Geology of the Potosi quadrangle, Grant County, Wisconsin, and Dubuque County, Iowa
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Precambrian geology of Florence West quadrangle, Florence County, Wisconsin, and Iron County, Michigan
No abstract available.
Wisconsin, Michigan↗
Precambrian geology of Florence East quadrangle, Florence County, Wisconsin, and Iron County, Michigan
No abstract available.
Michigan, Wisconsin↗
Geology and ground-water resources of Outagamie County, Wisconsin
Outagamie County is in east-central Wisconsin. It has no serious groundwater problem at present, but the county is important as a recharge area for the principal aquifers supplying water to Brown County and industrial Green Bay to the east. The county is covered by glacial drift and lake deposits of the Wisconsin stage of glaciation. In the northwestern quarter of the county these deposits rest upon Precambrian crystalline rocks; throughout the remainder of the county they are underlain by sandstone, limestone, dolomite, and shale of Cambrian and Ordovician age. ·where they are sufficiently thick, and where more productive formations are absent, glacial sand and gravel are an important source of ground water. The major sources, however, are the St. Peter sandstone, of Ordovician age, and the sandstones of the Upper Cambrian series. The Precambrian crystalline rocks, which underlie all the county, yield little or no water to wells. The regional dip of the Paleozoic bedrocks is 25 to 30 feet per mile eastward and southeastward. There are no major folds, but the thickness of each geologic unit may change from place to place because of predepositional or postdepositional erosion. There is no conclusive evidence of major faulting in the area. Ground water in Outagamie County occurs under both water-table (unconfined) and artesian (confined) conditions. The source of the ground water is precipitation which falls on the surface and percolates downward into the underlying permeable materials. Regional movement of ground water in the eastern third of the county is controlled by the bedrock structure, and the discharge is toward the east and south. Throughout the rest of the county the movement of water is controlled mainly by bedrock and surface topography, and the water moves toward the streams and bedrock valleys. Water-level :fluctuations follow definite patterns. Where the effects of pumping are at a minimum, water levels reach a high in April or May, decline through the summer months owing to natural discharge, and lack of recharge, and do not begin to recover until after the ground thaws in the spring. In areas of heavy pumping where this pattern is distorted, the lowest water levels occur in the early fall and recoveries begin in October or November after the period of heaviest pumping. Pumpage in the county was estimated to be about 9.0 million gallons per day (mgd) in 1951 and 1952. Nearly half of this was for industrial, commercial, and public-supply use along the Fox River. Wells, most of which are drilled by the cable-tool method, range in diameter from 3 to 16 inches and in depth from 10 or 20 feet to 804 feet. In the alluvium and glacial drift 1~- to 2¥2-inch driven wells are common. Pumping tests were made to determine the hydraulic characteristics of the aquifers at Seymour, Appleton, and Hortonville. The average coefficient of transmissibility at Seymour is about 18,000 gpd per foot; at Appleton it is about 19,000 gpd per foot. The coefficients of storage are 0.00022 and 0.00015 at Seymour and Appleton, respectively. Movement of ground water out of the county, assuming an average transmissibility of 18,000 gpd per foot, was calculated to be more than 10 mgd toward the southeast. The ground water differs greatly in chemical quality from well to well, but it is generally a very hard calcium magnesium bicarbonate water, some of it high in iron. To aid in determining the source of well waters, 22 chemical analyses were plotted on a logarithmic diagram to obtain characteristic patterns for waters from several geologic sources.
Wisconsin↗
Geology and ground-water resources of Rock County, Wisconsin
Rock County is in south-central Wisconsin adjacent to the Illinois State line. The county has an area of about 723 square miles and had a population of about 113,000 in 1957 ; it is one of the leading agricultural and industrial counties in the State. The total annual precipitation averages about 32 inches, and the mean annual temperature is about 48 ? F. Land-surface altitudes are generally between 800 and 00 feet, but range from 731 feet, where the Rock River flows into Illinois, to above 1,080 feet, at several places in the northwestern part of the county. The northern part of Rock County consists of the hills and kettles of a terminal moraine which slopes southward to a flat, undissected outwash plain. The southeastern part of the county is an area of gentle slopes, whereas the southwestern part consists of steep-sided valleys and ridges. Rock County is within the drainage basin of the Rock River, which flows southward through the center of the county. The western and southwestern parts of ,the county are drained by the Sugar River und Coon Creek, both of which flow into the Pecatonica River in Illinois and thence into the Rock River. The southeastern part of the county is drained by Turtle Creek, which also flows into Illinois before joining the Rock River. Nearly all the lakes and ponds are in the northern one-third of the county, the area of most recent glaciation. The aquifers in Rock County are of sedimentary origin and include deeply buried sandstones, shales, and dolomites of the Upper Cambrian series. This series overlies crystalline rocks of Precambrian age and supplies water to all the cities and villages in the county. The St. Peter sandstone of Ordovician age underlies all Rock County except where the formation has been removed by erosion in the Rock and Sugar River valleys, and perhaps in Coon Creek valley. The St. Peter sandstone is the principal source of water for domestic, stock, and small industrial wells in the western half of the county. This sandstone also yields some water to uncased wells that tap the deeper rocks of the Upper Cambrian series. East of the Rock River the Platteville, Decorah, and Galena formations undifferentiated, or Platteville-Galena unit, is the principal source of water for domestic and stock wells. Unconsolidated deposits of glacial origin cover most of Rock County and supply water to many small wells. In the outwash deposits along the Rock River, wells of extremely high capacity have been developed for industrial and municipal use. The most significant feature of the bedrock surface in Rock County is the ancestral Rock River valley, which has been filled with glacial outwash to a depth of at least 396 feet below the present land surface. East of the buried valley the bedrock has a fiat, relatively undissected surface. West of the valley the bedrock surface is rugged and greatly dissected. Ground water in Rock County occurs under both water-table and artesian conditions; however, because of the interconnection and close relation of all ground water in the county, the entire system is considered to be a single groundwater body whose surface may be represented by one piezometric map. Recharge occurs locally, throughout the county. Nearly all recharge is derived directly from precipitation that percolates downward to become a part of the groundwater body. Natural movement of water in the consolidated water-bearing units is generally toward the buried Rock and Sugar River valleys. Movement of water in the sandstones of Cambrian age was calculated to be about 44 million gallons a day toward the Rock River. Discharge from wells in Rock County in 1957 was about 23 million gallons a day. Nearly 90 percent of this water was drawn from the area along the Rock River. Drilled wells, most of which were drilled by the cable-tool method, range in diameter from 3 to 26 inches, and in depth from 46 to 1,225 feet. Driven wells in alluvium and glacial drift are usually 1? to 2? in
Wisconsin↗
Ground-water resources of Waupaca County, Wisconsin
Waupaca County is in east-central Wisconsin. No serious ground-water problems existed in 1960 except in a few localities where crystalline rock is near land surface or is covered by nearly impermeable till. The use of ground water for irrigation has not appreciably affected ground-water levels. The county is covered by Pleistocene till, glaciolacustrine (lake), glaciofluvial (stream), and eolian (wind) deposits. In the northern three-quarters of the county these deposits overlie Precambrian crystalline rocks; in the remainder, they overlie sandstone of Cambrian age and, to a minor extent, dolomite of the Prairie du Chien Group of Ordovician age. The deposits of Pleistocene age, particularly outwash, are the principal sources of ground water except in those areas where the saturated thickness is slight or the permeability low. The sandstone of Cambrian age is an important aquifer in the southeastern part of the county. The crystalline rocks of Precambrian age yield little water except from fractures, joints, and weathered zones, and they are a source of water only in areas where better aquifers are absent. Ground water in Waupaca County occurs under both water-table and artesian conditions. The source of this ground water is precipitation that falls on the county and percolates downward to the zone of saturation. Regional movement of ground water is to the Wolf River. In most of the county the direction of movement is eastward or southeastward, except in the southeastern corner of the county, where the movement is westward. Water-level fluctuations reflect the variations of ground-water storage or artesian pressure in response to variations in recharge and discharge. Declining water levels from 1956 to 1959 reflect a period of below-normal precipitation, and rising water levels in late 1959 and 1960 reflect above-normal precipitation. Average precipitation, runoff, and evapotranspiration in 1959 are estimated to be 1,000, 400, and 600 mgd (million gallons per day) respectively. Pumpage in the county was estimated to be about 4 mgd in 1959, and about half of this amount was used for public supplies. A pumping test of a well in outwash deposits near Waupaca indicated that at that point the coefficient of transmissibility is about 100,000 gpd (gallons per day) per ft, the permeability is about 1,000 gpd per sq ft, the coefficient of storage is about 0.2, and the specific capacity is 41 gpm (gallons per minute) per ft of drawdown. These hydraulic characteristics are probably in the same order of magnitude as the characteristics of outwash deposits in the county in general. The water from wells in Waupaca County, although hard and generally containing iron, is good for most purposes.
Wisconsin↗
Geology and water resources of Portage County, Wisconsin
Portage County has abundant resources of generally good quality water and, although water problems exist locally, depletion or general scarcity of water is not likely in the foreseeable future. The county receives annually about 31 inches of precipitation, of which about 21 inches is lost as evaportranspiration. The average annual water yield is about 10.6 inches and consists of about 10.3 inches of runoff to streams, about 0.2 inch of water which leaves the county as underflow, and about 0.1 inch of water which is used consumptively. The surface-water resources include 104 lakes, about 110 miles of streams that discharge about 600 cfs (cubic feet per second) to the Wisconsin, Waupaca, and Little Wolf Rivers, and the Wisconsin River which has an average flow of about 2.400 cfs. Extensive deposits of outwash sand and gravel, sandy till, and alluvium release annually about 460 cfs of ground water to the streams. The principal source of ground water is thick deposits of glacial drift that occur over all but the northwestern part of the county. Although as much as 100 feet of sandstone underlies the drift in the southern part, it is not an important aquifer. Impermeable crystalline rocks of Precambrian age underlie all the aquifers and limit the downward movement of water. The county has been divided into areas having similar geologic and hydrologic conditions. These areas are here named the "sand-plain province," the "drift province," and the "drift-crystalline-rock province." The sand-plain province and the eastern part of the drift province have the greatest potential for development of large ground-water supplies. Wells yielding 1,000 to 2,000 gpm (gallons per minute) can be developed in the sand-plain province and wells yielding about 500 gpm can be developed in the drift province. Nearly all the communities in the county have water resources adequate for future expansion. An exception to this is Junction City where only a limited supply of poor quality water is readily available. Additional supplies can be developed from ground water in the Mill Creek area or from the Wisconsin River. In the sand-plain and drift provinces, ground-water runoff is about 9 inches a year and surface runoff is about 1 inch a year and of short duration. In the drift-crystalline-rock province, however, ground-water runoff is about 2 inches a year and surface runoff is about 8 inches a year and varies greatly in rate of flow. Surface and ground water are closely interrelated throughout the county and constitute a single resource. Streams, lakes, and marshes are the visible part of the ground-water surface and ground water moves slowly and continuously toward these surface points of discharge. Pumping for irrigation has temporarily lowered water levels in the vicinity of wells but has not lowered regional water levels. Pumpage has intercepted and utilized some of the recharge that would have been rapidly discharged from the aquifer, but it has not materially depleted the flow of streams. The 1955-59 decline in water levels and lake stages is attributed to a deficiency in precipitation and not to the increased pumpage from irrigation wells. To prevent excessive declines in water levels, high-capacity wells should be adequately spaced about 2,500 feet between wells pumping 1,000 gpm for 90 days. In the Stevens Point area, heavy pumping of wells near the Plover River induces recharge to ground water and thus reduces local declines in the water level. The chemical quality of ground water is generally good, but, locally, hard water and undesirable amounts of iron require treatment.
Wisconsin↗
Water resources of Langlade County, Wisconsin
Langlade County depends almost exclusively on ground water pumped from the glacial sand and gravel deposits for its water needs. Well yields of 10 to 20 gallons per minute can be obtained from these deposits throughout most of the county. Yields of 500 to 1,000 gallons per minute are obtained for irrigation of crops from glacial outwash deposits in some areas of the county and particularly in the extensive 125-square-mile outwash plain in south-central Langlade County. Very low yields of less than 5 gallons per minute are obtainable for private domestic use from Precambrian crystalline rocks in areas of the county where overlying glacial material is thin. Glacial deposits are more than 400 feet thick in glacial moraine areas of east-central Langlade County; saturated thicknesses exceed 250 feet in the north-central part of the county. Horizontal hydraulic conductivity values of glacial material range from less than 1 foot per day in fine-grained glacial tills in western parts of the county to approximately 145 feet per day in outwash deposits. The transmissivity of glacial deposits ranges from essentially zero in areas of unsaturated glacial material to more than 40,000 feet squared per day in the outwash plain of southcentral Langlade County. Most surface and ground water originates from precipitation falling within the county. Streams and ground water flow into the county only in areas along its northern edge. Ground water supplies about 70 percent of the annual streamflow. Ground-water composition in Langlade County is similar to most ground water in the State and is of suitable quality for most uses. It is a calcium magnesium bicarbonate type. Concentrations of total dissolved solids are relatively low and range from 71 to 369 milligrams per liter, with a median value of 144 milligrams per liter. Dissolved iron and manganese concentrations exceeded secondary (aesthetic) standards in about 30 percent of all ground-water analyses. Values for total hardness as calcium carbonate ranged from 48 to 280 milligrams per liter for all samples. Ground water classified as very hard was confined to the southern part of the county where glacial deposits are higher in carbonate mineral content. An average of about 4.7 million gallons of water was pumped daily in Langlade County in 1983. Irrigation and fish rearing are the major ground-water uses in the county. An average of about 4.2 million gallons per day was pumped for irrigation during the months of June, July, and August. Results of this study show that present irrigation pumpage rates have little effect on groundwater levels in the Antigo Flats area.
Wisconsin↗
Geologic map of the Kieler quadrangle, Grant County, Wisconsin and Jo Daviess County, Illinois
No abstract available.
Iliinois, Wisconsin↗
Hydrogeology and ground-water quality of the county road a disposal site on the Bad River Indian Reservation, Ashland County, Wisconsin: 1997-98
The County Road A disposal site, located on the Bad River Indian Reservation, Ashland County, Wisconsin, contains papermill sludge generated by a former mill in the City of Ashland. Since the time of disposal (1968-1970) the site has been the subject of investigations by the U.S. Bureau of Indian Affairs, the U.S. Environmental Protection Agency, and private consultants. During 1997- 1998, an investigation was conducted by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency and the Natural Resources Department of the Bad River Indian Tribe, to evaluate the hydrogeology and groundwater quality of the disposal site, particularly with respect to the hydraulic connection between two ponds at the site and the shallow ground-waterflow system. Additional monitoring wells and well points were installed, and additional hydrogeologic, ground-water quality, and geophysical data were collected. The data from this and previous studies were integrated and interpreted.
Wisconsin↗
Ground-water resources and geology of Walworth County, Wisconsin
Population growth in Walworth County, Wisconsin, requires an increasing amount of ground water. Good quality water is available from the sand-and gravel, Niagara, Galena-Platteville, and sandstone aquifers in the county. As much as 15 gallons per minute (0.95 liters per second) can be obtained from individual wells almost everywhere in the county. Well yields of 1,000 gallons per minute (63 liters per second) are available from glacial drift where it contains sufficient thickness of saturated sand and gravel. The sand-and-gravel aquifer is an important source of municipal water. Estimated well yields from most of the Niagara aquifer, a Silurian age dolomite as thick as 125 feet (38.1 meters), exceed 100 gallons per minute (6.3 liters per second). The Niagara aquifer occurs in the eastern third of the county. The Galena-Platteville aquifer, chiefly dolomite, is present in the western half of the county where it is as thick as 325 feet (99.1 meters). Estimated yields from this aquifer exceed 500 gallons per minute (32 liters per second). The sandstone aquifer underlies the entire county and ranges from less than 800 feet (240 meters) thick in the northwest corner to more than 2,200 feet (670 meters) in the east. This aquifer is capable of yielding 1,000 gallons per minute (63 liters per second) to individual wells and is a principal source of municipal water.
Wisconsin↗
Changes in macrolichens of Douglas County, Wisconsin
Macrolichens collected in Douglas County, Wisconsin in the 1940s, 1970s and 2009 are compared in order to determine floristic changes. Species sensitive to disturbance, land use change, and possibly climate that have changed over these time spans are identified and suggested for further monitoring. The total lichen flora of Douglas County is compared with Harris’ 1977 publication of the lichens of the Straits of Mackinac.
Wisconsin↗
Ground-water resources and geology of Jefferson County, Wisconsin
A steadily increasing population in Jefferson County, Wisconsin, is expanding the need for good-quality ground water. This need can be met by good-quality water available from the sand-and-gravel, Galena-Platteville, and sandstone aquifers. As much as 15 gallons per minute (0.95 liters per second) can be obtained from wells almost everywhere in the county. Yields of more than 1,000 gallons per minute (63 liters per second) are available from glacial drift where it contains a sufficient thickness of saturated sand and gravel. The Galena-Platteville aquifer is a dolomite that occurs mainly in the eastern one-half of the county and is locally more than 300 feet (90 meters) thick. Estimated well yields from this aquifer exceed 500 gallons per minute (32 liters per second). The sandstone aquifer underlies nearly the entire county except for small areas in the northwest corner. It is more than 1,100 feet (330 meters) thick in the southwest along the Dane-Jefferson County line. This aquifer is capable of yielding more than 1,000 gallons per minute (63 liters per second) to wells in much of the county and is the principal source of municipal water. The chemical quality of water from the three aquifers is similar. The water is very hard, having a median hardness between 315 and 325 milligrams per liter. Median values for dissolved solids range between 325 and 349 milligrams per liter. Iron and manganese commonly are present in bothersome amounts (combined total exceeding 0.3 milligrams per liter. About 13.0 million gallons per day (0.570 cubic meters per second) of ground water was pumped in the county in 1972, 87 percent from the sandstone aquifer. About 62 percent of the total water pumped was for industrial and commercial purposes, 26 percent for residential use, and 12 percent for municipal, irrigation, and institutional use.
Wisconsin↗
Simulation of the shallow groundwater-flow system in the Forest County Potawatomi Community, Forest County, Wisconsin
The shallow groundwater system in the Forest County Potawatomi Comminity, Forest County, Wisconsin, was simulated by expanding and recalibrating a previously calibrated regional model. The existing model was updated using newly collected water-level measurements, inclusion of surface-water features beyond the previous near-field boundary, and refinements to surface-water features. The updated model then was used to calculate the area contributing recharge for seven existing and three proposed pumping locations on lands of the Forest County Potawatomi Community. The existing wells were the subject of a 2004 source-water evaluation in which areas contributing recharge were calculated using the fixed-radius method. The motivation for the present (2012) project was to improve the level of detail of areas contributing recharge for the existing wells and to provide similar analysis for the proposed wells. Delineated 5- and 10-year areas contributing recharge for existing and proposed wells extend from the areas of pumping to delineate the area at the surface contributing recharge to the wells. Steady-state pumping was simulated for two scenarios: a base-pumping scenario using pumping rates that reflect what the Community currently (2012) pumps (or plans to in the case of proposed wells), and a high-pumping scenario in which the rate was set to the maximum expected from wells installed in this area, according to the Forest County Potawatomi Community Natural Resources Department. In general, the 10-year areas contributing recharge did not intersect surface-water bodies. The 5- and 10-year areas contributing recharge simulated at the maximum pumping rate at Bug Lake Road may intersect Bug Lake. At the casino near the Town of Carter, Wisconsin, the 10-year areas contributing recharge intersect infiltration ponds. At the Devils Lake and Lois Crow Drive wells, areas contributing recharge are near cultural features, including residences.
Wisconsin↗
The 2016 groundwater flow model for Dane County, Wisconsin
A new groundwater flow model for Dane County, Wisconsin, replaces an earlier model developed in the 1990s by the Wisconsin Geological and Natural History Survey (WGNHS) and the U.S. Geological Survey (USGS). This modeling study was conducted cooperatively by the WGNHS and the USGS with funding from the Capital Area Regional Planning Commission (CARPC). Although the overall conceptual model of the groundwater system remains largely unchanged, the incorporation of newly acquired high-quality datasets, recent research findings, and improved modeling and calibration techniques have led to the development of a more detailed and sophisticated model representation of the groundwater system. The new model is three-dimensional and transient, and conceptualizes the county’s hydrogeology as a 12-layer system including all major unlithified and bedrock hydrostratigraphic units and two high-conductivity horizontal fracture zones. Beginning from the surface down, the model represents the unlithified deposits as two distinct model layers (1 and 2). A single layer (3) simulates the Ordovician sandstone and dolomite of the Sinnipee, Ancell, and Prairie du Chien Groups. Sandstone of the Jordan Formation (layer 4) and silty dolostone of the St. Lawrence Formation (layer 5) each comprise separate model layers. The underlying glauconitic sandstone of the Tunnel City Group makes up three distinct layers: an upper aquifer (layer 6), a fracture feature (layer 7), and a lower aquifer (layer 8). The fracture layer represents a network of horizontal bedding-plane fractures that serve as a preferential pathway for groundwater flow. The model simulates the sandstone of the Wonewoc Formation as an upper aquifer (layer 9) with a bedding-plane fracture feature (layer 10) at its base. The Eau Claire aquitard (layer 11) includes shale beds within the upper portion of the Eau Claire Formation. This layer, along with overlying bedrock units, is mostly absent in the preglacially eroded valleys along the Yahara River valley and in northeastern Dane County. Layer 12 represents the Mount Simon sandstone as the lowermost model layer. It directly overlies the Precambrian crystalline basement rock, whose top surface forms the lower boundary of the model. The model uses the USGS MODFLOW-NWT finite-difference code, a standalone version of MODFLOW-2005 that incorporates the Newton (NWT) solver. MODFLOW-NWT improves the handling of unconfined conditions by smoothing the transition from wet to dry cells. The model explicitly simulates groundwater–surface-water interaction with streamflow routing and lake-level fluctuation. Model input included published and unpublished hydrogeologic data from recent estimates of aquifer hydraulic conductivities. A spatial groundwater recharge distribution was obtained from a recent GIS-based, soil-water-balance model for Dane County. Groundwater withdrawals from pumping were simulated for 572 wells across the entire model domain, which includes Dane County and portions of seven neighboring counties—Columbia, Dodge, Green, Iowa, Jefferson, Lafayette, and Rock. These wells withdrew an average of 60 million gallons per day (mgd) over the 5-year period from 2006 through 2010. Within Dane County, 385 wells were simulated with an average withdrawal rate of 52 mgd. Model calibration used the parameter estimation code PEST, and calibration targets included heads, stream and spring flows, lake levels, and borehole flows. Steady-state calibration focused on the period 2006 through 2010; the transient calibration focused on the 7-week drought period from late May through July 2012. This model represents a significant step forward from previous work because of its finer grid resolution, improved hydrostratigraphic discretization, transient capabilities, and more sophisticated representation of surface-water features and multi-aquifer wells. Potential applications of the model include evaluation of potential sites for and impacts of new high-capacity wells, development of wellhead protection plans, evaluating the effects of changing land use and climate on groundwater, and quantifying the relationships between groundwater and surface water.
Wisconsin↗
Geology of the Little Commonwealth area, Florence County, Wisconsin
The Little Commonwealth exploration in northeastern Florence County, Wisconsin, is underlain by highly ferruginous clastic rocks that are stratigraphically equivalent to vitreous quartzite. The relationship between these rocks is one of abrupt facies change, with complete gradation between facies. This stratigraphic unit is conformably underlain by sericitic phyllite and unconformably overlain by slate and graywacke of the lower part of the Dunn Creek formation of upper Animikie age. The strata are vertical and minor structures due to tectonic movement are present. Some of the deformation may be of pre-diagenetic origin. Metamorphism of the Little Commonwealth rocks has developed abundant stilpnomelane, garnet, and martite. Metasomatism is indicated by the occurrence of tourmaline, pyrite, chalcopyrite, and arsenopyrite. The area is probably in the biotite zone of regional metamorphism.
Open-File Report↗
Simulation of the Groundwater-Flow System in Pierce, Polk, and St. Croix Counties, Wisconsin
Groundwater is the sole source of residential water supply in Pierce, Polk, and St. Croix Counties, Wisconsin. A regional three-dimensional groundwater-flow model and three associated demonstration inset models were developed to simulate the groundwater-flow systems in the three-county area. The models were developed by the U.S. Geological Survey in cooperation with the three county governments. The objectives of the regional model of Pierce, Polk, and St. Croix Counties were to improve understanding of the groundwaterflow system and to develop a tool suitable for evaluating the effects of potential water-management programs. The regional groundwater-flow model described in this report simulates the major hydrogeologic features of the modeled area, including bedrock and surficial aquifers, groundwater/surface-water interactions, and groundwater withdrawals from high-capacity wells. Results from the regional model indicate that about 82 percent of groundwater in the three counties is from recharge within the counties; 15 percent is from surface-water sources, consisting primarily of recirculated groundwater seepage in areas with abrupt surface-water-level changes, such as near waterfalls, dams, and the downgradient side of reservoirs and lakes; and 4 percent is from inflow across the county boundaries. Groundwater flow out of the counties is to streams (85 percent), outflow across county boundaries (14 percent), and pumping wells (1 percent). These results demonstrate that the primary source of groundwater withdrawn by pumping wells is water that recharges within the counties and would otherwise discharge to local streams and lakes. Under current conditions, the St. Croix and Mississippi Rivers are groundwater discharge locations (gaining reaches) and appear to function as 'fully penetrating' hydraulic boundaries such that groundwater does not cross between Wisconsin and Minnesota beneath them. Being hydraulic boundaries, however, they can change in response to water withdrawals. Tributary rivers act as 'partially penetrating' hydraulic boundaries such that groundwater can flow underneath them through the deep sandstone aquifers. The model also demonstrates the effects of development on groundwater in the study area. Water-level declines since predevelopment (no withdrawal wells) are most pronounced where pumping is greatest and flow between layered aquifers is impeded by confining units or faults. The maximum simulated water-level decline is about 40 feet in the deep Mount Simon aquifer below the city of Hudson, Wisconsin. Three inset models were extracted from the regional model to demonstrate the process and additional capabilities of the U.S. Geological Survey MODFLOW code. Although the inset models were designed to provide information about the groundwater-flow system, results from the inset models are presented for demonstration purposes only and are not sufficiently detailed or calibrated to be used for decisionmaking purposes without refinement. Simulation of groundwater/lake-water interaction around Twin Lakes near Roberts, in St. Croix County, Wisconsin, showed that groundwater represents approximately 5 to 20 percent of the overall lake-water budget. Groundwater-contributing areas to streams in western Pierce County are generally similar in size to the surface-water-contributing areas but do not necessarily correspond to the same land area. Transient streamflow simulations of Osceola Creek in Polk County demonstrate how stream base flow can be influenced not only by seasonal precipitation and recharge variability but also by systematic changes to the system, such as groundwater withdrawal from wells.
Scientific Investigations Report↗