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Research about Minnesota

Source-linked reports with geographic coverage including Minnesota.

At least 613 records · Page 34Linked to original sources
USGS1990

Effects of impoundments on water quality of streams in the Coteau des Prairies: Upper Minnesota River basin

Water-quality and streamflow data were collected in the Coteau des Prairies region of southwestern Minnesota and eastern South Dakota to document the water-quality characteristics of streams and impoundments in the Coteau, and to predict the effect of proposed impoundments on the quality of water in Coteau streams. Reconnaissance data collection at 66 stream and 24 impoundment sites plus 21 inlets and outlets during 1979, and intensive data collection at 4 stream and 4 impoundment plus 9 inlet and outlet sites during 1980-84, showed that major ions, nutrients, and suspended-sediment concentrations and suspendedsediment discharge differed widely in unimpounded streams, but that maximum and median suspended-sediment concentrations were significantly reduced in impounded streams. Peak daily suspended-sediment discharges were reduced at impoundment outlets relative to the sediment discharge at their inlets. The impoundments were found to have little or no effect on stream temperature and concentrations of dissolved oxygen, dissolved solids, and major ions. Elevated concentrations of fecal bacteria were found in unimpounded streams throughout the study area and the impoundments did not substantially reduce the number of bacteria transported in the impounded streams. During summer, elevated concentrations of nitrate, ammonia, and phosphorus were present in all the impoundments. Levels of productivity were not significantly related to concentrations of total phosphorus in the euphotic zone. Real levels of productivity differed among the impoundments however, and seemed to be affected by the occurrence and duration of thermal stratification. Periods of summer stratification and accumulation of late winter snow on pool ice were frequently accompanied by near total depletion of dissolved oxygen. During summer stratification the concentration of ammonia increased with time in the lower part of the water column in some impoundments.

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USGS1990

Simulation of ground-water flow in the St Peter aquifer in an area contaminated by coal-tar derivatives, St Louis Park, Minnesota

A model constructed to simulate ground-water flow in part of the Prairie du Chien-Jordan and St. Peter aquifers, St. Louis Park, Minnesota, was used to test hypotheses about the movement of ground water contaminated with coal-tar derivatives and to simulate alternatives for reducing the downgradient movement of contamination in the St. Peter aquifer. The model, constructed for a previous study, was applied to simulate the effects of current ground-water withdrawals on the potentiometric surface of the St. Peter aquifer. Multiaquifer wells served as conduits for vertical exchange of water from the St. Peter aquifer to the Prairie du Chien-Jordan aquifer. Model simulations predict that the multiaquifer wells have the potential to limit downgradient migration of contaminants in the St. Peter aquifer caused by cones of depression created around the multiaquifer wells. Differences in vertical leakage to the St. Peter aquifer may exist in areas of bedrock valleys. Model simulations indicate that these differences are not likely to affect significantly the general patterns of ground-water flow. Model simulations also indicated that drawdown caused by pumping two wells, each pumping at 75 gallons per minute and located about 1 mile southeast of the source of contamination, would be effective in controlling movement and volume of contaminated ground water in the immediate area of the source of contamination. Some contamination may already have moved beyond the influence of these wells, however, because of a complex set of hydraulic conditions.

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USGS1990

Simulation of ground-water flow in the Prairie du Chien-Jordan and overlying aquifers near the Mississippi River, Fridley, Minnesota

A three-dimensional, ground-water-flow model was developed to gain an improved understanding of the ground-water-flow system and its response to withdrawals near the Minneapolis Water Works in Fridley, Minnesota. Eight hydrogeologic units are represented in the ground-water-flow model. Aquifers represented are the unconfined-drift, confined-drift, St. Peter, and Prairie du Chien-Jordan. Confining units represented are the upper drift, basal-drift, Decorah-Platteville-Glenwood, and basal St. Peter confining units. The ground-water-flow model was calibrated for steady-state conditions fbr a period before substantial ground-water development (1885-1930) and for a period of significant pumping stress (winter conditions, 1970-79). The principle of superposition was used in the steady-state simulation for 1970- 79. Transient conditions were simulated for an aquifer test conducted at the Minneapolis Water Works site and for seasonal variations in ground-water withdrawals resulting in seasonal fluctuations of hydraulic heads of as much as about 45 ft. Sensitivity analysis indicated that hydraulic heads in the confined-drift and St. Peter aquifers and Prairie du Chien-Jordan aquifer were most affected by varying the vertical hydraulic conductivity of the upper drift confining unit and recharge to the confined-drift and St. Peter aquifers. Spatially variable leakage to the confined-drift and St. Peter aquifers in the steady-state simulation for 1885-1930 ranged from 1.0 to 2.3 inches per year. Leakage to the confined-drift and St. Peter aquifers in the steady-state simulation for 1970-79 increased 0 to 3.0 inches per year above the initial steady-state results. This increase represents additional leakage caused by the lowering of hydraulic heads due to ground-water withdrawals. Simulated leakage to the confined-drift and St. Peter aquifers for the transient simulation for 1987 varied both seasonally (0.4 to 2.1 inches per stress period) and spatially (2.6 to 5.7 inches per year).

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USGS1989

Hydrologic and water-quality characteristics of a Wetland receiving wastewater effluent in St. Joseph, Minnesota

Hydrologic and water-quality characteristics were determined for a wetland being used for tertiary treatment of wastewater in St. Joseph, Minnesota. The wetland consists of spruce-tamarack fen and a cattail marsh, with the wastewater being discharged into the fen, and the fen draining into the marsh. The wetland is underlain by flat-lying glacial outwash that ranges from 0 to greater than 20 m in thickness. Horizontal ground-water movement in the outwash aquifer is toward the wetland from the south, east, and west. There is a strong upward vertical hydraulic gradient (about 0.1) in the ground-water flow system beneath and around the wetland. Regionally, the glacial-outwash aquifer is unconfined, but it is confined or partly confined locally by peat deposits under the wetland. Analysis of the hydrologic balance of the fen from October 1985 through September 1986 indicates that the inflow was 44 percent ground water, 38 percent wastewater, 11 percent runoff (storm sewer), and 7 percent precipitation. The fen outflow was 93 percent surface water and 7 percent evapotranspiration. Inflow to the marsh was 74 percent surface water, 21 percent ground water, and 5 percent precipitation. Outflow from the marsh was 94 percent surface water and 6 percent evapotranspiration. Wastewater contributed 74,996, and 81 percent of the total suspended solids, total phosphorus, and total ammonia plus organic nitrogen in the fen, respectively. Other chemical inputs were from the storm sewer, ground water, and atmospheric deposition. The fen was found to retain 34, 14, and 14 percent of the suspended solids, total phosphorus, and total ammonia plus organic nitrogen, respectively. The marsh retained 44, 18, and 22 percent of these three constituents, respectively.

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USGS1989

Physiological assessment of deer populations by analysis of urine in snow

We compared the nutritional status of free-ranging white-tailed deer ( Odocoileus virginianus ) in 3 natural yards and 1 yard where deer were supplementally fed from 1 January to 31 March 1985 in northeastern Minnesota. We monitored deer nutritonal status by sequential collection and chemical analysis of urine in snow (snow-urine) for urea nitrogen (U), sodium (Na), potassium (K), calcium (Ca), and phosphorus (P). Dilution of urine by snow was corrected by comparing these data as ratios to creatinine (C). All deer remained in an early phase of undernutrition; however, declining trends of U:C, Na:C, and K:C in 2 natural yards indicated increasingly inadequate nutrition as winter progressed. Unaltered values of these ratios and P.C in snow-urine collected from the third natural yard reflected stable levels of nutrient availability. Significant (P < 0.05) elevations of Na:C, K:C, and P:C in 2 natural yards with similar snow regimes suggested initiation of nutritional recovery in deer during late March. In contrast, deep snow in the third natural yard restricted feeding activity and was associated with ratios that remained diminished. Elevated U:C, Na:C, and K:C provided physiological evidence of the higher nutritional status of supplementally fed deer throughout winter and their ability to increase nutrient intake during late March despite prolonged deep snow cover. Frequent and quantitative assessments of the physiological status of deer by snow-urine analysis provided an improved understanding of the relationship between snow cover and the nutritional well-being of these deer.

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USGS1989

Flow of ground water through fractured carbonate rocks in the Prairie du Chien-Jordan Aquifer, southeastern Minnesota

Contamination of groundwater from point and nonpoint sources (such as landfills, feedlots, agricultural chemicals applied to fields, and septic systems) is a recognized problem in the karst area of southeastern Minnesota. The US Geological Survey, in cooperation with the Minnesota Department of Natural Resources and the Legislative Commission on Minnesota Resources, Began a study in October 1987 to improve the understanding of local groundwater flow through karst terrain in southeastern Minnesota. The objectives of the study are to: (1) describe the orientations of systematic rock fractures and solution channels of the Prairie du Chien Group of Ordovician-age carbonate rocks in southeastern Minnesota, and, if possible, to define the principal and minor axes of these orientations; and (2) evaluate the effect of fractures and solution channels in the Prairie du Chien Group on the local flow of groundwater. Groundwater in the Upper Carbonate aquifer regionally flows toward the periphery of the aquifer and locally flows into streams and bedrock valleys. The hydraulic gradient in this aquifer generally is greatest near areas of groundwater seepage to streams. Regional groundwater flow in the Prairie du Chien-Jordan aquifer generally is to the south and east in much of Fillmore and Houston Counties and in the southern parts of Olmsted and Winona Counties. Groundwater seepage to selected streams was evaluated by current-meter measurements of downstream gains or losses of streamflow and by an experimental approach based on radon activity in streams. The activity of radon in groundwater ranges from two to four orders of magnitude greater than the activity in surface water; therefore, groundwater seepage to streams generally increases the in-stream radon activity.

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USGS1989

Cyclic injection, storage, and withdrawal of heated water in a sandstone aquifer at St. Paul, Minnesota: Field observations, preliminary model analysis, and aquifer thermal efficiency

In May 1980, the University of Minnesota began a project to evaluate the feasibility of storing heated (150 &deg;C (degree Celsius)) water in the deep (180 to 240 m (meters)) Franconia-Ironton-Galesville aquifer and later recovering it for space heating. The Aquifer Thermal-Energy Storage (ATES) system was doublet-well design in which the injection/withdrawal wells were spaced approximately 250 m apart. High-temperature water from the University's steam-generation facilities supplied heat for injection. Water was pumped from one of the wells through a heat exchanger, where heat was added or removed. Water then was injected back into the aquifer through the other well. The experimental plan for testing the ATES system consisted of a series of short-term hot-water injection, storage, and withdrawal cycles. Each cycle was 24-days long, and each injection, storage, and withdrawal step of the cycle was 8 days. The Franconia-Ironton-Galesville aquifer is a consolidated sandstone, approximately 60 m thick, the top of which is approximately 180 m below the land surface. It is confined above by the St. Lawrence Formation--a dolomitic sandstone 8-m thick--and below by the Eau Claire Formation--a shale 30-m thick. Initial hydraulic testing with inflatable packers indicated that the aquifer has four hydraulic zones with distinctly different values of relative horizontal hydraulic conductivity. The thickness of each zone was determined by correlating data from geophysical logs, core samples, and the inflatablepacker tests.

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USGS1989

Effects of controlled agricultural practices on water quality in the Minnesota sand-plain aquifer

Recent studies of Minnesota's sand plains indicate that ground-water chemistry is related to agricultural practices. Surficial sand-plain aquifers cover 8,000,000 acres of Minnesota and are a major source of water for domestic use, irrigation, and some municipal systems. The sand-plain aquifers consist of sand and gravel deposits that are from 20 to greater than 100 feet thick and are covered by a thin sandy loam that generally is less than 2 feet thick. Sand-plain aquifers are recharged by the downward percolation of precipitation through the soil root zone and the unsaturated zone in the sand to the water table. The water table is the upper surface of the zone of saturation and forms the top of the sand-plain aquifer. Sand-plain aquifers are susceptible to contamination by agricultural chemicals (fertilizers and pesticides), if downward-percolating recharge water contains these chemicals. The concentrations of nitrate, pesticides, and some other chemical constituents fluctuate seasonally and differ with depth below the water table (Anderson, 1989). Despite the availability of water-quality data for about 260 wells that were collected during previous studies in three U.S. Geological Survey (USGS) project areas in Minnesota, it is not known how concentrations of agricultural chemicals in ground water relate to the rate and timing of fertilizer and pesticide application or to the tillage practices used. Field-scale research is needed to determine the effects of different farming practices on the concentrations of nitrate, pesticides, and other agricultural chemicals in ground water in the unsaturated and saturated zones.

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USGS1989

Effect of urban runoff on the quality of lakes in Eagan, Minnesota

Sixteen lakes in the city of Eagan, Minnesota, were sampled during 1982-83 to detect water-quality changes that might have occurred because of urbanization since a previous study conducted during 1972-78. Each of the lakes was sampled five times to determine pH, specific conductance, dissolved oxygen, water temperature, transparency, and concentration of dissolved chloride. Three determinations of chlorophyll were made for each of the lakes near the end of the study, and additional determinations were made for a few lakes of particular interest. Most of the lakes have been incorporated into the city's storm-runoff system for use as retention basins during large storms. The chemistry of the lakes appears to be degraded by urban runoff. Chloride concentrations were significantly higher in six lakes than during the previous study, and remained elevated (about 30 milligrams per liter) in four other lakes. The association between increased chloride and specific conductance with runoff from urban areas suggests that the lakes are subject to contamination by chloride commonly present in urban runoff, and chloride concentrations harmful to aquatic life may have been associated with high specific conductance measured in one of the lakes. Analysis of the data collected for this study indicate that the chemistry of the lakes changes, adjusting to a variety of influences including (1) alternate loading and flushing by runoff, (2) excessive average-annual precipitation, (3) changing ground-water and lake interactions, and (4) changing land use in the lake watersheds. Some lakes affected by urban runoff had reduced concentrations of total phosphorus; however, other lakes unaffected by urban runoff also had significantly lower phosphorus, suggesting that increased precipitation may have diluted the lake water. Ten phosphorus-loading models tested or developed during the previous study generally were found to be inadequate for describing the results of this study. The trophic status of 12 lakes improved but declined in the other 4 lakes, and productivity increased 38 percent in what had been the least-eutrophic lake.

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USGS1989

Effects of agriculture on quality of water in surficial sand-plain aquifers in Douglas, Kandiyohi, Pope, and Stearns counties, Minnesota

The 245 water samples collected from 56 wells at 45 sites in surficial sand-plain aquifers that underlie 600 square miles of Douglas, Kandiyohi, Pope, and Stearns Counties in west-central Minnesota contained wide ranges in concentrations of some constituents--sulfate 2 to 160 mg/L (milligrams per liter), chloride 1.6 to 64 mg/L, nitrite plus nitrate nitrogen < (less than) 0.1 to 72 mg/L, ammonia <0.01 to 3.3 mg/L , iron <0.003 to 8.6 mg/L, and managanese <0.001 to 1.5 mg/L . Substantial fluctuations in these constituents over time were observed. Nitrate concentrations exceeded the Minnesota drinking-water standard of 10 mg/L (as N) in 50 percent of the wells sampled. Differences in concentrations of nitrate with depth below the water table were observed at 11 paired-well sites where one well was screened near the water table and another well was screened 10 or more feet below the water table. Similar differences in concentration with depth were observed in specific conductance, iron, chloride, and sulfate, but not as consistently. At eight sites, nitrate concentrations were higher at the water table (4.3 to 72 mg/L) than deeper in the aquifer (<0.1 to 27 mg/L). At the other three sites, nitrate concentrations were greater at depth than at the water table, although the contrast in concentrations was not as large. Increased concentration at depth is attributed to vertical mixing at the three sites, possibly caused by rapid infiltration of more dilute water from ephemeral ponds following storms. The more dilute water displaces the high-nitrate water to greater depth. Nitrate concentrations fluctuated seasonally in response to the combined effects of precipitation and agricultural practices (irrigation and fertilization). Nitrite plus nitrate nitrogen concentrations in one Stearns County well fluctuated from 35 mg/L in August 1982, to 72 mg/L in May 1983, to 18 mg/L in May 1984. In 12 wells for which historical data were available, the mean nitrate concentration during this study (1982-84) was greater than the mean concentration during previous studies (1965-78), although the amount of increase in nitrate concentrations observed over the previous 10 or more years was not as great as the seasonal fluctuations observed during this study. Short-term seasonal fluctuations are greater than apparent historical increases in nitrate concentration. Concentrations of sulfate, chloride, and, especially, nitrate were significantly higher in irrigated areas than in uncultivated areas. Mean nitrite plus nitrate nitrogen concentrations were 4.3 mg/L in uncultivated (natural) areas relatively unaffected by agriculture, 5.4 mg/L in nonirrigated cultivated areas, and 17 mg/L in irrigated cultivated areas. The mean nitrite plus nitrate nitrogen concentration in uncultivated areas was greater than the usually observed background levels of less than 1 mg/L (as nitrogen), which may indicate that areas thought to be natural actually are affected by agricultural land use. Several statistical tests indicate that nitrate concentrations are significantly higher in irrigated cultivated areas than in nonirrigated cultivated areas. The difference in nitrate concentrations between irrigated and nonirrigated areas suggests that nitrate from agricultural fertilizer is being leached during heavy rainfall or irrigation periods as a result of higher concentrations of nitrogen being maintained in the soil to enhance yields of corn and potatoes. Four of eight wells sampled for herbicides in west-central Minnesota had detectable concentrations of the triazine herbicide atrazine that ranged from 0.2 to 0.6 micrograms per liter. These concentrations were well below the water-quality guidelines published by the Canadian Inland Waters Directorate, Water Quality Branch, which specify 100 micrograms per liter as the maximum permissible concentration for the group of triazine herbicides in a raw drinking-water supply.

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USGS1989

Water resources of the Fond du Lac Indian Reservation, east-central Minnesota

Water resources in the Fond du Lac Indian Reservation meet the present (1987) needs for drinking-water supplies and other household uses with respect to water quality and quantity, and provide valuable ecological, recreational, and aesthetic benefits. Total annual water use in the Reservation is about 36.5 million gallons per year and per capita use is about 100 gallons per day. Practically all the water is used for domestic supply. Ground water is the source of all water supplies in the Reservation. Three aquifers are the source of ground water in the Reservation. Unconfined-drift aquifers consist of surficial outwash that extends over one third of the Reservation. Confined-drift aquifers consist of sand and gravel deposits that occur discontinuously at depths of 50 to 150 feet throughout the Reservation. The third aquifer is in crystalline bedrock that underlies the glacial drift. Surface-water resources in the Reservation consist of numerous wetlands, many shallow lakes, and streams that drain five basins. All the basins in the Reservation are part of the St. Louis River drainage system, except for a small area in the southcentral part of the Reservation that is part of the Kettle River basin. Stoney Brook, which is the major stream, drains three fourths of the Reservation. Average discharge from Stoney Brook during the 1984 water year was 82 cubic feet per second. The lakes in the Reservation, which are shallow and small, have a combined surface area of about 3,000 acres. Concentrations of constituents in ground-water samples met recommended and regulated limits set by the U.S. Environmental Protection Agency for drinking water except for samples collected from wells in the unconfined-drift aquifer that suggested limits for nitrate (one sample), iron (two samples), and manganese (six samples), were exceeded. Quality of water in the lakes and streams is suitable for native forms of plant and animal life.

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USGS1989

Cost-effectiveness of the streamflow-gaging program in Minnesota

A three-step analysis of the cost-effectiveness of the streamflow-gaging program in Minnesota is documented in this report. In the first step of the analysis, the data uses and funding sources were identified for the 96 continuous-record streamflow-gaging stations operated in 1985. Nineteen sources of funding and 42 uses were identified for the data collected in this program. Two stations were identified as producing data no longer sufficiently needed to warrant continuing their operation. Three other stations were identified as having uses specific to short-term studies. One station was destroyed in 1985. It is recommended that the remaining 90 station be maintained in the program for the foreseeable future. In the second step, multiple-linear-regression analysis was investigated as a possible method for providing the data collected at 23 stations. The multiple-linear-regression method was not sufficiently accurate to provide the needed data, and it is recommended that the 23 stations remain in the program. It also is recommended that flow-routing methods be investigated to see if they could provide the needed data for stations on the Red Lake River, the upper Minnesota River, and on the Mississippi River in the Minneapolis-St Paul metropolitan area. In the third step, the cost-effectiveness of collecting data from 77 of the remaining 90 stations was determined for the open-water period, April 1 through October 30. Data for 13 stations are provided to the U.S. Geological Survey or are collected at fixed intervals and were, therefore, not used in the analysis. The average standard error per station for estimation of the streamflow records is about 24 percent for the statewide network, about 11 percent for the stations operated by the St. Paul field office, about 22 percent for the stations operated by the Grand Rapids field office, and about 37 percent for the stations operated by the Montevideo field office. The current policy for collecting data from the 77 stations during the open-water period cost $198,000 in 1985. The estimated average standard error per station for the statewide network could be reduced from 24.4 percent to 20.6 percent at the $198,000 budget, if the minimum number of discharge measurements at each station were reduced from five to three during the open-water period and the remaining budget were used to make additional discharge measurements at stations with large standard errors. It is recommended that, before this data-collection plan is implemented, the effects of the plan on the cost of collecting data be evaluated for (1) possible increased lost record because of the data collection plan, and (2) the possible need for additional trips to visit noncontinuous-record stations. It also is recommended that the data-accuracy needs of the funding agencies be considered before the plan is implemented.

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USGS1989

Flow characteristics of the Clearwater River and tributaries from Clearbrook to Plummer, northwestern Minnesota

During March through October 1986, 52,560 acre-feet of water passed the continuous-record stream gaging station on the Clearwater River near Clearbrook, Minnesota, 4.8 river miles upstream from the Red Lake Indian Reservation. Flow at the downstream boundary of the Reservation totaled 93,770 acre-feet. The increase in Clearwater River flow in the reach bordering the Reservation equaled 32,950 acre-feet; 60 percent of the increase occurred during March, April, and May. During those months, flow in the Clearwater River was augmented by flow from Kiwosay Reservoir and Butcher Knife Creek, which are located on the Reservation. Daily streamflow records showed that flow in the river increased in the Reservation reach throughout the study except for 13 days during October when losses occurred. At the downstream Reservation boundary, all daily mean flows exceeded the 36 cubic feet per second minimum flow required by the Minnesota Department of Natural Resources for the gaging station at Plummer, Minnesota located 29.9 miles downstream from the Reservation boundary. Monthly flows generally followed expected seasonal trends, with the highest monthly totals occurring in April and May and the lowest monthly totals occurring during August, September, and October. Seasonal trends were modified by reservoir releases, withdrawals for irrigation, and return flows that resulted from drainage of adjacent wild-rice fields. A series of flow measurements showed that localized withdrawals and return flows at times exceeded 20 percent of total streamflow. Discharge measurements made during low flow indicated higher rates of groundwater discharge in the vicinity of the Kiwosay Reservoir than in other parts of the study reach. Measurements made during August indicated that groundwater discharge in the reach of the river bordering the Reservation resulted in a flow gain of about 20 percent. Analysis of long-term streamflow records showed that near-average hydrologic conditions prevailed during the study period.

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USGS1989

Water resources of the White Earth Indian Reservation, northwestern Minnesota

Water resources in the White Earth Indian Reservation meet the present (1988) needs for potable supply and other household uses and provide valuable ecological, recreational, and aesthetic benefits. Total annual water use in the Reservation is about 460 million gallons per year. Domestic supply from privately owned wells and municipal systems accounts for roughly three-fourths of the water use, and irrigation of croplands and nurseries accounts for approximately one-fourth, depending on rainfall. Glacial-drift aquifers are the source of ground water in the Reservation. Unconfined-drift aquifers consist of two surficial outwash deposits that extend over approximately one-fifth of the Reservation. One deposit trends along a north-south strip through the central part of the Reservation, and the other occupies the southeastern corner. Confined-drift aquifers are the most significant source of ground-water supply. These aquifers are discontinuous lenses of sand and gravel that hydraulically are poorly connected to each other. The aquifers are 50 to 300 feet below land surface and 5 to 25 feet thick. Yields from these aquifers typically range from 10 to 100 gallons per minute. Surface water in the Reservation consist of numerous lakes, wetlands, prairie potholes, and streams. The larger, deeper lakes in the eastern and southern parts of the Reservation support walleye and northern pike and provide recreational opportunities for swimming and boating. The shallower lakes and prairie potholes are used to produce wild rice and also are managed to provide waterfowl habitat. Most of the streams in the Reservation drain the headwater areas of basins that are part of the Red River of the North watershed; however, several small streams in the southeastern part drain to the Crow Wing River, which is part of the Mississippi River drainage system. The Wild Rice River drains the largest basin in the Reservation. Ground water is mostly a calcium magnesium bicarbonate type. Dissolvedsolids concentration of the ground water generally is greater in the deeper confined-drift aquifers than in the shallower unconfined-drift aquifers. The concentrations of sodium and sulfate in water from the confined-drift aquifers are higher in the northwestern part of the Reservation than in the rest of the aquifer. Except for elevated concentrations of iron and manganese, the quality of the ground water meets the criteria established by the U.S. Environmental Protection Agency (USEPA) for drinking water. Surface water also is a calcium magnesium bicarbonate type. Lake waters are hard and alkaline and are mesotrophic to eutrophic in productivity. Quality of the lake and stream water is suitable for native forms of freshwater biota, although the concentration of total recoverable mercury exceeds the 0.012 micrograms per liter maximum contaminant level; that level, established by USEPA for the organic form of dissolved mercury, is intended to protect against chronic effects on freshwater life. Available information, however, indicates that the amount of mercury in edible tissue from fish in alkaline lakes of northwestern Minnesota is within safe limits. The concentrations of phosphorus and nitrate in the streams are below levels that indicate pollution problems.

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