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o w W 1'..;J BASIC STUDIES Quality data for the period January 1941 to 1943 were obtained from the U.S. Department of Agriculture salinity laboratory at Riverside, Cal- ifornia, and the remainder, 1943 to 1964, were obtained from U.S. Geolog- ical Survey Water Supply Papers and provisional records and are based on data for the Yuma Main Canal below the Colorado River siphon (Table No. 17). C. Anal.yses Published quality of water records consist of a combination of stream discharges with chemical anlayses of stream water samples collected at more or less regular intervals. The reliability of the recards depends on the accuracy of the streamflow records, the frequency of collection and repre- sentativeness of the samples, the stability of the samples during the stor- age periods prior to the making of the analyses, the completeness and ac- curacy of the individual analyses, and the manner in which the individual samples are combined before analysis to represent increments of stream discharge. Most of the water analyses forming the basic data for the chemical records in this report were made in the laboratories of the Geological Survey at Washington, D.C., Albuquerque, New Mexico, and Salt Lake City, Utah, using standard procedures, by chemists specifically trained in water analysis. During the 24-year period cansidered there were numerous changes in laboratory techniques and procedures, mostly due to introduc- tion of new instrumental methods. New procedures were adopted only after careful investigation to insure results consistent with those obtained previously. Some of the quality of water records are based on analysis of samples by Bureau of Reclamation laboratories. Bureau of Reclamation results and methods have been checked by the Geological Survey to insure comparable records. Analyses by the Metropolitan Water District have been made by standarized procedures and appear to be comparable with analyses by the Geological Survey. It is probable that errors in the load computations due to errors in the analyses are less than those due to changes in the samples upon storage, inaccuracies in sampling, or inaccuracies in the determination of stream dis~harges. D. Studies of Certain Areas Special quality of water studies have been made in a number of irri- gated areas to determine storage and irrigation effects on water quality. Sufficient quality data have been collected qy the Bureau of Reclamation in two of these areas to indicate trends. 1. Eden Pro.iect Quality of water data were collected in the Eden Project area before the Colorado River Storage Project Act was passed in 1956. Data are 23