design approaches are available for using the Lower Virgin River Unit water quality. .'';''. r.J ~ . v': -.; The cost advantages of the Ion exchange/sldestream treatment process can be Incorporated Into the Harry Allen Station design If the 'technical and economic viability of the process can be confirmed through field demonstration. We recommend that such a program be considered by Reclamation and Nevada Power Company using the existing field test unit at Southern California Edison's Etiwanda Generating Station near San Bernardino, California. ." '';.'> ., '~:.l ::: ,~ iv ,::'C::.. ~:~~~; ~~ ',,1',,: