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I I I I I I I I I I I I I I I I I I I 3684 GRAND VALLEY UNIT - COLORADO The Grand Valley Unit is located in the western portion of Mesa and Garfield counties in western Colorado. Grand Junction in the southern part of the valley is .the largest Colorado city west of the Continental Divide. The area has about 71,000 acres of irrigated land Mith 38,000 of these acres served by the Grand Valley project. The valley was carved into the Mancos Shale formation by the Colorado River and its tributaries. This salt bearing shale is very thick, and as a result, it is estimated that the valley contributes 780,000 tons of salt annually to the Colorado River. It is estimated that 300,000 tons of this salt is contributed by on-farm irrigation practices and systems. The selected plan for removing a portion of this salt includes better management practices and physical improvements including canal lining, land leveling, subsurface drains and changing to drip or sprinkler irrigation systems. It is estimated that 410,000 tons of salt could be removed with the implementation of this program. This would reduce the salt concentration at Imperial Dam by 43 mg/L. Stage One of this project, which covers about 10% of the overall unit area, was initiated during the winter of 1980-81. The construction involved the lining of 6.8 miles of the Govern- ment Highline Canal. Additional work under Stage One will in- volve the consolidating of 13 laterals that now serve the recently lined section of canal into 11 and placing them in pipe sections. The contract for this work has been awarded and is expected to take 2 years for con~letion. A series of detention ponds and an interceptor ditch have been constructed above the lined canal section. A field station was constructed for use as project headquarters for the entire unit. It is estimated that Stage I will reduce the salt load by 24,000 tons per year and will lower the salt concentration by 2.5 mg/L of Imperial Dam. The estimated cost for this salinity reduction is $607,000 per mg/L (July '81). Planning for Stage II of the Grand Valley Unit has been initiated with the issuance of the plan of study and the public involvement programs. That planning is being scheduled such that as Definite Plan Report and Draft Environmental Statement will be available in early 1985, allowing for a construction start on Phase II in f isca1 year 1986. (updated 11/20/81) DS:cs -17-