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<br />at the same time these facilities have an impact that must be recognized and addressed <br />appropriately. <br /> <br />A primary goal of this document is to look at the issue more holistically and provide <br />background and options for water suppliers, water users, regulators, and other <br />stakeholders to make more informed decisions when they are evaluating the <br />appropriateness of using membranes to meet water quality treatment objectives. <br /> <br />RO/N F is one of the most effective treatment methods for removing high levels of salts <br />from ocean, brackish, and lower quality water sources. In addition to the removal of <br />salts, membranes are extremely efficient in removing high levels of other contaminants <br />such as nitrates, arsenic, organics precursors of disinfection by-products and emerging <br />contaminants of concern. This section briefly outlines those issues. For further detail <br />the reader should reference Appendix C. <br /> <br />3.1 Water Supply Limitations <br /> <br />The Colorado Water Conservation Board (CWCB) completed the first phase of the <br />Statewide Water Supply Initiative (SWSI) in 2004. SWSI explored at a statewide level <br />the existing water supplies and existing and projected water demands through the year <br />2030. This analysis was conducted in each of Colorado's eight major river basins. In <br />addition to examining water supplies and demands, SWSI explored the range of <br />potential options to meet the state's future water demands. The study concluded that <br />municipal and industrial (M&I) water needs will increase by over 600,000 acre-feet per <br />year by the year 2030. A portion of these future water demands will need to be met <br />using lower quality water sources. (Material excerpted from Colorado Water <br />Conservation Board. 2004. Statewide Water Supply Initiative. <br />http://cwcb.state.co.us/IWMD/P u bs. htm). <br /> <br />3.2 Sources and Trends in TDS <br /> <br />The ability to use water supplies containing high salt concentrations is important not only <br />because of the scarcity of high quality water sources, but also because of an observed <br />upward trend in total dissolved solids (TDS) in existing surface and groundwater <br />supplies. One cause of climbing salt concentrations can be linked to the high rates of <br />evapotranspiration in more arid climates as consumptive use from agriculture and <br />municipal and industrial uses increase. Where evapotranspiration (combined <br />evaporation from soils and transpiration by plants) exceeds combined precipitation and <br />irrigation, salts accumulate in the root zones of plants (Arizona Water Resource - <br />http://cals.arizona/edu/AZWATER/awr/ianOO/feature.htm, February 28,2007). <br /> <br />3.3 Practical Effects of Agricultural Irrigation on TDS <br /> <br />A primary factor influencing the use of RO for municipal drinking water is that the water <br />source is directly or indirectly impacted by agricultural return flows, such as in the major <br />river basins (Arkansas, Colorado, and South Platte) of the State. Irrigation of agricultural <br />crops concentrates salts in the return flows, which may be 15 to 50% of the irrigation <br />water application. This can result in concentration levels 2 to 7 times greater than in the <br /> <br />6 <br />