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Research about Minnesota

Source-linked reports with geographic coverage including Minnesota.

At least 505 records · Page 28Linked to original sources
USGS1997

Physical and chemical properties of water and sediments, Grand Portage and Wauswaugoning Bays, Lake Superior, Grand Portage Indian Reservation, northeastern Minnesota, 1993-96

This report is a compilation of data on the physical and chemical properties of water and sediments in Grand Portage and Wauswaugoning Bays of Lake Superior along the shoreline of the Grand Portage Indian Reservation. The data were collected during 1993-96 by the U.S. Geological Survey in cooperation with the Grand Portage Indian Reservation. The data include: (1) temperature, pH, and specific conductance measurements and dissolved oxygen concentrations; (2) Secchi disk transparency, alkalinity, and turbidity measurements; (3) fecal Coliform and fecal Streptococcal bacteria colony counts (per 100 milliliters of sample water); (4) major and minor ion, nutrient, and trace-metal concentrations; (5) dissolved and suspended residue concentrations; (6) pesticide, phenol, and asbestos concentrations; (7) suspended sediment trace-metal concentrations; and (8) bottom sediment trace-metal concentrations. Water samples were collected from nine sites; suspended and bottom sediment samples were collected from five sites. The data in this report can be used to evaluate present water-quality conditions and as a reference to monitor potential long-term changes in these conditions.

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USGS1997

Physical characteristics of stream subbasins in the lower Minnesota River basin, south-central Minnesota

Data that describe the physical characteristics of stream subbasins upstream from selected sites on streams in the Lower Minnesota River Basin, located in south-central Minnesota are presented in this report. The physical characteristics are the drainage area of the subbasin, the percentage area of the subbasin covered only by lakes, the percentage area of the subbasin covered by both lakes and wetlands, the main-channel length, and the main-channel slope. Stream sites include outlets of subbasins of at least 5 square miles, outfalls of sewage treatment plants, and locations of U.S. Geological Survey low-flow, high-flow, and continuous-record gaging stations.

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USGS1997

Hydrogeologic and water-quality data used to evaluate the effects of focused recharge on ground-water quality near Princeton, Minnesota, 1991-95

This study was part of the Management Systems Evaluation Area (MSEA) Program, a multi-scale, inter-agency initiative to evaluate the effects of agricultural systems on water quality in the midwest corn belt. The research was part of the U.S. Geological Survey Toxics Substances Hydrology Program. The research area was located in the Anoka Sand Plain about 5 kilometers southwest of Princeton, Minnesota. This report presents temperature, precipitation, soil-moisture, water-quality, and other data collected during 1991-95 to evaluate the effects of focused recharge on ground-water quality at the Princeton MSEA.

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USGS1997

Water-quality and hydrogeologic data used to evaluate the effects of farming systems on ground-water quality at the Management Systems Evaluation Area near Princeton, Minnesota, 1991-95

The Minnesota Management Systems Evaluation Area (MSEA) project was part of a multi-scale, inter-agency initiative to evaluate the effects of agricultural management systems on water quality in the midwest corn belt. The research area was located in the Anoka Sand Plain about 5 kilometers southwest of Princeton, Minnesota. The ground-water-quality monitoring network within and immediately surrounding the research area consisted of 73 observation wells and 25 multiport wells. The primary objectives of the ground-water monitoring program at the Minnesota MSEA were to: (1) determine the effects of three farming systems on ground-water quality, and (2) understand the processes and factors affecting the loading, transport, and fate of agricultural chemicals in ground water at the site. This report presents well construction, geologic, water-level, chemical application, water-quality, and quality-assurance data used to evaluate the effects of farming systems on ground-water quality during 1991-95.

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USGS1997

Quantity and quality of runoff from selected guttered and unguttered roadways in northeastern Ramsey County, Minnesota

Five roadway sections in northeastern Ramsey County, Minnesota were monitored during 1993-95, to evaluate water quality and loading of constituents from roadway runoff. Two snowmelt-runoff and five rainfall-runoff events were monitored per year at each site. Additional samples of rainfall were analyzed to determine if rainfall was a direct source of constituent loading to roadway runoff. Roadway-runoff samples were analyzed for selected physical properties, dissolved solids, nutrients, dissolved ions, selected metals, and semi-volatile compounds. Concentrations of dissolved ions such as sodium, chloride, and metals such as aluminum, chromium, lead, and zinc were detected at much greater levels for snowmelt-runoff samples than rainfall-runoff samples. Analysis of chemical samples from rainfall indicate that rainfall was not a direct source for most constituents. Dissolved nitrate and dissolved ammonia in rainfall, however, can contribute up to one-half the amounts detected in roadway runoff. Concentrations of total phosphorus and fecal Streptococcus bacteria were greater at unguttered sites than at guttered sites. Concentrations of dissolved solids, and some metals were greater at guttered sites than at unguttered sites. This suggests that the vegetated road ditches associated with unguttered sites may filter out heavier particles such as metals and solids, while contributing additional organic matter. Concentrations of aliiminum, copper, lead, and zinc exceeded chronic condition standard limits established by the Minnesota Pollution Control Agency for metropolitan storm water from 96 percent, 52 percent, 9 percent, and 20 percent of the samples collected, respectively. Chemical loadings of specific constituents, such as suspended solids, from an individual rainfall-runoff event accounted for greater than 90 percent of the cumulative loadings of that constituent for all monitored events at site 4, for the entire study period. Length of latent period was statistically compared to constituent concentration levels of total phosphorus, dissolved sulfate, and total zinc and there was a correlation. Constituent loads were not associated with latent period. No correlation was found between traffic volumes which ranged from 1,888 to 7,172 vehicles per day and constituent concentrations or loads for this study.

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USGS1997

Hydraulic properties and ground-water flow in the St Peter-Prairie du Chien-Jordan aquifer, Rochester area, southeastern Minnesota

The hydraulic properties were updated and their effects on ground-water flow in the St. Peter-Prairie du Chien-Jordan aquifer in the Rochester area in southeastern Minnesota were evaluated, using new information compiled since a study by Delin (1990). Since 1988, new information on the hydrogeology of the ground-water system in the Rochester area has become available from well-drilling and construction activity associated with Rochester's rapid growth. The St. Peter-Prairie du Chien-Jordan aquifer consists of the St. Peter Sandstone, the Prairie du Chien Group (limestones and dolomites), and the Jordan Sandstone. Horizontal hydraulic conductivity and transmissivity were determined from 15 aquifer tests and specific-capacity information compiled for 310 wells. A 140-square-mile area of the aquifer bounded on the west, south, and east by a ground-water divide contributes water to the Rochester, Minnesota, municipal wells. Transmissivities for the St. Peter-Prairie du Chien-Jordan aquifer in the study area range from less than 5,000 square feet per day (ft 2 /d) to greater than 20,000 ft 2 /d. Transmissivities greater than 20,000 ft 2 /d occur in the west-central, northwestern, and east-central parts of the study area. Transmissivities of less than 5,000 ft 2 /d occur in the northern, northeastern, central, and southern parts of the study area. The areas of greatest potential well yield coincide with areas of greatest transmissivity. Delin (1990) developed a ground-water-flow model to simulate flow of ground water in the St. Peter-Prairie du Chien-Jordan aquifer in the Rochester area. The 1988 Rochester model was rerun using revised horizontal hydraulic conductivity arrays in the model, based on the transmissivity distribution determined for this study. The results of the simulations using horizontal hydraulic conductivities based on the transmissivity distribution determined for this study may indicate that transmissivity values derived from specific-capacity information generally are too high. The transmissivity distribution determined for this study, however, is valid as an indicator of the spatial variability of the relative magnitude of transmissivity and potential well yield for the St. Peter-Prairie du Chien-Jordan aquifer in the study area. Water-level changes in wells from January through February 1988 to February through March 1995 ranged from -6.8 to +15.3 feet. Water-level changes in 12 Rochester municipal wells for the same period ranged from -7.4 to +8.0 feet. Water levels in wells generally rose in the northern and eastern parts of the study area and generally declined in the southwestern and western parts. Near Rochester, water levels in wells generally declined near the city boundaries and showed little change or rose in the central part of the city. Water-level changes from 1988 to 1995 near the ground-water divide generally were less than 2 feet, resulting in no appreciable changes in the location of the divide.

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USGS1997

Nitrate and pesticides in surficial aquifers and trophic state and phosphorus sources for selected lakes, eastern Otter Tail County, west-central Minnesota, 1993-96

Nitrate concentrations (as nitrogen) were analyzed in water from 73 wells completed in surficial aquifers. Water from about one-third of the wells had concentrations greater than 10 mg/L (milligrams per liter), the regulatory limit for drinking water established by the U.S. Environmental Protection Agency. Nitrate concentrations: (1) were greater in water from wells in agricultural settings than in nonagricultural settings; (2) were not greater in water from shallow wells (25 feet deep or less) in settings with rapid soil permeability than with moderate soil permeability, probably because the effects of permeability were offset by the effects of land use and well depth; and (3) were greater in water from shallow wells (25 feet deep or less) than from deep wells (greater than 25 feet deep). Triazine herbicides were detected in water from 23 of the 73 sampled wells by immunoassay tests. Most of these wells are in agricultural settings. Ten pesticides, which included seven triazine herbicide compounds, were detected in water from 19 of 25 wells analyzed by gas chromatography/mass spectrometry. Atrazine and deethylatrazine, a degradation product of atrazine, were detected in water from 18 and 16 wells, respectively. None of the detected pesticides had concentrations that exceeded their respective regulatory limits for drinking water established by the U.S. Environmental Protection Agency. Four lakes in the Otter Tail River Basin, which in downstream order are Little Pine, Big Pine, Rush, and Otter Tail Lakes, ranged in trophic state from upper oligotrophic to lower eutrophic. The Secchi disk transparencies were 4.0 to 7.4 feet, chlorophyll a concentrations (epilimnetic) were 4.4 to 28 micrograms per liter, and total phosphorus concentrations (epilimnetic) were less than 0.010 to 0.022 mg/L (except one concentration of 0.060 mg/L). The trophic state of these lakes may have become less eutrophic from upstream to downstream lakes. Major external sources of phosphorus to Big Pine Lake were the Otter Tail and Toad Rivers. The phosphorus load from these two streams during March 16, 1995, to March 15, 1996 was 10,400 pounds. The phosphorus load from the Toad River (5,730 pounds) was greater than from the Otter Tail River (4,670 pounds) even though streamflow from the Toad River was about 70 percent less than the Otter Tail River. Phosphorus removal from Big Pine Lake through the Otter Tail River outlet during the 1-year period was 8,460 pounds. The total annual accumulation of phosphorus, which includes an estimated 700 pounds from ground-water discharge, was 2,640 pounds. The accumulated phosphorus probably was utilized by phytoplankton or was absorbed by nonliving particulate matter that eventually settled into bottom sediments. Bottom sediments were an internal source of phosphorus to Little Pine and Big Pine Lakes. Increased total phosphorus concentrations (hypolimnetic) of 0.037 to 0.120 mg/L at depth during August 9-10, 1995, indicated phosphorus release from bottom sediments. The increased phosphorus probably was associated with anoxic conditions in the hypolimnion during summer stratification. Phosphorus at depth in Little Pine and Big Pine Lakes was mostly orthophosphate. During the fall turnover of the lakes, this orthophosphate may have circulated to near the lake surface and became an available nutrient for phytoplankton during the following growing season. The internal phosphorus load to Little Pine Lake may have been important because about three-fourths of the lake probably became stratified and anoxic in the hypolimnion. The internal phosphorus load to Big Pine Lake may not have been important because only a small portion of the lake became stratified and anoxic at depth.

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USGS1997

Techniques for estimating peak flow on small streams in Minnesota

Two statistically-derived techniques, regional regression equation and region of influence regression, that estimate peak flow on small, ungaged streams in Minnesota were developed. Both techniques relate physical and climatic characteristics to peak flow for 2-, 5-, 10-, 25-, 50-, and 100-year recurrence intervals. Regional regression equations were developed for each recurrence interval in each of six regions in Minnesota. The region of influence regression technique dynamically selects stations with characteristics similar to a site of interest. Thus, the region of influence regression technique allows use of a potentially unique set of stations for estimating peak flow at each site of interest. Two methods of selecting streamflow gaging stations, similarity and proximity, are recommended for use in the region of influence regression technique. The regional regression equation technique is recommended as a first estimate of peak flow in regions C, E, and F. The similarity method of the region of influence regression technique should be used as a first estimate in regions A and D. The proximity method should be used as a first estimate in region B. Tables showing the peak-flow-frequency data and basin characteristics for streamflow gaging stations, and regional peak-flow prediction equations, are documented.

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USGS1996

Nitrate in groundwater and water sources used by riparian trees in an agricultural watershed: A chemical and isotopic investigation in southern Minnesota

This study evaluates processes that affect nitrate concentrations in groundwater beneath riparian zones in an agricultural watershed. Nitrate pathways in the upper 2 m of groundwater were investigated beneath wooded and grass-shrub riparian zones next to cultivated fields. Because trees can be important components of the overall nitrate pathway in wooded riparian zones, water sources used by riparian trees and possible effects of trees on nitrate concentrations in groundwater were also investigated. Average nitrate concentrations in shallow groundwater beneath the cultivated fields were 5.5 mg/L upgradient of the wooded riparian zone and 3.5 mg/L upgradient of the grass-shrub zone. Shallow groundwater beneath the fields passed through the riparian zones and discharged into streams that had average nitrate concentrations of 8.5 mg/L (as N). Lateral variations of δD values in groundwater showed that mixing among different water sources occurred beneath the riparian zones. In the wooded riparian zone, nitrate concentrations in shallow groundwater were diluted by upwelling, nitrate-poor, deep groundwater. Upwelling deep groundwater contained ammonium with a δ 15 N of 5‰ that upon nitrification and mixing with nitrate in shallow groundwater caused nitrate δ 15 N values in shallow groundwater to decrease by as much as 19.5‰. Stream water penetrated laterally beneath the wooded riparian zone as far as 19 m from the stream's edge and beneath the grass-shrub zone as far as 27 m from the stream's edge. Nitrate concentrations in shallow groundwater immediately upgradient of where it mixed with stream water averaged 0.4 mg/L in the wooded riparian zone and 0.8 mg/L near the grass-shrub riparian zone. Nitrate concentrations increased toward the streams because of mixing with nitrate-rich stream water. Because nitrate concentrations were larger in stream water than shallow groundwater, concentrated nitrate in the streams cannot have come from shallow groundwater at these sites. Water sources of riparian trees were identified by comparing δD values of sap water, soil water, groundwater, and stream water. Soil water was the main water source for trees in the outer 4 to 6 m of one part of the wooded riparian zone and outer 10 m of another part. Groundwater was a significant water source for trees closer to the streams where the water table was less than about 2.1 to 2.7 m below the surface. No evidence was found in the nitrate concentration profiles that trees close to the streams that took up groundwater through their roots also took up nitrate from groundwater. The lack of such evidence is attributed to the nitrate concentration profiles being insufficiently sensitive indicators of nitrate removal by trees.

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USGS1996

Block and shear-zone architecture of the Minnesota River Valley subprovince: Implications for late Archean accretionary tectonics

The Minnesota River Valley subprovince of the Superior Province is an Archean gneiss terrane composed internally of four crustal blocks bounded by three zones of east-northeast-trending linear geophysical anomalies. Two of the block-bounding zones are verified regional-scale shears. The geological nature of the third boundary has not been established. Potential-field geophysical models portray the boundary zones as moderately north-dipping surfaces or thin slabs similar in strike and dip to the Morris fault segment of the Great Lakes tectonic zone at the north margin of the subprovince. The central two blocks of the subprovince (Morton and Montevideo) are predominantly high-grade quartzofeldspathic gneiss, some as old as 3.6 Ga, and late-tectonic granite. The northern and southern blocks (Benson and Jeffers, respectively) are judged to contain less gneiss than the central blocks and a larger diversity of syntectonic and late-tectonic plutons. A belt of moderately metamorphosed mafic and ultramafic rocks having some attributes of a dismembered ophiolite is partly within the boundary zone between the Morton and Montevideo blocks. This and the other block boundaries are interpreted as late Archean structures that were reactivated in the Early Proterozoic. The Minnesota River Valley subprovince is interpreted as a late accretionary addition to the Superior Province. Because it was continental crust, it was not subductible when it impinged on the convergent southern margin of the Superior Craton in late Archean time, and it may have accommodated to convergent-margin stresses by dividing into blocks and shear zones capable of independent movement.

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USGS1996

Survival of radiomarked canvasback ducklings in northwestern Minnesota

Duckling survival, an important factor affecting annual recruitment, has not been determined adequately for canvasbacks ( Aythya valisineria ). We investigated the magnitude, timing, and causes of mortality of canvasback ducklings from hatch to fledging at the Agassiz National Wildlife Refuge (NWR) in northwestern Minnesota during 1987-90. During the 4 years, 217 day-old ducklings were radiomarked and released in 52 broods. Another 141 ducklings were radiomarked at ≥ to 4 weeks of age. Survival was estimated with the Kaplan-Meier nonparametric estimator and the Weibull parametric model. Most mortalities occurred within 10 days after hatch. Total brood loss occurred in 18 (85%) of 52 broods released. The primary sources of mortality were predation principally by mink ( Mustela vison ), and exposure to precipitation and cold temperature. For combined years, females had lower survival than males ( P =0.03). If the disparate survival between sexes of canvasbacks observed in this study is representative of canvasbacks in their breeding range, this phenomenon contributes to reduced reproductive potential and the male-biased sex ratio of the species.

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USGS1996

Relation of land use to nitrate in the surficial aquifer along the Straight River, north-central Minnesota, 1992-93

The U.S. Geological Survey studied the relation of land use to nitrate concentrations in the surficial aquifer along the Straight River near Park Rapids in north-central Minnesota (see adjacent map) during 1992 to 1993. Concern about health hazards to humans and livestock from use of ground water contaminated by nitrate prompted the study. Data collected for this study included: (1) water levels from 38 monitoring wells; (2) nitrate-nitrogen concentrations in ground-water samples from 34 monitoring wells; and (3) land use determined for 2.5-acre parcels throughout the study area. Eighteen of the monitoring wells were installed as nested pairs; the other 20 wells were installed singly. The wells were screened near the water table except the deep wells of each nested pair, which were screened near the bottom of the aquifer.

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USGS1996

Simulation of wastewater effects on dissolved oxygen during low streamflow in the Red River of the North at Fargo, North Dakota, and Moorhead, Minnesota

Pursuant to Section 303(d) of the Clean Water Act, both North Dakota and Minnesota identified part of the Red River of the North (Red River) as water-quality limited. The states are required to determine the total maximum daily load (TMDL) that can be discharged to a water-quality limited reach from various pollution sources without contravening water-quality standards (U.S. Environmental Protection Agency, 1991). A work group consisting of local, State, and Federal agency representatives that was organized in June 1994 decided that a TMDL should be developed in phases for a subreach of the Red River at Fargo, N. Dak., and Moorhead, Minn. (fig. 1). In the first phase, which is the basis for this report, the focus is on attainment of the instream dissolved-oxygen (DO) standard during low streamflows, and only Fargo and Moorhead wastewater-treatment-plant discharges and Sheyenne River inflow are considered. The study reach begins about 0.1 mile (mi) downstream (north) of the 12th Avenue North bridge in Fargo and extends 30.8 mi downstream to a site 0.8 mi upstream of the confluence of the Buffalo and Red Rivers (fig. 1). Nitrification of total ammonia (ammonia) from Fargo and Moorhead wastewater consumes most of the DO in the study reach (Wesolowski, 1994). Because the new (1995) Fargo plant already is nitrifying its wastewater, the work group needed to determine the maximum ammonia concentration for wastewater from the nonnitrifying Moorhead plant. To accomplish this task, the Red River at Fargo Water-Quality (RRatFGO QW) model (Wesolowski, 1994, 1996b) was used to simulate the effects of various wastewater-management alternatives during low streamflow. This report presents the results of those simulations to determine the usefulness of the model for management decisions. The simulations and report were completed in cooperation with the North Dakota Department of Health.

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USGS1996

Conversion of the Twin Cities metropolitan area numerical ground-water-flow model from the Trescott-Larson computer code to the McDonald-Harbaugh computer code

A numerical model of ground-water flow in the Twin Cities metropolitan area was converted from the TrescottLarson computer code to the McDonald-Harbaugh computer code to facilitate current and future use of the model using up-to-date computer software and hardware. Differences exist between the two computer codes in how headdependent source-sink functions, including leaky rivers, springs and seepage faces (drains), and head-dependent flux boundaries, are formulated. Because of differences in the formulation and calculation of the conductance terms, the conductance values for the head-dependent source-sink functions from the Trescott-Larson Twin Cities model were multiplied by the area of the appropriate model cell for conversion to the McDonald-Harbaugh Twin Cities model. Leaky rivers were simulated using the river package in the McDonald-Harbaugh Twin Cities model, springs and seepage faces were simulated using the drain package, and head-dependent flux boundaries were simulated using the general-head boundary package. Hydraulic heads and flows in the aquifer system calculated by the McDonald-Harbaugh Twin Cities model were compared to those calculated by the Trescott-Larson Twin Cities model to verify that the results calculated by the two models are similar. Mean differences in calculated hydraulic heads for the drift, drift and St. Peter aquifer, and drift and Prairie du Chien-Jordan aquifer model layers ranged from 1.1 to 1.6 feet. Mean differences in calculated hydraulic heads for the drift and Ironton-Galesville aquifer, drift and Eau Claire confining unit, and drift and Mount Simon-Hinckley aquifer model layers were 0.4 feet or less. Large differences in calculated hydraulic heads at a few cells probably were due to differences in the solution methods used in the McDonald-Harbaugh and Trescott-Larson computer codes to calculate hydraulic heads at and near model layer boundaries. Differences in calculated flow rates for the McDonald-Harbaugh and Trescott-Larson Twin Cities models were less than 0.3 cubic feet per second for recharge and the head-dependent source-sink functions. Differences in calculated flow in and flow out of constant-head cells for each model layer for the two models ranged from about 2 cubic feet per second for the Mount Simon-Hinckley aquifer model layer to about 45 cubic feet per second for the Prairie du ChienJordan aquifer model layer. The differences between the net flow rates at constant-head cells calculated by the two models for each model layer were much smaller, ranging from 0.01 cubic feet per second for the Ironton-Galesville and Mount Simon-Hinckley aquifer model layers to 8.39 cubic feet per second for the St. Peter aquifer model layer. Differences in the calculated ground-water budgets for the two models were 5.3 percent for the total sources and 4.4 percent for the total sinks.

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USGS1996

Analysis of hydrogeologic properties in the Prairie du Chien-Jordan aquifer, Shakopee Mdewakanton Sioux Community, southeastern Minnesota

The Prairie du Chien-Jordan aquifer is a major source of water for many communities in southeastern Minnesota. The water-supply well for the Shakopee Mdewakanton Sioux Community derives water from the Jordan part of the aquifer. An aquifer test in the Prairie du Chien-Jordan aquifer in the area of the Shakopee Mdewakanton Sioux Community was completed in November 1995. The test consisted of pumping water from a public works well open to the Jordan part of the aquifer and measuring drawdown in this well and two observation wells. This was followed by measuring recovery in the wells after the pumping was terminated. The Neuman (1974) method for unconfined aquifers was used to analyze data collected from the two observation wells during the drawdown and recovery periods, resulting in a range of estimated aquifer hydraulic properties. Aquifer transmissivity ranged from 4,710 to 7,660 ft 2 /d and aquifer storativity ranged from 8.24 x 10 -5 to 1.60 x 10 -4 . These values are generally in close agreement for all four sets of data, given the limitations of the test, indicating that the test results are accurate and representative of the aquifer hydrogeologic properties. The lack of late-time data made it impossible to accurately assess aquifer specific yield.

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USGS1996

Hydrogeology and ground-water quality of glacial-drift aquifers, Leech Lake Indian Reservation, north-central Minnesota

Among the duties of the water managers of the Leech Lake Indian Reservation in north-central Minnesota are the development and protection of the water resources of the Reservation. The U.S. Geological Survey, in cooperation with the Leech Lake Indian Reservation Business Committee, conducted a three and one half-year study (1988-91) of the ground-water resources of the Leech Lake Indian Reservation. The objectives of this study were to describe the availability and quality of ground water contained in glacial-drift aquifers underlying the Reservation. Aquifers and confining units are present throughout the entire thickness of the glacial drift in the study area, which includes the Leech Lake Indian Reservation and adjacent parts of Beltrami, Hubbard, Itasca, and Cass Counties in north-central Minnesota, an area of approximately 2,145 square miles. An unconfined aquifer underlies most of the central and north-central parts of the study area. The saturated thickness of the aquifer ranges from 0 to about 105 feet. Horizontal hydraulic conductivity, estimated from 19 slug tests, ranges from 0.6 to 31 feet per day. The transmissivity of the aquifer ranges from 19 to more than 20,000 feet squared per day and is greatest in an area from west of Cass Lake to Lake Winnibigoshish. Theoretical maximum well yields range from less than 10 to about 2,000 gallons per minute. The unconfined and uppermost confined aquifers are physically and hydraulically separated by a fine-grained confining unit, consisting of till or lake deposits, that ranges in thickness from 3 to 254 feet. The thickness of the uppermost confined aquifer ranges from 5 to about 53 feet. On the basis of specific-capacity data, the transmissivity of the aquifer ranges from less than 100 feet squared per day in the northeastern and southeastern parts of the study area to about 21,000 feet squared per day near Cass Lake. Theoretical maximum well yields range from less than 10 to about 2,600 gallons per minute. Recharge to the ground-water system is predominantly from precipitation that infiltrates to the saturated zone. An analysis of four hydrographs for observation wells screened in the unconfined aquifer indicated spring recharge amounts during 1989 of 1-4 inches. Discharge from the ground-water system occurs by leakage to streams, lakes, and wetlands, evapotranspiration, withdrawals by wells, and underflow to the southeast within the Mississippi River Valley. Streamflow measurements indicate that ground-water discharge to the Mississippi River is greater in the western part of the study area between Cass Lake and Lake Winnibigoshish than in the eastern part downstream from Lake Winnibigoshish. The general regional direction of ground-water flow in the unconfined and uppermost confined aquifers is to the east and southeast. Ground-water flow is also toward the Mississippi River and the three large lakes in the study area, Lake Winnibigoshish and Cass and Leech Lakes. Water moves through the ground-water system predominantly horizontally in the aquifers, whereas vertical components of flow are significant in confining units. Downward leakage of water occurs in highland areas where ground water flows downward from overlying till to the uppermost confined aquifer. Water moves vertically upward from deep to shallow aquifers in areas of regional discharge, the Mississippi River, Cass Lake, Lake Winnibigoshish. and Leech Lake. Waters from both the unconfined and uppermost confined aquifers generally are suitable for domestic consumption, crop irrigation, and most other uses. Concentrations of iron and manganese in water from both aquifers frequently exceed levels that may impart an undesirable taste or odor to water. Calcium and bicarbonate are the predominant ions in water from both the unconfined and uppermost confined aquifers. Water from both the unconfined and uppermost confined aquifers is hard to very hard, averaging 187 and 247 milligrams per liter as calcium carbonate, respectively. Differences in the mean concentrations of constituents in waters from the unconfined and uppermost confined aquifers vary. The mean concentrations of chloride, manganese, dissolved organic carbon, sulfate, and dissolved iron were greater for water from the unconfined aquifer than for water from the uppermost confined aquifer. Conversely, the mean concentrations of calcium, potassium, silica, sodium, fluoride, and boron were greater for water from the uppermost confined aquifer than for water from the unconfined aquifer. These higher concentrations of naturally occurring constituents in waters from the uppermost confined aquifer may occur because of the longer flow paths and longer residence times of water in the uppermost confined aquifer as compared to the unconfined aquifer. Nutrients include nitrogen and phosphorus species. The mean concentrations of dissolved nitrogen (NO 2 + NO 3 , dissolved) and total phosphorus were about 5 and 1.5 times greater for water from the unconfined aquifer than for water from the uppermost confined aquifer, respectively. None of the water samples had concentrations of dissolved nitrogen greater than the maximum contaminant level established by the U.S. Environmental Protection Agency (10 milligrams per liter) and only one water sample had a concentration greater than 3 milligrams per liter. Water collected from wells completed in the unconfined aquifer in residential and recreational land-use areas had concentrations of arsenic, cadmium, chromium, copper, lead, mercury, and cyanide equal to or less than 6 micrograms per liter. Concentrations of organic-acid herbicides in water from three wells screened in the unconfined aquifer in managed-forest land-use areas were all below detection levels. Concentrations of U.S. Environmental Protection Agency priority pollutants in water from three wells screened in the unconfined aquifer and from one well screened in the uppermost confined aquifer were also all below detection levels.

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