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ARCADIS <br />may be attributed to the reinitiation of mine dewatering in 2008. An evaluation of surface water <br />composition at the upstream Purgatoire River station reveals that river water does not meet the defined <br />criteria for irrigation water for protection of 100 percent yield of alfalfa. Modeling results indicate that <br />mixing of sodium -rich mine discharge waters with river water results in an increase in the SAR of the <br />resultant mixture, but does not result in a sufficient increase in EC to meet the established criteria for <br />protection of alfalfa yields. Although theoretical surface and mine water mixtures do not result in a <br />composition that is protective of alfalfa yields, when the proportion of mine discharge is maintained below <br />approximately 2 percent of the total discharge, little shift in the composition of surface water is expected. <br />7. References <br />Ayers, R.S. and D.S. Westcot. 1985. Water Quality for Agriculture. Food and Agriculture Organization of <br />the United Nations. Paper 29. <br />Colorado Water Quality Control Division (WQCD). 2008. Implementing Narrative Standards in Discharge <br />Permits for the Protection of Irrigated Crops. Water Quality Permits Policies and Procedures. March 10. <br />Lesch, S.M. and D.L. Suarez. 2009. Technical Note; A Short Note on Calculating the Adjusted SAR Index. <br />Transactions of the American Society of Agricultural and Biological Engineers. Vol. 52(2): 493-496. <br />New Elk Coal Company (NECC), LLC. 2012. New Elk Mine Annual Hydrologic Monitoring Report. October <br />25. <br />Tetra Tech Inc. (Tetra Tech) 2012. Purgatoire River Watershed Monitoring Raton Basin, Colorado 2012 <br />Monitoring Report. July. <br />United States Geological Survey (USGS) Gw Chart tool <br />(hftp://water.usgs.gov/nrp/gwsoftware/GW—Chart/GW—Chart.html) <br />Page <br />cWsersVwMwpsmW*atlko lMmvosohmndDm%m wym6aWfibs�con toudwUc6uftihnmekCDW%OacewaWw&enceasseswwtnana.d= 8/8 <br />