| OCR Text |
Show WATER QUALITY Regionally, water quality as expressed by total dissolved solids (TDS) concentrations is generally of lower quality than in many other parts of the Nation, The Colorado River enters the Region at concen- trations exceeding 500 mg/l and varies between 600 and 900 mg/l at major diversion points within the Region. Salinity increases in the Colorado River are due principally to inputs from saline springs and the concentrating effects of consumptive use and surface evaporation from reservoir and river water surfaces. In the headwaters of the Gila, TDS concentrations are generally less than 500 mg/l; and, in the middle reaches, the dissolved salt content usually ranges from about 500 to 1,000 mg/l. Water quality is generally good in most of the headwaters of the Little Colorado River but at its confluence with the Colorado River, it contains very high concentrations of dissolved solids from saline springs located near its mouth. The Colorado River has a hardness (as calcium carbonate) varying from about 330 mg/l at Lee Ferry, Arizona, to about 370 mg/l at Imperial Dam. Downstream at Yuma, Arizona, the hardness increases to 700 mg/l. Although fluoride content ranges from a trace to about k or 5 mg/l> it is normally about 1 mg/l or less in most water of the Region. Sediment concentrations in surface water of the Region range from very high to moderate. The areas of greatest sediment yield are located in northwestern Arizona and southwestern Utah where sediment concentrations as great as 700,000 parts per million have been measured and 500,000 ppm observations are not unusual. Nutrients from manmade sources have caused excessive algal growttis in Las Vegas Bay of Lake Mead, and in isolated cases, bacterial concen- trations have exceeded desirable levels in streams below smaller com- munities. Occasional overflows and breaks in mining waste disposal systems have resulted in fish kills. The mineral quality of ground water ranges from excellent to unsuit- able for any purpose, containing from less than 100 to more than 100,000 mg/l of dissolved solids. Major sandstone aquifers in the Plateau Uplands of northern Arizona contain water having consistently more than 10,000 mg/l dissolved solids. The ground water ranges from soft to very hard, from less than 60 mg/l to more than 180 mg/l of calcium carbonate. Tlie concentrations of the minor constituents such as iron, magnesium, and silica vary considerably throughout the Region; but, except for fluoride and nitrate, the concentrations are not objectionable for most uses. Boron concentrations of O.U mg/l have been observed in the Colorado River at Imperial Dam. |
