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w::::. ~-_... c.n 1'0 . SlJ~1.~1.r\F\Y SlIr:ET Gr.ll,d V:111 ".: l'n i r ------- Sl.,t''-" 1'....~, . LOCATION lv.:.lted 111 l,.{e~t-c12ntral tI,€ CQ!or.:Jdo River bl'- ilnd Mack, and includin,l!; The Gr.:Jt\d Valley Urli.t is Co!or,Jc!') i11,)f'l:S the ["02,1CI1 l~f tween tlie t0wns of Palisade the city of Grand Junction. PURPOSE The purpose of the unit is to rt!duce the salt added to the Colorado River as a result of conveyance system seepage and agricultural pract ices in the unit ar~a. The pi an for rcduc i ng sal t load i. ng is to be aecampl ished through a two-segment program involving improvements to the water delivery and on-farm ircigat ion systems. It is anticipated that this two-part program would reduce the amount of ground water percolating into highly saline soils and the underlying shale of the Mancos FOrnlation, thereby decreasing salt loading to t.he Colorado River. BACKGROUND A study W'as initi<.ited in FY 1972 to detenuine ...mat salt loading reductions could be achieved by reduc- ing the seepage losses in conveyance systems in the Grand Valley Unit. area. Studies included detenni- Ilat ion of irrigated acreage. canal and lateral sizing, determinntion of the location, capacity and condition of present canal and lateral structures. . Based on these prel iminary studies. the Grand Val- ley Unit, a componellt of the Colorado River Basin Salinity Control Proje;:t. W'.J.s authorized for con- struction in 197[~. Development of the unit is planned in tW'o stages to alloW' Reclamation to begin construction in a portion of the unit where plans and des igns are completp. where data can be gather- ed to assess the impacts of initial development Apri I IqR~ P;l~e I of :2 while study and ptannin~ e,mtinues on the r<o'st of the lInit, .:In.-I wlH'r", n<o't envirul1m~nt:.t impact.., \,JL'r~ not signifi.cant. As p<lrt of the plan ,)[ J~v~l.'p- m<!nt for Sta.ee On~, 6.8 miles of the Governnwnt Hi~hline Canal have been concrete-lined and cruss drainage f.1cllities have been completed. The Grand Valley Fie.ld Station, loIhi.:h is also canple.te. will serve as construction headquarters for the overall unit and after construction ~ill be used for opara- tion and maintenance or for other project \Jse9. Stage One construction will be complete .....tIen 13 op~n channel laterals presently serving the area under the Government Highline Canal have been con- solidated into 12 pipe laterals; this construction is currently underway. As part of a monitoring plan for Stage One. meas- urements and samples are taken bi-monthly from observation wells to provide base data for evalu- ating the effects of the unit on ground-W'ater floW's and quality. In addition to ground-water monitor- ing, the progrsm includes weekly mea,<;urements of water quantity and quality in tributary drains. Samples are also taken from canals where they enter and leave the St.age One area. Results from the waler quality testing W'ill be used to assess the eHectiveness of St<lge One development in reducing salt loading to the Colorado River. wildlife resources are also being monitored in the Stage One area to detennine the project's effect on ~ildlife and wil~life populations. STATUS A plan of study for Stage Two W'as published in October 1981, and investigations were initiated in November 1981. Stage r....o investig.ltions are to in- clude a re-evalu.ltion of various alternatives, and becau~e nonlining options W'ere only marginally evaluated before authorization, salinity control No . , . , ICAL[O,IIIU' c-4N~l ,""USAO~ '" ItCO'ANOS ~/~ERSION 0':'11 ,.