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USGS1983

Water-level changes in the high plains regional aquifer, northwestern Oklahoma, predevelopment to 1980

During 1978, the U.S. Geological Survey began a 5-year study of the High Plains regional aquifer system to provide hydrologic information for evaluation of the effects of long-term development of the aquifer and to develop computer models for prediction of aquifer response to alternative changes in ground-water management (Weeks, 1978). This report is one of a series presenting hydrologic information of the High Plains aquifer in Oklahoma. The predevelopment to 1980 water-level changes in the High Plains regional aquifer in Oklahoma are shown for Harper, Ellis, Woodward, Dewey, and Roger Mills Counties, on the east, and for the Oklahoma Panhandle, consist- ing of Cimarron, Texas, and Beaver Counties, on the west. About 1,470 water-level measurements in the Panhandle were used in compiling the predevelopment water-table map (Havens, 1982c). In the remaining area to the east about 150 water-level measurements from the 1950's to the 1970's are representative of predevelopment water levels. For the 1980 water-table map, about 330 measurements were made in the Panhandle and about 350 measurements in the eastern area by the Oklahoma Water Resources Board (Havens, 1982b).

Water-Resources Investigations Report↗

USGS2009

Three-dimensional numerical model of ground-water flow in northern Utah Valley, Utah County, Utah

A three-dimensional, finite-difference, numerical model was developed to simulate ground-water flow in northern Utah Valley, Utah. The model includes expanded areal boundaries as compared to a previous ground-water flow model of the valley and incorporates more than 20 years of additional hydrologic data. The model boundary was generally expanded to include the bedrock in the surrounding mountain block as far as the surface-water divide. New wells have been drilled in basin-fill deposits near the consolidated-rock boundary. Simulating the hydrologic conditions within the bedrock allows for improved simulation of the effect of withdrawal from these wells. The inclusion of bedrock also allowed for the use of a recharge model that provided an alternative method for spatially distributing areal recharge over the mountains. The model was calibrated to steady- and transient-state conditions. The steady-state simulation was developed and calibrated by using hydrologic data that represented average conditions for 1947. The transient-state simulation was developed and calibrated by using hydrologic data collected from 1947 to 2004. Areally, the model grid is 79 rows by 70 columns, with variable cell size. Cells throughout most of the model domain represent 0.3 mile on each side. The largest cells are rectangular with dimensions of about 0.3 by 0.6 mile. The largest cells represent the mountain block on the eastern edge of the model domain where the least hydrologic data are available. Vertically, the aquifer system is divided into 4 layers which incorporate 11 hydrogeologic units. The model simulates recharge to the ground-water flow system as (1) infiltration of precipitation over the mountain block, (2) infiltration of precipitation over the valley floor, (3) infiltration of unconsumed irrigation water from fields, lawns, and gardens, (4) seepage from streams and canals, and (5) subsurface inflow from Cedar Valley. Discharge of ground water is simulated by the model to (1) flowing and pumping wells, (2) drains and springs, (3) evapotranspiration, (4) Utah Lake, (5) the Jordan River and mountain streams, and (6) Salt Lake Valley by subsurface outflow through the Jordan Narrows. During steady-state calibration, variables were adjusted within probable ranges to minimize differences between model-computed and measured water levels as well as between model-computed and independently estimated flows that include: recharge by seepage from individual streams and canals, discharge by seepage to individual streams and the Jordan River, discharge to Utah Lake, discharge to drains and springs, discharge by evapotranspiration, and subsurface flows into and out of northern Utah Valley from Cedar Valley and to Salt Lake Valley, respectively. The transient-state simulation was calibrated to measured water levels and water-level changes with consideration given to annual changes in the flows listed above.

Utah↗

USGS1995

Use of surface and borehole geophysics to delineate the glacial-drift stratigraphy of northeastern St. Joseph County, Indiana

Inverse models of direct current electrical- resistivity sounding data and normal-resistivity and natural-gamma logs were used to assist delineation of the glacial-drift stratigraphy in a 580-square- kilometer area of northeastern St. Joseph County, Indiana. Unconsolidated deposits in the study area are composed of glacial-drift, including outwash, till, and lacustrine sediments; thicknesses range from about 15 to more than 70 meters. The glacial outwash deposits are mostly composed of sand and gravel and are the primary source of drinking water to northeastern St. Joseph County. The glacial till and glacio-lacustrine deposits contain a larger fraction of clay than the outwash deposits and may retard ground-water flow between shallow and deeper sand and gravel aquifers. Results of the geophysical measurements collected during this study indicate that glacial-drift deposits in the area north and east of the St. Joseph River are mostly composed of sand and gravel with inter-layered clay-rich deposits that are laterally discontinuous. In the area south of the St. Joseph River, the thickness of sand and gravel deposits diminishes, and clay-rich deposits dominate the stratigraphy. The presence of an electrically conductive bedrock, the Ellsworth Shale, beneath the glacial-drift deposits is identified in inverse models of direct current electrical-resistivity sounding data.

Water-Resources Investigations Report↗

USGS1974

Oak Glen water-resources development study using modeling techniques, San Bernardino County, California

Hydrologic, digital-model, and economic analyses were made to determine the most efficient balance of conjunctive use of local ground water and surface water--specifically, whether additional ground-water supplies can be developed in the Oak Glen study area, San Bernardino County, Calif., for local use and also for export to the adjacent Yucaipa area, and what will be the effects of imported water available in 1980. The hydrologic analysis showed that transmissivity values of the aquifer in the Oak Glen study area ranged from 1,000 to 6,750 gallons per day per foot or their equivalent 134 to 902 feet squared per day (12 to 84 metres squared per day) and that net annual recharge in the area was about 1,940 acre-feet (2.39 cubic hectometres) per year. The volume of ground water in storage in 1970 was about 86,000 acre-feet (106 cubic hectometres). The digital-model analysis included building and verifying a steady-state and a non-steady-state model. The steady-state model was considered to be verified when the model-generated water levels approximated the measured 1949 water levels, which were assumed to represent steady-state water-level conditions. The non-steady-state model was verified for 1949-70, and the model satisfactorily reproduced the measured water-level changes for the study area during that period. Water-level changes in the ground-water basin were predicted from 1971 to 1980 using as representative average annual pumpage that from 1966 to 1970 and 1971. The model also predicted water-level changes from 1971 to 1980 using the maximum pumpage capacities of the wells under recharge conditions for average, wet, and dry periods. The predicted water-level changes in the Oak Glen study area were used to calculate the average costs of pumping water for 1980. The comparable average costs of importing water from an alternative supply and the capital costs of well construction were also determined. The economic evaluation suggests the following: (1) Increase ground-water pumping for local use, (2) reduce well-water import to the lower parts of the Oak Glen study area from adjacent areas to the west, (3) short term prior to 1980 overdevelopment appears to be feasible with export to Yucaipa, and (4) tunnel development or new shallow wells at the higher altitudes could help alleviate the water problem.

California↗

USGS1999

Case study for delineating a contributing area to a water-supply well in a fractured crystalline-bedrock aquifer, Stewartstown, Pennsylvania

The Trouts Lane well field in Stewartstown, Pa., was selected as a case study for delineating a contributing area in a fractured crystalline-bedrock aquifer. The study emphasized the importance of refining the understanding of boundary conditions and major heterogeneities that affect ground-water movement to the supply well by conducting (1) fracture-trace mapping, (2) borehole logging and flow measurements, (3) ground-water level monitoring, (4) aquifer testing, and (5) geochemical sampling. Methods and approach used in this study could be applicable for other wells in crystalline-bedrock terranes in southeastern Pennsylvania. Methods of primary importance for refining the understanding of hydrology at the Trouts Lane well field were the aquifer tests, water-level measurements, and geophysical logging. Results from the constant-discharge aquifer test helped identify a major north-south trending hydraulic connection between supply well SW6 and a domestic-supply well. Aquifer-test results also indicated fractures that transmit most water to the supply well are hydraulically well-connected to the shallow regolith and highly weathered schist. Results from slug tests provided estimates of transmissivity and the nonuniform distribution of transmissivity throughout the well field, indicating the water-producing fractures are not evenly distributed and ground-water velocities must vary considerably throughout the well field. Water levels, which were easy to measure, provided additional evidence of hydraulic connections among wells. More importantly, they allowed the water-table configuration to be mapped. Borehole geophysics and flow measurements within the well were very useful because results indicated water entered supply well SW6 through bedrock fractures at very shallow depths—less than 60 ft below land surface; therefore, the area providing recharge to the well is probably in the immediate vicinity. Preliminary delineations of the contributing area and the 90-day time-of-travel area were computed from a steady-state water budget and a time-of-travel equation. This easy approach provides insight into the size (but not the shape) of contributing areas. Three other approaches were used to refine the contributing-area shape: (1) uniform-flow equation, (2) water-table mapping, and (3) numerical modeling. The contributing areas computed from each approach differed depending on the simplification of the hydrogeologic framework that was made in each method of analysis. Although the approaches vary in complexity, regardless of the approach used, an estimate of the water-table configuration in the vicinity of the well field was key for making the best possible delineation of the contributing area. A major limitation of this investigation was the inability to refine the delineation of the time-of-travel area. A time-of-travel area is based on the distance water travels in a given time. Because a few discrete fractures probably supply a significant amount of water to supply well SW6, the effective porosity (and hence, traveltime) of ground water is best estimated using tracers.

Water-Resources Investigations Report↗

USGS2003

Simulation of ground-water flow and land subsidence in the Antelope Valley ground-water basin, California

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley ground-water basin is about 940 square miles and is separated from the northern part of Antelope Valley by faults and low-lying hills. Prior to 1972, ground water provided more than 90 percent of the total water supply in the valley; since 1972, it has provided between 50 and 90 percent. Most ground-water pumping in the valley occurs in the Antelope Valley ground-water basin, which includes the rapidly growing cities of Lancaster and Palmdale. Ground-water-level declines of more than 200 feet in some parts of the ground-water basin have resulted in an increase in pumping lifts, reduced well efficiency, and land subsidence of more than 6 feet in some areas. Future urban growth and limits on the supply of imported water may continue to increase reliance on ground water. To better understand the ground-water flow system and to develop a tool to aid in effectively managing the water resources, a numerical model of ground-water flow and land subsidence in the Antelope Valley ground-water basin was developed using old and new geohydrologic information. The ground-water flow system consists of three aquifers: the upper, middle, and lower aquifers. The aquifers, which were identified on the basis of the hydrologic properties, age, and depth of the unconsolidated deposits, consist of gravel, sand, silt, and clay alluvial deposits and clay and silty clay lacustrine deposits. Prior to ground-water development in the valley, recharge was primarily the infiltration of runoff from the surrounding mountains. Ground water flowed from the recharge areas to discharge areas around the playas where it discharged either from the aquifer system as evapotranspiration or from springs. Partial barriers to horizontal ground-water flow, such as faults, have been identified in the ground-water basin. Water-level declines owing to ground-water development have eliminated the natural sources of discharge, and pumping for agricultural and urban uses have become the primary source of discharge from the ground-water system. Infiltration of return flows from agricultural irrigation has become an important source of recharge to the aquifer system. The ground-water flow model of the basin was discretized horizontally into a grid of 43 rows and 60 columns of square cells 1 mile on a side, and vertically into three layers representing the upper, middle, and lower aquifers. Faults that were thought to act as horizontal-flow barriers were simulated in the model. The model was calibrated to simulate steady-state conditions, represented by 1915 water levels and transient-state conditions during 1915-95 using water-level and subsidence data. Initial estimates of the aquifer-system properties and stresses were obtained from a previously published numerical model of the Antelope Valley ground-water basin; estimates also were obtained from recently collected hydrologic data and from results of simulations of ground-water flow and land subsidence models of the Edwards Air Force Base area. Some of these initial estimates were modified during model calibration. Ground-water pumpage for agriculture was estimated on the basis of irrigated crop acreage and crop consumptive-use data. Pumpage for public supply, which is metered, was compiled and entered into a database used for this study. Estimated annual pumpage peaked at 395,000 acre-feet (acre-ft) in 1952 and then declined because of declining agricultural production. Recharge from irrigation-return flows was estimated to be 30 percent of agricultural pumpage; the irrigation-return flows were simulated as recharge to the regional water table 10 years following application at land surface. The annual quantity of natural recharge initially was based on estimates from previous studies. During model calibration, natural recharge was reduced from the initial

Water-Resources Investigations Report↗

USGS1984

An assessment of cumulative impacts of coal mining on the hydrology in part of the Powder River structural basin, Wyoming: A progress report

The U.S. Geological Survey and the Wyoming Department of Environmental Quality are involved in a cooperative effort to assess the probable cumulative impacts of coal mining on the hydrology of a part of the Powder River Structural Basin in Wyoming. It was assumed that the principal impacts on the ground-water system due to mining will occur in the relatively shallow aquifers which can be grouped into three homogeneous aquifers, namely, the Wyodak coal, the overburden, and the under burden. Emphasis of this report is on the results of analysis of surface-water resources in the Caballo Creek drainage. A surface-water model of the Caballo Creek drainage was developed using the Hydrological Simulation Program-Fortran model to help assess the impacts of mining activities on streamflow. The Caballo Creek drainage was divided into 10 land segments and 6 stream reaches in the modeling process. Three simulation runs show little, if any, change in streamflow between pre- and post-mining conditions and very little change between pre-mining and during-mining conditions. The principal reason for the absence of change is the high infiltration rate used in the model for all three conditions.

Wyoming↗

USGS2005

Simulation of ground-water flow and areas contributing ground water to production wells, Cadillac, Michigan

Ground water is the primary source of water for domestic, municipal, and industrial use within the northwest section of Michigan's Lower Peninsula. Because of the importance of this resource, numerous communities including the city of Cadillac in Wexford County, Michigan, have begun local wellhead protection programs. In these programs, communities protect their ground-water resources by identifying the areas that contribute water to production wells, identifying potential sources of contamination, and developing methods to cooperatively manage and minimize threats to the water supply. The U.S. Geological Survey, in cooperation with the city of Cadillac, simulated regional ground-water flow and estimated areas contributing recharge and zones of transport to the production well field. Ground-water flow models for the Clam River watershed, in Wexford and Missaukee Counties, were developed using the U.S. Geological Survey modular three-dimensional finite-difference ground-water flow model (MODFLOW 2000). Ground-water flow models were calibrated using the observation, sensitivity, and parameter estimation packages of MODFLOW 2000. Ground-water-head solutions from calibrated flow models were used in conjunction with MODPATH, a particle-tracking program, to simulate regional ground-water flow and estimate areas contributing recharge and zones of transport to the Cadillac production-well field for a 10-year period. Model simulations match the conceptual model in that regional ground-water flow in the deep ground-water system is from southeast to northwest across the watershed. Areas contributing water were determined for the optimized parameter set and an alternate parameter set that included increased recharge and hydraulic conductivity values. Although substantially different hydrologic parameters (assumed to represent end-member ranges of realistic hydrologic parameters) were used in alternate numerical simulations, simulation results differ little in predictions of the size of the contributing area to the city well field. However, increasing recharge and hydraulic conductivity values appreciably affected the shape of the contributing area and zone of contribution of reacharge. Simulation results indicate that the region immediately to the south and southeast of the well field is contributing water to the production wells. Detailed aquifer characterization would be needed to describe and simulate the heterogeneous glacial deposits in the watershed.

Michigan↗

USGS2004

Evaluation of the Feasibility of Freshwater Injection Wells in Mitigating Ground-Water Quality Degradation at Selected Well Fields in Duval County, Florida

The Fernandina permeable zone contains brackish water in parts of Duval County, Florida. Upward flow from the Fernandina permeable zone to the upper zone of the Lower Floridan aquifer increases chloride concentrations in ground water in parts of Duval County. Numerical models of the ground-water flow system in parts of Duval, St. Johns, and Clay Counties, Florida, were used to (1) estimate the vertical flows between the low-quality water of the Fernandina permeable zone and the high-quality water of the upper zone of the Lower Floridan aquifer in the vicinity of Deerwood 3 and Brierwood well fields, based on 2000 ground-water withdrawal rates; (2) determine how such vertical flows change as several scenarios of injection, withdrawal, and intervening rest periods are simulated in the two well fields; and (3) evaluate the effects of changes in less certain hydraulic parameters on the vertical flows between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer. The ground-water flow system was simulated with a four-layer model using MODFLOW-2000, which was developed by the U.S. Geological Survey. The first layer consists of specified-head cells simulating the surficial aquifer system with prescribed water levels. The second layer simulates the Upper Floridan aquifer. The third and fourth layers simulate the upper zone of the Lower Floridan aquifer and the Fernandina permeable zone, respectively. Average flow conditions in 2000 were approximated with a steady-state simulation. The changes in upward flow from the Fernandina permeable zone due to periods of injections and withdrawals were analyzed with transient simulations. The grid used for the ground-water flow model was uniform and composed of square 250-foot cells, with 400 columns and 400 rows. The active model area encompasses about 360 square miles in parts of Duval, St. Johns, and Clay Counties, Florida. Ground-water flow simulation was limited vertically to the bottom of the Fernandina permeable zone. The steady-state ground-water flow model was calibrated using time-averaged 2000 heads at 20 control points. Environmental-water heads in the Fernandina permeable zone were calculated for wells with variable water density. Transmissivity of the Upper Floridan aquifer, the upper zone of the Lower Floridan aquifer, and the Fernandina permeable zone, and the leakance of the intermediate confining unit, the middle semiconfining unit, and the semiconfining unit were obtained from regional ground-water flow models and adjusted until a reasonable fit between simulated and computed heads was obtained. The calibrated hydraulic properties from the steady-state ground-water flow model, and the calibrated storage coefficient from the transient model, were used to simulate hypothetical transient scenarios of injection, withdrawal, and intervening rest periods to assess changes in flow between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer. Based on the simulated flows between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer and the 18 million gallons per day of water available for injection, the reversal of the prevailing upward flow from the Fernandina permeable zone was not achieved. However, steady-state and transient simulations indicate that the upward flow of water from the Fernandina permeable zone could be reduced by as much as 64 percent, from 0.11 to 0.04 cubic foot per second, if only injection periods are simulated.

Water-Resources Investigations Report↗

USGS1997

Hydrogeology and water chemistry of Montezuma Well in Montezuma Castle National Monument and surrounding area, Arizona

Increasing population and associated residential and commercial development have greatly increased water use and consumption in the Verde Valley near Montezuma Well, a unit of Montezuma Castle National Monument in central Arizona. Flow from Montezuma Well and water levels in eight wells that are measured annually do not indicate that the ground-water system has been affected by development. Additional data are needed to develop an adequate ground-water monitoring program so that future effects of development can be detected. Monitoring the ground-water system would detect changes in discharge from the Montezuma Well or changes in the ground-water system that might indicate a potential change of flow to the well. Water samples were collected, and field measurements of specific conductance, pH, temperature, and dissolved oxygen were made throughout the pond at Montezuma Well during an exploration in May 1991. The exploration included two fissures in the bottom of the pond that were filled with sand. The sand in the fissures was kept in suspension by water entering the pond. Water chemistry indicates that the ground water from the area is a mixed combination of calcium, magnesium, sodium, and bicarbonate type water. The analyses for 18O/16O and 2H/1H show that the water from the wells and springs in the area, including Montezuma Well, has been exposed to similar environmental conditions and could have had similar flow paths. The MODFLOW finite-difference ground-water model was used to develop an uncalibrated interpretive model to study possible mechanisms for discharge of water at Montezuma Well. The study presents the hypothesis that ground water in the Supai Formation is the source of discharge to Montezuma Well because of the differences between the surface elevation of the pond at Montezuma Well and the stage in the adjacent Wet Beaver Creek. A series of simulations shows that upward flow from the Supai Formation is a possible mechanism for discharge to Montezuma Well, and that a geologic structure in the Supai Formation could play a role in the upward movement of water to Montezuma Well. The mechanism for inflow from the Verde Formation is not understood; however, this study concludes that the Verde Formation, Supai Formation, and other underlying rock units are probably the sources of water to Montezuma Well.

Water-Resources Investigations Report↗

USGS1992

Geohydrology and simulated ground-water flow, Plymouth-Carver aquifer, southeastern Massachusetts

The Plymouth-Carver aquifer underlies an area of 140 square miles and is the second largest aquifer in areal extent in Massachusetts. It is composed primarily of saturated glacial sand and gravel. The water-table and bedrock surface were mapped and used to determine saturated thickness of the aquifer, which ranged from less than 20 feet to greater than 200 feet. Ground water is present mainly under unconfined conditions, except in a few local areas such as beneath Plymouth Harbor. Recharge to the aquifer is derived almost entirely from precipitation and averages about 1.15 million gallons per day per square mile. Water discharges from the aquifer by pumping, evapotranspiration, direct evaporation from the water table, and seepage to streams, ponds, wetlands, bogs, and the ocean. In 1985, water use was about 59.6 million gallons per day, of which 82 percent was used for cranberry production. The Plymouth-Carver aquifer was simulated by a three-dimensional, finite difference ground-water-flow model. Most model boundaries represent the natural hydrologic boundaries of the aquifer. The model simulates aquifer recharge, withdrawals by pumped wells, leakage through streambeds, and discharge to the ocean. The model was calibrated for steady-state and transient conditions. Model results were compared with measured values of hydraulic head and ground-water discharge. Results of simulations indicate that the modeled ground-water system closely simulates actual aquifer conditions. Four hypothetical ground-water development alternatives were simulated to demonstrate the use of the model and to examine the effects on the ground-water system. Simulation of a 2-year period of no recharge and average pumping rates that occurred from 1980-85 resulted in water-level declines exceeding 5 feet throughout most of the aquifer and a decrease of 54 percent in average ground-water discharge to streams. In a second simulation, four wells in the northern part of the area were pumped at 10.4 million gallons per day in excess of rates simulated in the steady-state model for the four wells. This resulted in water-level declines of 2 feet or more in an area of 25 square miles and a decline in average ground-water discharge to streams of 6 percent. When this pumpage was simulated as recharge to the aquifer, water levels beneath the recharge area rose more than 40 feet, and ground-water discharge remained equal to average discharge in the calibrated steady-state model. In a third simulation, all 21 existing production wells were pumped at nearly the design capacity of 17.8 million gallons per day; this pumping rate produced water-level declines of less than 2 feet throughout most of the aquifer. When simulated pumpage was increased to 32.8 million gallons per day from existing wells and from 15 additional wells, the area where water-level declines exceeded 2 feet significantly increased. In another set of simulations, a well field close to a stream was pumped at rates of 2, 4, and 6 million gallons per day. At a pumping rate of 6 million gallons per day, ground-water discharge to the stream decreased 34 percent during periods of normal precipitation and 56 percent during drought conditions.

Massachusetts↗

USGS2008

Spatial Distribution of Ground-Water Recharge Estimated with a Water-Budget Method for the Jordan Creek Watershed, Lehigh County, Pennsylvania

This report presents the results of a study by the U.S. Geological Survey, in cooperation with the Pennsylvania Geological Survey, to illustrate a water-budget method for mapping the spatial distribution of ground-water recharge for a 76-square-mile part of the Jordan Creek watershed, northwest of Allentown, in Lehigh County, Pennsylvania. Recharge was estimated by using the Hydrological Evaluation of Landfill Performance (HELP) water-budget model for 577 landscape units in Jordan Creek watershed, delineated on the basis of their soils, land use/land cover, and mean annual precipitation during 1951-2000. The water-budget model routes precipitation falling on each landscape unit to components of evapotranspiration, surface runoff, storage, and vertical percolation (recharge) for a five-layer soil column on a daily basis. The spatial distribution of mean annual recharge during 1951-2000 for each landscape unit was mapped by the use of a geographic information system. Recharge simulated by the water-budget model in Jordan Creek watershed during 1951-2000 averaged 12.3 inches per year and ranged by landscape unit from 0.11 to 17.05 inches per year. Mean annual recharge during 1951-2000 simulated by the water-budget model was most sensitive to changes to input values for precipitation and runoff-curve number. Mean annual recharge values for the crop, forest, pasture, and low-density urban land-use/land-cover classes were similar (11.2 to 12.2 inches per year) but were substantially less for high-density urban (6.8 inches per year), herbaceous wetlands (2.5 inches per year), and forested wetlands (1.3 inches per year). Recharge rates simulated for the crop, forest, pasture, and low-density urban land-cover classes were similar because those land-use/land-cover classes are represented in the model with parameter values that either did not significantly affect simulated recharge or tended to have offsetting effects on recharge. For example, for landscapes with forest land cover, values of runoff-curve number assigned to the model were smaller than for other land-use/land-cover classes (causing more recharge and less runoff), but the maximum depth of evapotranspiration was larger than for other land-use/ land-cover classes because of deeper root penetration in forests (causing more evapotranspiration and less recharge). The smaller simulated recharge for high-density urban and wetland land-use/land-cover classes was caused by the large values of runoff-curve number (greater than 90) assigned to those classes. The large runoff-curve number, however, certainly is not realistic for all wetlands; some wetlands act as areas of ground-water discharge and some as areas of recharge. Simulated mean annual recharge computed by the water-budget model for the 53-square-mile part of the watershed upstream from the streamflow-gaging station near Schnecksville was compared to estimates of recharge and base flow determined by analysis of streamflow records from 1967 to 2000. The mean annual recharge of 12.4 inches per year simulated by the water-budget method for 1967-2000 was less than estimates of mean annual recharge of 19.3 inches per year computed from the RORA computer program and base flow computed by the PART computer program (15.1 inches per year). In theory, the water-budget method provides a practical tool for estimating differences in recharge at local scales of interest, and the watershed- average recharge rate of 12.4 inches per year computed by the method is reasonable. However, the mean annual surface runoff of 4.5 inches per year simulated by the model is unrealistically small. The sum of surface runoff and recharge simulated by the water-budget model (16.9 inches per year) is 7 inches per year less than the streamflow measured at the gaging station near Schnecksville (23.9 inches per year) during 1967-2000, indicating that evapotranspiration is overestimated by the water-budget model by that amount. This discrepancy ca

Scientific Investigations Report↗

USGS2000

Delineation and Analysis of Uncertainty of Contributing Areas to Wells at the Southbury Training School, Southbury, Connecticut

Contributing areas to public-supply wells at the Southbury Training School in Southbury, Connecticut, were mapped by simulating ground-water flow in stratified glacial deposits in the lower Transylvania Brook watershed. The simulation used nonlinear regression methods and informational statistics to estimate parameters of a ground-water flow model using drawdown data from an aquifer test. The goodness of fit of the model and the uncertainty associated with model predictions were statistically measured. A watershed-scale model, depicting large-scale ground-water flow in the Transylvania Brook watershed, was used to estimate the distribution of groundwater recharge. Estimates of recharge from 10 small basins in the watershed differed on the basis of the drainage characteristics of each basin. Small basins having well-defined stream channels contributed less ground-water recharge than basins having no defined channels because potential ground-water recharge was carried away in the stream channel. Estimates of ground-water recharge were used in an aquifer-scale parameter-estimation model. Seven variations of the ground-water-flow system were posed, each representing the ground-water-flow system in slightly different but realistic ways. The model that most closely reproduced measured hydraulic heads and flows with realistic parameter values was selected as the most representative of the ground-water-flow system and was used to delineate boundaries of the contributing areas. The model fit revealed no systematic model error, which indicates that the model is likely to represent the major characteristics of the actual system. Parameter values estimated during the simulation are as follows: horizontal hydraulic conductivity of coarse-grained deposits, 154 feet per day; vertical hydraulic conductivity of coarse-grained deposits, 0.83 feet per day; horizontal hydraulic conductivity of fine-grained deposits, 29 feet per day; specific yield, 0.007; specific storage, 1.6E-05. Average annual recharge was estimated using the watershed-scale model with no parameter estimation and was determined to be 24 inches per year in the valley areas and 9 inches per year in the upland areas. The parameter estimates produced in the model are similar to expected values, with two exceptions. The estimated specific yield of the stratified glacial deposits is lower than expected, which could be caused by the layered nature of the deposits. The recharge estimate produced by the model was also lower?about 32 percent of the average annual rate. This could be caused by the timing of the aquifer test with respect to the annual cycle of ground-water recharge, and by some of the expected recharge going to parts of the flow system that were not simulated. The data used in the calibration were collected during an aquifer test from October 30 to November 4, 1996. The model fit was very good, as indicated by the correlation coefficient (0.999) between the weighted simulated values and weighted observed values. The model also reproduced the general rise in ground-water levels caused by ground-water recharge and the cyclic fluctuations caused by pumping prior to the aquifer test. Contributing areas were delineated using a particle-tracking procedure. Hypothetical particles of water were introduced at each model cell in the top layer and were tracked to determine whether or not they reached the pumped well. A deterministic contributing area was calculated using the calibrated model, and a probabilistic contributing area was calculated using a Monte Carlo approach along with the calibrated model. The Monte Carlo simulation was done, using the parameter variance/covariance matrix generated by the regression model, to estimate probabilities associated with the contributing area to the wells. The probabilities arise from uncertainty in the estimated parameter values, which in turn arise from the adequacy of the data available to comprehensively describe the groundwater-flow sy

Water-Resources Investigations Report↗

USGS1980

Appraisal of the water resources of the Big Sioux aquifer, Brookings, Deuel, and Hamlin counties, South Dakota

The Big Sioux aquifer in Brookings, Deuel, and Hamlin Counties, South Dakota, has been extensively developed and in some areas discharge, principally by wells, from the aquifer may be exceeding recharge to the aquifer. A finite-difference method digital model was used to simulate steady-state conditions of the Big Sioux aquifer. Average annual water levels in the Big Sioux aquifer and base flow discharge of the Big Sioux River near Brookings for 1970 through 1976 were used in the model. The model-computed water levels were within a few feet of the actual annual average water levels and the computed annual average base flow was 66 cubic feet per second compared to the actual base flow of 58 cubic feet per second. The computer model was used to model transient conditions by simulating water levels and base flow from April through August 1976 and comparing the results with actual data. Evapotranspiration and pumpage changes were made for each month. There was no recharge from precipitation during the test period. Several different computer simulations were made using different estimates of hydrologic parameters and conditions. Specific yield was increased from 10 to 15 percent which resulted in a much greater base flow for each month. Effective depth of evapotranspiration was changed from 5 to 10 feet which resulted in a very large decrease in base flow. A computer simulation made without irrigation pumpage resulted in an increase in the base flow from 0.66 to 9 cubic feet per second for August 1976 in the Big Sioux River near Brookings. The actual base flow for August 1976 was .01 cubic foot per second. A water budget showed 22.2 inches of precipitation (average annual), 0.65 inch of surface runoff, 1.06 inches of ground-water outflow (base flow to river, 1970-76), and 20.49 inches of evapotranspiration. The water from the Big Sioux aquifer is a calcium bicarbonate type and specific conductance ranged from 407 to 1,790 micromhos per centimeter at 25°C. The water is generally very hard, having a mean of 454 milligrams per liter of hardness. A model simulation using all the pumpage that would be allowed by irrigation permits approved as of February 1979 simulated the withdrawal of 43,900 acre-feet of water for about 4 months during which time there was no recharge from precipitation. If there had been no pumping for that period, evapotranspiration would have been 7,800 acre-feet more than occurred under pumping conditions and discharge to streams would have increased by 3,600 acre-feet.

South Dakota↗

USGS1998

Statistical analysis and mathematical modeling of a tracer test on the Santa Clara River, Ventura County, California

To better understand flow processes, solute-transport processes, and ground-water/surface-water interactions on the Santa Clara River in Ventura County, California, a 24-hour fluorescent-dye tracer study was performed under steady-state flow conditions on a 28-mile reach of the river. The study reach includes perennial (uppermost and lowermost) subreaches and ephemeral subreaches of the lower Piru Creek and the middle Santa Clara River. Dye was injected at a site on Piru Creek, and fluorescence of river water was measured continuously at four sites and intermittently at two sites. Discharge measurements were also made at the six sites. The time of travel of the dye, peak dye concentration, and time-variance of time-concentration curves were obtained at each site. The long tails of the time-concentration curves are indicative of sources/sinks within the river, such as riffles and pools, or transient bank storage. A statistical analysis of the data indicates that, in general, the transport characteristics follow Fickian theory. These data and previously collected discharge data were used to calibrate a one-dimensional flow model (DAFLOW) and a solute-transport model (BLTM). DAFLOW solves a simplified form of the diffusion-wave equation and uses empirical relations between flow rate and cross-sectional area, and flow rate and channel width. BLTM uses the velocity data from DAFLOW and solves the advection-dispersion transport equation, including first-order decay. The simulations of dye transport indicated that (1) ground-water recharge explains the loss of dye mass in the middle, ephemeral, subreaches, and (2) ground-water recharge does not explain the loss of dye mass in the uppermost and lowermost, perennial, subreaches. This loss of mass was simulated using a linear decay term. The loss of mass in the perennial subreaches may be caused by a combination of photodecay or adsorption/desorption.

Water-Resources Investigations Report↗

USGS1984

Finite-element simulation of ground-water flow in the vicinity of Yucca Mountain, Nevada-California

A finite-element model of the groundwater flow system in the vicinity of Yucca Mountain at the Nevada Test Site was developed using parameter estimation techniques. The model simulated steady-state ground-water flow occurring in tuffaceous, volcanic , and carbonate rocks, and alluvial aquifers. Hydraulic gradients in the modeled area range from 0.00001 for carbonate aquifers to 0.19 for barriers in tuffaceous rocks. Three model parameters were used in estimating transmissivity in six zones. Simulated hydraulic-head values range from about 1,200 m near Timber Mountain to about 300 m near Furnace Creek Ranch. Model residuals for simulated versus measured hydraulic heads range from -28.6 to 21.4 m; most are less than +/-7 m, indicating an acceptable representation of the hydrologic system by the model. Sensitivity analyses of the model 's flux boundary condition variables were performed to assess the effect of varying boundary fluxes on the calculation of estimated model transmissivities. Varying the flux variables representing discharge at Franklin Lake and Furnace Creek Ranch has greater effect than varying other flux variables.

California, Nevada↗

USGS1986

Hydrogeology, ground-water flow, and tritium movement at low-level radioactive-waste disposal site near Sheffield, Illinois

Groundwater flow and tritium movement are described at and near a low-level radioactive waste disposal site near Sheffield, Illinois. Flow in the shallow aquifer is confined to three basins that ultimately drain into a stripmine lake. Most of the flow from the site is through a buried, pebbly sandfilled channel. Remaining flow is toward alluvium of an existing stream. Conceptual flow models for the two largest basins are used to improve definition of flow velocity and direction. Flow velocities range from about 25 to 2,500 ft/yr. Tritium was found in all three basins. The most extensive migration of tritium is coincident with buried channel. Tritium concentrations ranged from detection level to more than 300 nanocuries/L.

Illinios↗

USGS1997

Geohydrology and simulations of ground-water flow at Verona well field, Battle Creek, Michigan, 1988

Public water supply for the city of Battle Creek, Mich. is withdrawn from the Marshall Sandstone through wells at the Verona well field. Analysis of borehole acoustic televiewer, gamma, and single-point-resistance logs from wells in Bailey Park, near the well field, indicates 12 fracture zones in the Marshall Sandstone. Further interpretation of flow-meter and temperature logs from the same wells indicates that the fracture zones are locally interconnected but appear to remain isolated over a lateral distance of 3,000 feet. Organic chemicals were detected in water samples collected from water-supply wells in the Verona well field in 1981. In 1985, six water-supply wells were converted to purge wells to intercept organic chemicals and divert them from the remaining water-supply wells. Removal of these wells from service resulted in a water-supply shortage. A proposal in which an alternative purge system could be installed so that wells that are out of service may be reactivated was examined. A ground-water-flow model developed for this study indicates that, under the current purge configuration, most water from contaminant-source areas either is captured by purge wells or flows to the Battle Creek River. Some water, however, is captured by three water-supply wells. Model simulations indicate that with the addition of eight purge wells, the well field would be protected from contamination, most water from the contaminant-source areas would be captured by the purge system, and only a small portion would flow to the Battle Creek River. In an effort to augment the city's water supply, the potential for expansion of the Verona well field to the northeast also was investigated. Because of the addition of three municipal wells northeast of the well field, some water from the site of a gasoline spill may be captured by two water-supply wells. Ground water in the area northeast of Verona well field contains significantly lower concentrations of iron, manganese, and calcium carbonate than does water in the existing well field area. However, the Marshall Sandstone in this area has significantly lower transmissivities than those within Verona well field.

Michigan↗