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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Q <br />~ <br />~ <br />~ <br /> <br />SECTION 1 <br />INTRODUCTION <br /> <br />The primary water quality problem in the Colorado River <br />Basin (Fig. 1) is salinity. This concern tends to be so <br />dominant that it overshadows most other water quality con- <br />siderations. Fortunately, the salt pollution of the Colorado <br />River by either man-made or natural depletions and/or dis- <br />charges is not a general health hazard. Salinity is basi- <br />cally an economic problem in which a progressive build-up in <br />concentration toward the lower reaches causes a reduction of <br />the water's utility to urban and agricultural users. <br />Salinity increases in the Colorado River are not a <br />recent phenomenon. Salinity has been increasing as a <br />result of all water resource development projects since the <br />lBOO's when some degree of salt concentration due to irri- <br />gation was tolerated as the price for development (Law and <br />Skogerboe,1972). Salinity levels also fluctuate with <br />natural weathering and runoff processes. The Colorado River <br />and its tributaries travel more than 2,300 km from the <br />headwaters in the Rocky Mountains to the Gulf of California <br />and drain about 622,000 krn2 in seven states. The drainage <br />area is approximately one-twelfth of the area of the con- <br />terminous United States. The annual total salt burden is <br />about 10 million Megagrams (Mgm). <br />Concentrations of salinity in the Colorado River range <br />from less than 50 mg/l in the high mountain headwaters to <br />