WSP12647 ‎(2)‎

• File Number: 8282.400
• Description: Colorado River Operations and Accounting - Deliveries to Mexico
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1999
• Author: Environmental Defense Fund
• Title: A Delta Once More - Restoring Riparian and Wetland Habitat in the Colorado River Delta - Environmental Defense Fund - 06-01-99
• Water Supply Pro - Doc Type: Report/Study

A new wastewater treatment plant in Mexicali - to be
constructed in 2001- will improve the quality of some
of the effluent now sent via the New River to the Salton
Sea.

[See Box 1.] The plant is presently designed to discharge
treated effluent into the New River, where it will empty
into the Salton Sea. If instead this treated effluent is
discharged into the Rio Hardy basin, the Rio Hardy
wetlands might serve as part of the wastewater treat-
ment process. Both the Mexican government and the
u.s. EP A have indicated an interest in exploring options
for using treated water to enhance delta environments
(Eberhardt, 1996; Penas, 1999).

Yuma Desalting Plant

A proposal by the BaR to operate the Yuma Desalting
Plant and market the water would divert agricultural
wastewater flows from Ia Cienega de Santa Clara and
replace them with concentrated brine. [See Box 4.] This
would reduce the area of the wetland by 40 percent,
impacting wildlife, as well as the residents ?f nearby
Johnson ejido who serve as local ecotour gUIdes. Any
decision to operate the Yuma Desalting Plant will
require an environmental assessment and should require
that water be found to support la Cienega de Santa Clara.
This water should not be counted against the u.s. treaty
obligation to deliver Colorado River water to Mexico.

Lower Colorado Conservation Planning

The lower Colorado River basin has recently become a
focus for cooperative conservation efforts in the US.,
but to date, participants have been reluctant to include

the delta in planning efforts for the lower basin. One
potential source of support for delta ecosy~tems co~ld
be a system of off-site mitigation or mitigatIon bankmg
for lower basin water users whose diversions and
deliveries affect endangered species. Because delta wet-
lands are more extensive and in better condition than
riparian areas along the US. stretch of the Colorado
River, the delta is an important reservoir of species and
habitats that are threatened or endangered elsewhere.
The US. Fish and Wildlife Service is the lead federal
agency in the process, and could make the determina-
tion to include the delta in the scope of its overall
conservation program for the lower Colorado.

All American Canal and
Delivery of Water to Mexico

Colorado River water is guaranteed to Mexico in the
1944 water treaty with the United States.56 Mexico relies
on groundwater pumped from the border region to
augment its supplies, but plans by California and
Nevada to line the nearby All American Canal will
reduce seepage into these aquifers. Mexico has opposed
these plans on the grounds that the seepage is
" grandfathered" - in other words, a known conditio~
that existed at the time the original treaty was negotI-
ated, and therefore water to which Mexico is entitled.
In addition, Mexico has requested that its entire
allocation of water from the Colorado RiveT be
delivered at the Northern International Boundary, one
of two sites where water is currently deliveredY
Resolution of these issues will require negotiations
between the two countries and a possible amendment
to the 1944 treaty.

56 See Chapter 2, notes 15 and 20 for an explanation of U.S. treaty obligations to Mexico.
57 See Chapter 2 for further discussion.

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