Water Quality Management Studies for Water Resources Development in the Bear River Basin

Summary: The quality of water that develops in the proposed reservoirs of the Upper Bear River Storage Project will determine the possible uses of the water. Previous studies of water quality in the Bear River and its tributaries have reported water quality problems relating to nitrate ion, sanitary indicator bacteria, suspended solids, and phosphorus concentrations. Most point sources of water pollution inthe basin have been eliminated or improved in quality, but nonpoint sources of pollution continue to degrade the quality of the Bear River. Concentrations of phosphours have been sufficiently high to encourage dense algal growth and create eutrophic conditions in the proposed impoundments where other factors were not limiting. The present study intended to investigate these problems relative to the potential use of impounded water for municipal and industrial purposes. Past water quality information for the study area of the Bear River basin was reviewed including analysis of 208 areawide planning data and STORET data accumulated by the Utah Bureau of Water Pollution Control since 1977. Salinity components were found to be the major factors describing water quality in the Bear River, but nutrients and microbial pollution indicators were also very important. Nitrate concentrations were not found to have approached the 10 mg N*l^-1 standard in the historical data reviewed. Thirteen monthly water quality sampling and analyses were performed from 15 locations on the Bear River and its tributaries beginning above Oneida Reservoir, Idaho, and extending to the interstate highway bridge near Honeyville, Utah. These data indicate that the Cub River continues to be an important source of nutrients and microbiological pollution to the Bear River. The lower reaches of the Little Bear River occasionally accumulate undesirable concentrations of biochemical oxygen demand, nutrients, and fecal indicator bacteria. Increases in suspended solids and phosphorus loads in the Bear River and its tributaries were observed during spring snowmelt and runoff. Weston Creek, Fivemile Creek, and Deep Creek carried exceptionally high suspended solids and phosphorus loads during this time. A major increase in total phosphorus and orthophosphorus in the Bear River below the confluences of these streams was observed. Landsliding and erosion in the watersheds of these streams probably contribute substantially to their phosphorus and sediment loads. A water temperature model, empirical trophic state models, and a computerized reservoir eutrophical model (RESEN) were used to simulate the eutrophication potential of the proposed reservoirs. Since turbidity is expected to decrease over the length of the reservoirs allowing more light energy for photosynthesis, and since ample phosphorus will be available, the proposed Amalga Reservoir is likely to be eutrophic near the dam and in the Cub River branch. Similarly, the proposed Honeyville Reservoir is likely to be eutrophic near the dam and pools of anoxic water may develop below the thermocline. High populations of zooplankton could reduce summertime algal populations in the Honeyville Reservoir of mesotrophic to eutrophic conditions. Zooplankton grazing has been observed to substantially reduce algal populations in the existing Hyrum Reservoir on the Little Bear River. The proposed Lower Oneida Reservoir in Idaho will probably not thermally stratify, but will have a temperature regime similar to the existing Oneidea Reservoir and remain essentially completely mixed throughout the year. The depth of mixing of the water column is expected to limit algal grwoth and maintain this reservoir in an oligotrophic condition. The proposed Mill Creek and Avon Reservoirs on the Blacksmith Fork and Little Bear Rivers, respectively, will probably produce spring and fall algal blooms of mesotrophic to eutrophic proportions. Strong thermal stratification of these reservoirs in the late spring will isolate the epilimnion from phosphorus sources. Available phosphorus in the epilimnion will be exhausted through algal growth and settling, and phosphourus in the photic zone will not be replaced until destratification occurs in the fall. Reservoirs may remove phosphours from streams by trapping sediment and converting soluble phosphorus to algae or other plants that are retained in the reservoir. Lower phosphorus concentrations in the stream then result in less productive conditions in downstream reservoirs. The proposed upstream reservoirs on the Bear River or its tributaries are not expected to produce an appreciable improvement in downstream reservoirs, however. Phosphorus inputs from tributaries and nonpoint sources will probably negate phosphorus removal by these reservoirs. A study of chemical use by the Little Cottonwood water treatment plant revealed a general independence on raw water quality except for taste and odor. Assuming that water from the Honeyville Reservoir will receive conventional treatment and treatment with permanganate to control taste and odor in the same way as water is treated at the Little Cottonwood plant, treatment costs were estimated to be approximately $80 per acre ft. If trihalomethane compounds are formed from chlorination of the water, and concentrations exceed drinking water standards, treatment costs would increase by $6 to $190 per acre ft depending on the degree of removal required and the treatment method selected. If eutrophic cnoditions can be prevented from developing in the Honeyville Reservoir, concentrations of trihalomethane precursors produced by algal growth and decomposition would be expected to be low, and trihalomethane formation would not be expected to be a problem.