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rrOZ134 measures to reduce salinity: extending the Wellton-Mohawk Drain to permit drainage to be bypassed to the Santa Clara Slough; replacing about 40,000 acre-feet per year of bypassed drain water with additional water released from Imperial Dam; and constructing more drains at Wellton-Mohawk to permit selective pumping of drainage. .. Water users in the seven Colorado River Basin states were initially unwilling to make any concessions to Mexico on water quality. They pointed to the language of the treaty as proof that Mexico was compelled to accept drainage water of any quality as part of its allotment. Water law in the western united States recognizes the right to appropriate water for beneficial consumptive use--with some inevitable decrease in quality--and decrees that "first in time is first in right." International water law, however, generally follows the doctrine of riparian rights. Downstream users have the right to receive water that has not been degraded by upstream users. Faced with these conflicting legal theories, and convinced by the late 1960s of the need to reach an accommodation with Mexico, U.S. interests devised a new theory: that of "equivalent salt balance." An irrigation system in salt balance returns the same amount of salt in its drainage waters as was applied to the land. Salt neither accumulates in nor is leached from its soil. Proponents of the equivalent salt balance theory recommended that the U.S. substitute for Wellton-Mohawk drainage a quantity of higher-quality water sufficient to reduce the differential in salinity between Imperial and Morelos Dams to that which Mexico would experience if the project were in salt balance--about 280 ppm. As excess salts were gradually leached from the soils of Well ton-Mohawk , the amount of substitution water needed would decrease. Once the project reached salt balance, in the early 1980s, substitution for drain flows would no longer be necessary. 3