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WATER QUALITY PARAMETERS The history of the concentrations of important water constituents for the cities of this study has already been presented in Section 4. The period of interest for this study has been selected as the 20 years between 1970 and 1990. It is for this 20-year period that desalting system costs and benefits will be calculated. For comparison purposes, the various desalting techniques will be examined on the basis of the 1980 water quality and consumption figures for the selected communities, since 1980 is the midpoint of the study period. Historical information for the important water quality parameters was plotted to obtain projections of these parameters as needed. Such water qual- ity projections for total dissolved solids and total hardness are presented in Figs. 2 through 7 for the various cities. Conservatively, we have utilized extrapolations of salinity and hardness to the year 1980 for our desalting sys- tem calculations. The only city for which this straightforward approach is not applicable is Lamar. It is recognized that Lamar has experienced problems in obtaining sufficient supplies of water in the past from its source in the Clay Creek area. This fact was demonstrated again this year when the city was forced to ration water during July (see the "Lamar Tri-State Daily News", July 3, 1970). We have, therefore, assumed that for 1980 the Clay Creek wells will supply only 75 percent of the total water demand, with the remaining 25 percent coming from wells of the Arkansas River area. Water quality for the Arkansas River aquifer was obtained by averaging the chemical analyses. of the water from four wells in the area adjacent to Lamar. Water quality figures for Lamar were then based on blending water from these two sources in the proportions indicated ahove. WATER USAGE PARAMETERS As indicated earlier, the desalting techniques were examined based on the projected 1980 water quality and usage figures. The design capacity for de- salting systems was designated as the average day of water usage for the maxi- mum month in 1980 for eacb of the cities concerned. Primary concern for this study was centered on the assumption that each of the communities will be op- erating with a fully metered water system (even though oniy Lamar now operates this way). An alternate case study was considered for La Junta only which ex- amined an unmetered water system. This alternate case study is presented in Appendix B. . F th " " rom e report Colorado Ground Water Basic-Data Release No. 21 , Hydrogeo- logical Data for the Lower Arkansas River Valley, Colorado, by Thomas J. Major, R. Theodore Huss, and John E. Moore. Prepared by U.S. Geological Survey in cooperation with the Colorado Water Conservation Board and South- eastern Colorado Water Conservancy District, Denver, Colorado, 1970. 34