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<br /><"':l <br />~ <br />co <br />"'"'1 <br /> <br />ENVIRONMENTAL PROTECTION AGENCY <br />REGION VIII <br />Suite 900, 1860 Lincoln Street <br />Denver, Colorado 80203 <br /> <br />December 4, 1972 <br /> <br />Ref: AWPI <br /> <br />Mr. D. L. Crandall, Director <br />Upper Colorado Region <br />Bureau of Reclamation <br />P. O. Box 11568 <br />Salt Lake City, Utah 84111 <br /> <br />Dear Mr. Crandall: <br /> <br />The following evaluation of the water quality effects of the Upper <br />Gunnison Project, Colorado was prepared under the authority and in accord- <br />ance with provisions of the Federal Water Pollution Control Act as amended <br />and Executive Order 11507, dated February 5, 1970, and at the request of <br />your office. Section l02(b) of the Act requires that consideration shall <br />be given to inclusion of storage for regulation of streamflow for the <br />purpose of water quality control, except that such storage shall not be <br />provided as a substitute for adequate treatment or other methods of <br />controlling waste at the source. Section 7 of Executive Order 11507 <br />requires the preparation of a report describing the potential impact of <br />Federal water resource projects on water quality. <br /> <br />The most significant impacts of the proposed project on water quality <br />will be increased salinity (total dissolved solidS) concentrations in the <br />lower Colorado River where salinity concentrations have already reached <br />critical levels. Salt loading and salt concentrating effects of consump- <br />tive use or depletion are the primary causes of this salinity increase. <br />From analysis of the project area, it is estimated that new lands will <br />contribute a salt loading of 0.5 ton per acre or a total of 1,080 tons <br />annually. Supplemental service lands have probably been leached free of <br />all but minor amounts of soluble salts and will add only a small undeter- <br />minable amount of salt load to the river system. Use of project water <br />will deplete the Upper Gunnison and its tributaries by 9,700 acre-feet <br />annually. <br /> <br />The average annual present modified total dissolved solids concen- <br />trations of the Gunnison River at Grand Junction and of the Colorado <br />River at Lake Mead are about 646 and 760 milligrams per liter (mg/l), <br />respectively (Quality of Water Colorado River Basin, Progress Report <br />No.5). The dissolved solids concentrations in the Gunnison River at <br />Grand Junction and in the ColoradO River at Lees Ferry and all points <br /> <br />53 <br />