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At least 379 records · Page 21Linked to original sources
USGS1987

An evaluation of the bedrock aquifer system in northeastern Wisconsin

Ground water is a major source of water in northeastern Wisconsin. The lower Fox River valley, located between Lake Winnebago and Green Bay in northeastern Wisconsin, is the second largest population center in Wisconsin. By 1957, ground-water withdrawals had lowered the potentiometric surface of the aquifer system as much as 440 feet below prepumping levels. With the exception of the city of Green Bay, which converted from ground water to surface water (Lake Michigan) for their municipal water supply in 1957, ground-water withdrawals have continually increased. The report evaluates the bedrock aquifer system in northeastern Wisconsin and describes how the flow regimes in the system have been altered due to ground-water withdrawals. A three-dimensional finite-difference groundwater flow model was used to aid in evaluation of the regional flow system. In order to simplify the study of the aquifer system, the geologic units were grouped into eight geohydrologic units consisting of four aquifers and four confining beds. The aquifers are the more permeable sand and gravel layers in the surficial deposits (aquifer 4), Devonian dolomite-Silurian dolomite (aquifer 3), St. Peter Sandstone- Prairie du Chien Group-Jordan Sandstone Member of the Trempealeau Formation (aquifer 2), and the Galesville Sandstone-Eau Claire Sandstone-Mount Simon Sandstone (aquifer 1). The confining beds are the less permeable silts and clays in the surficial deposits (confining bed 4), Maquoketa Shale-Galena Dolomite-Decorah Shale-Platteville Formation (confining bed 3), St. Lawrence Member of the Trempealeau Formation-Franconia Sandstone (confining bed 2), and the Precambrian crystalline rock (confining bed 1). The following aquifer and confining-bed characteristics were determined to represent the aquifer system of northeastern Wisconsin and were used in the development of the model. Aquifer 4 acts as an upper boundary of the bedrock aquifer system. The hydraulic conductivity of aquifer 3 was 7.9 feet per day and the storage coefficient was estimated to be 0.01. Transmissivity input values to the model for aquifer 2 are based on hydraulic conductivities ranging from 3 to 8 feet per day. The storage coefficient for aquifer 2 was 0.0002. The transmissivity input values to the model for aquifer 1 are based on hydraulic conductivities ranging from 2.5 to 8 feet per day and the storage coefficient was 0.0002. Confining bed 4 acts as an upper confining unit for the underlying bedrock aquifers. A vertical hydraulic conductivity of 0.007 foot per day was assigned to represent confining bed 4. The vertical hydraulic conductivity of confining bed 3 was assigned values of 0.0001 to 0.000004 foot per day. A value of 0.00001 foot per day was used as the vertical hydraulic conductivity for confining bed 2. Confining bed 1 is a lower boundary of the system and was not modeled. Model simulations indicate that, by 1914, ground-water withdrawals from the aquifer system had already impacted the study area. Pumping in the Green Bay metropolitan area had lowered the potentiometric heads in aquifer 1 by 69 feet and in aquifer 2 by 55 feet. Model simulations indicate that, by 1981, ground-water withdrawals have caused a cone of depression centered in the city of De Pere area. The influence of the cone affects almost the entire study area and has significantly altered the horizontal and vertical flow regimes in the aquifer system. In 1981, computed drawdowns below the prepumping potentiometric surface of aquifer 1 range from 0 feet on the western side of the study area to 330 feet in the center of the cone of depression. In aquifer 2, the computed drawdown ranges from 0 feet on the western side of the study area to 253 feet in the center of the cone.

Wisconsin↗
USGS1983

Front-tracking model for convective transport in flowing ground water

A finite-difference numerical model that simulates the convective transport of water or tracer particles through porous media is described. It can be applied to one- or two-dimensional problems involving either steady-state or transient flow. The model tracks representative water or tracer particles, initially located along specified lines, as they move in response to the groundwater velocity filed. Aquifer properties may be both anisotropic and nonhomogeneous. Included in the report is a listing of the program along with input formats and test problem results. The front-tracking model provides a useful first approximation determining the movement of solutes in an aquifer, particularly in cases when dispersion and dilution is of minor consideration. (USGS)

Water-Resources Investigations Report↗
USGS1977

Theoretical drawdown due to simulated pumpage from the Ohio River alluvial aquifer near Siloam, Kentucky

Theoretical drawdown due to simulated pumpage was determined for a site near Siloam, Kentucky by using a digital ground-water-flow model. The maximum sustained yield of water from the single well was shown to be less than 900 gallons per minute, and, for a simulated pumping rate of 450 gallons per minute from each of several wells, the optimum placement for either minimum water-level drawdown or minimum spacing of multiple wells was found to be in a line parallel to and at a distance of about 370 to 600 feet from the Ohio River. An analytical method was used to verify the optimum placement of wells determined by the digital model. (Woodard-USGS)

Kentucky↗
USGS1991

Hydrology, water quality, and simulation of ground-water flow at a taconite-tailings basin near Keewatin, Minnesota

Taconite tailings, a waste product from processing of iron ore, have been deposited in a 2.5-square-mile containment basin near Keewatin, Minnesota, The basin, which is bounded by earthen dikes of compacted drift and clayey bouldery till, contains saturated tailings consisting of chert and other silica-rich particles that range from clay to coarse-sand size. Runoff from the tailings is slight and occurs only after heavy rains and snowmelt. Average discharge from the basin from April 1982 through June 1984 was about 0.6 cubic foot per second. Instantaneous discharge ranged from zero during much of the period to about 140 cubic feet per second following snowmelt in spring 1982. Daily mean discharge from the basin exceeded 20 cubic feet per second on two days during the period of study. Water levels in wells range from 0 to 25 feet below the tailings surface; seasonal fluctuations range from 2 to 8 feet. Ground water flows radially from a mound in the north-central part of the basin under a hydraulic gradient of 4.7 x 10 -3 feet per foot. Vertical flow also is downward to drift deposits beneath the tailings. Vertical gradients range from 7.0 x 10 -3 to 6.0 x 10 -1 feet per foot. Saturated thickness of the tailings ranges from about 1 to 35 feet. Estimated horizontal hydraulic conductivity ranges from about 1 to 500 feet per day. Transmissivities range from about 25 feet squared per day in fine tailings to about 350 feet squared per day in coarse tailings. Ground-water recharge from precipitation was 11.8 inches from October 1982 through September 1983. Ground-water outflow as leakage to the underlying drift deposits was 9.9 inches for the same period. Water collected from wells completed in the tailings and from the drainage ditch at the basin outlet is of a mixed type in which the magnesium concentration only slightly exceeds concentrations of calcium and sodium plus potassium, expressed in milliequivalents, and concentrations of sulfate and bicarbonate, expressed in milliequivalents, are equal. Concentrations of arsenic, fluoride, and nitrite plus nitrate in water from the tailings were notably greater than in water from adjacent aquifers. However, only fluoride, manganese, and nitrite plus nitrate concentrations equalled or exceeded State drinking-water standards. Suspended-sediment concentrations in streamflow ranged from less than 1 milligram per liter during low-flow periods to about 4,600 milligrams per liter following snowmelt in the spring of 1982. Numerical-model simulations of ground-water flow near the vicinity of the tailings basin indicate that, if areal recharge were doubled during spring and fall, water levels in wells could average about 4 feet above 1983 levels during these periods. Model results indicate that water levels in the tailings could possibly remain about 5 feet above 1983 levels at the end of the year. Water levels in the tailings at the outlet of the basin could be about 1 foot above 1983 levels during the spring stress period and could be nearly 1.5 feet above 1983 levels during the fall stress period. Under these hypothetical climatic conditions, ground-water contribution to discharge at the outlet could be about 50 cubic feet per second during spring and about 80 cubic feet per second during fall.

Minnesota↗
USGS1997

Geohydrology and Numerical Simulation of the Ground-Water Flow System of Molokai, Hawaii

A two-dimensional, steady-state, areal ground-water flow model was developed for the island of Molokai, Hawaii, to enhance the understanding of (1) the conceptual framework of the ground-water flow system, (2) the distribution of aquifer hydraulic properties, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-element code AQUIFEM-SALT, which simulates flow of fresh ground water in systems that may have a freshwater lens floating on denser underlying saltwater. Model results are in agreement with the general conceptual model of the flow system on Molokai, where ground water flows from the interior, high-recharge areas to the coast. The model-calculated ground-water divide separating flow to the northern and southern coasts lies to either the north or the south of the topographic divide but is generally not coincident with the topographic divide. On the basis of model results, the following horizontal hydraulic conductivities were estimated: (1) 1,000 feet per day for the dike-free volcanic rocks of East and West Molokai, (2) 100 feet per day for the marginal dike zone of the East Molokai Volcano, (3) 2 feet per day for the West Molokai dike complex, (4) 0.02 feet per day for the East Molokai dike complex, and (5) 500 feet per day for the Kalaupapa Volcanics. Three simulations to determine the effects of proposed ground-water withdrawals on water levels and coastal discharge, relative to model-calculated water levels and coastal discharge for 1992-96 withdrawal rates, show that the effects are widespread. For a withdrawal rate of 0.337 million gallons per day from a proposed well about 4 miles southeast of Kualapuu and 3 miles north of Kamiloloa, the model-calculated drawdown of 0.01 foot or more extends 4 miles southeast and 6 miles northwest from the well. For a withdrawal rate of 1.326 million gallons per day from the same well, the model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 9 miles northwest from the well. In a third scenario, the withdrawal rate from an existing well near Kualapuu was increased by 0.826 million gallons per day. The model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 8 miles northwest from the well. In all scenarios, coastal discharge is reduced by an amount equal to the additional withdrawal. Additional data needed to improve the understanding of the ground-water flow system on Molokai include: (1) a wider spatial distribution and longer temporal distribution of water-levels, (2) independent estimates of hydraulic conductivity, (3) improved recharge estimates, (4) information about the vertical distribution of salinity in ground water, (5) streamflow data at additional sites, and (6) improved information about the subsurface geology.

Water-Resources Investigations Report↗
USGS1983

Hydrology of the Little Androscoggin River Valley aquifer, Oxford County, Maine

The Little Androscoggin River valley aquifer, a 15-square-mile sand and gravel valley-fill aquifer in southwestern Maine, is the source of water for the towns of Norway, Oxford, and South Paris. Estimated inflows to the aquifer during the 1981 water year were 16.4 cubic feet per second from precipitation directly on the aquifer, 11.2 cubic feet per second from till covered uplands adjacent to the aquifer, and 1.4 cubic feet per second from surface-water leakage. Outflows from the aquifer were 26.7 cubic feet per second to surface water and 2.3 cubic feet per second to wells. A finite-difference ground-water flow model was used to simulate conditions observed in the aquifer during 1981. Model conditions observed in the aquifer during 1981. Model simulations indicate that a 50 percent reduction of average 1981 recharge to the aquifer would cause water level declines of up to 20 feet in some areas. Model simulations of increased pumping at a high yield well in the northern part of the aquifer indicate that resulting changes in the water table will not be sufficient to intercept groundwater contaminated by a sludge disposal site. Water in the aquifer is low in dissolved solids (average for 38 samples was 67 mg/L), slightly acidic and soft. Ground-water contamination has occurred near a sludge-disposal site and in the vicinity of a sanitary landfill. Dissolved solids in ground water near the sludge disposal site were as much as ten times greater than average background values for the aquifer. (USGS)

Water-Resources Investigations Report↗
USGS2004

Questa baseline and pre-mining ground-water quality investigation. 1. Depth to bedrock determinations using shallow seismic data acquired in the Straight Creek drainage near Red River, New Mexico

In late May and early June of 2002, the U.S. Geological Survey (USGS) acquired four P-wave seismic profiles across the Straight Creek drainage near Red River, New Mexico. The data were acquired to support a larger effort to investigate baseline and pre-mining ground-water quality in the Red River basin (Nordstrom and others, 2002). For ground-water flow modeling, knowledge of the thickness of the valley fill material above the bedrock is required. When curved-ray refraction tomography was used with the seismic first arrival times, the resulting images of interval velocity versus depth clearly show a sharp velocity contrast where the bedrock interface is expected. The images show that the interpreted buried bedrock surface is neither smooth nor sharp, but it is clearly defined across the valley along the seismic line profiles. The bedrock models defined by the seismic refraction images are consistent with the well data.

New Mexico↗
USGS2003

Recalibration of a ground-water flow model of the Mississippi River Valley alluvial aquifer in southeastern Arkansas, 1918-1998, with simulations of hydraulic heads caused by projected ground-water withdrawals through 2049

To evaluate the effects of projected ground water withdrawals, three scenarios were used to simulate a range of possible withdrawals. Five additional stress periods of 10 years each were added to the model to facilitate predictive scenario generation. The predictive scenarios control pumpage by either continuing 1997 pumpage into the future (scenario 1) or by increasing water-use trends into the future (scenario 2 and 3). The ASWCC Critical Ground Water area designation includes a requirement that a 50-percent saturated formation thickness be maintained. For this reason, the level of 50-percent saturated formation thickness is used as a reference surface in the scenario output presented. Animations of simulated heads changing through time are included on the compact disc in the "Animations" folder. In the animations, the level of 50 percent saturated formation thickness is indicated by a mesh surface and the dry cells appear as voids in the model surface.

Arkansas↗
USGS1998

Hydrogeology and simulation of ground-water flow in the Paluxy aquifer in the vicinity of Landfills 1 and 3, U.S. Air Force Plant 4, Fort Worth, Texas

Ground-water contamination of the surficial terrace alluvial aquifer has occurred at U.S. Air Force Plant 4, a government-owned, contractor-operated facility, northwest of Fort Worth, Texas. A poorly constructed monitoring well, P–22M, open to the underlying middle zone of the Paluxy aquifer was installed at landfill 3, October 1987, allowing leakage of contaminated ground water to reach the Paluxy aquifer. This well was plugged and abandoned in November 1995. Additionally, volatile organic compounds have been detected in fractures in the Goodland-Walnut confining unit, the hydrogeologic unit separating the terrace alluvial aquifer from the underlying Paluxy aquifer, beneath the western part of landfill 1. Volatile organic compounds in concentrations near the analytical detection limit were detected in the upper Paluxy prior to the drilling of well P–22M. The ground-water-flow simulation model described in this report was developed to examine the best logistically feasible location to install recovery wells to capture the low concentration (less than 100 micrograms per liter) trichloroethylene plume beneath landfills 1 and 3 (west Paluxy plume). Once the recovery wells were installed (1996), the simulation model was recalibrated with new data. This report documents the capture area of the installed recovery wells. Four geologic units are pertinent to this site-specific model. From oldest to youngest, these are the Glen Rose Formation, Paluxy Formation, Walnut Formation, and Goodland Limestone. The Glen Rose Formation is relatively impermeable in the study area and forms the confining unit underlying the Paluxy Formation. The Paluxy Formation forms the Paluxy aquifer, which is a public drinking water supply for the City of White Settlement. The Walnut Formation and Goodland Limestone form the Goodland-Walnut confining unit overlying the Paluxy aquifer. Near landfill 3, gamma-ray logs indicate three distinct zones of the Paluxy Formation; upper, middle, and lower. The formation is about 170-feet thick near landfill 3, and each zone is about 57-feet thick. Two steady-state simulations using the computer program MODFLOW were analyzed using the particle-tracking computer program, MODPATH. One simulation is the calibration simulation using Paluxy aquifer water-level data for May 1993. The second simulation includes the installed recovery wells. A variably spaced grid was designed for the model. The smallest grid cells, 25 by 25 feet, are in the vicinity of landfills 1 and 3. The largest cells, 4,864.5 by 1,441.5 feet, are at the northwestern corner of the model grid near the Parker-Tarrant County line. The modeling was accomplished with three layers representing the upper, middle, and lower zones of the Paluxy aquifer. Particles, which represent contaminant molecules moving in solution with the ground water, were tracked from well P–22M and an area below landfill 1, at the top of the upper zone of the Paluxy aquifer, for 9 years (forward tracking). The forward tracking estimates where contaminants might move by advection from 1987 to 1996. Analysis of backward tracking from the new recovery wells indicates that the simulated contributing area to the recovery wells intercepts the contaminant plume, minimizing off-site migration of the west Paluxy plume. To determine the effectiveness of the recovery wells, monitoring wells southeast of Building 14 have been installed (1996–97) for sampling.

Texas↗
USGS1978

Digital-model simulation of the glacial-outwash aquifer, Otter Creek-Dry Creek basin, Cortland County, New York

The city of Cortland, New York, and surrounding areas obtain water from the highly productive glacial-outwash aquifer underlying the Otter Creek-Dry Creek basin. Pumpage from the aquifer in 1976 was approximately 6.3 million gallons per day and is expected to increase as a result of population growth and urbanization. A digital ground-water model that uses a finite-difference approximation technique to solve partial differential equations of flow through a porous medium was used to simulate the movement of water within the aquifer. The model was calibrated to equilibrium conditions by comparing water levels measured in the aquifer in March 1976 with those computed by the model. Then, from the simulated water-level surface for March, a transient-condition run was made to simulate the surface as measured in September 1976. Computed water levels presented as contours are generally in close agreement with potentiometric-surface maps prepared from field measurements of March and September 1976.

New York↗
USGS1988

Leachate migration from an in-situ oil-shale retort near Rock Springs, Wyoming

Hydrogeologic factors influencing leachate movement from an in-situ oil-shale retort near Rock Springs, Wyoming, were investigated through models of ground-water flow and solute transport. Leachate, indicated by the conservative ion thiocyanate, has been observed ? mile downgradient from the retort. The contaminated aquifer is part of the Green River Formation and consists of thin, permeable layers of tuff and sandstone interbedded with oil shale. Most solute migration has occurred in an 8-foot sandstone at the top of the aquifer. Ground-water flow in the study area is complexly three dimensional and is characterized by large vertical variations in hydraulic head. The solute-transport model was used to predict the concentration of thiocyanate at a point where ground water discharges to the land surface. Leachate with peak concentrations of thiocyanate--45 milligrams per liter or approximately one-half the initial concentration of retort water--was estimated to reach the discharge area during January 1985. This report describes many of th3 advantages, as well as the problems, of site-specific studies. Data such as the distribution of thin, permeable beds or fractures might introduce an unmanageable degree of complexity to basin-wide studies but can be incorporated readily into site-specific models. Solute migration in the study area occurs primarily in thin, permeable beds rather than in oil-shale strata. Because of this behavior, leachate traveled far greater distances than might otherwise have been expected. The detail possible in site-specific models permits more accurate prediction of solute transport than is possible with basin-wide models. A major problem in site-specific studies is identifying model boundaries that permit the accurate estimation of aquifer properties. If the quantity of water flowing through a study area cannot be determined prior to modeling, the hydraulic conductivity and ground-water velocity will be poorly estimated.

Water Supply Paper↗
USGS1999

Geohydrology and numerical simulation of the ground-water flow system of Kona, Island of Hawaii

Prior to the early 1990's, ground-water in the Kona area, which is in the western part of the island of Hawaii, was withdrawn from wells located within about 3 mi from the coast where water levels were less than 10 feet above sea level. In 1990, exploratory drilling in the uplands east of the existing coastal wells first revealed the presence of high water levels (greater than 40 feet above sea level) in the Kona area. Measured water levels from 16 wells indicate that high water levels exist in a zone parallel to and inland of the Kona coast, between Kalaoa and Honaunau. Available hydrologic and geophysical evidence is generally consistent with the concept that the high ground-water levels are associated with a buried dike complex. A two-dimensional (areal), steady-state, freshwater-saltwater, sharp-interface ground-water flow model was developed for the Kona area of the island of Hawaii, to enhance the understanding of (1) the distribution of aquifer hydraulic properties, (2) the conceptual framework of the ground-water flow system, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-difference code SHARP. To estimate the hydraulic characteristics, average recharge, withdrawals, and water-level conditions for the period 1991-93 were simulated. The following horizontal hydraulic-conductivity values were estimated: (1) 7,500 feet per day for the dike-free volcanic rocks of Hualalai and Mauna Loa, (2) 0.1 feet per day for the buried dike complex of Hualalai, (3) 10 feet per day for the northern marginal dike zone (north of Kalaoa), and (4) 0.5 feet per day for the southern marginal dike zone between Palani Junction and Holualoa. The coastal leakance was estimated to be 0.05 feet per day per foot. Measured water levels indicate that ground water generally flows from inland areas to the coast. Model results are in general agreement with the limited set of measured water levels in the Kona area. Model results indicate, however, that water levels do not strictly increase in an inland direction and that a ground-water divide exists within the buried dike complex. Data are not available, however, to verify model results in the area near and inland of the model-calculated ground-water divide. Three simulations to determine the effects of proposed withdrawals from the high water-level area on coastal discharge and water levels, relative to model-calculated, steady-state coastal discharge and water levels for 1997 withdrawal rates, show that the effects are widespread. During 1997, the total withdrawal of ground water from the high water-level area between Palani Junction and Holualoa was about 1 million gallons per day. Model results indicate that it may not be possible to withdraw 25.6 million gallons per day of freshwater from this area between Palani Junction and Holualoa, but that it may be possible to withdraw between 5 to 8 million gallons per day from the same area. For a proposed withdrawal rate of 5.0 million gallons per day uniformly distributed to 12 sites between Palani Junction and Holualoa, the model-calculated drawdown of 0.01 foot or more extends about 9 miles north-northwest and about 7 miles south of the proposed well sites. In all scenarios, freshwater coastal discharge is reduced by an amount equal to the additional freshwater withdrawal. Additional data needed to improve the understanding of the ground-water flow system in the Kona area include: (1) a wider spatial distribution and longer temporal distribution of water levels, (2) improved information about the subsurface geology, (3) independent estimates of hydraulic conductivity, (4) improved recharge estimates, and (5) information about the vertical distribution of salinity in ground water.

Hawaii↗
USGS1995

Estimated availability of water from stratified-drift aquifers in the Concord River Basin, Massachusetts

An understanding of water availability in the Concord River Basin for public and private supply requires an understanding of the interaction between surface-water and ground-water systems. This understanding is needed because excessive ground-water withdrawals may reduce streamflows to unacceptable levels. The U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Management, Office of Water Resources, studied the Concord River Basin to estimate the volume of water available from stratified-drift aquifers. A combined hydrograph-separation and streamflow-duration-curve analysis indicates that 20.8 million cubic feet of water could be withdrawn from the stratified-drift aquifer above the South Acton streamflow-gaging station during a 102-day period of no recharge before streamflow would be reduced to a prescribed minimum level. This volume, which equals 2.85 million cubic feet per square mile of stratified drift, was used to estimate volume of available water in 17 aquifer areas in the Concord River Basin. The total volume of available water in the Concord River Basin is estimated to be 561 million cubic feet. Finite-difference ground-water-flow models for the River Meadow Brook aquifer area and the Sudbury and Concord aquifer area quantified the current and potential water availability. The results of three withdrawal simulations for each aquifer area indicate that the 1989 ground-water withdrawal rates would not exceed the volume of water that would be available during a 102-day period of no recharge if water-table drawdowns were not considered. However, results do indicate that volumes of withdrawn water would exceed the available water in the two aquifer areas if maximum lowering of the water table as a percentage of total saturated thickness were 10 and 65 percent at existing and hypothetical wells.

Massachusetts↗
USGS1995

Hydrogeology and ground-water flow of the drift and Platteville aquifer system, St. Louis Park, Minnesota

Three aquifers and two confining units have been delineated within the drift underlying the area near the site of a former coal-tar distillation and wood-preserving plant in St. Louis Park, Minnesota. The hydrogeologic units of the drift, in descending order, are the upper drift aquifer, the upper drift confining unit, the middle drift aquifer, the lower drift confining unit. and the lower drift aquifer. A contamination plume consisting of coal-tar derivatives exists in the drift aquifers and in the Platteville aquifer underlying the southern part of the plant site and areas to the south and east of the plant site. The upper drift aquifer has a maximum saturated thickness of about 25 feet. Horizontal hydraulic conductivities of the upper drift aquifer range from less than 1 to about 25 feet per day in peat areas and from about 50 to 400 feet per day in sand and gravel areas. The upper drift confining unit generally is less than 20 feet thick, with a maximum thickness of 62 feet. The saturated thickness of the middle drift aquifer generally is 20 to 30 feet in areas where the aquifer is both overlain and underlain by a confining unit. The horizontal hydraulic conductivity of the middle drift aquifer ranges from about 50 to 500 feet per day. The lower drift confining unit is as much as 50 feet thick. Model-computed vertical hydraulic conductivities for the upper and lower drift confining units ranged from 0.0002 to 5 feet per day. The lower drift aquifer consists of discontinuous sand and gravel deposits overlying Platteville Formation bedrock and has a maximum thickness of 20 feet where it is overlain by the lower drift confining unit. Water in the drift aquifers and in the Platteville aquifer generally flows from the northwest to the southeast under a hydraulic gradient of about 10 feet per mile. The drift confining units and the Glenwood confining unit. when present, control the vertical movement of water through the aquifers. Discontinuities in these confining units greatly influence patterns of ground-water flow. A numerical cross-sectional ground-water-flow model was used to test concepts of flow of ground water through the drift aquifers and the Platteville aquifer. particularly the effects of confining units and bedrock valleys on vertical flow. The model has eight layers representing, in descending order: ( 1) the upper drift aquifer. (2) the upper drift confining unit, (3) the middle drift aquifer, (4) the upper part of the lower drift confining unit, (5) the lower part of the lower drift confining unit and lower drift aquifer, (6) the Platteville aquifer and bedrock valley deposits, (7) the St. Peter aquifer, and (8) the Prairie du Chien-Jordan aquifer. A sensitivity analysis indicated that model-calculated hydraulic heads in the drift aquifers and in the Platteville aquifer were most sensitive to variations in: (1) the horizontal hydraulic conductivities of the middle drift aquifer, (2) the transmissivities of the Platteville and St. Peter aquifers, (3) the vertical hydraulic conductivities of the lower drift confining unit and the drift material filling the bedrock valley, and (4) the vertical hydraulic conductivity of the basal St. Peter confining unit. The model-calculated water budget indicated that recharge from infiltration of precipitation to the upper and middle drift aquifers and the upper drift confining unit accounts for about 41 percent of the total sources of water. The remaining 59 percent is from subsurface inflow from the west (through specified-head cells). About 70 percent of the outflow from the eastern model boundary was simulated as discharge from the model layers representing the Platteville aquifer and bedrock valley deposits and the St. Peter aquifer. The calibrated simulation indicated that about 99 percent of the total leakage of water from the drift aquifers and from the Platteville aquifer to the underlying St. Peter aquifer occurs through areas where the Glenwood confining unit is absent or discontinuous. Hypothetical changes of the hydraulic properties and the extent of confining units were simulated using the calibrated steady-state model. Increasing the vertical hydraulic conductivity of model layer 4, representing the upper part of the lower drift confining unit, by a factor of 100 in the western part of the cross section resulted in decreased model-calculated leakage to the St. Peter aquifer through the bedrock valley represented in the eastern part of the cross-sectional model. A hypothetical extension of vertical hydraulic conductivities representing the Glenwood confining unit along the entire cross-sectional model resulted in a 98 percent reduction in the model-calculated amount of water leaking from the Platteville aquifer and bedrock valley deposits to the underlying St. Peter aquifer. Model simulations indicate that vertical ground-water flow from the drift aquifers and from the Platteville aquifer to underlying bedrock aquifers is greatest through bedrock valleys. The convergence of flow paths near bedrock valleys and the greater volume of water moving through the valleys would likely result in both increased concentrations and greater vertical movement of contaminants in areas underlain by bedrock valleys as compared to areas not underlain by bedrock valleys. Model results also indicate that field measurements of hydraulic head might not help locate discontinuities in confining units and additional test drilling to locate discontinuities might be necessary.

Minnesota↗
USGS2007

Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Contrasting Glacial Valley-Fill Settings, Rhode Island

Areas contributing recharge and sources of water to a production well field in the Village of Harrisville and to a production well field in the Town of Richmond were delineated on the basis of calibrated, steady-state ground-water-flow models representing average hydrologic conditions. The study sites represent contrasting glacial valley-fill settings. The area contributing recharge to a well is defined as the surface area where water recharges the ground water and then flows toward and discharges to the well. In Harrisville, the production well field is composed of three wells in a narrow, approximately 0.5-mile-wide, valley-fill setting on opposite sides of Batty Brook, a small intermittent stream that drains 0.64 square mile at its confluence with the Clear River. Glacial stratified deposits are generally less areally extensive than previously published. The production wells are screened in a thin (30 feet) but transmissive aquifer. Paired measurements of ground-water and surface-water levels indicated that the direction of flow between the brook and the aquifer was generally downward during pumping conditions. Long-term mean annual streamflow from two streams upgradient of the well field totaled 0.72 cubic feet per second. The simulated area contributing recharge for the 2005 average well-field withdrawal rate of 224 gallons per minute extended upgradient to ground-water divides in upland areas and encompassed 0.17 square mile. The well field derived 62 percent of pumped water from intercepted ground water and 38 percent from infiltrated stream water from the Batty Brook watershed. For the maximum simulated well-field withdrawal of 600 gallons per minute, the area contributing recharge expanded to 0.44 square mile to intercept additional ground water and infiltration of stream water; the percentage of water derived from surface water, however, was the same as for the average pumping rate. Because of the small size of Batty Brook watershed, most of the precipitation recharge in the watershed was withdrawn by the well field at the maximum rate either by intercepted ground water or indirectly by infiltrated stream water. Because the production wells are screened in a thin and transmissive aquifer in a small watershed, simulated ground-water traveltimes from recharge locations to the discharging wells were relatively short: 93 percent of the traveltimes were 10 years or less. In Richmond, the production well field is composed of two wells adjacent to and east of the Wood River in a moderately broad, approximately 1.2-mile-wide, valley-fill setting. The wells are screened in a transmissive aquifer with saturated thickness greater than 60 feet. Streamflow measurements in Baker Brook, a tributary to the Wood River 0.4 mile north of the well-field site, indicated that natural net loss of streamflow between the upland-valley contact and a downstream site was 0.12 cubic feet per second under average hydrologic conditions. Simulated areas contributing recharge for the maximum well-field pumping rate of 675 gallons per minute and for one-half the maximum rate extended northeastward from the well field to ground-water divides in upland areas. The area contributing recharge also included a remote, isolated area on the opposite side of the Wood River from the well field. The model simulation indicated that the well field did not derive any of its water from the Wood River because of the large watershed and associated quantity of ground water available for capture by the well field. The area contributing recharge for one-half the maximum rate was 0.31 square mile and the primary source of water to the well field was direct precipitation recharge. Fifteen percent of the water withdrawn from the production wells, however, was obtained from Baker Brook, indicating the importance of even small, distant tributary streams to the contributing area to a well. The area contributing recharge on the opposite side of the Wood River is

Scientific Investigations Report↗
USGS1984

Ground-water resources of the White River basin, Randolph County, Indiana

The two major aquifer systems in Randolph County, Indiana are sand and gravel and bedrock (limestone, dolomite, and shale of Silurian to Odovician age). The average thickness of the sands and gravels is 15 ft, and the aquifers are areally discontinuous. The bedrock aquifer underlies the entire study area and is estimated to be 150 ft in thickness. Six pumping plans simulated in the two systems by a five-layer, digital, ground-water-flow model provide data for an assessment of the water-yielding potential of the systems. The model indicates that as much as 2.5 million gallons per day can be pumped from the aquifers at some locations. This and similar rates of pumping may cause drawdown greater than 5 feet in 10 to 50 percent of the study area. About half the stream reaches were reduced in flow by more than 10 percent by the simulated pumping. However, reaches where discharge exceeded more than 2 cubic feet per second were not affected to this degree. (USGS)

Indiana↗
USGS2004

Vertical gradients in water chemistry and age in the southern High Plains Aquifer, Texas, 2002

The southern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of New Mexico and Texas. Despite the aquifer's importance to the overall economy of the southern High Plains, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey's National Water-Quality Assessment Program, water samples from nested, short-screen monitoring wells installed in the southern High Plains aquifer at two locations (Castro and Hale Counties, Texas) were analyzed for field parameters, major ions, nutrients, trace elements, dissolved organic carbon, pesticides, stable and radioactive isotopes, and dissolved gases to evaluate vertical gradients in water chemistry and age in the aquifer. Tritium measurements indicate that recent (post-1953) recharge was present near the water table and that deeper water was recharged before 1953. Concentrations of dissolved oxygen were largest (2.6 to 5.6 milligrams per liter) at the water table and decreased with depth below the water table. The smallest concentrations were less than 0.5 milligram per liter. The largest major-ion concentrations generally were detected at the water table because of the effects of overlying agricultural activities, as indicated by postbomb tritium concentrations and elevated nitrate and pesticide concentrations at the water table. Below the zone of agricultural influence, major-ion concentrations exhibited small increases with depth and distance along flow paths because of rock/water interactions and mixing with water from the underlying aquifer in rocks of Cretaceous age. The concentration increases primarily were accounted for by dissolved sodium, bicarbonate, chloride, and sulfate. Nitrite plus nitrate concentrations at the water table were 2.0 to 6.1 milligrams per liter as nitrogen, and concentrations substantially decreased with depth in the aquifer to a maximum concentration of 0.55 milligram per liter as nitrogen. Dissolved-gas and nitrogen-isotope data from the deep wells in Castro County indicate that denitrification occurred in the aquifer, removing 74 to more than 97 percent of the nitrate originally present in recharge. There was no evidence of denitrification in the deep part of the aquifer in Hale County. After correcting for denitrification effects, the background concentration of nitrate in water recharged before 1953 ranged from 0.4 to 3.2 milligrams per liter as nitrogen, with an average of 1.6 milligrams per liter as nitrogen. The d15N composition of background nitrate at the time of recharge was estimated to range from 9.6 to 12.3 per mil. Mass-balance models indicate that the decreases in dissolved oxygen and nitrate concentrations and small increases in major-ion concentrations along flow paths can be accounted for by small amounts of silicate-mineral and calcite dissolution; SiO2, goethite, and clay-mineral precipitation; organic-carbon and pyrite oxidation; denitrification; and cation exchange. Mass-balance models for some wells also required mixing with water from the underlying aquifer in rocks of Cretaceous age to achieve mole and isotope balances. Carbon mass transfers identified in the models were used to adjust radiocarbon ages of water samples recharged before 1953. Adjusted radiocarbon ages ranged from less than 1,000 to 9,000 carbon-14 years before present. Radiocarbon ages were more sensitive to uncertainties in the carbon-14 content of recharge than uncertainties in carbon mass transfers, leading to 1-sigma uncertainties of about ?2,000 years in the adjusted ages. Despite these relatively large uncertainties in adjusted radiocarbon ages, it appears that deep water in the aquifer was considerably older (at least 1,000 years) than water near the water table. There was essentially no change in ground-water age with depth in deeper parts of the aquifer, indicating that water in that

Texas↗
USGS2002

Near-real-time simulation and internet-based delivery of forecast-flood inundation maps using two-dimensional hydraulic modeling--A pilot study for the Snoqualmie River, Washington

A system of numerical hydraulic modeling, geographic information system processing, and Internet map serving, supported by new data sources and application automation, was developed that generates inundation maps for forecast floods in near real time and makes them available through the Internet. Forecasts for flooding are generated by the National Weather Service (NWS) River Forecast Center (RFC); these forecasts are retrieved automatically by the system and prepared for input to a hydraulic model. The model, TrimR2D, is a new, robust, two-dimensional model capable of simulating wide varieties of discharge hydrographs and relatively long stream reaches. TrimR2D was calibrated for a 28-kilometer reach of the Snoqualmie River in Washington State, and is used to estimate flood extent, depth, arrival time, and peak time for the RFC forecast. The results of the model are processed automatically by a Geographic Information System (GIS) into maps of flood extent, depth, and arrival and peak times. These maps subsequently are processed into formats acceptable by an Internet map server (IMS). The IMS application is a user-friendly interface to access the maps over the Internet; it allows users to select what information they wish to see presented and allows the authors to define scale-dependent availability of map layers and their symbology (appearance of map features). For example, the IMS presents a background of a digital USGS 1:100,000-scale quadrangle at smaller scales, and automatically switches to an ortho-rectified aerial photograph (a digital photograph that has camera angle and tilt distortions removed) at larger scales so viewers can see ground features that help them identify their area of interest more effectively. For the user, the option exists to select either background at any scale. Similar options are provided for both the map creator and the viewer for the various flood maps. This combination of a robust model, emerging IMS software, and application interface programming should allow the technology developed in the pilot study to be applied to other river systems where NWS forecasts are provided routinely.

Water-Resources Investigations Report↗