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w ~ ~".. ~ . The bulk of the field-oriented research on diffuse-source salinity has been performed by three groups. 1) the Utah State uni'versity group in the Price River drainage (the western area); 2) the U.S. Geological Survey in the badlands of 8adger Wash, and 3) the Colorado State University group in the area between Grand Junction and West Salt Creek (Fig. 3.1), which includes the Badger Wash drainage basin (the eastern area) . Definitions Natural sources of salinity are either diffuse or point sources. Saline point sources are associated with a specific site such as a spring or seep as well as saline effluents of urban, industrial and agricultural origin. Diffuse-sources in contrast (Chilingar, 1956, Gorham, 1961), and salinity results from exposure and erosion of saline rocks or soils. There should be many point sources within a diffuse- source area. Salinity may be defined as the total quantity of inorganic soluble constituents residing within an aqueous solution. As such, it is often termed total dissolved solids (TDS). Salinity (solute concentration or SC) is customarily expressed in mg/l or ppm, or in units of specific electrical conductance most commonly at a reference temperature of 25 DC. Electrical conductance (EC) has been widely used to determine salinity because solutes are primarily charged particles, and the total positive or negative charge correlates highly with salinity (SC). il 'I ~ ~ . I SC = k EC (1-l) 'I where SC and EC are given in mg/l and ~mho/cm, respectively, and k is a constant ranging from 0.55 to 0.65 unless the solution has an unusual composition (Hem, 1970). Solute load (SL) is defined as the weight of solutes discharged per unit time. It is equal to the product of SC and water discharge (Q). . I 1 ,I SL = (SC)Q (1-2) "I 1 The unit of Q is expressed as weight per time when SC ppm, and it is expressed as volume per time when SC is expressed in is expressed in I ~ 1 2 ,