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<br />ALTERNATE CASE FOR LA JUNTA <br /> <br />All communities were examined with the assumption that complete metering <br />of water would be practiced in each city even though only Lamar currently does <br />so. To gain insight into the differences between metered and unmetered sys- <br />tems, an alternate case for La Junta using an unmetered water system was con- <br />sidered. The analysis of this alternate case revealed that whereas unit water <br />cost (cent/lOOO gal) for the unmetered system was lower, the total annual cost <br />for water was higher than for the metered system because of the much higher <br />water usage rate. <br /> <br />ADVANCED DESALTING CONCEPTS <br /> <br />Under a separate contract with the Office of Saline Water, Bresler and <br />Associates of New York investigated the use of advanced ion exchange/reverse <br />osmosis desalting systems for the cities of Ft. Morgan, La Junta, and Las <br />Animas. These systems appear to give a marginally lower water cost for Las <br />Animas, and significantly lower water costs for Ft. Morgan and La Junta than <br />standard reverse osmosis systems. <br /> <br />There are two factors that should be considered relative to the applica- <br />bility of the results using tpe ion exchange/reverse osmosis system. The <br />first is that the reverse osmosis unit is assumed to operate at 95 percent <br />product water recovery rate, whereas for the straight reverse osmosis system <br />(without ion exchange pretreatment) we assumed that the product water recovery <br />rate would qe a maximum of 75 percent if there was no calcium sulfate precipi- <br />tation problem up to this limit. The.technical concept appears sound in that <br />the ion exchange unit removes calcium so that the water flowing through the <br />reverse osmosis unit should not be constrained by scale formation; however, re- <br />verse osmosis units desalting municipal water supplies on a practical scale <br />have operated at no higher than 40 - 80 percent product water recovery rates. <br />Wh~reas operation at 75 percent appears to be a practical assumption, we wish <br />to point out that the 95 percent product recovery rate has not yet been demon- <br />strated. The other factor of concern is that the quality of the product water <br />produced at the higher product recovery rates will have high salinity levels <br />as compared to that which has been achieved from straight reverse osmosis sys- <br />tems operating at the lower product water yield rates (for membranes having <br />similar salt rejection rates). <br /> <br />CONCLUSIONS AND RECOMMENDATIONS <br /> <br />The following conclusions can be made concerning this study: <br /> <br />1. Several desalting methods are technically feasible for improving mu- <br />nicipal water supplies in the Colorado communities studied. <br /> <br />2 <br />