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. 002899 . streams. During the Spring runoff study when suspended solids concentrations were relatively high, the calcium and magnesium concentrations together were not equal to the total hardness determined in the field by EDTA titration (see Table 3). The higher hardness values obtained by titration are likely due to the presence of sign i fi cant concentrati ons of the other hardness- producing metals (especially iron) associated with the suspended solids. This explanation is especially plausible since no inhibitors were used in the EDTA titration procedure. . . Alkalinity Alkalinity is a measurement of the buffering capacity of the carbonate- bicarbonate system present in surface waters. It is important that sufficient alkalinity exist in streams to prevent wide fluctuations in pH which may be harmful to the aquatic environment. Stream measurements indicated a widespread range of total alkalinity concentrations as CaC03, ranging from 40 mg/l near the headwaters to 175 mg/l near Rangely, Colorado (see the profiles in Fig. 7). Alkalinity measurements were generally highest during the "low flow" period. The lower Milk Creek station (MC-20) exhibited an average alkalinity concentration of 331 mg/l as CaC03, while Yellow Creek (YC-3) contained an average alkalinity of more than 1500 mg/l as CaC03 during each study. period. . . Salinity High salinity (TDS) concentrations may produce adverse effects in drinking water supplies and in irrigated crops. A large effort is currently underway by the Colorado River Basin Salinity Forum (1975) to mitigate these impacts by reducing salinity in the Colorado River basin, including the White River. As shown in Fig. 8 the White River in its lower reaches becomes a significant carrier of salinity, a fact shown most clearly by the salinity increases measured during "low flow". At that time (Fan, 1975) the salinity near the headwaters averaged 123 mg/l, while in the 200 km (125 mil reach downstream to Rangely this concentration increased by more than four times to 557 mg/l. Mean TDS concentrations exceeded the criteria of 500 mg/l in the White River near Rangely (RM 78.2), and in Yellow Creek, Little Beaver Creek, Mi 11 er Creek, Big Beaver Creek, and Mil k Creek. The greatest incremental increase in salinity concentrations in the White River (80%) occurred in the 38.8 km (24.1 mil reach between Buford (WR-ll) and Meeker (WR-6), which includes the tributaries Miller Creek and Coal Creek/Little Beaver Creek. This stream reach also includes the tributaries Curtis Creek and Flag Creek (which were not sampled), and the 'iMeeker Dome" area which has been previously documented as a significant source of highly-sal ine groundwater and surface runoff (EPA, 1972). Unfortunately, the scope of the present study did not allow an intensive investigation of the non-point sources of salinity in this area. The data from the Fall "low flow" study does show, however, that only approximately 50% of the increase in salinity load in the White River between stations WR-ll and WR-6 (58 metric tons per day) could be attributed to tributary loads (excluding Flag Creek, which was not sampled, and Curtis Creek, which . . . . 25 . 'il,,)