Snake, Yakima and other tributaries, has a 

 usage factor only half that of the Snake 

 River because of the high flow rate in the 

 Columbia. The Yakima River at Cle Elum has 

 a very low usage factor because of the low 

 watershed occupancy. Large increases in 

 usage factors between 1910 and 1950 are 

 accompanied by marked increases in the con- 

 stituents of the water. 



Prediction of Constituents 

 in Year 20051 



Table 36 lists the predicted water 

 quality constituents in the year 2000, ob- 

 tained by relating the change in the water- 

 shed usage factor between 1910 and 1950 with 

 the change in the constituents during that 

 period. By direct proportion, tliis consti- 

 tuent was then projected to the year 2000 

 by the change in the usage factor between 

 1950 and 2000. It should be stressed that 

 these predictions are gross approximations 

 and that past changes in water qiiality may 

 not necessarily be reflected in like future 

 changes. With the increased use of complex 

 chemical substances in industry, the house- 

 hold and in agriculture, substances will be 

 added to the streams not now present, or 

 present now in minute quantities. 



Table 36 lists predictions only on 

 those substances where sufficient background 

 data are available for a prediction. Not 

 shown are such constituents of quality as 

 pH, temperature, boron, fluoride, specific 

 conductance, carbon dioxide, ammonia, dis- 

 solved oxygen and the trace elements like 

 copper and aluminum. Dissolved oxygen 

 changes are discussed elsewhere in this 

 report. PH values rise with increasing 

 quantities of irrigation retiirn flow. In 

 the future it can be expected that the pH 

 values in the water will be 0.1 to 0.3 

 higher than in 1955. Carbon dioxide (where 

 the pH is less than 8) and ammonia should 

 more than double in the futiire as organic 

 matter in the rivers undergoes decomposition. 

 Trace elements should show a marked increase 

 with the advent of more metal and chemical 

 industries and the use of more pesticides 

 and weed killers. 



The estimated future water quality 

 characteristics in table 36 all arpear quite 

 reasonable excepting for total solids and 

 iron in the Columbia River at Pasco and 

 iron in the Wenatchee River. Estimated 

 values for the Columbia River at Pasco, the 



Wenatchee and Okanogan Rivers are subject 

 to more question than the ottiers since the 

 data for these river estimates are more 

 limited than it is on the other locations. 

 Since these are yearly weighted average 

 values, it can be expected that during the 

 late summer and autwnn (when stream flows 

 are low, irrigation returns are large and 

 food industry waste discharges are great) 

 most of the values shov;n in table 36 will 

 be exceeded by 10 to 100 percent. Applying 

 the "Watershed Usage Factors" to the differ- 

 ences in the maxim.tim monthly water quality 

 values shovin in tlie tables on 'Vater Quality 

 Comparisons", estimated maximum future con- 

 stituent values are obtained and given in 

 table 37. These maximum values for each 

 constituent at a particular location vjill 

 not all be of maximum value during the same 

 time period. Time periods of maximum con- 

 centrations should not exceed one month in 

 dtu"ation. In computing these future consti- 

 tuent concentrations, it was assumed that 

 there would be no future change in river 

 flows. If river discharges are increased 

 during the summer and autunn through con- 

 struction of increased iirpoundments, these 

 constituent values will be decreased through 

 dilution. The most accurate method of pre- 

 dicting future water quality would be on a 

 weight basis, taking stream discharge into 

 accoTint. This is not possible throughout 

 the Basin because of limited past and future 

 discharge data. 



Hydrogen ion (pH) and carbonate alka- 

 linity values will be high in several loca- 

 tions during the summer or autumn. From a 

 study of present values, it is predicted 

 that future pH and carbonate alkalinity 

 values can be expected to reach or exceed 

 the following magnitudes during a month or 

 so at the following locations: 



Instifficient data and studies are 

 available to make a reasonably reliable 



99 



