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Show * l CEA Report Environmental SALINITY THE COLORADO RIVER is naturally more saline than most rivers in the United States due to the geologic history of the region. Many of the sedimentary formations in the area were created when inland seas flooded the region, leaving salt deposits behind as the plateau uplifted and the seas regressed and evaporated. As rainwater and snowmelt run over these sedimentary rocks, salts are dissolved out and transported to the river. The EPA estimates that the natural salinity level in the lower basin was 334 parts per million ( PPM). Development of the river as a water resource has dramatically increased salinity levels. Evaporation from the surface of the many reservoirs along the Colorado River contributes about 12% of the salinity level. High salinity levels have important legal, economic and ecological ramifications. • Evaporation from the surface of reservoirs increases the salinity of the water because when the water evaporates, the salts are left behind. Irrigation for agriculture increases salinity because diverted water leaches salt out of saline soils and then delivers it to the river through groundwater flow. High salinity levels have an economic impact on water users due to damage to household appliances and automobile cooling systems, decreased cleaning efficiency, reduced crop yields, and increased need for desaliniza- tion to meet US water obligations to Mexico. The increase in salinity, due to Powell reservoir alone, costs water users over $ 25 million annually. 3,5 Evaporation from Powell reservoir increases salinity by 26.5 PPM each year. 4' 5 Although there have been no studies documenting environmental impacts of salinity upon species in the Colorado River, increasing salinity levels will eventually cause environmental degradation. 800 200 Pre- dam level 1972 IW salirijfy( ppm) 1995 Figure 4 Salinity levels at Imperial Dam. Pre- dam salinity as estimated by the EPA. page 7 |