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At least 991 records · Page 55Linked to original sources
USGS1998

Hydrogeologic framework of the Michigan Basin regional aquifer system

Mississippian and younger geologic units form a regional system of aquifers and confining units in the central Lower Peninsula of Michigan. The area of the regional aquifer system is about 22,000 square miles. The aquifer system consists of three bedrock aquifers, which are separated by confining units. Bedrock aquifers and confining units are overlain by surficial glaciofluvial aquifers, which are complexly intercalated with confining beds composed of glacial till and fine-grained lacustrine deposits. Geophysical and geologic logs were used to characterize the hydrogeologic framework of this regional aquifer system and to delineate and map boundaries of aquifers and confining units. Geophysical logs and water-quality data were used to delineate the base of freshwater within the aquifer system and to determine geologic controls on the distribution of freshwater in the aquifer-system units. Pleistocene glaciofluvial deposits are the largest reservoir of fresh ground water in the mapped region, and the thickness of this aquifer unit exceeds 900 feet in some areas. The Saginaw aquifer, the composite of sandstones of Pennsylvanian age, typically ranges in thickness from 100 to 350 feet in areas where this unit is used for water supply. In the western part of the aquifer system, the Saginaw aquifer is separated from glacial deposits by 100 to 150 feet of Jurassic "red beds." "Red beds" are a confining unit, and the Saginaw aquifer contains saline water where it is overlain by these deposits. The Saginaw confining unit, which is principally shale, separates the Saginaw aquifer from the underlying Parma-Bayport aquifer. Thickness of the Saginaw confining unit is about 50 feet in the eastern and the southern parts of the aquifer system, about 100 feet in the north, and 100 to 250 feet in the west. The Parma-Bayport aquifer, which consists mostly of permeable sandstones and carbonates, is 100 to 150 feet thick in most areas. The ParmaBayport aquifer contains freshwater only in subcrop areas where it is in direct hydraulic connection with glacial deposits. Dissolved-solids concentration of ground water increases down regional dip in the ParmaBayport aquifer, and saline water or brine is present in this aquifer where it is overlain by the Saginaw confining unit. The Michigan confining unit, which is about 300 to 400 feet thick in most of the area mapped, is primarily interbedded shale, carbonate, and evaporite. This confining unit overlies the Marshall aquifer, which consists of one or more stratigraphically continuous sandstones of Mississippian age. Composite thickness of blanket sandstones that form the Marshall aquifer is typically 75 to 200 feet. Freshwater is present in the Marshall aquifer only in areas where it is a subcrop beneath glacial deposits. Dissolved-solids concentration of ground water in the Marshall aquifer increases down regional dip, and saline water or brine is present in this unit where it underlies beds of the Michigan confining unit. The Mississippian Coldwater Shale forms the base of the regional aquifer system. Relief on the base of freshwater is about 600 feet. Altitudes of the base of freshwater are low (200 to 400 feet) along a 30- to 45-mile-wide north-south-trending corridor near the center of the aquifer system. The trend of this corridor corresponds to an area where thickness of the Saginaw aquifer ranges from 100 to 370 feet. In isolated areas in the northern and the western parts of the aquifer system, the altitude of the base of freshwater is below 400 feet; however, the altitude is above 400 feet in most of the mapped area. In the southern and the northern parts of the aquifer system, where the Saginaw aquifer is thin or absent, altitudes of the base of freshwater range from 700 to 800 feet and from 500 to 700 feet, respectively. Geologic controls on the distribution of freshwater in the regional aquifer system are (1) direct hydraulic connection between sandstone aquifers and freshwater-bearing, permeable glacial deposits; (2) impedance of upward discharge of saline water from sandstones by lodgment tills with very low permeability; (3) impedance of recharge of freshwater to bedrock (or discharge of saline water from bedrock) by very low permeability Jurassic "red beds"; and (4) the presence of units characterized by very low vertical-hydraulic-conductivity, which are within and between sandstone units.

Michigan↗
USGS2002

Geology and hydrogeology of the Caribbean Islands aquifer system of the Commonwealth of Puerto Rico and the U.S. Virgin Islands

Poorly lithified to unconsolidated carbonate and clastic sedimentary rocks of Tertiary (Oligocene to Pliocene) and Quaternary (Pleistocene to Holocene) age compose the South Coast aquifer and the North Coast limestone aquifer system of Puerto Rico; poorly lithified to unlithified carbonate rocks of late Tertiary (early Miocene to Pliocene) age make up the Kingshill aquifer of St. Croix, U.S. Virgin Islands. The South Coast aquifer, North Coast limestone aquifer system, and Kingshill aquifer are the most areally extensive and function as the major sources of ground water in the U.S. Caribbean Islands Regional Aquifer-System Analysis (CI-RASA) study area. In Puerto Rico's South Coast ground-water province, more than 1,000 meters of clastic and carbonate rocks of Oligocene to Pliocene age infill the South Coast Tertiary Basin. The pattern of lithofacies within this basin appears to have been controlled by changes in base level that were, at times, dominated by tectonic movement (uplift and subsidence), but were also influenced by eustasy. Deposition of the 70-kilometer long and 3- to 8-kilometer wide fan-delta plain that covers much of the South Coast ground-water province occurred largely in response to glacially-induced changes in sea level and climate during the Quaternary period. Tectonic movement played a much less important role during the Quaternary. The North Coast ground-water province of Puerto Rico is underlain by homoclinal coastal plain wedge of carbonate and siliciclastic rocks that infill the North Coast Tertiary Basin and thicken to more than 1,700 meters. A thin basal siliciclastic sequence of late Oligocene age is overlain by a thick section of mostly carbonate rocks of Oligocene to middle Miocene age. Globigerinid limestone of late Miocene to Pliocene age crops out and lies in the shallow subsurface areas of northwestern Puerto Rico. Oligocene to middle Miocene age rocks tentatively can be divided into five depositional sequences and associated systems tracts; these rocks record carbonate and minor siliciclastic deposition that occurred in response to changes in relative sea level. The Cibao Formation represents the most complex of these sequences and contains a varied facies of carbonate, mixed carbonate-siliciclastic, and siliciclastic rocks that reflect differential uplift, subsidence, and transgression of the sea. Uplift, graben formation, and gradual shallowing of the sea are reflected within the bathyal-dominated sedimentary facies of the Kingshill Limestone in St. Croix, U.S. Virgin Islands. Reef-tract limestone beds of Pliocene age were subject to exposure, resubmergence, and meteoric leaching of aragonitic skeletal debris; these beds contain patchy lenses of dolomite that are restricted to a small, structurally-controlled embayment. The South Coast aquifer, the principal water-bearing unit of Puerto Rico's South Coast ground-water province, consists of boulder- to silt-size detritus formed by large and small coalescing fan deltas of Pleistocene to Holocene age. Deep well data indicates that it is possible to vertically separate and group a highly complex and irregular-bedded detrital sequence that underlies distal parts of the fan-delta plain into discrete water-bearing units if correlated with 30- to 40-meter thick, eustatically-controlled depositional cycles. Lithofacies maps show that greatest hydraulic conductivity within the fan-delta plain is generally associated with proximal fan and midfan areas. Distal and interfan areas are least permeable. Alluvial valley aquifers located in the western part of the South Coast ground-water province are important local sources of water supply and appear to contain some of the same physical and hydraulic characteristics as the South Coast aquifer. Older sedimentary rocks within the basin are poor aquifers; conglomeratic beds are well-cemented, and carbonate beds do not contain well-developed solution features, except locally where the beds are overlain by alluvium. Ground-water occurs under unconfined conditions in proximal and midfan areas. Confined conditions within deeper parts of the system and in interfan and some midfan areas are created largely by the intercalated nature of discontinuous fine-grained beds that retard vertical ground-water movement. The development of water resources in southern Puerto Rico has modified the hydrologic system of the South Coast aquifer considerably. Under predevelopment conditions, the South Coast aquifer was recharged in the unconfined, proximal fan and some midfan areas by infrequent rainfall and seepage from streams near the fan apex. Discharge occurred as seabed seepage, baseflow discharge along the lower coastal reach of streams, seepage to coastal wetlands, or evapotranspiration in areas underlain by a shallow water table. Under development conditions, seepage from irrigation canals and areal recharge from furrow irrigation represented a principal mechanism for recharge to the aquifer. Increased ground-water withdrawals in the 1960's and 1970's resulted in declines in the water table to below sea level in some places and intrusion of salt water into the aquifer. By the middle 1980's, a reduction in ground-water withdrawals and a shift from furrow irrigation to drip-irrigation techniques resulted in the recovery of water levels. Under present-day (1986) conditions, regional ground-water flow is coastward but with local movement to some well fields. In addition to the discharge mechanisms described above, ground-water discharges also to coastal canals. The North Coast limestone aquifer system consists of limestone, lesser amounts of dolomite, and minor clastic detritus of Oligocene to Pliocene age that form an unconfined upper aquifer and a confined lower aquifer; these aquifers are separated by a clay, mudstone, and marl confining unit. Topographic relief and incision of carbonate coastal plain rocks by streams are the principal factors controlling the direction of ground-water flow. The North Coast limestone aquifer system is recharged principally by precipitation that enters the upper and lower aquifers where they crop out. Regional groundwater movement from the upper aquifer is to the major rivers, wells, coastal wetlands, coastal, nearshore, and offshore springs, or as seabed seepage. Regional discharge from the lower aquifer is to the major rivers along its unconfined parts or where the confining unit has been breached by streams. Discharge from the lower aquifer also occurs in the San Juan area where the Mucarabones Sand provides an avenue for diffuse upward ground-water flow. Transmissivity within the upper limestone aquifer appears to be largely regulated by the thickness of the freshwater lens. The lens is thickest and transmissivity is greatest in interstream areas that lie in a zone that closely corresponds to the landwardmost extent of the underlying saltwater wedge. Hydraulic conductivity of the upper aquifer generally increases in a coastward direction and reflects lithologic control, karstification in the upper 30 to 100 meters of the section, and enhanced permeability in a zone of freshwater and saltwater mixing. Transmissivity of the lower aquifer is an order of magnitude smaller than that of the upper aquifer; highest transmissivities in the lower aquifer largely correspond to a coarse grainstone-packstone and coral-patch-reef depositional facies contained within the outcropping parts of the Montebello Limestone Member and its subsurface equivalents. Porosity within the North Coast limestone aquifer system is high in grainstone-packstones and low in wackestone and marl. Dolomitized zones and moldic grainstone-packstone strata are the most porous carbonate rocks, but occur in thin beds that usually are only a few meters thick. Processes of karstification that include the development of caverous zones and large vugs, and dissolution along possible regional fracture sets has enhanced permeability within the upper part of the aquifer system. Stratigraphic and lithologic control play an important role controlling permeability within the lower part of the system. The Kingshill aquifer of St. Croix, in large part, is composed of deepwater limestone that contains only microscopic pores and is poorly permeable; however, the upper part of the aquifer, a shallow-water skeletal and reef limestone, is fairly permeable, but restricted in areal extent. Permeability within these uppermost beds of the aquifer has been enhanced by meteoric leaching, dissolution within a mixing zone of saltwater and fresh water, and dolomitization. However, most large-yield wells completed in the Kingshill aquifer are also screened in alluvium that overlies or infills incised channels. The alluvial deposits serve as a temporary storage zone for rainfall, runoff, and ground water slowly entering the Kingshill aquifer.

Puerto Rico↗
USGS2001

Geologic framework of the San Juan structural basin of New Mexico, Colorado, Arizona, and Utah, with emphasis on Triassic through Tertiary rocks

The San Juan Basin Regional Aquifer-System Analysis began in 1984. This report describes rocks of Triassic through Tertiary age in the basin and also describes the regional geologic and stratigraphic framework of the basin's multilayered aquifer system. Maps showing altitude of top, depth to top, and thickness of major geologic units were prepared using geographic information system technology. Results presented form the basis for ground-water flow modeling and geochemical studies of the basin.

Professional Paper↗
USGS1996

Hydrogeologic framework of the Edwards-Trinity aquifer system, west-central Texas

The Edwards-Trinity aquifer system underlies about 42,000 square miles of west-central Texas, where mostly gently dipping Lower Cretaceous strata comprise three regional aquifers and two regional confining units. The aquifers are the Edwards Aquifer of the Balcones fault zone, the Trinity Aquifer of the Balcones fault zone and Hill County, and the Edwards-Trinity Aquifer of the Edwards Plateau and Trans-Pecos. The Navarro-Del Rio confining unit confines the downdip part of the Edwards Aquifer, and the Hammett confining unit confines the updip, basal part of the Trinity Aquifer and a small southeastern fringe of the Edwards-Trinity Aquifer. Transmissivity averages less than 10,000 feet squared per day throughout more than 90 percent of the study area as the result of widespread cementation and secondary mineral growth. However, in fractured and leached rocks in the Balcones fault zone, transmissivity averages about 750,000 feet squared per day in the Edwards aquifer, which occupies less than 10 percent of the area.

Texas↗
USGS1997

Hydrogeology and ground-water flow in the Edwards-Trinity aquifer-system, west-central, Texas

Two finite-element ground-water flow models were developed for the Edwards–Trinity aquifer system, west-central Texas, to gain a better understanding of the flow system; one ground-water flow model was developed at a large scale to simulate the regional system and contiguous, hydraulically connected units, and one model was constructed at a smaller more detailed scale to simulate the most active areas of the system. The study area is divided into four geographic subareas: the Trans-Pecos (9,750 square miles), the Edwards Plateau (23,750 square miles), the Hill Country (5,500 square miles), and the Balcones fault zone (3,000 square miles). The major aquifers within the study area are the Edwards–Trinity aquifer underlying the Trans-Pecos and Edwards Plateau, the Trinity aquifer underlying the Hill Country, and the Edwards aquifer in the Balcones fault zone. Hydraulically connected aquifers include the High Plains aquifer north of the Edwards Plateau, and the Cenozoic Pecos alluvium aquifer adjacent to both the Trans-Pecos and the Edwards Plateau along the Pecos River. Minor contiguous aquifers include the Dockum, Ellenburger– San Saba, Marble Falls, Hickory, and Lipan, which is adjacent to the Colorado River in Tom Green and Concho Counties, Texas. The ground-water flow equations solved by the finite-element method are based on conservation of mass and energy. The equation for ground-water flow assumes laminar flow through a porous media. In places, the Edwards–Trinity aquifer system is a fractured karst system in which ground water flows through caverns and other features of secondary porosity development. The regional and subregional models were constructed to synthesize the known hydrologic boundaries and geologic structures into a heterogeneous continuum model of the karst ground-water flow system, rather than simulate the flow through specific fractures and caverns. A heterogeneous continuum or equivalent porous media approach uses an effective transmissivity and anisotropy for each element of the models. The models are calibrated both on water levels (representing potential energy) and estimates of recharge and discharge (for a realistic mass balance). A two-dimensional one-layer large-scale model (55,600 square miles) was developed for the Edwards–Trinity aquifer system and contiguous, hydraulically connected units, in westcentral Texas. A quasi-three-dimensional, multilayer more detailed scale ground-water flow model (12,300 square miles) was applied to the major aquifers of the Edwards–Trinity aquifer system in the Hill Country and the Balcones fault zone, and in part of the Edwards Plateau. The ground-water flow system in most of the study area within the Trans-Pecos and Edwards Plateau can be approximated with a one-layer regional model under steady-state conditions. Regionally, the Edwards–Trinity aquifer system in the Trans-Pecos and Edwards Plateau has been relatively static. Potentiometric maps from predevelopment and postdevelopment (winter 1974–75) indicate small differences in water levels. In local areas in the Trans-Pecos (in Pecos and Reeves Counties), ground-water withdrawals have exceeded recharge resulting in more than 300 feet of drawdown. Measurable differences between the 1974 and predevelopment potentiometric surfaces have been observed in small areas in the Trans-Pecos and in the northwestern part of the Edwards Plateau. The largest water-level declines in the Trans-Pecos have been observed in Pecos and Reeves Counties, and declines greater than 300 feet have been measured in Reeves County. Comparison of pre- and postdevelopment water budgets for the regional model indicates that the increase in groundwater withdrawals has captured 20 percent of the water that would have naturally discharged to streams, and 30 percent of the natural discharge to springs after ground-water development. Induced recharge from streams to the ground-water system increased by 12 percent in the postdevelopment simulation compared to the predevelopment simulation.

Texas↗
USGS2004

Summary of the hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces in the eastern United States

The Appalachian Valley and Piedmont Regional Aquifer-System Analysis study (1988-1993) analyzed rock types in the 142,000-square-mile study area, identified hydrogeologic terranes, determined transmissivity distributions, determined the contribution of ground water to streamflow, modeled ground-water flow, described water quality, and identified areas suitable for the potential development of municipal and industrial ground-water supplies. Ground-water use in the Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces exceeds 1.7 billion gallons per day. Thirty-three rock types in the study area were analyzed, and the rock types with similar water-yielding characteristics were combined and mapped as 10 hydrogeologic terranes. Based on well records, the interquartile ranges of estimated transmissivities are between 180 to 17,000 feet squared per day (ft 2 /d) for five hydrologic terranes in the Valley and Ridge; between 9 to 350 ft 2 /d for two terranes in the Blue Ridge; and between 9 to 1,400 ft 2 /d for three terranes in the Piedmont Physiographic Province. Based on streamflow records, the interquartile ranges of estimated transmissivities for all three physiographic provinces are between 290 and 2,900 ft 2 /d. The mean ground-water contribution to streams from 157 drainage basins ranges from 32 to 94 percent of mean streamflow with a median of 67 percent. In three small areas in two of the physiographic provinces, more than 54 percent of ground-water flow was modeled as shallow and local. Although ground-water chemical composition in the three physiographic provinces is distinctly different, the water generally is not highly mineralized, with a median dissolved-solids concentration of 164 milligrams per liter, and is mostly calcium, magnesium, and bicarbonate. Based on aquifer properties and current pumpage, areas favorable for the development of municipal and industrial ground-water supplies are underlain by alluvium of glacial origin near the northeastern part of the study area, by clay-free carbonate rocks primarily in the Valley and Ridge Physiographic Province, and by siliciclastic rocks in the three northernmost Mesozoic basins.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗
USGS1996

Estimated hydrologic characteristics of shallow aquifer systems in the Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces based on analysis of streamflow recession and base flow

Inferences are drawn about properties of aquifer systems from the interpretation of streamflow records in the Appalachian Valley and Ridge, Piedmont, and Blue Ridge physiographic provinces. The analysis is divided into two parts--analysis of streamflow recession and base-flow analysis. Analysis of recession yields information about aquifer diffusivity and variation in specific yield. Base-flow analysis is used to develop water balances for representative basins in the study area.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗
USGS1996

Hydrogeologic terranes and potential yield of water to wells in the Valley and Ridge Physiographic Province in the eastern and southeastern United States

The Valley and Ridge Physiographic Province is underlain by deformed sedimentary rock of Paleozoic age including dolomite, limestone, shale, and sandstone. Regolith (soil, sediment, and weathered rock) covers the Paleozoic rock throughout most of the province. Local differences in lithology, structure, and weathering can result in four orders of magnitude variation in the water-yielding properties of the geologic units that underlie the area. Selected rock types, however, can account for a substantial part of this variation because of the unique way in which these dense, consolidated sedimentary rock types deform and weather to produce secondary openings. On the basis of relations among rock type, water-yielding openings, and water-yielding properties (as indicated by specific capacity), the regolith and consolidated rock were classified and mapped as five hydrogeologic terranes alluvium, dolomite, limestone, argillaceous carbonate rock, and siliciclastic rock. The hydrogeologic terranes are named after the predominant outcrop lithology within them. The western toe of the Blue Ridge Mountains is classified as a subdivision of the dolomite hydrogeologic terrane that may produce yields of water in excess of 1,000 gallons per minute (gal/min) to public and industrial supply wells. Specific-capacity data for homogeneous data sets, which consist of all wells that have the same characteristics in regard to casing diameter, primary use of the water, and topographic setting, revealed significant differences in water-yielding properties among the five hydrogeologic terranes. According to results of Tukey statistical tests at a probability (alpha level) of 0.05, 8 out of 10 pairs of hydrogeologic terranes (for example, alluvium/limestone) had significantly different median specific-capacity values. The median value for public and industrial supply wells in the western toe is three times greater than the value for comparable wells in the dolomite hydrogeologic terrane elsewhere. Estimates of potential yields to public and industrial supply wells were calculated from specific-capacity data for most-productive wells, which have casing diameter of 7 in. or more, discharge water primarily for public or industrial supply, and are in a valley. Median constant drawdowns, calculated from reported drawdowns, were assumed to be between 10 and 90 ft for wells completed in each of the five hydrogeologic terranes, and well-entrance losses were assumed to be negligible. Estimated interquartile ranges in potential yields to 412 mostproductive wells in the five hydrogeologic terranes were 170 to 580 gal/min, alluvium; 210 to 1,400 gal/min, dolomite; 80 to 720 gal/min, limestone; 65 to 850 gal/min, argillaceous carbonate rock; and 70 to 280 gal/min, siliciclastic rock.

Alabama, Georgia, Maryland, New Jersey, Pennsylvan↗
USGS1997

Water quality in the Appalachian Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces, eastern United States

Chemical quality of ground water, spring water, and surface water differs substantially among the three physiographic provinces. Maps showing regional variations for 18 water properties and constituents are included in this Regional Aquifer System Analysis study report. Systematic variations in water quality are due to differences in geologic and hydrologic factors that include the dominant lithology, the availability of soluble minerals, and the degree of exposure of water to rock. Most ground water in the study area is low in concentrations of dissolved minerals, is moderately hard, and is slightly acidic. Spring water is generally harder than ground water and is slightly alkaline; whereas, surface water is softer than the ground water and is also slightly alkaline.

Alabama, Delaware, Georgia, Maryland, New Jersey, ↗
USGS1999

The Midwestern Basins and Arches regional aquifer system in parts of Indiana, Ohio, Michigan, and Illinois — Summary

The Midwestern Basins and Arches aquifer system is composed of surficial deposits of Pleistocene and Holocene age and of Silurian and Devonian age carbonate rock in parts of Indiana, Illinois, Michigan, and Ohio. The study area encompasses a complex of structural arches--the Cincinnati, Findlay, and Kankakee arches--and it is bounded on the east, north, and west by the Appalachian, Michigan, and Illinois basins, respectively. This report describes the hydrogeologic framework, hydrology, and geochemistry of the Midwestern Basins and Arches.

Illinois, Indiana, Michigan, Ohio↗
USGS1996

Hydrogeologic framework of the Midwestern Basins and Arches region in parts of Indiana, Ohio, Michigan, and Illinois

The rocks that make up the regional Silurian and Devonian carbonate aquifer System in Ohio, Indiana, and adjacent states, consists of limestones, dolomites, varied amounts of terrigenous clastics, and evaporates. The carbonate-rock aquifer system is underlain by Ordovician shales and interbedded carbonate rocks that are virtually impermeable and regionally extensive. These units collectively form a barrier to ground-water flow that effectively limits the transfer of significant quantities of water through the base of the Silurian and Devonian carbonate aquifer. Where the shales and siltstones that make up the upper confining unit are present, the carbonate-rock aquifer is confined above by Devonian and Mississippian shales and siltstones. Where the confining unit above the aquifer has been eroded, the overlying glacial sediments partly confine the carbonate-rock.

Professional Paper↗
USGS2000

Regional ground-water flow and geochemistry in the midwestern Basins and Arches aquifer system in parts of Indiana, Ohio, Michigan, and Illinois

This report synthesizes information on the regional ground-water flow and geochemistry in the Midwestern Basins and Arches aquifer system in parts of Indiana, Ohio, Michigan, and Illinois. Aquifers that compose this water-table aquifer system include glacial aquifers and an underlying, areally extensive carbonate-rock aquifer. Water within the aquifers is most commonly a Ca-Mg-HCO 3 type or a Ca-Mg-SO 4 type. In general, the distribution of hydrochemical facies within the aquifer system is controlled by the mineralogy of the aquifer material, rather than by a chemical evolution of water along general directions of regional ground-water flow. Some ground-water flow systems within the aquifer system provide base flow to streams in response to ground-water recharge events. Other (often deeper) ground-water flow systems respond minimally to variations in ground-water recharge from precipitation and provide a fairly constant supply of water to streams. Streamflow hydrographs and base-flow duration curves were used to estimate such components of base flow in selected streams for long-term steady-state conditions in the aquifer system. Mean sustained ground-water discharge (discharge from fairly stable ground-water flow systems) ranges from 3 to 50 percent of mean ground-water discharge (discharge from all ground-water flow systems) to the selected stream reaches. These percentages indicate that 50 to 97 percent of base flow in the streams within the study area can be attributed to transient ground-water flow systems, which typically have a major component of local-scale flow. Because ground-water flow across the external boundaries of the aquifer system is minimal, such percentages indicate that most ground-water flow in the aquifer system is associated with seasonally transient local flow systems. Results of a ground-water flow model that was calibrated by use of regression methods and that simulates regional flow systems within the aquifer system (approximately 10 percent of total ground-water flow in the aquifer system) indicate that most water (99 percent) in simulated regional flow systems is from recharge at the water table. Most water (78 percent) discharges from simulated regional flow systems to the principal streams. Less than 3 percent of water in simulated regional flow systems discharges to the Ohio River, Lake Erie, or downdip areas in the Illinois (structural) Basin. Simulations also indicate that most of the Midwestern Basins and Arches aquifer system is characterized by alternating regional recharge and discharge areas at intervals of less than every 10 miles along the dominant regional trends of the potentiometric surfaces in the aquifers. Such alternating regional recharge and discharge areas result in the absence of long flow paths from the very highest regional potentiometric levels to the very lowest regional potentiometric levels. The presence of tritiated ground water (less than 50 years old) across most of the aquifer system also indicates that the aquifer system receives recharge across most of the study area. The northeastern part of the aquifer system near Lake Erie differs from the rest of the system with respect to regional ground-water flow and chemistry. Specifically, part of the northeastern part of the aquifer system can be characterized as a broad area (tens of miles) of weak regional discharge (less than 0.5 inch per year). Results of the regional ground-water flow model indicate that regional flow systems have a limited ability to carry ground water away from this area; thus precipitation is prevented from recharging the regional flow systems in this part of the aquifer system. Some ground water recharged during Pleistocene glaciation was found in this area.

Illinois, Indiana, Michigan, Ohio↗
USGS1998

Geologic framework of the Willamette Lowland aquifer system, Oregon and Washington

This report describes the Cenozoic geology of the Willamette Lowland physiographic province, and the geologic framework of the regional ground-water flow system. Five regional hydrogeologic units are identified and described. The report includes maps showing the altitude of the top and the thickness of each hydrogeologic unit.

Professional Paper↗
USGS1998

Hydrogeologic framework of the Willamette Lowland aquifer system, Oregon and Washington

This report summarizes the hydraulic characteristics of the materials that make up the Willamette Lowland aquifer system, ground-water movement in the aquifer system, estimates of ground-water recharge, ground-water quality characteristics, construction and use of cross-sectional numerical ground-water flow models, hydrologic controls on ground-water movement, water budgets and flow paths, and a description and application of a conceptual model.

Professional Paper↗
USGS1999

Geologic framework for the Puget Sound aquifer system, Washington and British Columbia

The Puget-Willamette study area is composed of two distinct subareas, the Puget Sound Lowland and the Willamette Lowland. The study area for this report is the Puget Sound Lowland, which is located in western Washington and in a small part of southwestern British Columbia, Canada. The lowland encompasses an area of about 17,610 square miles and contains about 2,615 square miles of saltwater. The unconsolidated Quaternary deposits that compose the Puget Sound aquifer system underlie about 7,183 square miles of the study area. The extent of the Puget Sound aquifer system is delineated by its lateral and basal boundaries above the Tertiary and older rock units, called the basement confining unit, and the lateral extent of the glacial drift from the last glaciation, the Fraser Glaciation. The unconsolidated Quaternary deposits which compose the aquifer system consist of alluvium, glacial, and interglacial deposits. Of the unconsolidated deposits at the land surface, 1,570 square miles are covered by alluvium, 2,293 square miles are covered by coarse-grained deposits, and about 3,320 square miles are covered by fine-grained deposits. The alluvium and coarse-grained deposits generally compose the aquifer units, and the fine-grained deposits generally compose the semi-confining to confining units. Four glaciations and three interglaciations are recognized in the Puget Sound Lowland. As a result, the unconsolidated Quaternary deposits consist of one to four regional drift sequences and as many as eight local ones. These sequences are generally separated by unconformities and by interglacial fluvial and lacustrine deposits. These sequences produce an alternating pattern of coarse- and fine-grained deposits from land surface to depths of more than 3,000 feet. The unconsolidated Quaternary and Recent deposits within the lowland were grouped into local aquifer units and semiconfining and confining units based on their lithologic and hydraulic characteristics. These units were then grouped into regional aquifer units in order to assess the ground-water resources and describe the ground-water flow on a regional basis. The designated regional hydrogeologic units are the alluvial valley aquifers, the surficial semiconfining unit, the Fraser aquifer unit, the confining unit, and the Puget aquifer.

British Columbia, Oregon, Washington↗
USGS1998

Hydrogeologic framework of the Puget Sound aquifer system, Washington and British Columbia

This report presents the generalized hydrogeologic framework of the Puget Sound aquifer system in Washington and British Columbia. The framework includes a conceptual model of the division of the aquifer system into regional hydrogeologic units for describing on a regional basis the ground-water flow in the system. The conceptual model is based on an analysis of historical data and on results of cross-sectional numerical models of ground-water flow.

British Columbia, Washington↗
USGS1997

Hydrologic budgets of regional aquifer systems of the United States for predevelopment and development conditions

Ground-water budgets are presented in this report for 14 regionally extensive aquifer systems; pumpage from 11 of these systems provided from 40 to 50 percent of the ground water withdrawn in the United States during the 1970's and 1980's. The budgets are based on simulation results from computer-based models developed as part of the Regional Aquifer-System Analysis Program of the U.S. Geological Survey. Most of the models cover large areas (30,000-300,000 square miles) and generally are constructed with coarse-mesh finite-difference grids designed to simulate regional ground-water flow. The groundwater budgets derived from these models generally do not include local flow that enters and exits regional aquifers after traveling only a few miles or flow in overlying surficial aquifers. Budgets are presented for predevelopment and recent pumping conditions for most of the aquifer systems.

Professional Paper↗