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<br />The determination of the soluble mineral conta~t of surfi~ial soils <br />is highly dependent upon the sampling and analytical methods used. The <br />effects of contact time and sediment-to-water ratios on rate and extent of <br />dissolution are extremely important. Since much of the salt is dependent upon <br />sediment load, contact time and sediment to water ratio must be considered. <br />Laronne [22J recommends a sediment to water ratio of 1 to 99. This ratio <br />allows for greater dissolution of salts and a better estimate of salinity <br />~ being contributed from erosion. <br /> <br />c.o <br />-.J <br />-l <br /> <br />Geochemistry <br /> <br />8. <br /> <br />Dissolution of efflorescence on the surface or minerals in <br />subsurface formations is a major source of salinity. Rllnoff from snowmelt and <br />thunderstorms, which causes alluvial, bank, and gully erosion, suspends solids <br />from barren marine shales. The increased concentrations of calcium, <br />magnesium, and sulfate in these waters are dlle to dissolution of gypsum <br />(calcium sulfate) and dolomite (calcium or magnesium carbonate). Much of the <br />sodium is contributed by exchange of calcium for sodium on clays found in <br />saline marine shales. <br /> <br />Point sources of salinity contribute chemical constituents that <br />reflect the mineralogy and the chemical reactions which occur in tIle rock <br />formations through which the ground waters flow. Natural springs are compo~ed <br />of waters whose subsurface flow paths are often deep, and movement of the <br />water is relatively slow. Therefore, salinity can be very high, often <br />exceeding 10,00U mg/L. Such spring waters vary in composition in the Basin. <br />The waters of highest salinity are of sodium chloride character due to highly <br />soluble halite. Other springs are high in concentrations of calcium and <br />sulfate due to contact with gypsum (hydrated calcium sulfate). <br /> <br />The water quality of many seeps throughout the Colorado River Ba~in <br />often reflects relatively shallow geology and mineralogy. Sodium, calcium, <br />and sulfate concentrations can be fairly high (4,000 to 10,000 mg/L). The <br />chemical makeup is due to a variety of reactions, including dissollltion of <br />gypsum, partial reprecipitation of carbonate minerals, and adsorption of <br />calcium- onto clays that have high amounts of exchangeable sodium and <br />magnesium. <br /> <br />Due to the extremely hot and and conditions throughout till:! Basin, <br />extensive evaporation can cause salinity of the surface waters to increase <br />greatly. Under such conditions, carbonate and hydrated sulfate minerals can <br />predpita te out along the streambeds. These characteristically whi te and <br />often fluffy minerals are highly soluble. A snowmelt or rainstorm event can <br />quickly flush these minerals back into the water, causing a temporary but <br />large increase in salinity. <br /> <br />An intensive water and sediment sampling study [23] was performed <br />in the Dirty Devil River Basin. Results of this study show that little <br />add(tional salt loading would occur due to dissolution of sediments. This <br />conclusion was supported by extensive chemical analysis which showed that most <br />minerals present in the channel sediments were relatively stable with regard <br />to extensive dissolution in this environment. <br /> <br />V-8 <br />