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At least 487 records · Page 27Linked to original sources
USGS1998

Lithostratigraphy, petrography, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of western Collier County, Florida

In 1996, seven cores were recovered in western Collier County, southwestern Florida, to acquire subsurface geologic and hydrologic data to support ground-water modeling efforts. This report presents the lithostratigraphy, X-ray diffraction analyses, petrography, biostratigraphy, and strontium-isotope stratigraphy of these cores. The oldest unit encountered in the study cores is an unnamed formation that is late Miocene. At least four depositional sequences are present within this formation. Calculated age of the formation, based on strontium-isotope stratigraphy, ranges from 9.5 to 5.7 Ma (million years ago). An unconformity within this formation that represents a hiatus of at least 2 million years is indicated in the Old Pump Road core. In two cores, Collier-Seminole and Old Pump Road, the uppermost sediments of the unnamed formation are not dated by strontium isotopes, and, based on the fossils present, these sediments could be as young as Pliocene. In another core (Fakahatchee Strand-Ranger Station), the upper part of the unnamed formation is dated by mollusks as Pliocene. The Tamiami Formation overlies the unnamed formation throughout the study area and is represented by the Ochopee Limestone Member. The unit is Pliocene and probably includes the interval of time near the early/late Pliocene boundary. Strontium-isotope analysis indicates an early Pliocene age (calculated ages range from 5.1 to 3.5 Ma), but the margin of error includes the latest Miocene and the late Pliocene. The dinocyst assemblages in the Ochopee typically are not age-diagnostic, but, near the base of the unit in the Collier-Seminole, Jones Grade, and Fakahatchee Strand State Forest cores, they indicate an age of late Miocene or Pliocene. The molluscan assemblages indicate a Pliocene age for the Ochopee, and a distinctive assemblage of Carditimera arata and Chione cortinaria in several of the cores specifically indicates an age near the early/late Pliocene boundary. Undifferentiated sands overlie the Pliocene limestones in two cores in the southern part of the study area. Artificial fill occurs at the top of most of the cores. The hydrologic confining units penetrated by these cores are different in different parts of the study area. To the west, a hard tightly cemented dolostone forms the first major confining unit below the water table. In the eastern part of the study area, confinement is more difficult to determine. A tightly cemented sandstone, much younger than the dolostones to the west and probably not laterally connected to them, forms a slight confining unit in one core. Thick zones of poorly sorted muddy unconsolidated sands form a slight confining unit in other cores; these probably are not correlative to either the sandstone or the dolostones to the west. The age and sedimentologic observations suggest a complex compartmentalization of the surficial aquifer system in southwestern Florida. The calibrations of dinocyst and molluscan occurrences with strontium-isotope stratigraphy allows us to expand and document the reported ranges of many taxa. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Florida↗
USGS2018

Groundwater chemistry and water-level elevations in bedrock aquifers of the Piceance and Yellow Creek watersheds, Rio Blanco County, Colorado, 2013–16

The Piceance and Yellow Creek watersheds in Rio Blanco County, Colorado, are known to contain important energy resources (oil shale and natural gas) and mineral resources (nahcolite). The primary sources of fresh groundwater in the Piceance and Yellow Creek watersheds are bedrock aquifers in the Uinta and Green River Formations. The aquifers are divided into an upper and lower aquifer separated by a regionally extensive semiconfining layer. These aquifers provide water to streams and springs in the watersheds and are an important resource to people living and working in the area. Development of energy and mineral resources has the potential to affect the quality of groundwater in several ways. The Bureau of Land Management and the U.S. Geological Survey began groundwater monitoring in 2010 to characterize the groundwater quality and water-level elevations of shallow bedrock aquifers in the Piceance and Yellow Creek watersheds. The purpose of this report is to present ground-water chemistry and water-level elevations collected during 2013–16. Comparisons are made to data that were collected from the bedrock aquifers from 2010 to 2012 to identify the potential for changes in water quality and water-level elevations. Appreciable changes in water-level elevations and hydraulic gradient were observed in early April 2015 in two wells completed in the upper and lower aquifers. The hydraulic gradient between the two wells was consistently downward from the upper aquifer to the lower aquifer during 2010–15; however, in early April 2015, the gradient changed from downward to upward between the two aquifers. Overall, water-level elevations declined by about 14 and 11 feet in the upper and lower aquifers, respectively, from 2013 to 2016. Previously published data estimated groundwater ages at 1,200 years old in the upper aquifer and 9,600 years old in the lower aquifer. These groundwater ages indicate that ground-water was recharged over thousands of years. With such long periods of time for aquifer recharge, declines in water-level elevation over short time steps (a few months) have important implications for sustainable management of this resource. Solution mining activities or drilling for oil and natural gas in the area could be related to the changes observed in water-level elevations in these wells; however, further investigation would be needed to evaluate causation. Changes in major-ion chemistry were evaluated in the bedrock aquifer using time series plots of select major-ion data from 2010 to 2016. Major-ion chemistry was variable for a single well from 2010 to 2016 where alkalinity and sulfate were the most variable constituents. One possible explanation for the observed changes in major-ion chemistry may be that the sample depth for that well no longer represents the most appreciable flow in the borehole. On a larger scale, potential changes in flow within the borehole may indicate changes in the regional flow system. Methane and volatile organic compound concentrations were evaluated using a similar approach to that of major ions and had similar findings. Methane concentrations in wells sampled from 2010 to 2016 were generally constant. The only exception was observed at a single well where the range of methane concentrations was from 57.4 (2010) to 4.02 milligrams per liter (2013). This is the same well where changes in water-level elevation, hydraulic gradient, and major-ion chemistry were observed, providing multiple lines of evidence to indicate change in the bedrock aquifers. Sampling of a well located in an area with little energy development but where faults or fractures could provide a path for the migration of fluids indicate mixing of groundwater between the upper and lower aquifers.

Colorado↗
USGS2002

Surface-water characteristics and quality on the Osage Reservation, Osage County, Oklahoma, 1999

Concern about the effects of early oil-industry practices of surface disposal of produced-brine water prompted an investigation of the surface-water quality on the Osage Reservation. About 38,600 oil wells have been drilled on the Osage Reservation since drilling began in 1896. The Osage Reservation comprises three major drainage basins. The Caney River Basin is in the northeast, the Bird Creek Basin is in the southeast, and the Salt Creek Basin in the west. Variations in streamflow on the Osage Reservation during a year primarily result from variations in the quantity and frequency of rainfall, evapotranspiration, and reservoir operations. Most streams do not flow during low rainfall periods in late summer, early fall, and in winter. Percent of mean annual discharge is largest during March through June, averaging 54 to 62 percent and smallest during December, January, July, and August, averaging only 14 to 21 percent. The basin areas of Caney River in the reservation (251 square miles), Salt Creek (273 square miles), and Sand Creek (227 square miles) are about the same and the basin areas of the Bird Creek Basin (418 square miles) and Homily Creek Basin (383 square miles) are similar in area. One hundred forty surface-water sites were sampled once during either February, March or August 1999. The surface-drainage areas, incremental basins, between sample sites along a stream, range in size from 0.26 to 123 square miles with a median of 8.6 square miles. Total number of oil wells upgradient of the samples sites is 31,432 or 80 percent of the total in the reservation. The total number of oil wells in the Caney River Basin in the reservation (2,975 wells), Salt Creek Basin (4,619 wells), and Sand Creek Basin (3,858 wells) are about the same and the total number of oil wells in the Bird Creek Basin (8,858 wells) and Hominy Creek Basin (7,842 wells) are similar. The number of oil wells per square mile in the incremental basins ranges for 0.86 to 154. Surface-water quality monitoring had been conducted previously at two sites included in this study. Dissolved chloride concentrations for the two samples collected during 1999 were equaled or exceeded at both sites by the historical data. There is no statistically significant difference between the distribution of the dissolved chloride concentrations from the surface water and nearby ground-water samples. The surface-water quality samples had significantly lesser concentrations of dissolved solids, sulfate, and nitrite plus nitrate as nitrogen than the ground-water samples. Chloride yield, reported in tons per day per square mile, is the chloride load divided by the basin area upstream of the sample site. The mean of the chloride yields for all the samples was 0.07 ton per day per square mile. Many sample locations where yields were greater than 0.07 ton per day per square mile were areas where dissolved chloride concentrations from surface-water samples were greater than 250 milligrams per liter in an earlier water-quality investigation. An investigation of possible relations between the surface-water quality data and the oil-well construction data for the incremental basins and for 1-mile radial distance upstream in the incremental basins was conducted. The oil-well data also were grouped by the time periods of activity into pre-1930, 1930 to 1970, and post-1970. These groups attempt to account for differences in industry drilling and producing practices associated with various periods. No statistically significant correlations were found between the surface-water quality data and the oil-well construction data.

Oklahoma↗
USGS2018

Evaluation of the Source and Transport of High Nitrate Concentrations in Ground Water, Warren Subbasin, California

Ground water historically has been the sole source of water supply for the Town of Yucca Valley in the Warren subbasin of the Morongo ground-water basin, California. An imbalance between ground-water recharge and pumpage caused ground-water levels in the subbasin to decline by as much as 300 feet from the late 1940s through 1994. In response, the local water district, Hi-Desert Water District, instituted an artificial recharge program in February 1995 using imported surface water to replenish the ground water. The artificial recharge program resulted in water-level recoveries of as much as 250 feet in the vicinity of the recharge ponds between February 1995 and December 2001; however, nitrate concentrations in some wells also increased from a background concentration of 10 milligrams per liter to more than the U.S. Environmental Protection Agency (USEPA) maximum contaminant level (MCL) of 44 milligrams per liter (10 milligrams per liter as nitrogen). The objectives of this study were to: (1) evaluate the sources of the high-nitrate concentrations that occurred after the start of the artificial-recharge program, (2) develop a ground-water flow and solute-transport model to better understand the source and transport of nitrates in the aquifer system, and (3) utilize the calibrated models to evaluate the possible effect of a proposed conjunctive-use project. These objectives were accomplished by collecting water-level and water-quality data for the subbasin and assessing changes that have occurred since artificial recharge began. Collected data were used to calibrate the ground-water flow and solute-transport models. Data collected for this study indicate that the areal extent of the water-bearing deposits is much smaller (about 5.5 square miles versus 19 square miles) than that of the subbasin. These water-bearing deposits are referred to in this report as the Warren ground-water basin. Faults separate the ground-water basin into five hydrogeologic units: the west, the midwest, the mideast, the east and the northeast hydrogeologic units. Water-quality analyses indicate that septage from septic tanks is the primary source of the high-nitrate concentrations measured in the Warren ground-water basin. Water-quality and stable-isotope data, collected after the start of the artificial recharge program, indicate that mixing occurs between imported water and native ground water, with the highest recorded nitrate concentrations in the midwest and the mideast hydrogeologic units. In general, the timing of the increase in measured nitrate concentrations in the midwest hydrogeologic unit is directly related to the distance of the monitoring well from a recharge site, indicating that the increase in nitrate concentrations is related to the artificial recharge program. Nitrate-to-chloride and nitrogen-isotope data indicate that septage is the source of the measured increase in nitrate concentrations in the midwest and the mideast hydrogeologic units. Samples from four wells in the Warren ground-water basin were analyzed for caffeine and selected human pharmaceutical products; these analyses suggest that septage is reaching the water table. There are two possible conceptual models that explain how high-nitrate septage reaches the water table: (1) the continued downward migration of septage through the unsaturated zone to the water table and (2) rising water levels, a result of the artificial recharge program, entraining septage in the unsaturated zone. The observations that nitrate concentrations increase in ground-water samples from wells soon after the start of the artificial recharge program in 1995 and that the largest increase in nitrate concentrations occur in the midwest and mideast hydrogeologic units where the largest increase in water levels occur indicate the validity of the second conceptual model (rising water levels). The potential nitrate concentration resulting from a water-level rise in the midwest and mideast hydrogeologic units was estimated using a simple mixing-cell model. The estimated value is within the range of concentrations measured in samples from wells, further indicating the validity of the second conceptual model. A ground-water flow model and a solute-transport model were developed for the Warren ground-water basin for the period 1956-2001. MODFLOW-96 was used for the ground-water flow model and MOC3D was used for the solute-transport model. The model cell size is about 500 feet by 500 feet and the models were discretized vertically into three layers. The models were calibrated using a trial-and-error approach using water-level and nitrate-concentration data collected between 1956-2001. In order to better match the measured data, low fault hydraulic characteristic values were required, thereby compartmentalizing the ground-water basin. In addition, it was necessary to parameterize the specific yield distribution for the top model layer where unconfined ground-water conditions occur into three homogeneous zones. Separate sets of specific- yield values were needed to simulate the drawdown and subsequent water-level recovery. In addition, the calibrated natural recharge was about 83 acre-feet per year. The entrainment of unsaturated-zone septage was simulated as recharge having an associated nitrate concentration. The volume of recharge was a function of the measured water-level rise between 1994-98 and the moisture content of the unsaturated zone. The nitrate concentration of the recharge water was a weighted function of the assumed nitrate concentration in the infiltrating water associated with the overlying land use. The simulated hydraulic head and nitrate concentration results were in good agreement with the measured data indicating that the mechanism for the increase in nitrate concentrations was rising water levels entraining high-nitrate septage in the unsaturated-zone. The calibrated models were used to simulate the possible effects of a planned conjunctive-use project in the western part of the ground-water basin. The simulated project included the addition of a new recharge pond and a new extraction well. In addition, recharge at two existing recharge ponds was increased and three existing production wells were pumped, treated in a nitrate-removal facility, and used for water supply. The simulated hydraulic heads increased in the west, the mideast, and parts of the east hydrogeologic units; however, the simulated hydraulic heads decreased in the midwest and northeast hydrogeologic units. The simulated nitrate concentrations increased to above the MCL of 44 milligrams per liter (10 milligrams per liter as nitrogen) in parts of the west as a result of the increase in simulated hydraulic head. The simulated nitrate concentrations decreased in part of the midwest hydrogeologic unit as a result of the artificial recharge and pumping from the nitrate-removal wells. The simulated nitrate concentrations increased to above the MCL of 44 milligrams per liter in part of the mideast and parts of the east hydrogeologic units beneath commercial land-use areas.

California↗
USGS1978

Plan of study for the High Plains regional aquifer-system analysis in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

The Ogallala Formation and associated Tertiary and Quarternary deposits form the principal aquifers supporting irrigation in the High Plains of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The volume of water in storage within the aquifers is declining in most of the High Plains because water is being withdrawn in excess of the rate of replenishment. The U.S. Geological Survey has initiated a 5-year study of the High Plains aquifer system to develop the geohydrologic data base and computer models of the ground-water flow system needed to evaluate the response of the aquifer,system to ground-water management alternatives. This report describes the objectives, plan, and organization of the study and outlines the work to be accomplished in each state in the study area.

Colorado, Kansas, Nebraska, New Mexico, Oklahoma, ↗
USGS1964

Geology and hydrology of the West Milton area, Saratoga County, New York

This report describes the geology, ground-water conditions, streamflow characteristics, and quality of water in the West Milton area, Saratoga County, N.Y. The West Milton area is in the east-central part of New York in the hilly region that forms a transition zone between the Adirondack Mountains and the Hudson-Mohawk valley lowland. Bedrock underlying the area consists of crystalline rocks of Precambrian age and sandstone, dolomite, limestone, and shale formations of Cambrian and Ordovician age. The formations have been moderately folded and have been displaced as much as several hundred feet' along at least three northeast-trending normal faults. The bedrock is overlain in nearly all parts of the area by a layer of unconsolidated deposits which ranges in thickness from a few feet to more than 200 feet. The unconsolidated deposits are of Pleistocene age and consist of unstratified materials (till) laid down by glacial ice at stratified sediments deposited by glacial meltwaters. The topography of the bedrock surface differs greatly from the topography of the land surface. Although not evident in the present topography, at least two channels, cut in bedrock by preglacial streams, pass through the area. Ground-water supplies adequate to satisfy domestic requirements can be obtained from wells in any part of the area. Large ground-water supplies may be taken from coarse-grained stratified deposits comprising two aquifers in the valley of Kayaderosseras Creek. The Atomic Energy Commission has pumped as much as 1 mgd from a horizontal well drawing from the uppermost aquifer which is composed of flood-plain deposits. Part of the water yielded by this well during extended periods of pumping is induced flow from the creek. Three nearby vertical wells drilled by the Commission comprise a separate well field capable of yielding at least 2 mgd and possibly as much as 3 mgd from the deeper stratified deposits underlying the valley. A pumping test showed that at near the center of this well field the coefficient of transmissibility is about 125,000 gpd per ft and the coefficient of storage is about 0.0003. The water obtained from the sand and gravel has a hardness of about 125 ppm and contains about 150 ppm of dissolved solids. Most of the Government reservation is drained by Glowegee Creek, one of the larger tributaries of Kayaderosseras Creek. The average streamflow of Kayaderosseras Creek at West Milton is 141 cfs or about 1.5 cfs per sq. mi. The monthly mean discharge has ranged from a low of 21.7 cfs in September 1958 to a high of 866 cfs in March 1936, and the annual mean discharge has ranged from 94.5 cfs in 1941 to 198 cfs in 1952. The mean annual flood is 1,740 cfs and the 50-year flood is 5,300 cfs. Streamflow data have been collected on Glowegee Creek since 1948 at a station 0.5 mile south of West Milton. The average streamflow of Glowegee Creek at this station is 41 cfs or about 1.5 cfs per sq mi. The mean annual flood is 740 cfs and the 50-year flood is 2,250 cfs. The quality of the water in both Kayaderosseras Creek and Glowegee Creek is satisfactory for public supply and most industrial purposes. The mineral content of both streams is low--the dissolved-solids content averaging about 93 ppm in Kayaderosseras Creek and about 131 ppm in Glowegee Creek. The average hardness of water in Kayaderosseras Creek and Glowegee Creek is 68 ppm and 102 ppm, respectively. During periods of low flow, suspended sediment discharge in both streams is less than 10 tons per day, but during periods of high flow, the sediment discharge has been as great as 163 tons per day in Glowegee Creek and 437 tons per day in Kayaderosseras Creek.

Water Supply Paper↗
USGS1996

Description of the ground-water flow system in the Portland Basin, Oregon and Washington

An increasing dependence on ground-water resources in the Portland Basin has made it necessary for State and local governments to evaluate the capability of the ground-water system to meet present and future demands for water. This report describes the regional ground-water system and provides a conceptualization of the aquifer system. Aquifer geometry, recharge, ground-water flow directions, ground-water/surface water relations, water use, and water-level changes with time are presented.

Water Supply Paper↗
USGS1995

Listings of model values for the simulation of ground-water flow in the Cimarron River alluvium and terrace deposits from Freedom to Guthrie, Oklahoma

This report contains MODFLOW input and output listings for the simulation of ground-water flow in alluvium and terrace deposits associated with the Cimarron River from Freedom to Guthrie, Oklahoma. These values are to be used in conjuction with the report, 'Geohydrology of alluvium and terrace deposits of the Cimarron River from Freedom to Guthrie, Oklahoma,' by G.P. Adams and D.L. Bergman, published as U.S. Geological Survey Water-Resources Investigatons Report 95-4066. The simulation used a digital ground-water flow model and was evaluated by a management and statistical program.

Open-File Report↗
USGS1977

Ground-water data for Michigan, 1976

The purpose of this report is to make available the records of water levels in principal aquifers of the State through 1976 and to compile related data, such as records of ground-water pumpage. Also included in the report are data on municipal, public, and industrial water-supply facilities. Records of water levels in areas of heavy pumpage and in areas where changes are principally due to natural influences are illustrated or tabulated to allow comparison between these types of water-level fluctuations. Water levels and related data provide a record for the evaluation of available ground-water supplies. The long-term records serve as a framework to which short-term records may be related. This report is written for persons, municipalities, industries, institutions, consultants, drillers, and hydrologists interested in the groundwater resources of the State.

Michigan↗
USGS1995

Listings of model input and selected output values for the simulation of ground-water flow near Los Alamos, North-central New Mexico

This report contains listings of model input and selected output values for the simulation of ground-water flow near Los Alamos, north- central New Mexico. This simulation was developed by the U.S. Geological Survey in cooperation with Los Alamos National Laboratory (Frenzel, P.F., 1995, Geohydrology and simulation of ground-water flow near Los Alamos, north-central New Mexico: U.S. Geological Survey Water-Resources Investigations Report 95-4091). The simulation used the U.S. Geological Survey modular flow model code (McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference ground-water flow model: Techniques of Water-Resources Investigations of the United States Geological Survey, book 6, chap. A1). The listings in this report are in compressed format on a 1.44-megabyte IBM-PC1 compatible floppy disk. Software is included for decompression to ASCII format.

Open-File Report↗
USGS1996

Summary of hydrogeologic controls on ground-water flow at the Nevada Test Site, Nye County, Nevada

The underground testing of nuclear devices has generated substantial volumes of radioactive and other chemical contaminants below ground at the Nevada Test Site (NTS). Many of the more radioactive contaminants are highly toxic and are known to persist in the environment for thousands of years. In response to concerns about potential health hazards, the U.S. Department of Energy, under its Environmental Restoration Program, has made NTS the subject of a long-term investigation. Efforts supported through the U.S. Department of Energy program will assess whether byproducts of underground testing pose a potential hazard to the health and safety of the public and, if necessary, will evaluate and implement steps to remediate any of the identified dangers. Test-generated contaminants have been introduced over large areas and at variable depths above and below the water table throughout NTS. Evaluating the risks associated with these byproducts of underground testing presupposes a knowledge of the source, transport, and potential receptors of these contaminants. Ground-water flow is the primary mechanism by which contaminants can be transported significant distances away from the initial point of injection. Flow paths between contaminant sources and potential receptors are separated by remote areas that span tens of miles. The diversity and structural complexity of the rocks along these flow paths complicates the hydrology of the region. Although the hydrology has been studied in some detail, much still remains uncertain about flow rates and directions through the fractured-rock aquifers that transmit water great distances across this arid region. Unique to the hydrology of NTS are the effects of underground testing, which severely alter local rock characteristics and affect hydrologic conditions throughout the region. Any assessment of the risk must rely in part on the current understanding of ground-water flow, and the assessment will be only as good as the understanding itself. This report summarizes what is known and inferred about ground-water flow throughout the NTS region. The report identifies and updates what is known about some of the major controls on ground-water flow, highlights some of the uncertainties in the current understanding, and prioritizes some of the technical needs as related to the Environmental Restoration Program. An apparent deficiency in the current understanding is a lack of knowledge about flow directions and rates away from major areas of testing. Efforts are necessary to delineate areas of downgradient flow and to identify factors that constrain and control flow within these areas. These efforts also should identify the areas most critical to gaining detailed understanding and to establishing long-term monitoring sites necessary for effective remediation.

Nevada↗
USGS1979

A digital model for simulation of ground-water hydrology in the Houston area, Texas

This report documents the construction and calibration of a digital model for the simulation of hydrologic conditions in the Chicot and Evangeline aquifers in the Houston area of southeastern Texas. The model is a five-layer finite-difference model, with a grid pattern of 63 x 67 nodes representing an area of 27,000 square miles, for simulation of three- dimensional ground-water flow. The hydrologic properties and processes modeled were ground-water withdrawals, transmissivities, storage coefficients of the aquifers and clays, quantity of water derived from storage in the clays, and vertical hydraulic conductivity and vertical leakage. The model, which simulates water-level declines, changes in storage in the clay layers, and land-surface subsidence, was calibrated by use of historical records from 1890 to 1975. It is very sensitive to variations in transmissivities and to variations in water-table and artesian storage. It is less sensitive to variations in clay storage.

Texas↗
USGS1999

Simulation of the effects of development of the ground-water flow system of Long Island, New York

Extensive development on Long Island since the late 19th century and projections of increased urbanization and ground-water use makes effective water-resource management essential for preservation of the island's hydrologic environment and maintenance of a reliable source of water supply. This report presents results of a ground-water flow simulation analysis of the effects of development on the Long Island ground-water system. It describes ground-water levels, stream-flow, and the ground-water budget for the predevelopment period (pre-1900), the 1960's drought, and a more recent (1968-83) period with significant hydrologic stress. The report also presents estimated effects of a proposed water-supply strategy for the year 2020. Long Island has three major aquifers-the upper glacial (water-table), the Magothy, and the Lloyd aquifers-that are separated to varying degrees by confining units. Before development, recharge from precipitation entered the ground-water system at a rate of more than 1.1 billion gallons per day. An equal amount discharged to streams (41 percent), the shore (52 percent), and subsea boundaries (7 percent) . Urbanization and withdrawal of more than 400 Mgal/d (million gallons per day) from wells have resulted in local effects that include declines in ground-water levels, drying up and burial of streams and wetlands, reduction of ground-water recharge by increased overland flow to the ocean, a general decrease in ground-water discharge, and salt water intrusion. In some areas, the reduction in recharge is mitigated by leakage from water-supply and wastewater disposal lines, and infiltration of storm water through recharge basins. During 1968-83, a net loss of 240 Mgal/d from the ground-water system caused a decrease in ground-water discharge to streams (135 Mgal/d), to the shore (82 Mgal/d), and to subsea boundaries (23Mgal/d).The greatest adverse effects have been in western Long Island, where the most severe development has occurred. This analysis shows stream base flow to be highly sensitive to water-table fluctuations, and long streams to be more sensitive than short ones. A water-supply scenario for the year 2020 was simulated that employs redistribution of pumping centers to mitigate extreme local effects . Although the net stress on the ground-water system was projected to increase 57 Mgal/d (24 percent) above that of 1968-83, redistribution of ground-water withdrawals across the island would allow recovery of cones of depression in western Long Island, thereby reducing the threat of salt water intrusion and increasing base flow of some streams . The increased stress would cause a net decrease in base flow island wide of 44 Mgal/d; total base flow would be 281 Mgal/d - 39 percent below predevelopment levels or 14 percent below 1968-83 levels. The most severe effects would be in Nassau and western Suffolk Counties.

New York↗
USGS2006

Questa baseline and premining ground-water quality investigation 18. Characterization of brittle structures in the Questa Caldera and their potential influence on bedrock ground-water flow, Red River Valley, New Mexico

This report presents a field-based characterization of fractured and faulted crystalline bedrock in the southern portion of the Questa caldera and its margin. The focus is (1) the identification and description of brittle geological structures and (2) speculation on the potential effects and controls that these structures might have on the potential fluxes of paleo to present-day ground water in relation to natural or mining-related metal and acid loads to surface and ground water. The entire study area is pervasively jointed with a few distinctive patterns such as orthogonal, oblique orthogonal, and conjugate joint sets. Joint intensity, the number of joints measured per unit line length, is high to extreme. Three types of fault zones are present that include partially silicified, low- and high-angle faults with well-developed damage zones and clay-rich cores and high-angle, unsilicified open faults. Conceptually, the joint networks can be thought of as providing the background porosity and permeability structure of the bedrock aquifer system. This background is cut by discrete entities such as the faults with clay-rich cores and open faults that may act as important hydrologic heterogeneities. The southern caldera margin runs parallel to the course of the Red River Valley, whose incision has left an extreme topographic gradient at high angles to the river. Many of the faults and fault intersections run parallel to this assumed hydraulic gradient; thus, these structures have great potential to provide paleo and present-day, discrete and anisotropic pathways for solute transport within the otherwise relatively low porosity and permeability bedrock background aquifer system. Although brittle fracture networks and faults are pervasive and complex, simple Darcy calculations are used to estimate the hydraulic conductivity and potential ground-water discharges of the bedrock aquifer, caldera margin, and other faults in order to gain insight into the potential contributions of these features to the ground-water and surface-water flow systems. These calculations show that, because all of these features are found along the Red River in the Cabin Springs-Columbine Park-Goat Hill fan area, their combined effect increases the probability that the bedrock aquifer ground-water flow system provides discharge to the Red River along this reach.

New Mexico↗
USGS2006

Evaluation of the ground-water flow model for northern Utah Valley, Utah, updated to conditions through 2002

This report evaluates the performance of a numerical model of the ground-water system in northern Utah Valley, Utah, that originally simulated ground-water conditions during 1947-1980 and was updated to include conditions estimated for 1981-2002. Estimates of annual recharge to the ground-water system and discharge from wells in the area were added to the original ground-water flow model of the area. The files used in the original transient-state model of the ground-water flow system in northern Utah Valley were imported into MODFLOW-96, an updated version of MODFLOW. The main model input files modified as part of this effort were the well and recharge files. Discharge from pumping wells in northern Utah Valley was estimated on an annual basis for 1981-2002. Although the amount of average annual withdrawals from wells has not changed much since the previous study, there have been changes in the distribution of well discharge in the area. Discharge estimates for flowing wells during 1981-2002 were assumed to be the same as those used in the last stress period of the original model because of a lack of new data. Variations in annual recharge were assumed to be proportional to changes in total surface-water inflow to northern Utah Valley. Recharge specified in the model during the additional stress periods varied from 255,000 acre-feet in 1986 to 137,000 acre-feet in 1992. The ability of the updated transient-state model to match hydrologic conditions determined for 1981-2002 was evaluated by comparing water-level changes measured in wells to those computed by the model. Water-level measurements made in February, March, or April were available for 39 wells in the modeled area during all or part of 1981-2003. In most cases, the magnitude and direction of annual water-level change from 1981 to 2002 simulated by the updated model reasonably matched the measured change. The greater-than-normal precipitation that occurred during 1982-84 resulted in period-of-record high water levels measured in many of the observation wells in March 1984. The model-computed water levels at the end of 1982-84 also are among the highest for the period. Both measured and computed water levels decreased during the period representing ground-water conditions from 1999 to 2002. Precipitation was less than normal during 1999-2002. The ability of the model to adequately simulate climatic extremes such as the wetter-than-normal conditions of 1982-84 and the drier-than-normal conditions of 1999-2002 indicates that the annual variation of recharge to the ground-water system based on streamflow entering the valley, which in turn is primarily dependent upon precipitation, is appropriate but can be improved. The updated transient-state model of the ground-water system in northern Utah Valley can be improved by making revisions on the basis of currently available data and information.

Utah↗
USGS1975

The Miocene aquifer system in Mississippi

A large amount of information is available on the aquifers of Mississippi. Reports resulting from various areal studies have described the ground-water resources of the areas concerned, but no reports dealing specifically with the statewide occurrence of individual aquifer systems have been prepared previously. A series of "aquifer atlases" was deemed the most effective way to point out the character, the potential, and the extent of development of the aquifers and thereby provide water managers with data needed for efficient utilization of available resources. This report on the Miocene aquifer system is the first in the series. Information on the aquifers was obtained in the cooperative programs of the U.S. Geological Survey with the Mississippi Board of Water Commissioners and other State and Federal agencies.

Mississippi↗
USGS1971

Summary of ground-water hydrological data in Michigan in 1970

The purpose of this report is to make available the records of groundwater levels in principal aquifers of the State through 1970 and to compile other related data, such as records of ground-water pumpage, data on municipal, public and industrial water-supply facilities, and the effects of precipitation on ground-water levels. Records of water levels in areas of heavy pumpage, and in areas where changes are principally from natural influences, are illustrated or tabulated to allow comparison between these types of water- level fluctuations. The water levels and related data provide a day-to-day record for the evaluation of available ground-water supplies. The long-term records serve as a framework to which short-term records may be related. This report is written for those persons, municipalities, industries, institutions, consultants, drillers, and hydrologists interested in the ground-water resources of the State.

Michigan↗