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At least 721 records · Page 40Linked to original sources
USGS1991

Documentation of a computer program to simulate aquifer-system compaction using the modular finite-difference ground-water flow model

Removal of ground water by pumping from aquifers may result in compaction of compressible fine-grained beds that are within or adjacent to the aquifers. Compaction of the sediments and resulting land subsidence may be permanent if the head declines result in vertical stresses beyond the previous maximum stress. The process of permanent compaction is not routinely included in simulations of ground-water flow. To simulate storage changes from both elastic and inelastic compaction, a computer program was written for use with the U.S. Geological Survey modular finite-difference ground- water flow model. The new program, the Interbed-Storage Package, is designed to be incorporated into this model. In the Interbed-Storage Package, elastic compaction or expansion is assumed to be proportional to change in head. The constant of proportionality is the product of the skeletal component of elastic specific storage and the thickness of the sediments. Similarly, inelastic compaction is assumed to be proportional to decline in head. The constant of proportionality is the product of the skeletal component of inelastic specific storage and the thickness of the sediments. Storage changes are incorporated into the ground-water flow model by adding an additional term to the right-hand side of the flow equation. Within a model time step, the package appropriately apportions storage changes between elastic and inelastic components on the basis of the relation of simulated head to the previous minimum (preconsolidation) head. Two tests were performed to verify that the package works correctly. The first test compared model-calculated storage and compaction changes to hand-calculated values for a three-dimensional simulation. Model and hand-calculated values were essentially equal. The second test was performed to compare the results of the Interbed-Storage Package with results of the one-dimensional Helm compaction model. This test problem simulated compaction in doubly draining confining beds stressed by head changes in adjacent aquifers. The Interbed-Storage Package and the Helm model computed essentially equal values of compaction. Documentation of the Interbed-Storage Package includes data input instructions, flow charts, narratives, and listings for each of the five modules included in the package. The documentation also includes an appendix describing input instructions and a listing of a computer program for time-variant specified-head boundaries. That package was developed to reduce the amount of data input and output associated with one of the Interbed-Storage Package test problems.

Techniques of Water-Resources Investigations↗
USGS1985

Simulated effects of increased recharge on the ground-water flow system of Yucca Mountain and vicinity, Nevada-California

A study was performed to assess the potential effects of changes in future climatic conditions on the groundwater system in the vicinity of Yucca Mountain, the site of a potential mined geologic repository for high-level nuclear wastes. These changes probably would result in greater rates of precipitation and, consequently, greater rates of recharge. The study was performed by simulating the groundwater system, using a two-dimensional, finite-element, groundwater flow model. The simulated position of the water table rose as much as 130 meters near the U.S. Department of Energy 's preferred repository area at Yucca Mountain for a simulation involving a 100-percent increase in precipitation compared to modern-day conditions. Despite the water table rise, no flooding of the potential repository would occur at its current proposed location. According to the simulation, springs would discharge south and west of Timber Mountain, along Fortymile Canyon, in the Amargosa Desert near Lathrop Wells and Franklin Lake playa, and near Furnace Creek Ranch in Death Valley, where they presently discharge. Simulated directions of groundwater flow paths near the potential repository area generally would be the same for the baseline (modern-day climate) and the increased-recharge simulations, but the magnitude of flow would increase by 2 to 4 times that of the baseline-simulation flow. (USGS)

California, Nevada↗
USGS2001

Simulation of ground-water flow in the Mojave River basin, California

The proximity of the Mojave River ground-water basin to the highly urbanized Los Angeles region has led to rapid growth in population and, consequently, to an increase in the demand for water. The Mojave River, the primary source of surface water for the region, normally is dry-except for a small stretch of perennial flow and periods of flow after intense storms. Thus, the region relies almost entirely on ground water to meet its agricultural and municipal needs. Ground-water withdrawal since the late 1800's has resulted in discharge, primarily from pumping wells, that exceeds natural recharge. To better understand the relation between the regional and the floodplain aquifer systems and to develop a management tool that could be used to estimate the effects that future stresses may have on the ground-water system, a numerical ground-water flow model of the Mojave River ground-water basin was developed, in part, on the basis of a previously developed analog model. The ground-water flow model has two horizontal layers; the top layer (layer 1) corresponds to the floodplain aquifer and the bottom layer (layer 2) corresponds to the regional aquifer. There are 161 rows and 200 columns with a horizontal grid spacing of 2,000 by 2,000 feet. Two stress periods (wet and dry) per year are used where the duration of each stress period is a function of the occurrence, quantity of discharge, and length of stormflow from the headwaters each year. A steady-state model provided initial conditions for the transient-state simulation. The model was calibrated to transient-state conditions (1931-94) using a trial-and-error approach. The transient-state simulation results are in good agreement with measured data. Under transient-state conditions, the simulated floodplain aquifer and regional aquifer hydrographs matched the general trends observed for the measured water levels. The simulated streamflow hydrographs matched wet stress period average flow rates and times of no flow at the Barstow and Afton Canyon gages. Steady-state particle-tracking was used to estimate travel times for mountain-front and streamflow recharge. The simulated travel times for mountain-front recharge to reach the area west of Victorville were about 5,000 to 6,000 years; this result is in reasonable agreement with published results. Steady-state particle-tracking results for streamflow recharge indicate that in most subareas along the river, the particles quickly leave and reenter the river. The complaint that resulted in the adjudication of the Mojave River ground-water basin alleged that the cumulative water production upstream of the city of Barstow had overdrafted the ground-water basin. In order to ascertain the effect of pumping on ground-water and surface-water relations along the Mojave River, two pumping simulations were compared with the 1931-90 transient-state simulation (base case). The first simulation assumed 1931-90 pumping in the upper region (Este, Oeste, Alto, and Transition zone model subareas) but with no pumping in the remainder of the basin, and the second assumed 1931-90 pumping in the lower region (Centro, Harper Lake, Baja, Coyote Lake, and Afton Canyon model subareas) but with no pumping in remainder of the basin. In the upper region, assuming pumping only in the upper region, there was no change in storage, recharge from the Mojave River, ground-water discharge to the Mojave River, or evapotranspiration when compared with the base case. In the lower region, assuming pumping only in the upper region, there was storage accretion, decreased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. In the upper region, assuming pumping only in the lower region, there was storage accretion, decreased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. In the lower region, assuming pumping only in the lower region, there was less storage depletion, increased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. Overall, pumping in the lower region does not negatively affect the upper region; however, pumping in the upper region negatively affects the lower region by decreasing recharge from the Mojave River. Streamflow, pumpage, and water-level data from calendar years 1995-99 were used to validate the calibrated ground-water flow model, that is, to test that the ground-water flow model will duplicate measured data for a noncalibration period without modification of the model parameters. In general, the simulated results are in good agreement with the measured data, and the simulated hydrographs for wells in the floodplain and regional aquifers follow the measured water-level trends. Simulated streamflow data for the 1995-99 wet and dry stress periods at the Lower Narrows, Barstow, and Afton Canyon were compared with the measured data for average streamflow for the same periods; in general, the model reflects 1995-99 streamflow conditions. The simulation results also indicate that the streambed conductance values calibrated to the 1931-94 conditions reasonably simulate the 1995-99 conditions and therefore can be used for predictive purposes. To visualize the magnitude, spatial distribution, and timing of water-level changes in the basin through time, simulated hydraulic heads for 1932-99 were compared with simulated hydraulic heads for 1931. Greater than average annual inflows to the Mojave River from the headwaters during the late 1930's and throughout much of the 1940's resulted in simulated hydraulic heads that were higher than the 1931 hydraulic heads along the Mojave River in most model subareas. Parts of the Baja and Harper Lake model subareas had declines in the simulated hydraulic head because of the increase in agricultural pumpage. By 1960, the simulated hydraulic heads were lower than the simulated hydraulic heads for 1931 in all model subareas of the floodplain and the regional aquifers because of pumpage. After 1960, the size and the magnitude of the areas of the regional aquifer for which simulated hydraulic heads were lower than those for 1931 continued to increase until the end of the simulation (1999). Along the Mojave River, hydraulic heads fluctuated in the floodplain aquifer in response to recharge during years with large inflows with little apparent effect on the simulated hydraulic heads in the regional aquifer. Three water-management alternatives were evaluated to determine their effect on ground-water resources using the calibrated ground-water flow model. The water-management alternatives consider the artificial recharge of imported water allocated to the Mojave Water Agency (MWA): the first assumes that zero percent of the MWA allocation is available (alternative 1), the second assumes that 50 percent of the MWA allocation is available (alternative 2), and the third assumes that 100 percent of the MWA allocation is available (alternative 3). Each of the three water-management alternatives were evaluated for a 20-year drought. Streamflow conditions were simulated using the 20-year drought of 1945-64 with associated calibrated stream parameters. Management alternative 1 results in a reduction in ground-water recharge from the Mojave River compared with average recharge for 1995-99; this reduction is reflected in simulated hydraulic-head declines between 1999 and 2019 of as much as 45 feet. Management alternatives 2 and 3 result in no change in recharge from the Mojave River for management alternative 2 and a small increase for management alternative 3 when compared with recharge for management alternative 1. The artificial recharge of imported water causes increases in simulated hydraulic head for both management alternatives at each of the artificial-recharge sites. Some of the increases are related to water that recharges into areas of low transmissivity which implies that the recharge operations may benefit from being distributed over a larger area.

California↗
USGS1982

A digital-computer model of the Big Sioux aquifer in Minnehaha County, South Dakota

A finite-difference digital model was used to simulate steady-state conditions of the Big Sioux aquifer in Minnehaha County. Average water levels and average base flow discharge (4.9 cu ft/s) of the Big Sioux River were based on data from 1970 through 1979. The computer model was calibrated for transient conditions by simulating monthly historic conditions for 1976. During 1976, pumpage was offset mostly by surface-water recharge to the aquifer from January through June and ground-water discharge from storage from July through December. Measured drawdowns during 1976 generally were less than 2 feet except in the Sioux Falls city well field where drawdowns were as much as 15 feet. The model was used to study the effects of increased withdrawals under three hypothetical hydrologic situations. One hypothetical situation consisted of using 1976 pumping rates, recharge, and evapotranspiration but the Big Sioux River dry. The pumping rate after 16 months was decreased by 40 percent from the actual pumping rate for that month in order to complete the monthly simulation without the storage being depleted at a nodal area. The second hypothetical situation consisted of a pumpage rate of 44.4 cubic feet per second from 60 wells spaced throughout the aquifer under historic 1976 hydrologic conditions. The results were that the aquifer could supply the additional withdrawal. The third hypothetical situation used the same hydrologic conditions as the second except that recharge was zero and the Big Sioux River was dry downstream from row 54. After 18 monthly simulations, the pumping rate was decreased by 44 percent to prevent pumping wells from depleting the aquifer, and, at that rate, 63 percent of the water being pumped was being replaced by water from the river. (USGS)

Water-Resources Investigations Report↗
USGS1987

Movement and fate of crude-oil in contaminants in the subsurface environment at Bemidji, Minnesota: Chapter C in U.S. Geological Survey program on toxic waste--ground-water contamination: Proceedings of the Third technical meeting, Pensacola, Florida, March 23-27, 1987

On August 20, 1979, a pipeline break in a remote area near Bemidji, Minn. (fig. C-l), resulted in the release of 1.5x10 5 L (liters) of crude oil. Although about 1.1x10 5 L were removed from the site as part of the cleanup, some crude oil infiltrated the ground and percolated to the water table. The spill occurred in the recharge area of a local flow system that discharges to a small lake 300 m (meters) downgradient (Hult, 1984). The aquifer is a pitted and dissected outwash plain underlain at a depth of about 20 m by low-permeability till. Crude oil is floating on the water table about 8 m below land surface and has migrated about 20 m as a separate fluid phase. Soluble petroleum derivatives have dissolved in and are moving with ground water. Volatile constituents are migrating through the unsaturated zone by diffusion. The abstracts presented in this chapter provide an overview of ongoing efforts to combine the results of interdependent, interdisciplinary research into the comprehensive understanding of the physical, chemical, and biological processes that will be needed to develop predictive models of contaminant mobilization, transport, and fate. Franzi investigates the relationship between depositional and post-depositional processes and the heterogeneity and anisotropy of the aquifer. Post-depositional subsidence and collapse caused by melting of stagnant ice has created significant geomorphic and hydrogeologic structures. Miller describes a preliminary ground-water flow and chemical-transport model used to assess the effect of these hydrologic discontinuities, estimate aquifer properties, and to guide continuing field work. Abstracts by Siegel, Bennett, and Berndt describe studies of dissolved inorganic constituents and parameters done to characterize the geochemical environments in and around the site. An anoxic zone, probably plume shaped, extends downgradient of the oil pool and into an oxic zone that surrounds the contamination. Carbonate minerals are actively dissolving in the oxic spray zone upgradient of the oil pool where oil is being mineralized, whereas quartz is dissolving underneath the oil by organic-acid complexation. Selective leaching experiments show that fractionation of metals is also occurring where the aquifer matrix is contaminated. Morphological analysis of quartz sand grains clearly show unusual rock-water interactions are occurring in the anaerobic contaminant zone. Preliminary analysis indicates the possibility of an organic/quartz interaction that is significantly increasing the mobility of silica through the system. Predictions of the evolution and ultimate geometry of contaminant plumes resulting from spills require quantitative descriptions of the rate of mass transfer from the organic fluid to ground water. Pfannkuch presents laboratory and field work that describe how the the rate of oil dissolution, and therefore the strength of the contaminant source, is controlled by fluctuations in ground-water velocity and water-table fluctuations.

Minnesota↗
USGS1996

A three-dimensional method-of-characteristics solute-transport model (MOC3D)

This report presents a model, MOC3D, that simulates three-dimensional solute transport in flowing ground water. The model computes changes in concentration of a single dissolved chemical constituent over time that are caused by advective transport, hydrodynamic dispersion (including both mechanical dispersion and diffusion), mixing (or dilution) from fluid sources, and mathematically simple chemical reactions (including linear sorption, which is represented by a retardation factor, and decay). The transport model is integrated with MODFLOW, a three-dimensional ground-water flow model that uses implicit finite-difference methods to solve the transient flow equation. MOC3D uses the method of characteristics to solve the transport equation on the basis of the hydraulic gradients computed with MODFLOW for a given time step. This implementation of the method of characteristics uses particle tracking to represent advective transport and explicit finite-difference methods to calculate the effects of other processes. However, the explicit procedure has several stability criteria that may limit the size of time increments for solving the transport equation; these are automatically determined by the program. For improved efficiency, the user can apply MOC3D to a subgrid of the primary MODFLOW grid that is used to solve the flow equation. However, the transport subgrid must have uniform grid spacing along rows and columns. The report includes a description of the theoretical basis of the model, a detailed description of input requirements and output options, and the results of model testing and evaluation. The model was evaluated for several problems for which exact analytical solutions are available and by benchmarking against other numerical codes for selected complex problems for which no exact solutions are available. These test results indicate that the model is very accurate for a wide range of conditions and yields minimal numerical dispersion for advection-dominated problems. Mass-balance errors are generally less than 10 percent, and tend to decrease and stabilize with time.

Water-Resources Investigations Report↗
USGS2004

Simulation of ground-water flow and evaluation of water-management alternatives in the Assabet River Basin, Eastern Massachusetts

Water-supply withdrawals and wastewater disposal in the Assabet River Basin in eastern Massachusetts alter the flow and water quality in the basin. Wastewater discharges and stream-flow depletion from ground-water withdrawals adversely affect water quality in the Assabet River, especially during low-flow months (late summer) and in headwater areas. Streamflow depletion also contributes to loss of aquatic habitat in tributaries to the river. In 19972001, water-supply withdrawals averaged 9.9 million gallons per day (Mgal/d). Wastewater discharges to the Assabet River averaged 11 Mgal/d and included about 5.4 Mgal/d that originated from sources outside of the basin. The effects of current (2004) and future withdrawals and discharges on water resources in the basin were investigated in this study. Steady-state and transient ground-water-flow models were developed, by using MODFLOW-2000, to simulate flow in the surficial glacial deposits and underlying crystalline bedrock in the basin. The transient model simulated the average annual cycle at dynamic equilibrium in monthly intervals. The models were calibrated to 19972001 conditions of water withdrawals, wastewater discharges, water levels, and nonstorm streamflow (base flow plus wastewater discharges). Total flow through the simulated hydrologic system averaged 195 Mgal/d annually. Recharge from precipitation and ground-water discharge to streams were the dominant inflow and outflow, respectively. Evapotranspiration of ground water from wetlands and non-wetland areas also were important losses from the hydrologic system. Water-supply withdrawals and infiltration to sewers averaged 5 and 1.3 percent, respectively, of total annual out-flows and were larger components (12 percent in September) of the hydrologic system during low-flow months. Water budgets for individual tributary and main stem subbasins identified areas, such as the Fort Meadow Brook and the Assabet Main Stem Upper subbasins, where flows resulting from anthropo-genic activities were relatively large percentages, compared to other subbasins, (more than 20 percent in September) of total out-flows. Wastewater flows in the Assabet River accounted for 55, 32, and 20 percent of total nonstorm streamflow (base flow plus wastewater discharge) out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September. The ground-water-flow models were used to evaluate water-management alternatives by simulating hypothetical scenarios of altered withdrawals and discharges. A scenario that included no water management quantified nonstorm stream-flows that would result without withdrawals, discharges, septic-system return flow, or consumptive use. Tributary flows in this scenario increased in most subbasins by 2 to 44 percent relative to 19972001 conditions. The increases resulted mostly from variable combinations of decreased withdrawals and decreased infiltration to sewers. Average annual nonstorm streamflow in the Assabet River decreased slightly in this scenario, by 2 to 3 percent annually, because gains in ground-water discharge were offset by the elimination of wastewater discharges. A second scenario quantified the effects of increasing withdrawals and discharges to currently permitted levels. In this simulation, average annual tributary flows decreased in most subbasins, by less than 1 to 10 percent relative to 19972001 conditions. In the Assabet River, flows increased slightly, 1 to 5 percent annually, and the percentage of wastewater in the river increased to 69, 42, and 27 percent of total nonstorm streamflow out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September. A third set of scenarios quantified the effects of ground-water discharge of wastewater at four hypothetical sites, while maintaining 19972000 wastewater discharges to the Assabet River. Wastewater, discharged at a constant rate that varied among sites from 0.3 to 1

Scientific Investigations Report↗
USGS2007

Hydrogeologic investigation, water chemistry analysis, and model delineation of contributing areas for City of Tallahassee public-supply wells, Tallahassee, Florida

Ground water from the Upper Floridan aquifer is the sole source of water supply for Tallahassee, Florida, and the surrounding area. The City of Tallahassee (the City) currently operates 28 water-supply wells; 26 wells are distributed throughout the City and 2 are located in Woodville, Florida. Most of these wells yield an ample supply of potable water; however, water from several wells has low levels of tetrachloroethylene (PCE). The City removes the PCE from the water by passing it through granular-activated carbon units before distribution. To ensure that water-supply wells presently free of contamination remain clean, it is necessary to understand the ground-water flow system in sufficient detail to protect the contributing areas. Ground-water samples collected from four public-supply wells were analyzed for tritium ( 3 H), chlorofluorocarbons (CFCs), and sulfur hexafluoride (SF 6 ). Using data for the CFC compounds, apparent ground-water ages ranged from 7 to 31 years. For SF 6 , the apparent ages tended to be about 5 to 10 years younger than those from CFCs. Apparent ages based on the tritium/tritiogenic helium-3 ( 3 H/ 3 He trit ) method ranged from 26 to 33 years. The three dating methods indicate that the apparent age of ground water generally decreases from northern to southern Leon County. This southward trend of decreasing ages is consistent with increasing amounts of recharge that occur as ground water moves from north to south. The ground-water age data derived by geochemical and tracer analyses were used in combination with the flow model and particle tracking to determine an effective porosity for the Hawthorn clays and Upper Floridan aquifer. The effective porosities for the Upper Floridan aquifer that resulted in best model matches were averaged to produce an effective porosity of 7 percent, and the effective porosities for the Hawthorn clays that resulted in a match were averaged to produce an effective porosity of 22 percent. Probabilistic contributing areas were determined for 26 City wells using MODFLOW and MODPATH. For each probabilistic contributing area delineated, the model was run 100 times and the results were analyzed statistically. For each of the 100 runs, a different hydraulic conductivity for each of the zones was assigned to the Upper Floridan aquifer. The hydraulic conductivities were generated randomly assuming a lognormal probability distribution; the mean of the distribution was equal to the hydraulic conductivity from the calibrated model. The 5-year time-dependent capture zones (TDCZs), assuming effective porosities of 0.1, 1, and 7 percent for four representative wells, were delineated. The higher probabilities of capture (greater than 40, 60, and 80 percent) were similar for all effective porosities, and the TDCZ delineated using a 7-percent porosity was slightly smaller; the lower probabilities of capture (greater than 10 and 20 percent) showed a large range of variability.

Florida↗
USGS1985

Geohydrology of the High Plains Aquifer, western Kansas

The High Plains aquifer underlies 174,050 sq mi of eight states (Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming) and contains approximately 3.3 billion acre-ft of water in storage. Saturated thicknesses within the aquifer are as great as 600 ft near the southern border of southwest Kansas. The aquifer is replenished primarily by infiltration from precipitation. Average precipitation at the Garden City Experiment Station is 18.93 in/yr. Groundwater flow is generally from west to east under unconfined conditions. Hydraulic connection with subcropping consolidated aquifers allows ground water to flow vertically in minor quantities. The aquifer is depleted primarily by irrigation. Hydraulic conductivity estimates from 1,612 lithologic logs had an average value of 75 ft/day, with a standard deviation of 35 ft/day. Specific yields estimated from the same lithologic logs had a mean of 0.17 and a standard deviation of 0.047. Water from the High Plains aquifer in Kansas generally is suitable for human and animal consumption and irrigation of crops. Typically, it is a calcium bicarbonate type water, with concentrations of total dissolved solids ranging from 250 to 500 mg/L. The quality of water in the aquifer deteriorates toward the east due to mixing with recharge water containing dissolved minerals leached from the overlying soil and unsaturated zones and mineralized water from adjacent bedrock units. The simulated water budget for the steady state model of predevelopment (pre-1950) conditions in the High Plains aquifer in northwest Kansas showed that annual recharge to the aquifer from infiltration of precipitation was 87,000 acre-ft/yr and from boundary inflow, 21,000 acre-ft/yr. Annual discharge from the aquifer was 108,000 acre-ft/yr, including 81,000 acre-ft/yr from leakage to streams, 23,000 acre-ft from outflow at the boundaries of the aquifer, and 4,000 acre-ft from municipal and industrial pumpage. (Lantz-PTT)

Water-Resources Investigations Report↗
USGS2003

Possible Extent and Depth of Salt Contamination in Ground Water Using Geophysical Techniques, Red River Aluminum Site, Stamps, Arkansas, April 2003

A surface-geophysical investigation of the Red River Aluminum site at Stamps, Arkansas, was conducted in cooperation with the Arkansas Department of Environmental Quality to determine the possible extent and depth of saltwater contamination. Water-level measurements indicate the distance to water level below land surface ranges from about 1.2 to 3.9 feet (0.37 to 1.19 meters) in shallow monitor wells and about 10.5 to 17.1 feet (3.20 to 5.21 meters) in deeper monitoring wells. The two-dimensional, direct-current resistivity method identified resistivities less than 5 ohm-meters which indicated possible areas of salt contamination occurring in near-surface or deep subsurface ground water along four resistivity lines within the site. One line located east of the site yielded data that demonstrated no effect of salt contamination. Sections from two of the five data sets were modeled. The input model grids were created on the basis of the known geology and the results and interpretations of borehole geophysical data. The clay-rich Cook Mountain Formation is modeled as 25 ohm-meters and extends from 21 meters (68.9 feet) below land surface to the bottom of the model (about 52 meters (170.6 feet)). The models were used to refine interpretation of the resistivity data and to determine extent of saltwater contamination and depth to the Cook Mountain Formation. Data from the resistivity lines indicate both near-surface and subsurface saltwater contamination. The near-surface contamination appears as low resistivity (less than 5 ohm-meters) on four of the five resistivity lines, extending up to 775 meters (2,542.8 feet) horizontally in a line that traverses the entire site south to north. Model resistivity data indicate that the total depth of saltwater contamination is about 18 meters (59 feet) below land surface. Data from four resistivity lines identified areas containing low resistivity anomalies interpreted as possible salt contamination. A fifth line located just east of the site showed no saltwater contamination.

Water-Resources Investigations Report↗
USGS1980

Hydrologic analysis of the proposed Badger-Beaver Creeks artificial-recharge project: Morgan County, Colorado

A hydrologic analysis of the proposed Badger-Beaver Creeks artificial-recharge project in Morgan County, Colo., was made with the aid of three digital computer models: A canal-distribution model, a ground-water flow model, and a stream-aquifer model. Statistical summaries of probable diversions from the South Platte River based on a 27-year period of historical flows indicate that an average-annual diversion of 96,000 acre-feet and a median-annual diversion of 43,000 acre-feet would be available. Diversions would sustain water in ponds for waterfowl habitat for an average of about five months per year, with a miximum pond surface area of about 300 acres with the median diversions and a maximum pond surface area of about 1,250 acres at least one-half of the years with the historic diversions. If the annual diversion were 43,000 acre-feet, recharge to the two alluvial aquifers would raise water levels sufficiently to create flowing streams in the channels of Beaver and Badger Creeks while allowing an increase in current ground-water pumping. The only area of significant waterlogging would be along the proposed delivery canal on the west edge of Badger Creek valley. If the total water available were diverted, the aquifer system could not transmit the water fast enough to the irrigation areas to avoid considerable waterlogging in the recharge areas. The impact of the proposed project on the South Platte River basin would be minimal once the ground-water system attained steady-state conditions, but that may take decades with a uniform diversion of the 43,000 acre-feet annually.

Colorado↗
USGS2001

Effects of land use and travel time on the distribution of nitrate in the Kirkwood-Cohansey aquifer system in southern New Jersey

Residents of the southern New Jersey Coastal Plain are increasingly reliant on the unconfined Kirkwood-Cohansey aquifer system for public water supply as a result of increasing population and restrictions on withdrawals from the deeper, confined aquifers. Elevated nitrate concentrations above background levels have been found in wells in the surficial aquifer system in agricultural and urban parts of this area. A three-dimensional steady-state ground-water-flow model of a 400-square-mile study area near Glassboro, New Jersey, was used in conjunction with particle tracking to examine the effects of land use and travel time on the distribution of nitrate in ground and surface water in southern New Jersey. Contributing areas and ground-water ages, or travel times, of water at ground-water discharge points (streams and wells) in the study area were simulated. Concentrations of nitrate were computed by linking land use and age-dependent nitrate concentrations in recharge to the discharge points. Median concentrations of nitrate in water samples collected during 1996 from shallow monitoring wells in different land-use areas were used to represent the concentration of nitrate in aquifer recharge since 1990. On the basis of upward trends in the use of nitrogen fertilizer, the concentrations of nitrate in aquifer recharge in agricultural and urban areas were assumed to have increased linearly from the background value in 1940 (0.07 mg/L as N) to the 1990 (2.5-14 mg/L as N) concentrations. Model performance was evaluated by comparing the simulation results to measured nitrate concentrations and apparent ground-water ages. Apparent ground-water ages at 32 monitoring wells in the study area determined from tritium/helium-3 ratios and sulfur hexafluoride concentrations favorably matched simulated travel times to these wells. Simulated nitrate concentrations were comparable to concentrations measured in 27 water-supply wells in the study area. A time series (1987-98) of nitrate concentrations at base-flow conditions in three streams that drain basins of various sizes and with various land uses was compared to simulated concentrations in these streams. In all three of the streams, a reasonable fit to the measured concentrations was achieved by multiplying the simulated concentration by 0.6. Because nitrate appeared to move conservatively (not degraded or adsorbed) in ground water to wells, the apparent non-conservative behavior in streams indicates that about 40 percent of the nitrate in aquifer recharge is removed by denitrification in the aquifer near the streams and (or) by in-stream processes. The model was used to evaluate the effects of various nitrate management options on the concentration of nitrate in streams and water-supply wells. Nitrate concentrations were simulated under the following management alternatives: an immediate ban on nitrate input, reduction of input at a constant rate, and fixed input at the current (2000) level. The time required for water to move through the aquifer results in a time lag between the reduction of nitrate input in recharge and the reduction of nitrate concentration in streams and wells. In the gradual-reduction alternative, nitrate concentrations in streams and wells continued to increase for several years after the reduction was enacted. In both the immediate-ban and gradual-reduction alternatives, nitrate concentrations remained elevated above background concentrations long after nitrate input ceased. In the fixed-use alternative, concentrations in streams and wells continued to increase for 30 to 40 years before reaching a constant level. The spatial distributions of simulated nitrate concentrations in streams in 2000 and 2050 were examined with the assumption of no change in land use, nitrate concentration in recharge, or ground-water withdrawals. As expected, nitrate concentrations were highest in agricultural areas and lowest in largely undeveloped areas.

New Jersey↗
USGS1997

Ground-water flow in the Saginaw aquifer in the vicinity of the north Lansing well field, Lansing Michigan — Part 2, simulations with a regional model using a reduced cell size

Vinyl chloride has been detected in water from the Saginaw aquifer near Lansing Board of Water and Light wells in the north Lansing well field. These public-supply wells have the potential to withdraw contaminated ground water. The effects of reduced grid spacing for the existing TriCounty regional ground-water-flow model on local ground-water movement were investigated. This refinement of the grid eliminated multiple wells in a cell and reduced the number of wells represented as weak sinks. Two pumping scenarios were developed to investigate the effects of pumping conditions, plume size, and hypothetical purge well locations on the movement of the vinyl chloride plume in the Saginaw aquifer. Under 1995 pumping conditions, water that originates in the central portion of the Saginaw aquifer known to be contaminated with vinyl chloride is prevented from reaching Lansing Board of Water and Light supply wells when hypothetical purge wells located west of the plume are simulated as pumping either 100 gallons per minute or 200 gallons per minute. Purge wells located north of the plume are effective at preventing contamination from reaching Lansing Board of Water and Light supply wells when simulated as pumping 200 gallons per minute. Water that originates within and surrounding the area known to be contaminated with vinyl chloride is not prevented from reaching Lansing Board of Water and Light supply wells under 1995 conditions using either purge well location or pumping rate. Under 1997 pumping conditions, water that originates in the central portion of the Saginaw aquifer known to be contaminated with vinyl chloride is prevented from reaching Lansing Board of Water and Light supply wells when hypothetical purge wells located either west or north of the plume are simulated as pumping 200 gallons per minute. Water that originates within and surrounding the area known to be contaminated with vinyl chloride is not prevented from reaching Lansing Board of Water and Light supply wells under 1997 conditions using either purge well location or pumping rate.

Michigan↗
USGS2003

Simulation of ground-water flow and rainfall runoff with emphasis on the effects of land cover, Whittlesey Creek, Bayfield County, Wisconsin, 1999-2001

The effects of land cover on flooding and base-flow characteristics of Whittlesey Creek, Bayfield County, Wis., were examined in a study that involved ground-water-flow and rainfall-runoff modeling. Field data were collected during 1999-2001 for synoptic base flow, streambed head and temperature, precipitation, continuous streamflow and stream stage, and other physical characteristics. Well logs provided data for potentiometric-surface altitudes and stratigraphic descriptions. Geologic, soil, hydrography, altitude, and historical land-cover data were compiled into a geographic information system and used in two ground-water-flow models (GFLOW and MODFLOW) and a rainfall-runoff model (SWAT). A deep ground-water system intersects Whittlesey Creek near the confluence with the North Fork, producing a steady base flow of 17?18 cubic feet per second. Upstream from the confluence, the creek has little or no base flow; flow is from surface runoff and a small amount of perched ground water. Most of the base flow to Whittlesey Creek originates as recharge through the permeable sands in the center of the Bayfield Peninsula to the northwest of the surface-water-contributing basin. Based on simulations, model-wide changes in recharge caused a proportional change in simulated base flow for Whittlesey Creek. Changing the simulated amount of recharge by 25 to 50 percent in only the ground-water-contributing area results in relatively small changes in base flow to Whittlesey Creek (about 2?11 percent). Simulated changes in land cover within the Whittlesey Creek surface-water-contributing basin would have minimal effects on base flow and average annual runoff, but flood peaks (based on daily mean flows on peak-flow days) could be affected. Based on the simulations, changing the basin land cover to a reforested condition results in a reduction in flood peaks of about 12 to 14 percent for up to a 100-yr flood. Changing the basin land cover to 25 percent urban land or returning basin land cover to the intensive row-crop agriculture of the 1920s results in flood peaks increasing by as much as 18 percent. The SWAT model is limited to a daily time step, which is adequate for describing the surface-water/ground-water interaction and percentage changes. It may not, however, be adequate in describing peak flow because the instantaneous peak flow in Whittlesey Creek during a flood can be more than twice the magnitude of the daily mean flow during that same flood. In addition, the storage and infiltration capacities of wetlands in the basin are not fully understood and need further study.

Wisconsin↗
USGS2010

Simulation of ground-water flow and solute transport in the Glen Canyon aquifer, East-Central Utah

The extraction of methane from coal beds in the Ferron coal trend in central Utah started in the mid-1980s. Beginning in 1994, water from the extraction process was pressure injected into the Glen Canyon aquifer. The lateral extent of the aquifer that could be affected by injection is about 7,600 square miles. To address regional-scale effects of injection over a decadal time frame, a conceptual model of ground-water movement and transport of dissolved solids was formulated. A numerical model that incorporates aquifer concepts was then constructed and used to simulate injection. The Glen Canyon aquifer within the study area is conceptualized in two parts—an active area of ground-water flow and solute transport that exists between recharge areas in the San Rafael Swell and Desert, Waterpocket Fold, and Henry Mountains and discharge locations along the Muddy, Dirty Devil, San Rafael, and Green Rivers. An area of little or negligible ground-water flow exists north of Price, Utah, and beneath the Wasatch Plateau. Pressurized injection of coal-bed methane production water occurs in this area where dissolved-solids concentrations can be more than 100,000 milligrams per liter. Injection has the potential to increase hydrologic interaction with the active flow area, where dissolved-solids concentrations are generally less than 3,000 milligrams per liter. Pressurized injection of coal-bed methane production water in 1994 initiated a net addition of flow and mass of solutes into the Glen Canyon aquifer. To better understand the regional scale hydrologic interaction between the two areas of the Glen Canyon aquifer, pressurized injection was numerically simulated. Data constraints precluded development of a fully calibrated simulation; instead, an uncalibrated model was constructed that is a plausible representation of the conceptual flow and solute-transport processes. The amount of injected water over the 36-year simulation period is about 25,000 acre-feet. As a result, simulated water levels in the injection areas increased by 50 feet and dissolved-solids concentrations increased by 100 milligrams per liter or more. These increases are accrued into aquifer storage and do not extend to the rivers during the 36-year simulation period. The amount of change in simulated discharge and solute load to the rivers is less than the resolution accuracy of the numerical simulation and is interpreted as no significant change over the considered time period.

Utah↗
USGS2004

Simulation of runoff and wetland storage in the Hamden and Lonetree watershed sites within the Red River of the North Basin, North Dakota and Minnesota

Re-establishment of wetlands has been promoted by various groups to control future floods in the Red River of the North Basin in North Dakota and Minnesota. Therefore, a study was conducted to simulate runoff and wetland storage in the Hamden and Lonetree watershed sites in the Red River of the North Basin. Data from geographic information system analyses, collected weather data, additional historic weather data, and geomorphology were used in a wetlands hydrologic model to simulate precipitation accumulation, snowmelt, evapotranspiration, soil infiltration, seepage to ground water, surface runoff, and streamflow. Simulated daily mean water volumes for the soil and wetlands in the Hamden and Lonetree watershed sites showed that the soils of the two sites stored as much water as the wetlands throughout most of the simulation period. Total simulated runoff for the Hamden watershed site for the period of record was reduced about 38 percent by increasing the Bisson Lake spillage threshold from 0.009 to 0.60. The additional simulated storage at the larger spillage threshold led to reductions in simulated runoff. Simulated daily mean streamflows for the Hamden watershed site at a Bisson Lake spillage threshold of 0.60 were less than those simulated for the same day at a Bisson Lake spillage threshold of 0.009. However, the peak streamflows simulated for June 2000 and April 2001 at a spillage threshold of 0.60 were about the same as those simulated at a spillage threshold of 0.009. Simulated runoff during flood conditions in April and June 2000 and March and April 2001 was reduced 1 to 6 percent for an increased spillage threshold. Total runoff for the period of record was reduced about 31 percent for the increased spillage threshold. Simulation results indicate total streamflow from a flood event may be reduced by wetland storage, but peak streamflows during a flood event may not be affected substantially.

Scientific Investigations Report↗
USGS1989

Analysis of the effect of pumping on ground-water flow in the Springfield Plateau and Ozark aquifers near Springfield, Missouri

Pumpage of water from the Ozark aquifer for public supply and industry use by the city of Springfield and surrounding communities in southwestern Missouri has significantly altered the potentiometric surface of the aquifer. Springfield is located on a regional groundwater divide that trends east and west across southern Missouri. Groundwater that once flowed north and south from the divide now moves toward Springfield. Drawdown in the Ozark aquifer beneath Springfield has increased about 50 ft near the center of the city since 1974. The area of well influence also has increased, most notably to the south and southwest, because of increased pumpage by Springfield and new groundwater withdrawals in rapidly increasing communities, such as Republic and Nixa. Changes in the potentiometric surface of the Ozark aquifer, and to a lesser extent the Springfield Plateau aquifer, resulting from stresses applied by pumpage of water supply wells has altered the hydrologic budget of the Springfield area. Downward leakage of groundwater through the Ozark confining unit has increased from about 10 cu ft/sec to about 18 cu ft/sec because drawdown in the Ozark aquifer has resulted in an increased vertical hydraulic gradient across the confining unit. Minimal quantities of water are supplied by increased upward leakage through the St. Francois confining unit. Model simulations indicate substantial quantities of water are still (1987) being removed from storage within the Ozark and Springfield Plateau aquifers and the hydrologic system is not in equilibrium at this time. (USGS)

Water-Resources Investigations Report↗
USGS2004

Evaluation of strategies for balancing water use and streamflow reductions in the upper Charles River basin, eastern Massachusetts

The upper Charles River basin, located 30 miles southwest of Boston, Massachusetts, is experiencing water shortages during the summer. Towns in the basin have instituted water-conservation programs and water-use bans to reduce summertime water use. During July through October, streamflow in the Charles River and its tributaries regularly falls below 0.50 cubic foot per second per square mile, the minimum streamflow used by the U.S. Fish and Wildlife Service as its Aquatic Base Flow standard for maintaining healthy freshwater ecosystems. To examine how human water use could be changed to mitigate these water shortages, a numerical ground-water flow model was modified and used in conjunction with response coefficients and optimization techniques. Streamflows at 10 locations on the Charles River and its tributaries were determined under various water-use scenarios and climatic conditions. A variety of engineered solutions to the water shortages were examined for their ability to increase water supplies and summertime streamflows. Results indicate that although human water use contributes to the problem of low summertime streamflows, human water use is not the only, or even the primary, cause of low flows in the basin. The lowest summertime streamflows increase by 12 percent but remain below the Aquatic Base Flow standard when all public water-supply pumpage and wastewater flows in the basin are eliminated in a simulation under average climatic conditions. Under dry climatic conditions, the same measures increase the lowest average monthly streamflow by 95 percent but do not increase it above the Aquatic Base Flow standard. The most promising water-management strategies to increase streamflows and water supplies, based on the study results, include wastewater recharge to the aquifer, altered management of pumping well schedules, regional water-supply sharing, and water conservation. In a scenario that simulated towns sharing water supplies, streamflow in the Charles River as it exits the basin increased by 18 percent during July through September and an excess water-supply capacity of 13.4 cubic feet per second, above and beyond average use, would be available to all towns in the basin. These study results could help water suppliers and regulators evaluate strategies for balancing ground-water development and streamflow reductions in the basin.

Massachusetts↗