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<br />, 001991 <br /> <br />- , <br /> <br />Pitt et aI, August 2001. Replacing the Bypass Flow On The Colorado RiVei'. <br /> <br />Pumped groundwater would be diverted through the Yuma Mesa Conduit, north towards. the <br />Colorado River.37 Their proposal would increase groUndwater pumping over the most recent 10- <br />year average by 50,000 acre:"feet per year for 5 years and 30,000 acre-feet per year thereafter.38 <br />Y A WRMG recommends that Arizona trade 25,000 acre-feet per year of pumped groundwater <br />for a period of 10 years (subject to renewal) in exchange for financial support from BOR, For a <br />modest $8.80 per acre-foot, BOR can secure water to replace MODE flows diminished by the <br />lease of water from WMIDD. Calculated alternatively, it adds $2 to the cost of an acre-f~t of <br />water leased from WMIDD. <br /> <br />, However, before any changes are made to the Yunia Area groundwater pumping regime, BOR <br />must evaluate the environmental impacts with a full review as required by the National <br />Environmental Policy ACt.39 Expected impacts, include loss of groundwater flows to the Gila <br />River and the Colorado River mainstem in its limitrophe reach, loss of groundwater flows to <br />Mexico, and lowering of water tables in adjacent aquifers and surface waters. Further impacts <br />include increased salinity in the Colorado River mainstem from the balarice of groundwater <br />pumped from the Yuma Mesa area that Yuma area irrigation districts will claim as return flows. <br />Significantly, the salinity of Yuma Mesa groundwater is' expected to increase over time. <br />increasing the salinity of pumped water, and leading to increased water irrigation rates and an <br />increased need for groundwater pumping. Furthermore, increased groundwater pumping <br />reinforces the extraordinarily high rates of water use for irrigation in the Yuma area irrigation, <br />districts. If the BOR were to give Yuma area irrigators incentives to conserve water, <br />groundwater problems might be solved with the added ben~fit of reduced depletions to the <br />Colorado River mainstem. BOR must evaluate these impacts and weigh them agaiilst the <br />potential benefits of Yuma area groundwater pumping. , <br /> <br />An additional uncertainty of the Y A WRMG proposal is the term of the arrangement. Arizona's <br />recent population growth boom is likely to continue, and with it, Arizona's urban water demand. ' <br />After the 10-year term of Y A WRMG's proposal, Arizona has the option to refuse contract <br />renewal with BOR. Thus it is important that BOR evaluate the Y A WRMG proposal as a <br />, temporary source of water. Finally, the Y A WRMG's 'proposal 'would facilitate the routing of <br />pumped Yuma Mesa groundwater to the Yuma DeSalting Plant, which is problematic for reasons <br />outlined in the section below (see Operation of the Yuma Desalting Plant). ' <br /> <br />Because the Y A WRMG has indicated some urgeqcy to the need for increasing groundwater <br />pumping in the Yuma Mesa area, it is likely that pumping may begin before the end of the <br />interim period for which the federal government receives credit for water conserved by the lining <br />of theCoachella Canal. Under these circumstances, BOR will be receiving 25,000 acre-feet of <br />water for which it has no obligation. BOR would then be free to use .this "new" water to <br /> <br />37 The YA WRMG proposal includes the construction of a trifurcation structure at the terminus of the Yuma Mesa <br />Conduit, allowing pumped groundwater to be diverted'to the Colorado River, the MODE, or the Yuma Desalting <br />Plant. For reasons discussed below (see Operation of the Yuma Desalting Plant), treatment of pumped groundwa~ <br />at the Yuma Desalting Plant may not be feasible. <br />38 Y A WRMG, supra note 36. <br />, 3942 D.S.C. ~ 4321-4370 (1994). <br /> <br />10 <br />