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<br />APPENDIX OM Excerpts from the Published Literature <br /> <br />o <br />l\:l Information on which the analysis in the front part of this paper was based was taken primarily <br />,..... from three papers: <br />W <br /> <br />Eisenhauer, R. J., 1986, Characterization of Glenwood Springs and Dotsero Springs Source Aquifers: <br />U. S. Bureau of Reclamation paper REC-ERC-86-1. <br /> <br />Eisenhauer, R. J., 1983, Characterization of Glenwood Springs and Dotsero Springs: U. S. Bureau of <br />Reclamation paper REC-ERC-83-1O. <br /> <br />Geldon, A. L., 1989, Hydrogeology of the Leadville limestone and other Paleozoic rocks in north- <br />western Colorado, with results of aquifer tests at Glenwood Springs: U. S. Geological Survey Water- <br />Resources Report 87-4195. <br /> <br />1. Background <br /> <br />From Eisenhauer: <br /> <br />A number of sources contribute to high salinity levels in the Colorado River. Approximately half of <br />the present salt concentration in the Colorado River is man induced (Le., irrigation return flow, <br />reservoir evaporation, exports of water, municipal and indus-trial consumption. or contamination), <br />while the other half is due to natural sources (Le.. direct salt loading from natural springs and weath- <br />ering of mineral-bearing rocks). The Colorado River drains a total of 663 000 sq km (256 000 sq mi) <br />in the United States and Mexico and carries a salinity burden that has historically averaged about 10 <br />million metric tons (11 million tons) annually. <br />The Colorado River at its headwaters in the mountains of north-central Colorado has a <br />salinity of only about 50 mg/L (milligrams per liter). The salinity progressively increases downstream <br />as a result of water diversions and salt contributions from a variety of sources and in 1977 averaged <br />about 820 mg/L at Imperial Dam, the last major diversion point in the United States. Unless control <br />measures are undertaken, the concentration will continue to increase, reaching levels estimated by the <br />Bureau of Reclamation at 1150 to 1210 mg/L at Imperial Dam by the year 2000. Water of 1000 mg! <br />L or less is generally considered to be satisfactory for irrigating most crops although concentrations <br />of 500 mg/L can have detrimental effects on salt-sensitive crops. The U.S. Public Health Service <br />recommends that public drinking water supplies should contain less than 500 mg/L. <br />Salinity not only has economic effects on water users in the lower basin States. but is also an <br />important factor in international relations with Mexico. which is guaranteed an annual supply of 1.5 <br />million acre-ft of Colorado River water by a 1944 treaty. In 1973, the United States and Mexico <br />agreed that the water delivered to Mexico from the main stem of the river would have a salinity of no <br />more than 115 mg/L greater than the average salinity of water at Imperial Dam. <br />In recognition of these facts. Congress passed the Colorado River Basin Salinity Control Act <br />(Public Law 93-320) in June 1974. Title 11 of that act authorized the Secretary of the Interior to <br />construct, operate. and maintain four specific salinity control units in the Upper Basin as the initial <br />stage of the Colorado River <br /> <br />A-I <br />