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<':Iii. .' . . . , . , .' _.G, ~ """'" --J 00 SECTION I INTRODUCTION The primary water quality problem in the Colorado River Basin (Fig. 1) is ""S<l.1inity. This concern tends to be so dominant that it overshadows most other water "quality consideraUona. Fortunately, theaalt .pollution of the Colorado .River by either man-made or natural depletions and/or discharges is not a . general health hazard. Salinity is basically an economic problem in which a progressive build-up in concentration toward ~he lower reaches causes a reduc- tion of the water's utility to urban and agricultural users. Salinity increases in the Colorado River are not a recent phenomenon. Salinity has been increasing as a result of all water reSource development projects since the 1800's when some degree of salt concentration due to irri- gation was tolerated as the price for development (Law and Skogerboe, 1972). Salinity levels also fluctuate with natural weathering and runoff processes. The Colorado River and its tributaries travel more than 2,300 kID from the headwaterszin the Rocky Mountains to the Gulf of California and drain about 6ZZ,OOO kID in seven states. The drainage area is approximately one-twelfth of the area of the conterminous United States. The annual total salt burden is about 10 million Megagrams (Mgm). Concentrations of salinity in the Colorado River range from less than 50 mg/l in the high mountain headwaters to more than 85D mg/l at Imperial Dam. Further deterioration of Colorado River quality is expected as a result of water and energy resource development. This will occur even if salinity reduction measures are instituted although it would occur at a slower rate. If no salinity control measures are developed, it is anticipated that salinity increases at Imperial Dam will range from 1,150 mg/l (USDI, BR, 1979a) to 1,340 mg/l (Colorado River Board of California, 1970) by the year ZOllO. All of the salinity control planning which has been done to date has .been oriented toward only reducing the salt load of the Colorado River. The eco- nomics of control have not been of overriding concern. Furthermore, develop- ment of cost-effective programs or the construction of projec~s with benefit- cost ratios greater than one has not been high priority even though costs have. been compared to estimated annual damages at Imperial- Dam. The argume~t presented in favor of the non-economic approach is that. Congress (PL 93-3Z0) mandated certain projects and that these projects would include specific construction items such as canal linings. However, since that legislation was passed the results of numerous invest~6ations have be~ome available which permit the formulation of cost-effective salinitycc>ntrol programs. 1 :, -..~ ~ '