WSP03020

• File Number: 8278.400
• Description: Title I - Mexican Treaty and Minute 242
• Basin: Colorado Mainstem
• Date: 1/1/2000
• Author: IBWC
• Title: Minute 242 Annual Report
• Water Supply Pro - Doc Type: Annual Report

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1998 1,214
A VERAGE ANNUAL SALINITY (U.S, COUN1)
AS TOTAL DISSOLVED SOLIDS (continued)
YEAR (PPM)
I 1999 I 1,242 I
2000 1,173

The above data show that the salinity in 2000 was lower than that ofthe water customarily delivered
on the land boundary, which averaged about 1,540 ppm for the lO-year period 1963-1972.

Beginning in late 1995, Mexico objected to peaks in salinity at the Northerly International Boundary
(NIB) and to the salinity levels in waters delivered at the land boundary. The IBWC addressed
these matters through an International Task Force arrangement involving the federal water agencies
of each country. The effort is for adjustments in operational practices at those periods where high
salinity is a significant problem for Mexico.

Mexico utilizes the treaty waters diverted at Morelos Dam for irrigation and domestic uses in the
Mexicali Valley and conveys someofthese waters via aqueducCto Tecatean(rTijuana~M'exico's
concern with an occasional salinity peak comes at those times when Mexico's water delivery
demands are low. Salinity readings during 2000 indicate insignificant peaks at this delivery point.

Mexico utilizes some NIB delivered waters along with water from wells near San Luis, Sonora for
mixing the drainage waters that the United States continues to deliver at the Southerly Land
Boundary (SLB). Mexico uses this combination of waters to irrigate 93,860 acres around the
Mexicali Valley in Sonora known as the Left Bank unit. Mexico is concerned over'reduced crop
yields and deteriorating soil quality and increased ground water salinity. Mexico, in this respect,
requested that all its treaty deliveries be made at the NIB. This proposal was not practical to the
United States in that the United States is not able to prevent all these drainage waters from discharge
to Mexico at the SLB and continues to have the right to make these deliveries as part of the treaty
volume. Further, this would require release of stored water in the United States that is fully
appropriated. Finally, there is the need to understand the problem in the Mexican irrigation system
and all the factors better that influence increasing soil and groundwater salinity and lower crop
yields.

As a matter of cooperation, the International Task Force has narrowed the perceived effects to a
period of four months of the year and examined scenarios of actions in each country that may be
carried out to ameliorate salinity peaks during those periods. The United States shall continue to
meet its legal obligations as described in Minute 242 by continuing to make the land boundary
deliveries with the salinity in the waters customarily delivered at that point.

The Yuma Desalting Plant (YDP) has been off-line since the first part of 1993, when the concrete
lining of the Wellton-Mohawk drainage canal was damaged by flood waters from the Gila River.
The damages were repaired.

During 2000, the YDP continued to be on standby status while the U.S. Bureau of Reclamation
reviewed alternatives for complying with the salinity differential.

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