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N o c.D -.J Research and Technology~-OWRT) have been engaged in an tntensive testing program. on the Wellton-Mohawk drain. A test facility, built mostl,y from materials salvaged from OWRTinstallations being closed out, is now being used to ~ther information on the quality of the drain, test pretreatment systems and permit prospective equipment bidders to test their equipment on actual Wellton-Mohawk drain \~ter. This should result in better bids and a more trouble-free plant. A "Preliminary Engineering Design Report" has just been completed by . Burns and Roe, a prominent architect-engineer firm, under contract to OWRT. The report is currently being reviewed by the Bureau and OWRT and will be used as the basis for the final design. We are also busil,y en~ged in the collection of field data, foundation studies of the proposed desalting plant site, alinement and surveys for the new section of the Coachella Canal and the extension of the bypass channel to the Arizona-Sonora boundary. A public hearing on the Draft Environmental statement lias held in Yuma., A:dzona, on October 5, and we are addressing the points raised. at the hearing and other comments received by mail. We hope to file the Final Environmental Statement with the Council on Envirorunental Quality sometime in February. After the requisite 30-day waiting periOd, barring unforeseen delays, we will issue the first invitation for bids for the construction of a concrete siphon to replace the existing metal flume near Yuma.. i" , Negotiations for contract modifications, land acquisitions, and other ' matters are proceeding with the Wellton-Mohawk Irri~tion and Drainage District, .... . the Imperial Irri~tion District, and the Coachella Valley County Water District:' ~ The one feature of the project that has stimulated the greatest interest is the approx:l.ma.tely lOO-mgd desalting plant. Questions have been raised re~rding the processes contemplated, the problems associated with scale-up, its reliability, etc. I think it is proper to address some of those questions here. ) Let's see if we can't put things into perspective. When construction of 726-foot-high Hoover Dam was authorized in 1928, the highest dam in the world was Arrowrock Dam on the Boise River at 349 feet. In 1933, before Hoover Dam was completed, 4l7-foot-high OWyhee Dam on the OWyhee River was completed. Comparing this to the situation existing in desalting, we see that the largest membrane desalting plant existing today is the 3 mgd plant at Foss Reservoir in Oklahoma.. Thus, we can see that the desalting plant will be about 35 tiIDes bigger than the biggest existing plant. ~ But the comparison isn't totally valid. Membrane desalting plants are built up by combining a large number of standard size modules and if the modules have been proven, then the problems are those of plumbing, flow control, instrumentation, ease of replacements, etc. These are vexing problems, but not . insurmountable. Useful information is being provided by such well-designed pla.nt~ as the .8 mgd electrodialysis plant at Sanibel Island and the .5 mgd reverse ~. osmosis plant at Rotunda Beach, both in Florida, and of course by the testing L 5 ,',,-,