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At least 73 records · Page 4Linked to original sources
USGS2016

The Maryland Coastal Plain Aquifer Information System: A GIS-based tool for assessing groundwater resources

Groundwater is the source of drinking water for ∼1.4 million people in the Coastal Plain Province of Maryland (USA). In addition, groundwater is essential for commercial, industrial, and agricultural uses. Approximately 0.757 × 109 L d –1 (200 million gallons/d) were withdrawn in 2010. As a result of decades of withdrawals from the coastal plain confined aquifers, groundwater levels have declined by as much as 70 m (230 ft) from estimated prepumping levels. Other issues posing challenges to long-term groundwater sustainability include degraded water quality from both man-made and natural sources, reduced stream base flow, land subsidence, and changing recharge patterns (drought) caused by climate change. In Maryland, groundwater supply is managed primarily by the Maryland Department of the Environment, which seeks to balance reasonable use of the resource with long-term sustainability. The chief goal of groundwater management in Maryland is to ensure safe and adequate supplies for all current and future users through the implementation of appropriate usage, planning, and conservation policies. To assist in that effort, the geographic information system (GIS)–based Maryland Coastal Plain Aquifer Information System was developed as a tool to help water managers access and visualize groundwater data for use in the evaluation of groundwater allocation and use permits. The system, contained within an ESRI ArcMap desktop environment, includes both interpreted and basic data for 16 aquifers and 14 confining units. Data map layers include aquifer and ­confining unit layer surfaces, aquifer extents, borehole information, hydraulic properties, time-series groundwater-level data, well records, and geophysical and lithologic logs. The aquifer and confining unit layer surfaces were generated specifically for the GIS system. The system also contains select groundwater-quality data and map layers that quantify groundwater and surface-water withdrawals. The aquifer information system can serve as a pre- and postprocessing environment for groundwater-flow models for use in water-supply planning, development, and management. The system also can be expanded to include features that evaluate constraints to groundwater development, such as insufficient available drawdown, degraded groundwater quality, insufficient aquifer yields, and well-field interference. Ultimately, the aquifer information system is intended to function as an interactive Web-based utility that provides a broad array of information related to groundwater resources in Maryland’s coastal plain to a wide-ranging audience, including well drillers, consultants, academia, and the general public.

Special Paper of the Geological Society of America↗
USGS1978

Evaluation of the geologic and hydrologic factors related to the waste-storage potential of Mesozoic aquifers in the southern part of the Atlantic Coastal Plain, South Carolina and Georgia

This report describes the subsurface distribution of rocks of Cretaceous to Late Jurassic(?) age in the Atlantic. Coastal Plain, South Carolina and Georgia, and examines their potential for deep-well waste storage. For mapping purposes a waste-storage "operational unit" is established and defined. It is a sand or sandstone layer, 20 feet or more in thickness, that is immediately overlain and underlain by a layer of shale or clay, 20 feet or more in thickness, and which occurs in regional chronostratigraphic units (Units A, B, C, D, E, F, G(?), and H(?)) of Mesozoic age in areas where each of these units contains nonusable ground water. Nonusable ground water is defined as water that contains sodium chloride in excess of 10,000 mg/L. Using a group of geohydrologic parameters derived from or combining 21 categories of basic data, established from study and interpretation of well cuttings and geophysical logs, a series of 32 regional maps and 8 stratigraphic cross sections was constructed. For each of the eight geologic units delineated in the subsurface, the maps illustrate the distribution of waste-storage potential in terms of areal extent, depth below land surface, sand-shale geometry, and the approximate sodium chloride concentration of a unit's nonusable ground water.

Georgia, South Carolina↗
USGS2001

Linking hyporheic flow and nitrogen cycling near the Willamette River: A large river in Oregon, USA

Several approaches were used to characterize ground water/surface water interactions near the Willamette River - A large (ninth order) river in Oregon, USA. A series of potentiometric surface maps demonstrated the presence of highly dynamic hydraulic gradients between rivers and the adjacent aquifer. Hyporheic zone gradients extended on the order of hundreds of meters. River gains and losses at the river stretch scale (tens of kilometers) were consistent with fluxes implied by the potentiometric surface maps, and apparently reflect regional ground water/surface water interactions. Gains and losses of up to 5-10% of streamflow were observed at this scale. On the river reach scale (1-2 km), gains and losses on the order of 5% of streamflow were interpreted as representing primarily local hyporheic exchange. Isotopic and chemical data collected from shallow hyporheic zone wells demonstrated interaction between regional ground water and river water. The origin of sampled hyporheic zone water ranged from a mixture dominated by regional ground water to water containing 100% river water. The common assumption that ground and river water mix primarily in the river channel is not applicable in this system. Isotopic and chemical data also indicated that significant (nearly complete) vegetative nitrate uptake and/or nitrate reduction occurred in water from 4 of 12 hyporheic zone sites. In these cases, it was primarily nitrate transported to the hyporheic zone in regional ground water that was removed from solution. Isotopes of water and nitrate indicated that hyporheic zone water sampled at two sites was composed of water originating as river water and demonstrated that significant vegetative nitrate uptake and nitrate reduction occurred along these hyporheic zone flowpaths. Thus, the hyporheic zone may, in some instances, serve to remove nitrate from river water. Additional investigations with chemical tools and microbial enzyme assays were conducted at one hyporheic site. A strong vertical redox gradient was observed, with nitrate-limited denitrification potential in deeper sediment and both nitrification and denitrification potential in shallower sediment. Since nitrogen cycling is strongly affected by redox conditions, nitrogen cycling in the hyporheic zone of this large-river system likely is affected by dynamics of ground water/surface water interactions that control fluxes of nitrogen and other redox species to hyporheic zone sediment.

Oregon↗
USGS2004

Developing index maps of water-harvest potential in Africa

The food security problem in Africa is tied to the small farmer, whose subsistence farming relies heavily on rain-fed agriculture. A dry spell lasting two to three weeks can cause a significant yield reduction. A small-scale irrigation scheme from small-capacity ponds can alleviate this problem. This solution would require a water harvest mechanism at a farm level. In this study, we looked at the feasibility of implementing such a water harvest mechanism in drought prone parts of Africa. A water balance study was conducted at different watershed levels. Runoff (watershed yield) was estimated using the SCS curve number technique and satellite derived rainfall estimates (RFE). Watersheds were delineated from the Africa-wide HYDRO-1K digital elevation model (DEM) data set in a GIS environment. Annual runoff volumes that can potentially be stored in a pond during storm events were estimated as the product of the watershed area and runoff excess estimated from the SCS Curve Number method. Estimates were made for seepage and net evaporation losses. A series of water harvest index maps were developed based on a combination of factors that took into account the availability of runoff, evaporation losses, population density, and the required watershed size needed to fill a small storage reservoir that can be used to alleviate water stress during a crop growing season. This study presents Africa-wide water-harvest index maps that could be used for conducting feasibility studies at a regional scale in assessing the relative differences in runoff potential between regions for the possibility of using ponds as a water management tool. ?? 2004 American Society of Agricultural Engineers.

Applied Engineering in Agriculture↗
USGS2022

Satellite remote sensing of crop water use across the Missouri River Basin for 1986–2018 period

Understanding historical crop water use (CWU) dynamics is important to improve land and water management. In this study, well-validated (coefficient of determination = 0.91, percent bias = 4%, and percent root mean square error = 11.8%) Landsat-based actual evapotranspiration (ETa) time-series estimations were used to (1) assess summer season CWU (CWU-Su) dynamics, (2) investigate CWU-Su trends over the study period (1986–2018; 33 years) at the regional- and pixel-scales, and (3) attribute CWU-Su driving factors across Missouri River Basin. Spatial variability of the ETa estimations along with the observed bimodal probability density distribution of ETa highlighted a strong relation between land cover and water uses across the basin. The bimodal distribution of ETa also indicated the presence of two major landcovers in the basin. The drier foothill regions in northwestern Missouri River Basin, dominated by grassland/shrubland, showed lower ETa (< 500 mm/year), whereas cropland dominated regions in lower semi-humid basin and forested subbasins exhibited higher ETa (> 600 mm/year). The CWU-Su anomalies revealed the vulnerability of the basin to year-to-year weather conditions. The CWU-Su trend analysis revealed a significant positive trend (p < 0.1) at the regional-scale affecting 30% of basin’s cropland pixels. The cropland pixels under positive CWU-Su trend were found to be clustered in the eastern and central Missouri River Basin as a result of the combined effect of increased crop production area, increased crop yields, crop practice shifts to higher biomass crops, and increased irrigated land. The effect of improved irrigation and water management practices on reducing CWU-Su was observed in western Missouri River Basin, which had a stable major crop throughout the study period. Overall, the study highlights the usefulness of Landsat imagery and remote sensing-based ETa modeling approaches in generating historical time-series ETa maps over a wide range of elevation, vegetation, and climate.

Missouri River Basin↗
USGS1979

Map showing general chemical quality of surface water in the Kaiparowits coal-basin area, Utah

This is one of a series of maps that describe the geology and related natural resources in the Kaiparowits coal-basin area, Utah Published sources of water-quality data used in the preparation of this map included Iorns, Hembree, Phoenix, and Oakland (1964), Goode (1966, 1969), U.S. Bureau of Land Management (1976), and U.S. Geological Survey (1961-75). Sources of unpublished data include the U.S. Bureau of Reclamation and the Southeastern Utah Association of Governments. Some of the unpublished data was provided by Vaughn Hansen Associates of Salt Lake City, Utah, whose assistance is gratefully acknowledged.

Utah↗
USGS1993

Geohydrologic systems in Kansas — Geohydrology of the lower aquifer unit in the western interior plains aquifer system

The purpose of the investigation is to provide a description of the principal geohydrologic systems in Upper Cambrian through Lower Cretaceous rocks in Kansas. This investigation was made as part of the Central Midwest Regional Aquifer-System Analysis (CMRASA). The CMRASA is one of several major investigations by the U.S. Geological Survey of regional aquifer systems in the United States. These regional investigations are designed to increase knowledge of the flow regime and hydrologic properties of major aquifer systems and to provide quantitative information for the assessment, development, and management of water supplies. The CMRASA study area includes all or parts of 10 Central Midwestern States (Jorgensen and Signor, 1981), as shown of the envelope cover. This Hydrologic Investigations Atlas, which consists of a series of chapters, presents a description of the physical framework and geohydrology of principal aquifers and confining systems in Kansas. Chapter H presents the geohydrology of the upper aquifer unit in the Western Interior Plains aquifer system. The physical framework of the aquifer system in relation to other systems is described by maps and sections showing areal extent and the thickness of rocks that compose the unit. The physical framework of the upper aquifer unit is described in detail in chapter D of the atlas (Hansen and others, in press). The hydrology of the system in relation to that of other systems is described in this chapter by maps showing the altitude of fluid levels and the direction of water movement within the unit. The chemical composition of water in the system is described by maps that show the distribution of dissolved-solids concentrations and the differences in water types on the basis of principal chemical constituents. Chapter A of this atlas series (Wolf and others, 1990) describes the relation of principal geohydrologic systems in Kansas and presents a more detailed discussion of the methods and data used to prepare and ensure consistency among the sets of maps.

Kansas↗
USGS2007

Ground water flow modeling with sensitivity analyses to guide field data collection in a mountain watershed

In mountain watersheds, the increased demand for clean water resources has led to an increased need for an understanding of ground water flow in alpine settings. In Prospect Gulch, located in southwestern Colorado, understanding the ground water flow system is an important first step in addressing metal loads from acid-mine drainage and acid-rock drainage in an area with historical mining. Ground water flow modeling with sensitivity analyses are presented as a general tool to guide future field data collection, which is applicable to any ground water study, including mountain watersheds. For a series of conceptual models, the observation and sensitivity capabilities of MODFLOW-2000 are used to determine composite scaled sensitivities, dimensionless scaled sensitivities, and 1% scaled sensitivity maps of hydraulic head. These sensitivities determine the most important input parameter(s) along with the location of observation data that are most useful for future model calibration. The results are generally independent of the conceptual model and indicate recharge in a high-elevation recharge zone as the most important parameter, followed by the hydraulic conductivities in all layers and recharge in the next lower-elevation zone. The most important observation data in determining these parameters are hydraulic heads at high elevations, with a depth of less than 100 m being adequate. Evaluation of a possible geologic structure with a different hydraulic conductivity than the surrounding bedrock indicates that ground water discharge to individual stream reaches has the potential to identify some of these structures. Results of these sensitivity analyses can be used to prioritize data collection in an effort to reduce time and money spend by collecting the most relevant model calibration data.

Groundwater Monitoring & Remediation↗
USGS2005

Climate science and famine early warning

Food security assessment in sub-Saharan Africa requires simultaneous consideration of multiple socio-economic and environmental variables. Early identification of populations at risk enables timely and appropriate action. Since large and widely dispersed populations depend on rainfed agriculture and pastoralism, climate monitoring and forecasting are important inputs to food security analysis. Satellite rainfall estimates (RFE) fill in gaps in station observations, and serve as input to drought index maps and crop water balance models. Gridded rainfall time-series give historical context, and provide a basis for quantitative interpretation of seasonal precipitation forecasts. RFE are also used to characterize flood hazards, in both simple indices and stream flow models. In the future, many African countries are likely to see negative impacts on subsistence agriculture due to the effects of global warming. Increased climate variability is forecast, with more frequent extreme events. Ethiopia requires special attention. Already facing a food security emergency, troubling persistent dryness has been observed in some areas, associated with a positive trend in Indian Ocean sea surface temperatures. Increased African capacity for rainfall observation, forecasting, data management and modelling applications is urgently needed. Managing climate change and increased climate variability require these fundamental technical capacities if creative coping strategies are to be devised.

Philosophical Transactions of the Royal Society B:↗
USGS1985

Percentage change in saturated thickness of the High Plains aquifer, west-central Kansas, 1950 to average 1983-85

Continuing studies are being made in west-central Kansas to provide up-to-date information to aid in the management of groundwater for irrigation. This report, prepared in cooperation with the Western Kansas Groundwater Management District No. 1, presents the fifth in a series of studies that uses a statistical technique, called kriging, to produce hydrologic maps that are used as management tools. Kriging is a statistical technique that was used to interpolate water level altitudes at the center of each 1-square-mile section in the study area based on measured water levels at 165 observation wells. These interpolation altitudes (1,859 in all), along with bedrock surface and base year water table altitudes, were used to prepare a geohydrologic map illustrating percentage change in saturated thickness. Saturated thickness, as used in this report, is the thickness of the High Plains aquifer between the groundwater surface indicated by water table altitudes and the bedrock surface. Because irrigation development in west-central Kansas was minimal prior to 1950, the saturated thickness during 1950 represented a nearly static condition in the aquifer. Thus, the effects of irrigation withdrawalson the volume of water in storage could be related to the decrease or percentage change in saturated thickness of the aquifer from 1950 to average saturated thickness during 1983-85.

Kansas↗
USGS1992

Assessment of sediment contamination at Great Lakes Areas of Concern: the ARCS Program Toxicity-Chemistry Work Group strategy

In response to a mandate in Section 118(c)(3) of the Water Quality Act of 1987, a program called Assessment and Remediation of Contaminated Sediments (ARCS) was established. Four technical work groups were formed. This paper details the research strategy of the Toxicity-Chemistry Work Group. The Work Group's general objectives are to develop survey methods and to map the degree of contamination and toxicity in bottom sediments at three study areas, which will serve as guidance for future surveys at other locations. A related objective is to use the data base that will be generated to calculate sediment quality concentrations by several methods. The information needed to achieve these goals will be collected in a series of field surveys at three areas: Saginaw Bay (MI), Grand Calumet River (IN), and Buffalo River (NY). Assessments of the extent of contamination and potential adverse effects of contaminants in sediment at each of these locations will be conducted by collecting samples for physical characterization, toxicity testing, mutagenicity testing, chemical analyses, and fish bioaccumulation assays. Fish populations will be assessed for tumors and external abnormalities, and benthic community structure will be analyzed. A mapping approach will use low-cost indicator parameters at a large number of stations, and will extrapolate by correlation from traditional chemical and biological studies at a smaller number of locations. Sediment toxicity testing includes elutriate, pore water and whole sediment bioassays in a three-tiered framework. In addition to the regular series of toxicity tests at primary mater stations, some stations are selected for a more extensive suite of tests.

Journal of Aquatic Ecosystem Health↗
USGS2011

Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California

During the late Pleistocene, emergent groundwater supported persistent and long-lived desert wetlands in many broad valleys and basins in the American Southwest. When active, these systems provided important food and water sources for local fauna, supported hydrophilic and phreatophytic vegetation, and acted as catchments for eolian and alluvial sediments. Desert wetlands are represented in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits. Groundwater discharge deposits contain information on the timing and magnitude of past changes in water-table levels and, thus, are a source of paleohydrologic and paleoclimatic information. Here, we present the results of an investigation of extensive groundwater discharge deposits in the central Mojave Desert at Valley Wells, California. We used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at Valley Wells, which we dated using radiocarbon, luminescence, and uranium-series techniques. We also analyzed the sediments and microfauna (ostracodes and gastropods) to reconstruct the specific environments in which they formed. Our results suggest that the earliest episode of high water-table conditions at Valley Wells began ca. 60 ka (thousands of calendar yr B.P.), and culminated in peak discharge between ca. 40 and 35 ka. During this time, cold (4–12 °C) emergent groundwater supported extensive wetlands that likely were composed of a wet, sedge-rush-tussock meadow mixed with mesic riparian forest. After ca. 35 ka, the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the Last Glacial Maximum (LGM). The water table dropped further after the LGM, and xeric conditions prevailed until modest wetlands returned briefly during the Younger Dryas cold event (13.0–11.6 ka). We did not observe any evidence of wet conditions during the Holocene at Valley Wells. The timing of these fluctuations is consistent with changes in other paleowetland systems in the Mojave Desert, the nearby Great Basin Desert, and in southeastern Arizona, near the border of the Sonoran and Chihuahuan Deserts. The similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late Pleistocene in desert wetlands scattered throughout the American Southwest were likely driven by synoptic-scale climate processes.

California↗
USGS2017

Everglades Depth Estimation Network (EDEN)—A decade of serving hydrologic information to scientists and resource managers

Introduction The Everglades Depth Estimation Network (EDEN) provides scientists and resource managers with regional maps of daily water levels and depths in the freshwater part of the Greater Everglades landscape. The EDEN domain includes all or parts of five Water Conservation Areas, Big Cypress National Preserve, Pennsuco Wetlands, and Everglades National Park. Daily water-level maps are interpolated from water-level data at monitoring gages, and depth is estimated by using a digital elevation model of the land surface. Online datasets provide time series of daily water levels at gages and rainfall and evapotranspiration data ( https://sofia.usgs.gov/eden/ ). These datasets are used by scientists and resource managers to guide large-scale field operations, describe hydrologic changes, and support biological and ecological assessments that measure ecosystem response to the implementation of the Comprehensive Everglades Restoration Plan. EDEN water-level data have been used in a variety of biological and ecological studies including (1) the health of American alligators as a function of water depth, (2) the variability of post-fire landscape dynamics in relation to water depth, (3) the habitat quality for wading birds with dynamic habitat selection, and (4) an evaluation of the habitat of the Cape Sable seaside sparrow.

Florida↗
USGS2014

Origins and delineation of saltwater intrusion in the Biscayne aquifer and changes in the distribution of saltwater in Miami-Dade County, Florida

Intrusion of saltwater into parts of the shallow karst Biscayne aquifer is a major concern for the 2.5 million residents of Miami-Dade County that rely on this aquifer as their primary drinking water supply. Saltwater intrusion of this aquifer began when the Everglades were drained to provide dry land for urban development and agriculture. The reduction in water levels caused by this drainage, combined with periodic droughts, allowed saltwater to flow inland along the base of the aquifer and to seep directly into the aquifer from the canals. The approximate inland extent of saltwater was last mapped in 1995. An examination of the inland extent of saltwater and the sources of saltwater in the aquifer was completed during 2008–2011 by using (1) all available salinity information, (2) time-series electromagnetic induction log datasets from 35 wells, (3) time-domain electromagnetic soundings collected at 79 locations, (4) a helicopter electromagnetic survey done during 2001 that was processed, calibrated, and published during the study, (5) cores and geophysical logs collected from 8 sites for stratigraphic analysis, (6) 8 new water-quality monitoring wells, and (7) analyses of 69 geochemical samples. The results of the study indicate that as of 2011 approximately 1,200 square kilometers (km 2 ) of the mainland part of the Biscayne aquifer were intruded by saltwater. The saltwater front was mapped farther inland than it was in 1995 in eight areas totaling about 24.1 km 2 . In many of these areas, analyses indicated that saltwater had encroached along the base of the aquifer. The saltwater front was mapped closer to the coast than it was in 1995 in four areas totaling approximately 6.2 km 2 . The changes in the mapped extent of saltwater resulted from improved spatial information, actual movement of the saltwater front, or a combination of both. Salinity monitoring in some of the canals in Miami-Dade County between 1988 and 2010 indicated influxes of saltwater, with maximum salinities ranging from 1.4 to 32 practical salinity units (PSU) upstream of the salinity control structures. Time-series electromagnetic induction log data from monitoring wells G–3601, G–3608, and G–3701, located adjacent to the Biscayne, Snapper Creek, and Black Creek Canals, respectively, and upstream of the salinity control structures, indicated shallow influxes of conductive water in the aquifer that likely resulted from leakage of brackish water or saltwater from these canals. The determination that saltwater influxes were recent is supported by the similarity in the oxygen and hydrogen stable isotope composition in samples from the Snapper Creek Canal, 1.6 kilometers (km) inland of a salinity control structure, and in samples from well G–3608, which is adjacent to the canal, as well as by the relative ages of the water sampled from well G–3608 and other wells open to the aquifer below the saltwater interface. Historical and recent salinity information from the Card Sound Road Canal, monitoring well FKS8 located adjacent to the canal, and the 2001 helicopter electromagnetic survey indicated that saltwater may occasionally leak from this canal as far inland as 15 km. This leakage may be prevented or reduced by a salinity control structure that was installed in May 2010. Saltwater also may have leaked from the Princeton Canal. Results of geochemical sampling and analysis indicate a close correspondence between droughts and saltwater intrusion. Tritium/helium-3 apparent (piston-flow) ages determined from samples of saltwater with chloride concentrations of about 1,000 milligrams per liter (mg/L) or greater generally corresponded to a period during which droughts were frequent. Comparison of average daily air temperatures in Miami, Florida, with estimates of recharge temperatures determined from the dissolved gas composition in water samples indicated that saltwater likely entered the aquifer in April or early May when water levels are typically at their lowest during the year. Conversely, most of the samples of freshwater with chloride concentrations less than about 1,000 mg/L indicate recharge temperatures corresponding to air temperatures in mid to late May when rainfall and water levels in the aquifer increase, and the piston-flow ages of these samples correspond to wet years. The piston-flow ages of freshwater samples generally were younger than ages of samples of saltwater. Saltwater samples that were depleted in boron, magnesium, potassium, sodium, and sulfate, and enriched in calcium relative to the concentrations theoretically produced by freshwater/seawater mixing, generally were found to be associated with areas where saltwater had recently intruded. The calcium to (bicarbonate + sulfate) molar ratios (Ca/(HCO 3 +SO 4 )) of these samples generally were greater than 1. Saltwater samples from some of the monitoring wells, however, indicated little or no enrichment or depletion of these ions relative to the theoretical freshwater/seawater mixing line, and the Ca/(HCO 3 +SO 4 ) molar ratios of these samples generally were less than 1. Results indicated that aquifer materials are approaching equilibrium with seawater at these well locations.

Florida↗
USGS1987

An interactive program to display user-generated or file-based maps on a personal computer monitor

PC MAP-MAKER is an ADVANCED BASIC program written to provide users of IBM XT, IBM AT, and compatible computers with a straight-forward, flexible method to display geographical data on a color or monochrome PC (personal computer) monitor. Data can be political boundaries such as State and county boundaries; natural curvilinear features such as rivers, drainage areas, and geological contacts; and points such as well locations and mineral localities. Essentially any point defined by a latitude and longitude and any line defined by a series of latitude and longitude values can be displayed using the program. PC MAP MAKER allows users to view tabular data from U.S. Geological Survey files such as WATSTORE (National Water Data Storage and Retrieval System) in a map format in a time much shorter than required by sending the data to a line plotter. The screen image can be saved to disk for recall at a later date, and hard copies can be printed with a dot matrix printer. The program is user-friendly, using menus or prompts to guide user input. It is fully documented and structured to allow the user to tailor the program to the user 's specific needs. The documentation includes a tutorial designed to introduce users to the capabilities of the program using the State of Colorado as a demonstration map area. (Author 's abstract)

Open-File Report↗
USGS1978

Planning report for the southeastern limestone regional aquifer system analysis

The southeastern limestone aquifer system is one of the major sources of ground water in the United States. Over 3 billion gallons of water are pumped daily making the aquifer the principal source of municipal, industrial, and agricultural water supply in large parts of Florida and Georgia and to a lesser extent in South Carolina, and Alabama. Another important use is the disposal of industrial wastes and treated sewage into parts of the limestone system containing saline water. A variety of problems have developed in the aquifer in recent years, principally declining water levels, saltwater intrusion in coastal areas, water-quality degradation, and inadequate supplies of fresh ground water locally. In 1978 the U.S. Geological Survey began a study whose goal is to provide a complete description of the hydrogeologic framework, geochemistry, and regional flow system of the limestone aquifer. A 4-year effort is planned that will include: (1) synthesis of all existing data and presentation on a series of regional hydrogeological and geochemical maps; (2) obtaining new hydrogeological information to fill data voids -- particularly where ongoing State and Federal programs are not likely to generate such data; and (3) design and calibration of a regional digital model of the aquifer system and detailed models of problem areas. Computer simulation will be used extensively to assess the effects of large withdrawals of ground water and waste injection into the aquifer.

Alabama, Florida, Georgia, South Carolina↗
USGS2017

A foundation for future assessment and management of groundwater resources

Sequence stratigraphic models for the Pleistocene to Holocene sediments of the Los Angeles (LA) Basin will provide better understanding of regional groundwater flow and have helped identify seawater intrusion pathways into important groundwater aquifers. Because groundwater provides more than one-third of the municipal water supply for the coastal LA Basin, the aquifer architecture of this system is a high priority for groundwater managers. Seismic and sequence stratigraphy are now incorporated into groundwater resource assessments and environmental investigations. By evaluating subsurface data using sequence stratigraphy, the geometry and distribution of aquifer and aquitard sediments are defined, thus groundwater contaminant plumes and sea water intrusion pathways are better understood. The U. S. Geological Survey (USGS), in cooperation with Los Angeles County Department of Public Works and the Water Replenishment District of Southern California undertook an investigation of the groundwater stratigraphy of the Wilmington – Long Beach area of the LA Basin. Sequence stratigraphic methods were used to integrate preexisting groundwater well data with: (1) new borehole observations, (2) structural and physical properties data derived from geophysical measurements, (3) hi-resolution seismic reflection data obtained offshore of the present shoreline, and (4) vintage oil company exploration seismic reflection data from both onshore and offshore of the shoreline. These data were used to construct a series of Pleistocene to Holocene environment of deposition maps that show the overall progradation of sequences seaward over time. In addition, seawater intrusion pathways into coastal groundwater aquifers were identified and mapped. On a more regional scale, a vintage Texaco seismic reflection data set from the greater LA Basin was interpreted and integrated with a regional network of multi-level ground-water monitoring wells. The sequence stratigraphic correlation shows that many of the defined groundwater aquifers are not correlative. For example, one of the major groundwater supply aquifers, the Silverado Aquifer, when tied to the seismic reflection data has different ages depending on location. This new understanding demonstrates the need for a re-evaluation of the Pleistocene to Holocene stratigraphy using existing seismic reflection data integrated with well data from the LA Basin in order to understand the regional distribution of groundwater aquifers.

Conference Paper↗
USGS1979

Evaluation of the geologic and hydrologic factors related to the waste-storage potential of Mesozoic aquifers in the southern part of the Atlantic Coastal Plain, South Carolina and Georgia

The report describes the subsurface distribution of rocks of Cretaceous to Late Jurassic( ) age in the Atlantic Coastal Plain , South Carolina, and Georgia, and examines their potential for deep-well waste storage into th part of the regional sediment mass which lies below the deepest zones containing usable ground waters. For the study, usable ground water is considered to be that which contains less than 10,000 mg/L dissolved solids. Using a group of geohydrologic parameters derived from or combining 21 categories of basic data, established from study and interpretation of well cuttings and geophysical logs, a series of 32 regional maps and 8 stratigraphic cross sections was constructed. For each of the eight geologic units delineated in the subsurface, the maps illustrate the distribution of waste-storage potential in terms of areal extent, depth below land surface, sand-shale geometry, and the approximate sodium chloride concentration of a unit 's nonusable ground water. In areas where the geologic units contain nonusable ground water, the depth below land surface and the thickness of potential waste-storage reservoir and reservoir-seal combinations are variable. The range in variability appears to be broad enough to meet the need for a wide choice among the geologic requirements that would normally be considered in selecting specific waste-storage sites for detailed examination. (Woodard-USGS)

Georgia, South Carolina↗