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PART V HISTORICAL AND PRESENT SALINITY CONDITIONS e Powerplants and new industries are no longer allowed to dis- charge 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. ~. Potential New Sources of Salt Loading e 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 for- mations. Many of the sediments deposited in drier periods are capable of transmitting water, but these aquifers are frequently sandwiched be- tween hundreds or even thousands of feet of impermeable shales (aqui- cludes). These aquifers are, therefore, static and often saline. Many static and saline aquifers are present in the Colorado River Basin. Drilling and mining activities can disrupt aquicludes and mobilize these saline static aquifers. 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. Some States have enacted drilling and ground water laws to protect water quality. In the Colorado River Basin, ground water laws and strict enforcement are essential to prevent further saline aquifer movement and salt loading. Many small saline ground water springs and/ or flowing wells that probably are linked to drilling activities have been identified in the basin and listed in previous progress reports. Seismograph drilling activities may he particularly disruptive to shallow ground water systems, and stricter regulation and enforcement should be considered. The Meeker Dome Salinity Project described in Part VII is one area where Reclamation has plugged abandoned oil exploration drilling holes anticipating that the aquifers are static and the saline water would not find another path back to the surface. 6. Method of Chemical Analysis e It has been found that water samples high in calcium sulfate salts retain water when evaporated at 1800 C and thus yield high TDS results. TDS was changed from a measurement of 1800 C residue to the sum of ionic constituents for some of the USGS records used in past reports. Since the Colorado River waters are high in sulfates, this may have 27