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Water Quality 21 maximum discharge and is an indication of dilution of surface water with snowmelt. Maximum values occurred during late winter and early spring before the onset of snowmelt. Dissolved-oxygen concentrations in the Fraser River at Tabemash ranged from 8.0 to 11.5 mg/L, with a median of 9.6 mg/L (table 4). Dissolved-oxygen concentrations were inversely related to stream temperature, which is a primary factor controlling the solubility of oxygen in water. The State of Colorado instream water-quality standard for dissolved-oxygen concentration in the Fraser River is 6.0 mg/L except during periods of fish spawning when the standard is raised to 7.0 mg/L (table 4) (Colorado Department of Public Health and Environment, 2002). No dissolved-oxygen concentrations mea- sured during this study were less than the standard. Values for pH in the Fraser River ranged from 7.8 to 8.6 (table 4). All measurements were within the State instream water-quality standard of 6.5-9.0 (Colorado Department of Public Health and Environment, 2002). Dissolved Solids, Major Ions, and Trace Elements The concentrations of dissolved solids in the Fraser River were low, ranging from 53 to 93 mg/L (table 4). These concen- trations reflected the high quality of the surface water and indicate the suitability of the water for drinking, residential, industrial, and irrigation purposes. The surface water was a calcium-bicarbonate type water throughout the study period (fig. 4). Samples from 10 of 11 ground-water wells were the same type water. During most of the year, the surface water primarily is base flow from ground-water discharge. The following discussion will only focus on the major ions chloride and sulfate and the trace ele- O Z w Q W J l- ZOc LL w !L 0OQ W = = > U J O ments iron and manganese, all of which have State of Colorado instream water-quality standards. Chloride concentrations overall were low (less than or equal to 9.0 mg/L.) in the Fraser River at Tabernash (table 4). Maximum concentrations typically occurred during late winter or early spring just prior to peak flow resulting from spring snowmelt. Minimum concentrations occurred during snowmelt runoff (fig. 9). It is likely that chloride in the river comes from nonpoint sources, including salt and gravel applications during winter, and discharges from wastewater-treatment facilities. All chloride concentrations were substantially below the State instream standard of 250 mg/L (Colorado Department of Public Health and Environment, 2002). Sulfate concentrations also were low (less than or equal to 4.5 mg/L) in the river. Like chloride, maximum concentrations of sulfate typically occurred during late winter or early spring just prior to peak flow resulting from spring snowmelt; mini- mum concentrations occurred after snowmelt runoff in mid- summer (fig. 9). All sulfate concentrations were substantially below the State instream standard of 250 mg/L (Colorado Department of Public Health and Environment, 2002). Iron concentrations were relatively high at the site, ranging from 73 to 354 µg/L, with a median concentration of 198 µg/L, (table 4). The elevated iron concentrations may be related to discharges of iron-rich ground water to the river in the vicinity of Tabernash. A large amount of variability in the iron concen- trations was present over the sampling period, but no seasonal patterns were discernible. The State chronic instream iron stan- dard of 300 Itg/L for the Fraser River site was exceeded in 1 of 19 samples (Colorado Department of Public Health and Envi- ronment, 2002). For trace elements such as iron and manganese, compliance with the State instream standard is met if the con- centration of the 85th percentile of all representative data is less 12 o- Dissolved sulfate Dissolved chloride 10 Discharge s A 6 / 4 / /A- I 2 V 00 00 m Cr) O O O O O O ? ? ? ? ? ? O O O O O O O O O O O O O O O O O O O O OD N In W N In 00 N 0 00 O ? O O O ? O O O ? O O O TIME 300 250 U 0 mZ UO 200 Z w -U) w 150 (D LU Q ? 2 100 LL 50 Figure 9. Dissolved sulfate and chloride concentrations and discharge atthe Fraser River below Crooked Creek at Tabernash, Colorado, 1998-2001.