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At least 1,783 records · Page 99Linked to original sources
USGS2006

Volatile organic compounds in the nation's ground water and drinking-water supply wells

This national assessment of 55 volatile organic compounds (VOCs) in ground water gives emphasis to the occurrence of VOCs in aquifers that are used as an important supply of drinking water. In contrast to the monitoring of VOC contamination of ground water at point-source release sites, such as landfills and leaking underground storage tanks (LUSTs), our investigations of aquifers are designed as large-scale resource assessments that provide a general characterization of water-quality conditions. Nearly all of the aquifers included in this assessment have been identified as regionally extensive aquifers or aquifer systems. The assessment of ground water (Chapter 3) included analyses of about 3,500 water samples collected during 1985-2001 from various types of wells, representing almost 100 different aquifer studies. This is the first national assessment of the occurrence of a large number of VOCs with different uses, and the assessment addresses key questions about VOCs in aquifers. The assessment also provides a foundation for subsequent decadal assessments of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program to ascertain long-term trends of VOC occurrence in these aquifers.

Circular↗
USGS1977

Nature and extent of ground-water-quality changes resulting from solid-waste disposal, Marion County, Indiana

Studies of seven landfills in the Indianapolis, Indiana, area indicate that in five of the landfills movement of ground water is from the deep aquifers into the uppermost aquifer. In the other two landfills, movement of ground water is from the shallow aquifers to the deeper aquifers, so that leachate is transported into the deeper aquifers. In all the landfills, the predominant direction of ground-water movement is lateral. Placing solid waste into the landfills has occasionally altered the local, but not the regional, flow patterns. Ground-water mounding at shallow depths beneath two of the landfills has caused flow toward the edges of the two fills. Leachate at these fills is moving downward and outward and has affected water quality at shallow depths. Pumping near two other landfills has reversed the direction of regional ground-water flow, allowing leachate to move toward the pumping wells. Leachate at the three remaining landfills is moving downgradient and is discharging into single streams adjacent to each landfill. (Woodard-USGS)

Indiana↗
USGS1999

Hydrogeology, ground-water quality, and sources of nitrate in lowland glacial aquifers of Whatcom County, Washington, and British Columbia, Canada

Ground water is an important source of domestic, municipal, and irrigation water supply throughout the Fraser-Whatcom Lowland, particularly for the 225-square mile agricultural area surrounding the Whatcom County communities of Lynden, Everson, Nooksack, and Sumas and the British Columbia communities of Abbotsford and Aldergrove. Population growth and developing ground-water-quality problems have increased the demand for additional sources of ground water. The U.S. Geological Survey, in cooperation with the Whatcom County Planning Department, collected water-level, lithologic, and water-quality data from 608 wells during 1990-92 to complete a regional appraisal of the ground-water system.

British Columbia;Washington↗
USGS1984

Ground-water resources of Limestone County, Texas

Limestone County, located in east-central Texas, has small to plentiful ground-water supplies available, depending upon the location within the county. The Wilcox Group in the eastern part of the county has adequate supplies to meet the expected water demands in the foreseeable future. The thicker zones of the Wilcox Group can supply yields in excess of 500 gallons per minute. The Midway Group can supply yields in excess of 100 gallons per minute from the Tehuacana Member of the Kincaid Formation. This represents the largest well yields from the Midway Group in Texas. The Midway Group elsewhere in the State is mostly a poor water producer and is not considered an aquifer. The Taylor Marl and Navarro Group furnish only small quantities of ground water to wells in the western part of the county where these units crop out. The Hosston and Travis Peak Formations are present at depths in excess of 2,000 feet. These formations, which contain slightly saline water in the western part of the county, could be expected to produce water with a temperature of about 150°F that might be used for heating purposes. About 0.9 million gallons per day of ground water was used for all purposes in 1980. This use has declined since 1955 but is expected to increase as additional public-supply and industrial wells are being developed. The Wilcox Group is capable of annually yielding at least 14,000 acre-feet or 11.6 million gallons per day of water to wells on a long-term basis. Generally, the ground water is of acceptable quality for most uses. Relatively high dissolved-solids and iron concentrations are the major water-quality problems. Water-quality problems that may be the result of man's activities are limited to a small oilfield area near Mexia. Lignite mining from the Wilcox Group is expected to take place in the foreseeable future. The collection of additional hydrologic data on the Wilcox would be desirable before, during, and after mining.

Texas↗
USGS1989

Ground-water resources of Williams County, Ohio, 1984-86

This report presents the results of a county-wide ground-water appraisal of Williams County, a mostly agricultural county of more than 36,000 people that is undergoing gradual commercial and industrial development. Most of the County's ground water is in the 80-to 320-foot thick cap of unconsolidated glacial sediments. The underlying Mississippian and older bedrock units are mostly Wisconsin till containing discontinuous lenses of sand and gravel. Two end moraines that cross the County form low northeast-southwest-trending ridges. Ground moraine covers the rest of the County except for fine sand and silt lacustrine sediments in the southeastern corner.The water-bearing sand and gravel bodies appear to be thickest and most widespread in the end moraines and thinnest and more localized in the lacustrine sediments. A generally productive (up to 1,000 gallons per minute) zone of sand and gravel and broken, weathered rock is present in places at the contact of the unconsolidated sediments and the shale. A study of well logs and aquifer tests shows that well yields of 500 gallons per minute are possible over all but the southeastern corner of the County. Transmissivities range from 2,800 to more than 64,300 feet squared per day. Storage coefficients that range from 0.0001 to 0.00038 indicate confined to semiconfined conditions. A gently southeast-sloping water-level surface was identified by measuring water levels in an 87-well network. A potentiometric-surface map constructed from these water-level measurements shows a fairly consistent gradient of 10 to 30 feet per mile across the County, which indicates that the unconsolidated sediments, on a large scale, act as one aquifer. Ground water flows toward the southeast. The recharge area for the ground-water system includes Williams County, and the area just to the northwest of Williams County, whereas the discharge areas are mainly the streams within and to the southeast of the County. Water quality in the unconsolidated sediments was evaluated through the analysis of samples from 48 wells. The predominately calcium magnesium bicarbonate type water generally is suitable for most uses, but is hard and high in iron. The median pH is 7.6, the median specific conductance is 600 microsiemens per centimeter, the median iron concentration is 1.4 milligrams per liter, and the median hardness (as CaCO3) is 290 milligrams per liter. Water in the southeastern corner of the County contains more sodium than elsewhere in the County. Seasonal variations in the ground-water quality are small. Analysis of four samples showed the water quality of area streams at base flow to be very similar, although slightly more dilute and less hard than the ground water.

Water-Resources Investigations Report↗
USGS2005

Simulation of ground-water flow in coastal Georgia and adjacent parts of South Carolina and Florida-predevelopment, 1980, and 2000

A digital model was developed to simulate steady-state ground-water flow in a 42,155-square-mile area of coastal Georgia and adjacent parts of South Carolina and Florida. The model was developed to (1) understand and refine the conceptual model of regional ground-water flow, (2) serve as a framework for the development of digital subregional ground-water flow and solute-transport models, and (3) serve as a tool for future evaluations of hypothetical pumping scenarios used to facilitate water management in the coastal area. Single-density ground-water flow was simulated using the U.S. Geological Survey finite-difference code MODFLOW-2000 for mean-annual conditions during predevelopment (pre?1900) and the years 1980 and 2000. The model comprises seven layers: the surficial aquifer system, the Brunswick aquifer system, the Upper Floridan aquifer, the Lower Floridan aquifer, and the intervening confining units. A combination of boundary conditions was applied, including a general-head boundary condition on the top active cells of the model and a time-variable fixed-head boundary condition along part of the southern lateral boundary. Simulated heads for 1980 and 2000 conditions indicate a good match to observed values, based on a plus-or-minus 10-foot (ft) calibration target and calibration statistics. The root-mean square of residual water levels for the Upper Floridan aquifer was 13.0 ft for the 1980 calibration and 9.94 ft for the 2000 calibration. Some spatial patterns of residuals were indicated for the 1980 and 2000 simulations, and are likely a result of model-grid cell size and insufficiently detailed hydraulic-property and pumpage data in some areas. Simulated potentiometric surfaces for predevelopment, 1980, and 2000 conditions all show major flow system features that are indicated by estimated peotentiometric maps. During 1980?2000, simulated water levels at the centers of pumping at Savannah and Brunswick rose more than 20 ft and 8 ft, respectively, in response to decreased pumping. Simulated drawdown exceeded 10 ft in the Upper Floridan aquifer across much of the western half of the model area, with drawdown exceeding 20 ft along parts of the western, northern, and southern boundaries where irrigation pumping increased during this period. From predevelopment to 2000 conditions, the simulated water budget showed an increase in inflow from, and decrease in outflow to, the general-head boundaries, and a reversal from net seaward flow to net landward flow across the coastline. Simulated changes in recharge and discharge distribution from predevelopment to 2000 conditions showed an increase in extent and magnitude of net recharge cells in the northern part of the model area, and a decrease in discharge or change to recharge in cells containing major streams and beneath major pumping centers. The model is relatively sensitive to pumping and the controlling head at the fixed-head boundary and less sensitive to the distribution of aquifer properties in general. Model limitations include: (1) its spatial scale and discretization, (2) the extent to which data are available to physically define the flow system, (3) the type of boundary conditions and controlling parameters used, (4) uncertainty in the distribution of pumping, and (5) uncertainty in field-scale hydraulic properties. The model could be improved with more accurate estimates of ground-water pumpage and better characterization of recharge and discharge.

Florida, Georgia, South Carolina↗
USGS1998

Ground water resources of the Mille Lacs Lake area, east-central Minnesota

The Mille Lacs Lake study area is a 960 mi 2 area containing the ground-water and surface-water drainages to both Mille Lacs Lake and the first 12 miles of the Rum River. Within this study area, available ground water occurs in saturated, overlapping, discontinuous, partially-connected, glacially-deposited (hereinafter, glacial) aquifers and in bedrock aquifers. No extensive glacial aquifer could be delineated. Surficial aquifers generally are less than 30 feet thick, but may exceed 78 feet. Lake Onamia is hydraulically connected with surficial aquifers on its north and south sides. Ground water enters Lake Onamia from an adjacent surficial aquifer with a hydraulic head of 1.56 feet near its eastern shore. Glacial aquifers buried beneath till form the uppermost confined (hereinafter, buried) aquifers and generally are from 3 to 15 feet thick, but may be as much as 118 feet thick. These buried aquifers generally occur beneath 10 to 60 feet of till and clay, but it may be as thick as 208 feet. Individual aquifers can be partially buried by till and therefore may contain surficial and buried areas. Most buried aquifers are isolated or only partially connected to other aquifers. Recharge water moves horizontally and vertically through other aquifers and through confining units to reach these buried aquifers. Discharge from these aquifers is through well withdrawals, flow to surface-water bodies, and leakage to other aquifers. Buried aquifers may yield as much as 500 gallons per minute in some locations. In most areas, the specific capacity of these aquifers is less than 1 gallon per minute per foot but may reach 41.6 gallons per minute per foot. Ground water from all aquifers is of the calcium magnesium bicarbonate type. Iron, manganese, and sodium in this ground water frequently exceeded U.S. Environmental Protection Agency drinking water standards and health advisories. The sodium health advisory was exceeded in 15 percent of samples.

Minnesota↗
USGS2008

Simulation of Ground-Water Flow and Optimization of Withdrawals from Aquifers at the Naval Air Station Patuxent River, St. Mary's County, Maryland

Potentiometric surfaces in the Piney Point-Nanjemoy, Aquia, and Upper Patapsco aquifers have declined from 1950 through 2000 throughout southern Maryland. In the vicinity of Lexington Park, Maryland, the potentiometric surface in the Aquia aquifer in 2000 was as much as 170 feet below sea level, approximately 150 feet lower than estimated pre-pumping levels before 1940. At the present rate, the water levels will have declined to the regulatory allowable maximum of 80 percent of available drawdown in the Aquia aquifer by about 2050. The effect of the withdrawals from these aquifers by the Naval Air Station Patuxent River and surrounding users on the declining potentiometric surface has raised concern for future availability of ground water. Growth at Naval Air Station Patuxent River may increase withdrawals, resulting in further drawdown. A ground-water-flow model, combined with optimization modeling, was used to develop withdrawal scenarios that minimize the effects (drawdown) of hypothetical future withdrawals. A three-dimensional finite-difference ground-water-flow model was developed to simulate the ground-water-flow system in the Piney Point-Nanjemoy, Aquia, and Upper Patapsco aquifers beneath the Naval Air Station Patuxent River. Transient and steady-state conditions were simulated to give water-resource managers additional tools to manage the ground-water resources. The transient simulation, representing 1900 through 2002, showed that the magnitude of withdrawal has increased over that time, causing ground-water flow to change direction in some areas. The steady-state simulation was linked to an optimization model to determine optimal solutions to hypothetical water-management scenarios. Two optimization scenarios were evaluated. The first scenario was designed to determine the optimal pumping rates for wells screened in the Aquia aquifer within three supply groups to meet a 25-percent increase in withdrawal demands, while minimizing the drawdown at a control location. The resulting optimal solution showed that pumping six wells above the rate required for maintenance produced the least amount of drawdown in the local potentiometric surface. The second hypothetical scenario was designed to determine the optimal location for an additional well in the Aquia aquifer in the northeastern part of the main air station. The additional well was needed to meet an increase in withdrawal of 43,000 cubic feet per day. The optimization model determined the optimal location for the new well, out of a possible 10 locations, while minimizing drawdown at control nodes located outside the western boundary of the main air station. The optimal location is about 1,500 feet to the east-northeast of the existing well.

Scientific Investigations Report↗
USGS1995

Hydrogeology and ground-water flow at the Muddy Brook riparian zone, north-central Connecticut

The hydrogeology and ground-water flow of Muddy Brook were investigated as part of a study to determine the effects of restoring agricultural riparian land to forest on water quality. Test-hole drilling, well installation, and slug-test analyses indicate that the part of Muddy Brook studied is underlain by thin stratified-drift deposits. These deposits are mostly less than 10 feet thick and have estimated horizontal hydraulic conductivities of 4 to 30 feet per day. Till deposits from 1 to 14 feet thick underlie the stratified-drift deposits and have estimated horizontal hydraulic conductivities of 0.1 and 4.3 feet per day. The water table in stratified drift is less than 10 feet below land surface during most of the year, and the horizontal hydraulic gradient varies seasonally and areally from 0.015 to 0.07 feet per foot. The horizontal hydraulic gradient in the till deposits is as great as 0.1 feet per foot. Vertical hydraulic gradients of as large as 0.4 feet per foot are present between the till and stratified drift and are predominantly upward from the till into the stratified drift but can reverse direction in response to recharge. Ground-water discharge to Muddy Brook comes mostly from the saturated stratified-drift deposits, and during April through September 1992, flowed at a rate of 0.015 to 0.027 cubic feet per second. Average ground-water velocity is about 1 feet per day in the stratified drift and about 0.2 foot per day through the till deposits. Discharge of ground water from the till can contribute as much as 0.006 cubic feet per second of water to the stratified drift.

Water-Resources Investigations Report↗
USGS2003

Evolving issues and practices in managing ground-water resources: Case studies on the role of science

Hydrologic stresses throughout the 20th century and presently (2003) have caused the depletion and degradation of our Nation’s vital ground-water resources in many areas. Management strategies have been and are being implemented to optimize use of our ground-water resources with respect to achieving sustainability while mitigating the consequences of future withdrawals. The seven case studies presented herein show how the U.S. Geological Survey (USGS) in cooperation with local, State and other Federal agencies, as well as the private sector, have addressed some of the complexities of ground-water management using scientifically-based hydrologic studies and hydrologic monitoring. It is clear that the managed conjunctive use of our combined ground-water and surface-water supplies, and the artificial recharge of our ground-water systems present both challenges and opportunities. How well we manage these options depends upon best science practices, improved understanding of the resources, and the informed consensus of all stakeholders.

Circular↗
USGS1960

Geology and ground-water resources of the Rawlins area, Carbon County, Wyoming

The Rawlins area in west-central Carbon County, south-central Wyoming includes approximately 634 square miles of plains and valleys grading into relatively rugged uplifts. The climate is characterized by low precipitation, rapid evaporation, and a wide range of temperature. Railroading and ranching are the principal occupations in the area. The exposed rocks in the area range in age from Precambrian through Recent. The older formations are exposed in the uplifted parts, the oldest being exposed along the apex of the Rawlins uplift. The formations dip sharply away from the anticlines and other uplifts and occur in the subsurface throughout the remainder of the area. The Cambrian rocks (undifferentiated), Madison limestone, Tensleep sandstone, Sun dance formation, Cloverly formation, Frontier formation, and Miocene and Pliocene rocks (undifferentiated) yield water to domestic and stock wells in the area. In the vicinity of the Rawlins uplift, the rocks of Cambrian age, Madison limestone, and Tensleep sandstone yield water to a few public-supply wells. The Cloverly formation yields water to public-supply wells in the Miller Hill and Sage Creek basin area. Wells that tap the Madison limestone, Tensleep sandstone, and Cloverly formation yield water under sufficient artesian pressure to flow at the land surface. The Browns Park formation yields water to springs that supply most of the Rawlins city water and supply water for domestic and stock use. Included on the geologic map are location of wells and test wells, depths to water below land surface, and location of springs. Depths to water range from zero in the unconsolidated deposits along the valley of Sugar Creek at the southern end of the Rawlins uplift to as much as 129 feet below the land surface in the Tertiary sedimentary rocks along the Continental Divide in the southern part of the area. The aquifers are recharged principally by precipitation that falls upon the area, by percolation from streams and ponds, and by movement of ground water from adjacent areas. Water is discharged from the ground-water reservoir by evaporation and transpiration, by seeps and springs, through wells, and by underflow out of the area. Although most water supplies in the area are obtained from springs, some domestic, stock, and public supplies are obtained from drilled wells, many yielding water under artesian pressure, and some flowing. Dissolved solids in the water from several geologic sources, ranging from 181 to 6,660 parts per million (ppm), indicate the varied chemical quality of ground water in the Rawlins area. Water from the Cambrian rocks, Tensleep sandstone, Cloverly formation, Frontier formation, Browns Park formation, and Miocene and Pliocene rocks is generally suitable for domestic and stock use. However, water yielded to the only well sampled in the lower part of the Frontier formation contained a high concentration of fluoride. Water from the rocks mentioned above contains less than 1,000 ppm of dissolved solids but in some places may contain iron in troublesome amounts. Water from the Madison limestone and Tensleep sandstone combined, Permian rocks, and Sundance formation contains more than 1,000 ppm of dissolved solids. Water in the Sundance, Cloverly, and Frontier :formations is very soft. More ground water can be obtained in the Rawlins area than is now being used. Many springs are undeveloped, and water can be obtained from additional wells without unduly lowering ground-water levels.

Water Supply Paper↗
USGS1996

Hydrogeology of, and simulation of ground-water flow in, a mantled carbonate-rock system, Cumberland Valley, Pennsylvania

The U.S. Geological Survey conducted a study in a highly productive and complex regolith-mantled carbonate valley in the northeastern part of the Cumberland Valley, Pa., as part of its Appalachian Valleys and Piedmont Regional Aquifer-system Analysis program. The study was designed to quantify the hydrogeologic characteristics and understand the ground-water flow system of a highly productive and complex thickly mantled carbonate valley. The Cumberland Valley is characterized by complexly folded and faulted carbonate bedrock in the valley bottom, by shale and graywacke to the north, and by red-sedimentary and diabase rocks in the east-southeast. Near the southern valley hillslope, the carbonate rock is overlain by wedge-shaped deposit of regolith, up to 450 feet thick, that is composed of residual material, alluvium, and colluvium. Locally, saturated regolith is greater than 200 feet thick. Seepage-run data indicate that stream reaches, near valley walls, are losing water from the stream, through the regolith, to the ground-water system. Results of hydrograph-separation analyses indicate that base flow in stream basins dominated by regolith-mantled carbonate rock, carbonate rock, and carbonate rock and shale are 81.6, 93.0, and 67.7 percent of total streamflow, respectively. The relative high percentage for the regolith-mantled carbonate-rock basin indicates that the regolith stores precipitation and slowly, steadily releases this water to the carbonate-rock aquifer and to streams as base flow. Anomalies in water-table gradients and configuration are a result of topography and differences in the character and distribution of overburden material, permeability, rock type, and geologic structure. Most ground-water flow is local, and ground water discharges to nearby springs and streams. Regional flow is northeastward to the Susquehanna River. Average-annual water budgets were calculated for the period of record from two continuous streamflow-gaging stations. Average-annual precipitation range from 39.0 to 40.5 inches, and averages about 40 inches for the model area. Average-annual recharge, which was assumed equal to the average-annual base flow, ranged from 12 inches for the Conodoguinet Creek, and 15 inches for the Yellow Breeches Creek. The thickly-mantled carbonate system was modeled as a three- dimensional water-table aquifer. Recharge to, ground-water flow through, and discharge from the Cumberland Valley were simulated. The model was calibrated for steady-state conditions using average recharge and discharge data. Aquifer horizontal hydraulic conductivity was calculated from specific-capacity data for each geologic unit in the area. Particle-tracking analyses indicate that interbasin and intrabasin flows of groundwater occur within the Yellow Breeches Creek Basin and between the Yellow Breeches and Conodoguinet Creek Basins.

Pennsylvania↗
USGS1970

Ground-water resources of the Clatsop Plains sand-dune area, Clatsop County, Oregon

Although the average annual precipitation of the Clatsop Plains is 78.5 inches, the area is not without problems of water supply. The Clatsop Plains area ix underlain by Tertiary bedrock of low permeability that stores and yields small quantities of ground water, which may be of poor chemical quality. This Tertiary bedrock furnishes only minor ground-water discharge to maintain the base flow of streams. The flow of rivers and creeks, normally abundant during the wet season, decreases greatly during the dry summer months. The lowlands are overlain by extensive deposits of dune and beach sand. The dune sand is permeable and can absorb and store, as fresh water, a large percentage of the annual precipitation. In the central part of the dune area, the saturated thickness of the sand ranges from 95 to more than 150 feet. Most of the ground water in the sand discharges to the ocean through beach-line seeps and underflow. Much of the water now being discharged to the ocean could be recovered by pumping from properly located, designed, and constructed wells. Three test wells drilled as part of this study are capable of yielding 100 gallons per minute although they are equipped with only short lengths of well screen. It is estimated that 2,500 acre-feet of ground water per year per square mile of area may be available for withdrawal in the 10 square mile area that is most favorable for development. The water from the dune sand is soft to moderately hard, has a low chloride concentration, and is of generally good chemical quality; however, at places it is weakly acidic and contains sufficient dissolved iron to make iron removal necessary for some uses. Ground water from shallow depths beneath a few swampy low-lying areas is brown and contains excessive concentrations of iron.

Water Supply Paper↗
USGS1996

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

This report presents results derived from a numerical model of the ground-water flow system in the Portland Basin, Oregon and Washington, that was used to test and refine the conceptual understanding of the flow system, estimate the effects of past and future human-caused changes to ground-water recharge and discharge on ground-water levels and streamflow, and determine priorities for ground-water monitoring and data collection that would facilitate improvements in the utility and accuracy of the model.

Water Supply Paper↗
USGS1995

Landscape approach to identifying environments where ground water and surface water are closely interrelated

Understanding the interaction of ground water and surface water is fundamental to solving many of the water resource problems facing the Nation. To facilitate efficient management of the Nation's water resources, a program of study and evaluation of the interaction of ground water and surface water is proposed that would emphasize intersite comparison between 24 environments throughout the Nation.

Conference Paper↗
USGS2004

Submarine ground-water discharge and its role in coastal processes and ecosystems

Submarine ground-water discharge (SGD) has recently been recognized as a phenomenon that can strongly influence coastal water and geochemical budgets and drive ecosystem change. For example, the discharge of nutrient-enriched ground water into coastal waters may contribute significantly to eutrophication and blooms of harmful algae. Similarly, the quantity of SGD can also directly affect the availability of fresh water to coastal communities, impact fragile coastal ecosystems such as estuaries and coral reefs, and influence geomorphology of shoreline features. Moore raised awareness of the global importance of SGD and much effort has been devoted to developing new tracer techniques and methods for the identification and quantification of SGD. Because the discharge of coastal ground water commonly occurs as diffuse seepage rather than focused discharge through identifiable springs, assessing SGD has remained difficult for both oceanographers and hydrologists. Through national and international research programs, Burnett, Moore, Charette, and others have developed a rigorous, systematic approach for quantifying SGD using a wide assortment of tracers and methods. Intercalibration experiments, such as those conducted in coastal waters off Australia, Brazil, and Long Island, NY, demonstrate that careful measurements can accurately quantify SGD, confirm some of the driving mechanisms (e.g. climatic and tidal forcing), and constrain the spatial and temporal scales at which these mechanisms operate. Now that approaches for rigorously quantifying SGD are becoming better established, scientists can now begin to investigate the wide variety of coastal processes affected by SGD.

Open-File Report↗
USGS2004

Factors affecting ground-water quality in Oakland County, Michigan

Ground water is water stored in pores within soil and rock beneath the land surface. When these pores are connected so that water can be transmitted to wells or springs, these bodies of soil and rock are termed aquifers, from two Greek words meaning “water” and “to bear.”

Michigan↗
USGS1999

Simulation of ground-water flow and pumpage in Kings and Queens Counties, Long Island, New York

The potential effects of using ground water as a supplemental source of supply in Kings and Queens Counties were evaluated through a 4-layer finite-difference ground-water-flow model with a uniform grid spacing of 1,333 feet. Hydraulic properties and boundary conditions of an existing regional ground-water-flow model of Long Island with a uniform grid spacing of 4,000 feet were refined for use in the finer grid model of Kings and Queens Counties. The model is calibrated to average pumping stresses that correspond to presumed steady-state conditions of 1983 and 1991. A transient-state simulation of the year-by- year transition between these two conditions was also conducted. Pumping scenarios representing public-supply withdrawals of 100, 150, and 400 million gallons per day (Mgal/d) were simulated to determine the duration of sustainable pumpage, defined as the length of time before a particular pumping rate induces landward hydraulic gradients from areas of salty ground water. The simulations indicate the following hydrologically feasible scenarios: (1) Pumpage of 100 Mgal/d could be sustained for about 10 months, followed by a 46-month period of pumping at reduced (1991) rates, to allow water levels to recover to 90 percent of 1991 levels. (2) Pumpage of 150 Mgal/d could be sustained for about 6 months, followed by a 79-month period of pumping at a reduced (1991) rate. (3) Pumpage of 400 Mgal/d could be sustained for about 3 months from an initial condition of maximum aquifer storage. Each of these scenarios could be modified by injecting surplus water from upstate reservoirs, available from January to May, into the proposed wells. Injection at half the pumpage rate during the recovery period reduces the recovery period to 14 months in scenario 1, 6 months in scenario 2, and 9 months in scenario 3.

New York↗