Mexican Salinity Problems:

No problems arose with regard to water deliveries to Mexico between 1945 and 1961 since the salinity of the waters delivered at the Northerly Boundary was generally within 100 parts per million (ppm) of the water at Imperial Dam, the last major diversion point for users in the United States. In 1961 two unrelated events occurred which affected the salinity of the Mexican water deliveries. First, the Wellton-Mohawk Irrigation and Drainage District (part of Gila Project authorized in 1947 and whose construction was completed in 1952) commenced operation of a system of drainage wells which discharged waters with approximately 6,000 ppm into the Colorado River below Imperial Dam but above the Mexican diversion point.

Second, there was a sizable reduction in river flows to Mexico in 1961 because of increased storage in Lake Mead in anticipation of the closure of the gates at Glen Canyon Dam in the Upper Basin in order to store water in Lake Powell. This increased the salinity of the water delivered to Mexico from an average of 800 parts per million (ppm) in 1960 to nearly 1,400 ppm in 1961 and to 1,500 ppm in 1962. In November 1961 Mexico strongly objected to the salinity of the Colorado River waters received by it and negotiations between the two governments took place to resolve the matter. The negotiations resulted on March 22, 1965, a 5- year agreement, designated Minute 218 on practical measures to reduce the salinity of waters reaching Mexico, with each side reserving its legal rights. Under it the United States took the following actions at a cost to it of $12 million:

1. Construction and operation of an extension to the existing Wellton-Mohawk drain so that the Wellton-Mohawk drainage water could either be bypassed at Morelos Dam or, at Mexico's option, received above Morelos Dam where it would be mingled with other Colorado River waters delivered to Mexico.

2. Construction of additional drainage wells in the Wellton-Mohawk Division which allowed selective pumping of the most saline drainage waters at times when Mexico would be bypassing Wellton-Mohawk drainage waters; i.e., during the winter months, and allowed the pumping of higher quality ground water at times when Mexico would be using Wellton-Mohawk water.

3. Replacement of a portion of the bypassed Wellton- Mohawk drainage waters - which resulted in the release of approximately 40,000 acre-feet per year of "stored water" from Imperial Dam in excess of the 1.5 maf per year guaranteed by the Treaty. Under the above measures taken by the United States, the quality of the water delivered to Mexico was improved from about an average of 1,500 ppm in 1962 to 1,240 ppm in 1971. Minute No. 218 was to expire in November 1970, and provided for consideration of a new Minute after the review of the conditions which gave rise to the problems. However, the Mexican officials did not want to enter into a long-term agreement in November 1970 since a new administration was assuming power in Mexico in December 1970. Minute No. 218 therefor was extended for a 1-year period. Negotiations commenced in 1971 with the new Echeverria administration. The United States, supported by the Committee of Fourteen, proposed a new Minute which would have provided Colorado River water to Mexico having the same salt concentration as would exist were the Wellton-Mohawk Division, and all other projects in the United States below the Imperial Dam, in salt balance; i.e., that the tonnage of salt in drainage waters delivered to Mexico would not exceed the tonnage of the salt in the water applied to these lands below the Imperial Dam in the United States, which contribute to the drainage waters. Under this proposal average salinity would have been reduced to about 1,130 ppm in 1973.

Mexico rejected this proposal because of the difference in quality between Colorado River water delivered to the United States water users at Imperial Dam and the quality of the waters delivered to Mexico. In the interim, Minute No. 218 was again continued.