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0, months of July-September are, 0.027 mg/l at Chatfield, and 0.035 mg/l at ~ Cherry Creek. A standard of 0.0074 mg/l applies to Dillon Reservoir from tQ. . ""-1 July-October. Criterion values of .05, ~l and 1.5 mg/l of phosphorus have Q) been selected to demonstrate the relative enrichment of various streams in Colorado, These enrichment values then reflect the potential for eutrophication in downstream lakes and reservoirs. Total Dissolved Solids Total.dissolved solids (TDS) or salinity is of concern in arid and semi-arid areas when water is consumptively (evapo-transpired) used. Application of irrigation water to saline soils leaches increased concentrations of TDS back to rivers. Transpiration by plants and evaporation from open water surfaces further concentrates the salts. TDS concentrations range from less than 50 ~ mg/l, in some Colorado mountain streams, to nearly 5000 mg/l in the lower Arkansas River. Saline springs in the Colorado River Basin contain over ,f 100,000 mg/l. Water with a TDS concentration less than 500 mg/l are preferred for public water supplies; however concentrations of 1000 mg/l are acceptable .'1ii ;~ (:: and occasionally higher concentrations are used without ill effects. CC) ", I';! tl:' Agricultural crops also exhibit a wide tolerance toTDS, with more sensitive' species being affected at 1500-1800 mg/l. Water quality standards have been ~ ~~ established for salinity in the Colorado River basin. The seven states in the iPl ,,-';jy ~ Colorado river basin have collectively agreed to maintain or decrease salinity concentrations of 879 mg/l at the Imperial Dam in California. For the purposes of this assessment, criteria values of 500, 1000, and 1500 mg/l have ~~:~ 1-:'l 'l~: been selected to show the range of TDS concentrations found in the waters of ~f~ .I.~" ~f\! Colorado. .',(\ ;;~ ~;2. -40- ~::j ..r:- ,,~ " ,-<i:,:' irJ --'---