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. . . -7- The 11 ppm reduction effected by United States operations in the 5th year was the resul t of: a) Reductions in salinity of return flows below Imperial Dam. (1) From the Well ton-Mohawk Irrigation and Drainage District due to decrease in salinity concentration of drainage waters from about 4130 ppm to 3790 ppm. (2) From the South Gila Valley due to decreases of 90 ppm in concentration and 3,000 acre-feet in the drainage waters pumped from that valley; and b) An increase in the average salinity of Colorado River waters at Imperial Dam of 22 ppm. There was a reduction in the salinity of the waters diverted by Mexico from the 4th year of 45 ppm due to Mexican voluntary operations - an increase of 25,700 acre- feet in the volume of Wellton-Mohawk drainage by-passed by Mexico during the 5th year, in addition to Minute No. 218 operations by the United States. 7. Summary of 5 Years of Operations During the 5-year period of operations under Minute No. 218: a) The average annual salinity of waters delivered to Mexico at the northerly boundary under United States operations of Minute No. 218 reduced from 1375 ppm in 1965 to 1280 ppm in 1970, an average of about 19 ppm per year. As a resul t of Mexican voluntary operations, the by-passing of additional Well ton-Mohawk drainage waters during the 5-year period, the average annual salinity of waters diverted by Mexico at Morelos Dam reduced from 1375 ppm in 1965 to 1139 ppm in 1970. b) The average annual salinity of the total annual quantity of Well ton- Mohawk drainage waters in the conveyance channel (above the first point of return to the river) reduced from 4870 ppm in 1965 to 3790 ppm in 1970, an average of 216 ppm per year. c) The average annual salinity of the total annual quantity of South Gila drainage waters discharged to the river channel reduced from 2510 ppm in 1965 to 2420 ppm in 1970, an average of 18 ppm per year.