Development of water supplies from surficial sand-plain aquifers in westcentral Minnesota has aroused public awareness of the possibility for degradation of water quality. The sand-plain areas are generally underlain by sandy soils that permit rapid infiltration of precipitation and, possibly, of surface contaminants. One hundred twenty-three wells were sampled in Hubbard, Morrison, Otter Tail, and Wadena Counties during 1979-81 to establish regional baseline water quality. The wells were chosen to provide optimum area! coverage based on geology, direction of ground-water flow, and extent of aquifer development.Water from the sand-plain aquifers is of the calcium bicarbonate type. The water is hard to very hard with disolved solids ranging from about 100 to 700 milligrams per liter. Locally, concentrations of dissolved solids, iron, manganese, and nitrate exceeded limits recommended by the Minnesota Pollution Control Agency for drinking water.
Eagle Lake occupies 890 acres of a 9,000-acre watershed in central Minnesota. Because of its proximity to Willmar, many homes and sunnier cabins have been built around the lake. At present (1978), the shore is more than 90 percent developed. One effect of this development is accelerated eutrophication, most commonly shown by algae blooms.An annual hydrologic budget for Eagle Lake was prepared for the 1978 water year in support of a nutrient study prepared by the University of Minnesota at Marris. Results show that the amount of water that flowed through Eagle Lake in the 1978 water year was 6,670 acre-feet. Inflow to the lake was 45 percent surface water, 22 percent ground water, and 33 percent precipitation. Outflow was 73 percent surface water, 25 percent evaporation, and slightly greater than 2 percent net change in lake storage.Estimates for the ground-water component were derived both as a residual in the hydrologic-budget equation and by flow-net analyses. The residual value of 1,450 acre-feet compared favorably with the flow-net value of 1,400 acre-feet.
Water samples were collected periodically from 124 wells completed in sand-plain aquifers in Hubbard, Morrison, Otter Tail, and Wadena Counties, Minnesota, to determine baseline water quality, provide data for evaluation of trends, and to investigate seasonal variations in concentrations of selected chemical constituents during a 3-year study that began in October 1979. Results of the study show that the water is predominantly a calcium bicarbonate type with low to moderate concentrations of dissolved solids (77 to 710 milligrams per liter), and that it generally is suitable chemically for most uses. Concentrations of most constituents are below limits for domestic consumption recommended by the Minnesota Pollution Control Agency and the U.S. Environmental Protection Agency. Concentrations of nitrite plus nitrate nitrogen, iron, and manganese in localized areas, however, exceed the recommended limits. Comparison of current data to historical data indicates that concentrations of nitrite plus nitrate nitrogen and chloride have increased in local agricultural areas.
Taconite tailings, a waste product from processing of iron ore, have been deposited in a 2.5-square-mile containment basin near Keewatin, Minnesota, The basin, which is bounded by earthen dikes of compacted drift and clayey bouldery till, contains saturated tailings consisting of chert and other silica-rich particles that range from clay to coarse-sand size.Runoff from the tailings is slight and occurs only after heavy rains and snowmelt. Average discharge from the basin from April 1982 through June 1984 was about 0.6 cubic foot per second. Instantaneous discharge ranged from zero during much of the period to about 140 cubic feet per second following snowmelt in spring 1982. Daily mean discharge from the basin exceeded 20 cubic feet per second on two days during the period of study.
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