7641 - Laserfiche WebLink

Home Browse Search

diversions and increased reservoir evaporation account for most of the increased depletions from 1960-80; however, no additional salt pickup or loading occurred with these depletions. The large quantities of water expected to be depleted for steam power generation, coal gasification, oil shale, and mineral development have not been realized in the past decade. Even where new coal-fired powerplants have been constructed, some of the water has been obtained from existing agricultural rights. While water uses have often changed, the total depletions have increased only slightly. In cases where powerplant water was obtained from existing agricultural supplies, salt pickup may have been reduced since irrigated lands in areas of coal deposits are often saline soils of Mancos Shale origin. Powerplants and new industries are no longer allowed to discharge saline cooling tower blowdown waters back to the river. This total containment policy resulted in some decreased salt loading during the 1970's. Leakage from evaporation ponds and other disposal methods may eventually allow some of these salts to reenter the river. 4. Reduced Flood Plains The reservoirs have also significantly reduced the peak flood flows downstream. The consequent reductions in the downstream flood plains result in decreased bank storage and possibly reduced salt flushing. At least temporarily, the area between the old and new flood plains may act as a salt sink, but the long-term salinity effects of the changes in the flood plains are not known. 5. Energy Exploration and Development Many of the geologic formations of the Colorado River Basin were deposited in marine (salt water) or brackish water environments. Sulfates and sodium chloride are prevalent salts in most of these formations. Many of the sediments deposited in drier periods are capable of transmitting water, but these aquifers are frequently sandwiched between hundreds or even thousands of feet of impermeable shales (aquicludes). These aquifers are, therefore, static and often saline. Many static and saline aquifers are present in the Colorado River Basin. When a path of flow is provided by drilling or mining, these aquifers are mobilized, and brackish or saline waters flow back to the surface. The development of energy resources, specifically coal, oil and gas, and oil shale, in the Colorado River Basin may contribute significant quantities of salt to the Colorado River. Salinity can be increased either by dissolution of minerals or consumption of good quality water. The location of fossil fuels are associated with marine derived formations. Any disturbance of the saline materials will increase the contact surfaces allowing for the dissolutions of previously unavailable soluble minerals. Salinity increases associated with the mining of coal can be attributed to leaching of coal spoil materials, discharge of saline ground waters, and increased sediment yields resulting from surface disturbing activities. Spoil materials have a greater permeability than undisturbed overburden, allowing most of the precipitation falling on the spoils to ~5