BOARD00345

• Board Meeting Date: 11/19/2001
• Description: ISF Section - Proposed ISF Recommendations for 2002
• Board Meetings - Doc Type: Memo

Pitt et aI, August 2001. Replacing the Bypass Flow On The Colorado River

Pumped groundwater would be diverted through the. Yuma Mesa Conduit, north towards the
Colorado River.37 Their proposal would increase groundwater pumping over the most recent 10-
year average by 50,000 acre-feet per year for 5 years and 30,000 acre-feet per year thereafter.38
Y A WRMG recommends that Arizona trade 25,000 acre-feet per year of pumped groundwater
for a period of 10 years (subject to renewal) in el{chRl\ge for financial support from BOR. For a
modest $8.80 per acre-foot, BOR can secure water to replace MODE flows diminished by the
lease of water from WMlDD. Calculated alternatively, it adds $2 to the cost of an acre-foot of
water leased from WMlDD, .

However, before any changes are made to the Yuma Area groundwater pumping regime, BOR
must evaluate the environmental impacts with a full review as required by the National
Environmental Policy ACt.39 Expected impacts include loss of groundwater flows to the Gila
River and the Colorado River mainstem in its limitrophe reach, loss of groundwater flows to
Mexico, and lowering of water tables in adjacent aquifers and surface waters. Further impacts
include increased salinity in the Colorado River mainstem from the balance of groundwater
pumped from the Yuma Mesa area that Yuma arl:a irrigation districts will claim as return flows,
Significantly, the salinity of Yuma Mesa groundwater is expected to increase over time,
increasing the salinity of pumped water, and leading to increased water irrigation rates and an
increased need for groundwater pumping. Furthennore, increased groundwater pumping
reinforces the extraordinarily high rates of watet use for irrigation in the Yuma area irrigation
districts. If the BOR were to give Yuma area. irrigators incentives to conserve water,
groundwater problems might be solved with the added benefit of reduced depletions to the
Colorado River mainstem. BOR must evaluate these impacts and weigh them against the
potential benefits of Yuma area groundwater pumping.

An additional uncertainty of the YAWRMG proposal is the tenn of the arrangement. Arizona's
recent population growth boom is likely to continue, and with it, Arizona's urban water demand.
After the 10-year tenn of YAWRMG's propo~al, Arizona has the option to refuse contract
renewal with BOR. Thus it is important that BOR evaluate the Y A WRMG proposal as a
temporary source of water. Finally, the Y A WltMG's proposal would facilitate the routing of
pumped Yuma Mesa groundwater to the Yuma Desalting Plant, which is problematic for reasons
outlined in the section below (see Operation of the YljIlla Desalting Plant)..
i

Because the Y A WRMG has indicated some urgendy to the need for increasing groundwater
pumping in the Yuma Mesa area, it is likely that pumping may begin before the end of the
interim period for which the federal government receives credit for water conserved by the lining
of theCoachella Canal. Under these circumstances,! BOR will be receiving 25,000 acre-feet of
water for which it has no obligation. BOR Would then be free to use this "new" water to

37 The Y A WRMG proposal includes the construction ofa trifur~ation structure at the terminus ofthe Yuma Mesa
Conduit, al10wing pumped groundwater to be diverted to the Colorado River, the MODE, or the Yuma Desalting
Plant, For reasons discussed below (see Operation of the VumaDesalting Plant), treatment of pumped groundwater
at the Yuma Desalting Plant may not be feasible.
38 Y A WRMG, supra note 36.
39 42 U,S.C, ~ 4321-4370 (1994),

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