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<br />~ e , .... <br /> <br />. <br /> <br />c <br />" <br />co <br /> <br />.' <br /> <br />. <br /> <br />EVALUATIONS OF EXISTING SALINITY CONDITIONS (continued) <br /> <br />The type of data obtained and the purpose of the sampl ing vary with <br />each stat ion. Many of the stat ions provide data for the Water Quality Im- <br />provement Program in Part VIII and special studies described in Part X. <br /> <br />8. Methods of Chemical Analyses <br /> <br />Published quality of water records consist of a combination of stream <br />discharges with chemical analyses of stream water samples collected at more <br />or less regular intervals. The reliability of the records depends on the <br />accuracy of the streamfLow records, the frequency of collection and repre- <br />sentativeness of the samples, the stability of the samples during the <br />storage periods prior to making of the analyses, and the completeness and <br />accuracy of the individual analyses. <br /> <br />Most of the chemical analyses of water samples wh ich provided the <br />water qualUy data were made in the laboratories of the Geological Survey <br />at Washington, DC, Albuquerque, New Mexico, and Salt Lake City, Utah, using <br />standard procedures by chemists specifically trained in water analysis. <br />Geological Survey analyses are now made only at the U.S. Geological Survey <br />National Water Quality Laboratory in Denver, Colorado. During the 38-year <br />period considered there were several changes in laboratory techniques and <br />procedures m0stly due to the introduction of new instrumental methods. New <br />procedures were adopted only after careful invest igat ion to insure results <br />consistent with those obtained previously. Some of the quality of water <br />records are based on analys is of samples by Water and Power Resoul-ces <br />Service laboratories. Water and Power Resources Service results and <br />methods have been checked by the Geological Survey to insure comparable <br />records. It is probable that errors in the load computations due to errors <br />in chemical analysis are less than those due to changes in the samples upon <br />storage, inaccuracies in sampling, or inaccuracies in the determination" of <br />stream discharges. <br /> <br />Prior to about 1970 the Geological Survey analyzed water qual ity on <br />a composite sample basis and also determined and published tile annual total <br />dissolved-solids loads. Since that time the results of the analysis in the <br />Colorado River Basin have been those of individual samples rather than <br />composites and no totals for the year have been computed. At present, <br />individual samples are taken and analyzed about once a month together with <br />daily conductivities. The annual total dissolved-solids loads since this <br />change, have been determined from daily conductivities applied to curves <br />and correlation factors relating conductivities and total dissolved-solids <br />concentrations. <br /> <br />C. Historic Conditions <br /> <br />1. Total Dissolved-Solids Concentrations <br /> <br />Historic streamfLows, salinity concentrations, and salt-load data for <br />the 20 key stations for the 1941-78 period of record are presented in <br /> <br />42 <br />