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. . r;/f9J Salinity Control by Canal Lining: The McElmo Creek Unit, Colorado W. Martin Rochel John W. Davison2 INTRODU crION The McElmo Creek Unit is a Bureau of Reclamation (Reclamation) sa- linity control investigation located in southwestern Colorado and is part of the Colorado River Water Quality Improvement Program (CRWQIP), a program to reduce salinity in the Colorado River. The unit was autho- rized for study by Public Laws 93-320 and 96-375 to determine the most cost effective means of reducing an annual average of 119,000 tons (108,000 metric tons) of salt from entering the San Juan River, a tribu- tary of the Colorado River, from the McElmo Creek Drainage. The result of salt loaded by the McElmo Creek Drainage measured at Imperial Dam, California, is approximately 12.7 milligrams per liter (mg/L). Imperial Dam is a location where standards of water quality, measured in mg/L of total dissolved solids, have been established in 1972 by the Colorado River Basin Salinity Control Forum and approved by the Environmental Protection Agency. The unit area is defined as the McElmo Creek Drainage and lies pre- dominantly in Montezuma County, Colorado (Figure 1). Several alterna- tives have been formulated to reduce salinity within the unit area and have included evaporation of saline water at various locations within the unit area, selectively withdrawing saline agricultrual lands, de- salting flows from McElmo Creek, using saline flows for industrial pur- poses such as coal slurry or cooling towers at nearby coal-fired gener- ating plant, improving on-farm irrigation management, draining aquifers storing saline groundwater, and improving the Montezuma Valley Irriga- tion Company's (MVI) irrigation distribution system by lining or combin- ing canal sections. Selection of a recommended plan was based upon a comparison of the alternatives using cost effectiveness as the primary consideration. Cost effecciveness is measured by dividing the annual cost to construct and operate an alternative for its useful life by the annual reduction of salt measured in mg/L. The alternatives also had to meet public ac- ceptance and comply with legal and institutional regulations to be complete. Results of the comparison indicated that improvements to the MVI irrigation distribution system was the best plan. Currently, Reclamation is completing its planning report for the McElmo Creek Unit. . lChief, Division of Planning, U.S. Bureau of Reclamation, Durango, Colorado, X., ASCE. 2Study Coordinator, Plan Formulation Branch, U.S. Bureau of Reclamation, Durango, Colorado Ot:~155S