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At least 1,693 records · Page 94Linked to original sources

USGS2019

Sediment trapping and carbon sequestration in floodplains of the lower Atchafalaya Basin, LA: Allochthonous vs. autochthonous carbon sources

Recent studies suggest that about 2 Pg of organic C is stored on floodplains worldwide. The present study indicates the Atchafalaya River, fifth largest river in the United States in terms of discharge, traps 30 mm/y of sediment on average within its floodplain, which is the highest average non‐episodic rate of fluvial deposition on the U.S. Coastal Plain. We installed sediment sampling stations at 23 sites, normally in transect, in the Atchafalaya Basin; these sites represent the range of hydrogeomorphic conditions on the floodplain based on hydrologic connectivity with the river main stem. The rate of sedimentation translates into about 12.5 Tg/y and includes 694 Mg/y of organic C. Highest sedimentation rates are associated with areas of high connectivity to channels and prograding deltaic processes. The δ 13 C content suggests that 35% of deposited C is derived from river‐suspended sediment compared to litterfall in the Basin. Thus, much of the organic C sequestered is allochthonous material. However, isolated interior sites with limited connectivity to the channel may generate and sequester large amounts of autochthonous C. The substantial trapping of both auto‐ and allochthonous C (392 Mg/y) make this freshwater‐forested floodplain critical in storage of material before reaching the coastal delta and estuary. This C deposition rate (340 g C m ‐2 y ‐1 ) exceeds all other rates reported in recent Blue Carbon and Tidal Freshwater Forested Wetland studies. Atchafalaya C sequestration occurs in/near areas with tidal influence and like other coastal systems is an important site for trapping mineral and organic sediment and in global C cycling.

Louisiana↗

USGS2021

A river of change—The Rio Grande in the Big Bend region

The Big Bend region is located within the heart of the Chihuahan Desert of North America. Within this region, the Rio Grande, referred to as the Rio Bravo in Mexico, is the international border between the United States and Mexico. The area known as the Big Bend is named after the large northerly bend that the river makes before flowing southeast to the Gulf of Mexico. This region is environmentally protected by both countries. Although large binational conservation efforts exist, the physical and ecological characteristics of the river have been substantially altered. Changes in Rio Grande hydrology (the seasonality, magnitude, duration, and variability in streamflow) have resulted in the widespread physical transformation of the river, resulting in the loss of important habitat for native and endangered fish and increased flood risk. U.S. Geological Survey (USGS) scientists, in cooperation with many other government agencies, universities, and non-governmental organizations (NGOs), are working to better understand these changes to inform management of the Rio Grande.

Texas↗

USGS2018

Optimization of salt marsh management at the Bombay Hook National Wildlife Refuge, Delaware, through use of structured decision making

Structured decision making is a systematic, transparent process for improving the quality of complex decisions by identifying measurable management objectives and feasible management actions; predicting the potential consequences of management actions relative to the stated objectives; and selecting a course of action that maximizes the total benefit achieved and balances tradeoffs among objectives. The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, applied an existing, regional framework for structured decision making to develop a prototype tool for optimizing salt marsh management decisions at the Bombay Hook National Wildlife Refuge in Delaware. Refuge biologists, refuge managers, and research scientists identified multiple potential management actions to improve the ecological integrity of eight salt marsh management units within the refuge and estimated the outcomes of each action in terms of performance metrics associated with each management objective. Value functions previously developed at the regional level were used to transform metric scores to a common utility scale, and utilities were summed to produce a single score representing the total management benefit that would be accrued from each potential management action. Constrained optimization was used to identify the set of management actions, one per salt marsh management unit, that would maximize total management benefits at different cost constraints at the refuge scale. Results indicated that for the objectives and actions considered here, total management benefits would increase consistently up to approximately \$300,000, but that further expenditures would yield diminishing return on investment. Management actions selected within optimal portfolios at total costs less than \$300,000 included hydrologic restoration, recontouring adjacent uplands to facilitate marsh migration, and burning the marsh. The prototype presented here provides a framework for decision making at the Bombay Hook National Wildlife Refuge that can be updated as new data and information become available. Insights from this process may also be useful to inform future habitat management planning at the refuge.

Delaware↗

USGS1993

Effects of underground mining and mine collapse on the hydrology of selected basins in West Virginia

The effects of underground mining and mine collapse on areal hydrology were determined at one site where the mined bed of coal lies above major streams and at two sites where the bed of coal lies below major streams. Subsidence cracks observed at land surface generally run parallel to predominant joint sets in the rocks. The mining and subsidence cracks increase hydraulic conductivity and interconnection of water-bearing rock units, which in turn cause increased infiltration of precipitation and surface water, decreased evapotranspiration, and higher base flows in some small streams. Water levels in observation wells in mined areas fluctuate as much as 100 ft annually. Both gaining and losing streams are found in mined areas. Mine pumpage and drainage can cause diversion of water underground from one basin to another. Areal and single-well aquifer tests indicated that near-surface rocks have higher transmissivity in a mine-subsided basin than in unmined basins. Increased infiltration and circulation through shallow subsurface rocks increase dissolved mineral loads in streams, as do treated and untreated contributions from mine pumpage and drainage. Abandoned and flooded underground mines make good reservoirs because of their increased transmissivity and storage. Subsidence cracks were not detectable by thermal imagery, but springs and seeps were detectable.

Water Supply Paper↗

USGS2012

Occurrence of pesticides in water and sediment collected from amphibian habitats located throughout the United States, 2009-10

Water and bed-sediment samples were collected by the U.S. Geological Survey (USGS) in 2009 and 2010 from 11 sites within California and 18 sites total in Colorado, Georgia, Idaho, Louisiana, Maine, and Oregon, and were analyzed for a suite of pesticides by the USGS. Water samples and bed-sediment samples were collected from perennial or seasonal ponds located in amphibian habitats in conjunction with research conducted by the USGS Amphibian Research and Monitoring Initiative and the USGS Toxic Substances Hydrology Program. Sites selected for this study in three of the states (California, Colorado, and Orgeon) have no direct pesticide application and are considered undeveloped and remote. Sites selected in Georgia, Idaho, Louisiana, and Maine were in close proximity to either agricultural or suburban areas. Water and sediment samples were collected once in 2009 during amphibian breeding seasons. In 2010, water samples were collected twice. The first sampling event coincided with the beginning of the frog breeding season for the species of interest, and the second event occurred 10-12 weeks later when pesticides were being applied to the surrounding areas. Additionally, water was collected during each sampling event to measure dissolved organic carbon, nutrients, and the fungus, Batrachochytrium dendrobatidis , which has been linked to amphibian declines worldwide. Bed-sediment samples were collected once during the beginning of the frog breeding season, when the amphibians are thought to be most at risk to pesticides. Results of this study are reported for the following two geographic scales: (1) for a national scale, by using data from the 29 sites that were sampled from seven states, and (2) for California, by using data from the 11 sampled sites in that state. Water samples were analyzed for 96 pesticides by using gas chromatography/mass spectrometry. A total of 24 pesticides were detected in one or more of the 54 water samples, including 7 fungicides, 10 herbicides, 4 insecticides, 1 synergist, and 2 pesticide degradates. On a national scale, aminomethylphosphonic acid (AMPA), the primary degradate of the herbicide glyphosate, which is the active ingredient in Roundup®, was the most frequently detected pesticide in water (16 of 54 samples) followed by glyphosate (8 of 54 samples). The maximum number of pesticides observed at a single site was nine compounds in a water sample from a site in Louisiana. The maximum concentration of a pesticide or degradate observed in water was 2,880 nanograms per liter of clomazone (a herbicide) at a site in Louisiana. In California, a total of eight pesticides were detected among all of the low and high elevation sites; AMPA was the most frequently detected pesticide, but glyphosate was detected at the highest concentrations (1.1 micrograms per liter). Bed-sediment samples were analyzed for 94 pesticides by using accelerated solvent extraction, gel permeation chromatography for sulfur removal, and carbon/alumina stacked solid-phase extraction cartridges to remove interfering sediment matrices. In bed sediment, 22 pesticides were detected in one or more of the samples, including 9 fungicides, 3 pyrethroid insecticides, p,p' -dichlorodiphenyltrichloroethane ( p,p' -DDT) and its major degradates, as well as several herbicides. Pyraclostrobin, a strobilurin fungicide, and bifenthrin, a pyrethroid insecticide, were detected most frequently. Maximum pesticide concentrations ranged from less than their respective method detection limits to 1,380 micrograms per kilogram (tebuconazole in California). The number of pesticides detected in samples from each site ranged from zero to six compounds. The sites with the greatest number of pesticides were in Maine and Oregon with six pesticides detected in one sample from each state, followed by Georgia with four pesticides in one sample. For California, a total of 10 pesticides were detected among all sites, and 4 pesticides were detected at both low and high elevation sites; tebuconazole and pyraclostrobin were the two most frequently detected pesticides in California. For the other six selected states, the most frequently detected pesticides in bed sediment were pyraclostrobin (detected in 17 of 42 samples), bifenthrin (detected in 14 of 42 samples), and tebuconazole (detected in 10 of 42 samples). The fungus, Batrachochytrium dendrobatidis (Bd), was detected in water samples in sites from four of the seven states during 2009 and 2010, and the number of zoospore equivalents per liter of water in samples where Bd was detected ranged from 1.6 to 343. Bd was not detected in water samples from sites in Georgia, Louisiana, and Oregon.

Data Series↗

USGS2009

Geologic Setting and Hydrogeologic Units of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

The Columbia Plateau Regional Aquifer System (CPRAS) covers approximately 44,000 square miles of northeastern Oregon, southeastern Washington, and western Idaho. The area supports a $6 billion per year agricultural industry, leading the Nation in production of apples and nine other commodities (State of Washington Office of Financial Management, 2007; U.S. Department of Agriculture, 2007). Groundwater availability in the aquifers of the area is a critical water-resource management issue because the water demand for agriculture, economic development, and ecological needs is high. The primary aquifers of the CPRAS are basalts of the Columbia River Basalt Group (CRBG) and overlying basin-fill sediments. Water-resources issues that have implications for future groundwater availability in the region include (1) widespread water-level declines associated with development of groundwater resources for irrigation and other uses, (2) reduction in base flow to rivers and associated effects on temperature and water quality, and (3) current and anticipated effects of global climate change on recharge, base flow, and ultimately, groundwater availability. As part of a National Groundwater Resources Program, the U.S. Geological Survey began a study of the CPRAS in 2007 with the broad goals of (1) characterizing the hydrologic status of the system, (2) identifying trends in groundwater storage and use, and (3) quantifying groundwater availability. The study approach includes documenting changes in the status of the system, quantifying the hydrologic budget for the system, updating the regional hydrogeologic framework, and developing a groundwater-flow simulation model for the system. The simulation model will be used to evaluate and test the conceptual model of the system and later to evaluate groundwater availability under alternative development and climate scenarios. The objectives of this study were to update the hydrogeologic framework for the CPRAS using the available geologic mapping and well information and to develop a digital, three-dimensional hydrogeologic model that could be used as the basis of a groundwater-flow model. This report describes the principal geologic and hydrogeologic units of the CPRAS and geologic map and well data that were compiled as part of the study. The report also describes simplified regional hydrogeologic sections and unit extent maps that were used to conceptualize the framework prior to development of the digital 3-dimensional framework model.

Idaho, Oregon, Washington↗

USGS1987

Ground-water quality assessment of the central Oklahoma Aquifer, Oklahoma; project description

In April 1986, the U.S. Geological Survey began a pilot program to assess the quality of the Nation's surface-water and ground-water resources. The program, known as the National Water-Quality Assessment (NAWQA) program, is designed to acquire and interpret information about a variety of water-quality issues. The Central Oklahoma aquifer project is one of three ground-water pilot projects that have been started. The NAWQA program also incudes four surface-water pilot projects. The Central Oklahoma aquifer project, as part of the pilot NAWQA program, will develop and test methods for performing assessments of ground-water quality. The objectives of the Central Oklahoma aquifer assessment are: (1) To investigate regional ground-water quality throughout the aquifer in the manner consistent with the other pilot ground-water projects, emphasizing the occurrence and distribution of potentially toxic substances in ground water, including trace elements, organic compounds, and radioactive constituents; (2) to describe relations between ground-water quality, land use, hydrogeology, and other pertinent factors; and (3) to provide a general description of the location, nature, and possible causes of selected prevalent water-quality problems within the study unit; and (4) to describe the potential for water-quality degradation of ground-water zones within the study unit. The Central Oklahoma aquifer, which includes in descending order the Garber Sandstone and Wellington Formation, the Chase Group, the Council Grove Group, the Admire Group, and overlying alluvium and terrace deposits, underlies about 3,000 square miles of central Oklahoma and is used extensively for municipal, industrial, commercial, and domestic water supplies. The aquifer was selected for study by the NAWQA program because it is a major source for water supplies in central Oklahoma and because it has several known or suspected water-quality problems. Known problems include concentrations of arsenic, chromium, selenium, and gross-alpha activity that exceed drinking-water standards. Suspected problems include possible contamination of the aquifer by oil-field brines and drilling fluids, pesticides, industrial chemicals, septic-tank effluent, fertilizers, and leakage from sewage systems and underground tanks used for storage of hydrocarbons. There are four major components of the Central Oklahoma aquifer project. The first component is the collection and analysis of existing information, including chemical, hydrologic, and land-use data. The second component is the geohydrologic and geochemical investigations of the aquifer flow system. The third component is the sampling for a wide variety of inorganic, organic, and radioactive constituents as part a regional survey that will produce a consistent set of data among all ground-water pilot projects. These data can be used to: (1) Define regional ground-water quality within the Central Oklahoma aquifer, and (2) compare water quality in the Central Oklahoma aquifer to the water quality in the other ground-water study units of the NAWQA program. The fourth component is topical studies that will address, in more detail, some of the major water-quality issues pertaining to the aquifer.

Open-File Report↗

USGS2019

Factors affecting the occurrence of lead and manganese in untreated drinking water from Atlantic and Gulf Coastal Plain aquifers, eastern United States—Dissolved oxygen and pH framework for evaluating risk of elevated concentrations

Groundwater samples collected during 2012 and 2013 from public-supply wells screened in the Atlantic and Gulf Coastal Plain aquifers of the eastern and southeastern U.S. rarely contained lead or manganese concentrations that exceeded drinking-water limits, despite having corrosive characteristics. Data indicate that the occurrence of dissolved lead and manganese in sampled groundwater, prior to its distribution or treatment, was related to several explanatory factors including the presence of source minerals, hydrologic position along the flow path, water-rock interactions, and associated geochemical conditions such as pH and dissolved oxygen (DO) concentrations. Elevated concentrations of lead compared to health-based benchmarks were associated with groundwater that is acidic (pH ≤ 6.5), oxygenated (DO ≥ 2 mg/L), and closer to recharge zones (relatively young water). Elevated concentrations of manganese were associated with groundwater that is acidic to neutral (pH ≤ 7.5), has low DO (<2 mg/L), and further from recharge zones (relatively old). Under these geochemical conditions, minerals that could sequester lead or manganese tended to be undersaturated, and adsorption by hydrous ferric oxide was limited. Under neutral to alkaline pH conditions, precipitation of impure calcium carbonate or phosphate compounds containing traces of lead or manganese (solid solutions) could maintain low concentrations of the trace elements. Additionally, adsorption of lead or manganese cations by hydrous ferric oxides (HFO) could be another attenuating factor where conditions are oxidizing and dissolved inorganic carbon concentrations are relatively low. A DO/pH framework was developed as a screening tool for evaluating risk of elevated lead or manganese, based on the occurrence of elevated lead and manganese concentrations and the corresponding distributions of DO and pH in the Atlantic and Gulf Coastal Plain aquifers. Validation of the DO/pH framework was accomplished using an independent national dataset that showed consistent results for elevated lead (pH ≤ 6.5; DO ≥ 2 mg/L) and manganese (pH ≤ 7.5; DO < 2 mg/L).

Atlantic and Gulf Coastal Plain aquifers↗

USGS1971

Bottom sediments on the continental shelf off the northeastern United States -- Cape Cod to Cape Ann, Massachusetts

These reconnaissance maps have been constructed to show the areal distribution of major types of bottom sediment and some of their constituents on the sea floor off Massachusetts between Cape Ann and Cape Cod (41°45'N and 42°50'N and west of 70°-00W). They are intended to serve as a guide to future detailed mapping of gravel, sand, silt clay, and organic carbon. Because sediment texture is in part a reflection of long-term hydrologic conditions, the maps will also help to infer the important sediment transport mechanisms in the area and thus they should be useful in problems relating to disposal of solid and liquid waste offshore.

Massachusetts↗

USGS2014

Application of hydrologic tools and monitoring to support managed aquifer recharge decision making in the Upper San Pedro River, Arizona, USA

The San Pedro River originates in Sonora, Mexico, and flows north through Arizona, USA, to its confluence with the Gila River. The 92-km Upper San Pedro River is characterized by interrupted perennial flow, and serves as a vital wildlife corridor through this semiarid to arid region. Over the past century, groundwater pumping in this bi-national basin has depleted baseflows in the river. In 2007, the United States Geological Survey published the most recent groundwater model of the basin. This model served as the basis for predictive simulations, including maps of stream flow capture due to pumping and of stream flow restoration due to managed aquifer recharge. Simulation results show that ramping up near-stream recharge, as needed, to compensate for downward pumping-related stress on the water table, could sustain baseflows in the Upper San Pedro River at or above 2003 levels until the year 2100 with less than 4.7 million cubic meters per year (MCM/yr). Wet-dry mapping of the river over a period of 15 years developed a body of empirical evidence which, when combined with the simulation tools, provided powerful technical support to decision makers struggling to manage aquifer recharge to support baseflows in the river while also accommodating the economic needs of the basin.

Arizona↗

USGS2012

Third International Seminar for Hydrology Professors

The Third International Seminar for Hydrology Professors was held at Purdue University in Lafayette, Indiana. There were 72 U.S. participants from 25 States and 19 participants from 15 other countries as follows: three from Canada; two each from Costa Rica and Peru; and one each from The Republic of China, Colombia, El Salvador, France, India, Republic of Korea, Mexico, New Zealand, Portugal, Romania, Turkey, and the United Arab Republic. Seventy-eight of the participants were college or university professors and 13 represented various state and national research and technical agencies.

Indiana↗

USGS2001

The tides and inflows in the mangroves of the Everglades (TIME) interdisciplinary project of the South Florida Ecosystem Program

The U. S. Geological Survey (USGS) has a prominent role in the Federal Government's comprehensive restoration plan for the south Florida ecosystem encompassing the Everglades-the largest remaining subtropical wilderness in the continental United States. USGS scientists, in collaboration with researchers from the National Park Service (NPS), other governmental agencies, and academia, are providing scientific information to land and resource managers for planning, executing, and evaluating restoration actions. One major thrust of the restoration effort is to restore the natural functioning of the ecosystem to predrainage conditions, an objective that requires knowledge of the hydrologic and hydraulic factors that affect the flow of water. A vast network of interlaced canals, rimmed with levees and fitted with hydraulic control structures, and highways, built on elevated embankments lined by borrow ditches and undercut by culverts, now act to control and direct the flow of water through the shallow low-gradient wetlands. As water flows south from Lake Okeechobee past the city of Miami and through Everglades National Park (ENP), it is diminished by canal diversions, augmented by seasonably variable precipitation, and depleted through evapotranspiration. Along its path, the shallow flowing water, referred to as sheet flow, interacts with surficial aquifers and is subject to the resistance effects of variably dense vegetation and forcing effects of winds. New scientific investigations are providing additional insight into the hydrologic and hydraulic processes governing the flow, and recent data-collection efforts are supplying more comprehensive data describing the flow behavior, both of which are benefiting development of improved numerical models to evaluate and restore the natural functioning of the ecosystem.

Florida↗

USGS1981

Geohydrology and numerical simulation of the alluvium and terrace aquifer along the Beaver-North Canadian River from the Panhandle to Canton Lake, northwestern Oklahoma

A quantitative description of the hydrologic system in alluvium and terrace deposits along the Beaver-North Canadian River in northwestern Oklahoma is needed as an aid for planning and management of the aquifer. A two-dimensional finite-difference model was used to describe the aquifer and to predict the effects of future ground-water withdrawals. The aquifer principally consists of three geologic units: Alluvium with an average thickness of 30 feet, low terrace deposits with an average thickness of 50 feet, and high terrace deposits with an average thickness of 70 feet. A thin cover of dune sand overlies much of the area and provides an excellent catchment for recharge, but is generally unsaturated. Hydraulic conductivity of the aquifer ranges from 0 to 160 feet per day and averages 59 feet per day. Specific yield is estimated to be 0.29. Recharge to the aquifer is approximately 1 inch annually. Under present conditions (1978), most discharge is the result of ground-water flow to the Beaver-North Canadian River at a rate of 36 cubic feet per second and to pumpage for public-supply, industrial, and irrigation use at a rate of 28 cubic feet per second. In 1978, the aquifer had an average saturated thickness of 31 feet and contained 4.07 million acre-feet of water. The model was used to predict future head response in the aquifer to various pumping stresses. For any one area, the pumping stress was applied until the saturated thickness for that area was less than 5 feet, at which time the pumping ceased. The results of the modeled projections show that if the aquifer is stressed from 1978 to 1993 at the 1977 pumpage rates and well distribution, the average saturated thickness will decrease 1.0 foot and the volume of water in storage will be 3.94 million acre-feet, or 97 percent of the 1978 volume. If the aquifer is stressed at this same rate until 2020, the average saturated thickness will decrease an additional 0.7 foot and the volume of water in storage will be 3.84 million acre-feet, or 94 percent of the 1978 volume. If all areas of the aquifer having a 1978 saturated thickness of 5 feet or more are stressed from 1978 to 1993 at a rate of approximately 1.4 acre-feet per acre per year, the average saturated thickness will decrease by 20.9 feet and the volume of water in storage will be 1.28 million acre-feet, or 31 percent of the 1978 volume. If the aquifer is stressed at this same rate until 2020, the average saturated thickness will decrease an additional 2.2 feet and the volume of water in storage will be 980,000 acre-feet, or 24 percent of the 1978 volume. The water in the aquifer is generally of the calcium bicarbonate type and is suitable for most uses. Most of the 30 water samples analyzed contained less than 500 milligrams of dissolved solids per liter.

Oklahoma↗

USGS1991

Review of water demand and water utilization studies for the Provo River drainage basin, and review of a study of the effects of the proposed Jordanelle Reservoir on seepage to underground mines, Bonneville unit of the central Utah project

Problem: Questions have been raised concerning the adequacy of available water to fulfill the needs of storage, exchanges, diversions, and instream flows, pursuant to existing water rights in the Provo River drainage basin part of the Bonneville Unit. Also, concern has been expressed about the potential for seepage of water from Jordanelle Reservoir to underground mines. The Utah Congressional Delegation requested that the U.S. Geological Survey (USGS) review the results of analyses performed by and for the USBR. Purpose and Scope: The purpose of this report is to present the results of the USGS review of (1) the hydrologic data, techniques, and model used by the USBR in their hydrologic analyses of the Provo River drainage basin and (2) the results of a study of the potential for seepage from the Jordanelle Reservoir to nearby underground mines. The USGS reviewed USBR-supplied water demands, water utilization studies, and models of seepage from Jordanelle Reservoir. The USBR estimated that about 90 percent of the water supply for Jordanelle Reservoir will be water from Strawberry Reservoir exchanged for water from the Provo River stored in Utah Lake. If the Utah State Engineer allows the USBR to claim an estimated 19,700 acre-feet of return flows from the CUP, only about 77 percent of the supply would be derived from exchange of existing water rights in Utah Lake. The USGS assumed that planned importations of water from the Uinta Basin will be available and deliverable to fulfill the proposed exchanges. Water rights and demands are important for determining water availability. The USGS did not conduct an independent review of water rights and demands. The USSR and Utah Division of Water Rights use different methods in some areas for determining stress on the system based on past records. The USSR used "historical observed diversions" and the Utah Division of Water Rights use "diversion entitlements", which may not be equal to the historical diversions. The USGS based its review upon water demands used by the USSR. The Utah Division of Water Rights has responsibility for granting and enforcing water rights, and the final decisions on how the rights will be adjudicated lies with the Utah Division of Water Rights and with the courts. The USGS review did not consider the draft water distribution plan for the Utah Lake drainage basin proposed by the Utah State Engineer (written commun., October 15,1991). This plan, when finalized, may have an effect on water availability to the CUP.

Utah↗

USGS1961

Effects of phosphate mining on the ground water of Anguar, Palau Islands, Trust Territory of the Pacific Islands

Mining of phosphate ore on Angaur Island by mechanized methods created large water-table lakes, which became filled with brackish or saline water. A hydrologic investigation was started in 1949 to determine whether the saline water in the lakes would spread to surrounding areas and cause damage to agricultural lands and the water supply. Angaur, which is in the Palau Islands in the southwestern part of Micronesia, is administered as part of the Trust Territory of the Pacific Islands, under a trusteeship granted to the United States by the United Nations. The island has an area of 3.2 square miles and has a maximum altitude of about 150 feet. The climate is tropical oceanic. The average annual temperature is 82 ? F; the average annual rainfall is about 125 inches; and the average relative humidity is about 80 percent. The northwestern third of Angaur (province A) consists topographically of a series of concentric ridges and depressions which are underlain largely by well-cemented coralline limestone of Pliocene, Pleistocene, and Recent ages. The remaining two-thirds of Angaur (province B} is a low plain underlain in the northern and central parts by a low platform of coralline rubble of Pleistocene and Recent age and in the southern part by sandy and rubbly beach deposits of Recent age. Province A contained extensive phosphate deposits of which more than 3 million tons were mined in 1909-55. Weekly water-level measurements at 35 wells, test holes, and lakes indicate that the water table averages about 2 feet above mean sea level in the beach deposits, about half a foot above mean sea level in the rubble deposits, and about 1.35 feet above mean sea level in the coralline limestone. Water samples obtained weekly at the observation sites indicate that the ground water in province A is not of uniform quality, as large variations in salinity occur throughout the area. In contrast, the ground water in province B is of relatively uniform quality, and contains less than 1,000 ppm (parts per million) of chloride in most places. In province A removal of earthy phosphate which had acted as a seal allowed the infiltration of saline water through solution channels exposed at the bottom of several of the lakes. The sampling program showed no indication of large-scale movement of saline water out of the lakes into adjacent ground water. Provinces A and B apparently function as independent ground-water units, and the quality of the ground water in province B has not been noticeably affected by mining activities in province A. The lakes were backfilled with limestone rubble to reduce the possibility of underground movement of saline water out of the lakes. The gross permeability of the backfill material is less than that of the surrounding limestone in province A, and, as the rate of influx of saline water was curtailed, the recharge of fresh water from rainfall tended to reduce the salinity of the ground water in the fill. In parts of the backfilled area the salinity of the water at the water table decreased rapidly in less than 1 year, as a layer of fresh water was built up at the water table.

Water Supply Paper↗

USGS1999

Altitude of the top of the Madison Limestone in the Black Hills area, South Dakota

This map is a product of the Black Hills Hydrology Study, which was initiated in 1990 to assess the quantity, quality, and distribution of surface water and groundwater in the Black Hills area of South Dakota (Driscoll, 1992). This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators. This map is part of a series of 1:100,000-scale maps for the study. The maps include a hydrogeologic map, structure-contour maps (altitudes of the tops of formations) for five formations that contain major aquifers in the study area, and potentiometric maps for these five major aquifers (the Inyan Kara, Minnekahta, Minnelusa, Madison, and Deadwood aquifers). The study area consists of the topographically defined Black Hills and adjacent areas located in western South Dakota. The Black Hills area is an elongated, dome-shaped feature, about 125 miles long and 60 miles wide, which was uplifted during the Laramide orogeny (Feldman and Heimlich, 1980). The oldest geologic units in the study arca arc Precambrian metamorphic and igneous rocks, which are exposed in the central core of the Black Hills. Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills. The bedrock sedimentary units typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift. Many of the sedimentary units contain aquifers, both within and beyond the study area. Recharge to these aquifers occurs from infiltration of precipitation upon the outcrops and, in some cases, from infiltration of streamflow (Hortness and Driscoll, 1998). Artesian conditions generally exist within these aquifers where an upper confining layer is present. Flowing wells and artesian springs that originate from confined aquifers are common around the periphery of the Black Hills. The purpose of this map is to show the altitude of the top (structure contours) of the Madison Limestone within the area of the Black Hills Hydrology Study. The depth to the top of the Madison Limestone can be estimated at a specific site by subtracting the altitude of the top of the formation from the topographic elevation. However, caution is urged in determining the depth to the top of the formation in areas on the map where the contours are approximately located.

South Dakota↗

USGS2000

Altitude of the Top of the Minnelusa Formation in the Black Hills area, South Dakota, 1999

This map is a product of the Black Hills Hydrology Study, which was initiated in 1990 to assess the quantity, quality, and distribution of surface water and ground water in the Black Hills area of South Dakota (Driscoll, 1992). This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators. This map is part of a series of 1:100,000-scale maps for the study. The maps include a hydrogeologic map, structure-contour maps (altitudes of the tops of formations) for five formations that contain major aquifers in the study area, and potentiometric maps for these five major aquifers (the Inyan Kara, Minnekahta, Minnelusa, Madison, and Deadwood aquifers). The study area consists of the topographically defined Black Hills and adjacent areas located in western South Dakota. The Black Hills area is an elongated, dome-shaped feature, about 125 miles long and 60 miles wide, which was uplifted during the Laramide orogeny (Feldman and Heimlich, 1980). The oldest geologic units in the study area are Precambrian metamorphic and igneous rocks, which are exposed in the central core of the Black Hills. Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills. The bedrock sedimentary units typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift. Many of the sedimentary units contain aquifers, both within and beyond the study area. Recharge to these aquifers occurs from infiltration of precipitation upon the outcrops and, in some cases, from infiltration of streamflow (Hortness and Driscoll, 1998). Artesian conditions generally exist within these aquifers where an upper confining layer is present. Flowing wells and artesian springs that originate from confined aquifers are common around the periphery of the Black Hills. The purpose of this map is to show the altitude of the top (structure contours) of the Minnelusa Formation within the area of the Black Hills Hydrology Study. The depth to the top of the Minnelusa Formation can be estimated at a specific site by subtracting the altitude of the top of the formation from the topographic elevation. However, caution is urged in determining the depth to the top of the formation in areas on the map where the contours are approximately located.

Hydrologic Atlas↗

USGS1999

Altitude of the top of the Deadwood Formation in the Black Hills area, South Dakota

This map is a product of the Black Hills Hydrology Study, which was initiated in 1990 to assess the quantity, quality, and distribution of surface water and ground water in the Black Hills area of South Dakota (Driscoll, 1992). This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators. This map is part of a series of 1:100,000-scale maps for the study. The maps include a hydrogeologic map, structure-contour maps (altitudes of the tops of formations) for five formations that contain major aquifers in the study area, and potentiometric maps for these five major aquifers (the Inyan Kara, Minnekahta, Minnelusa, Madison, and Deadwood aquifers). The study area consists of the topographically defined Black Hills and adjacent areas located in western South Dakota. The Black Hills area is an elongated, dome-shaped feature, about 125 miles long and 60 miles wide, which was uplifted during the Laramide orogeny (Feldman and Heimlich, 1980). The oldest geologic units in the study area are Precambrian metamorphic and igneous rocks, which are exposed in the central core of the Black Hills. Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills. The bedrock sedimentary units typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift. Many of the sedimentary units contain aquifers, both within and beyond the study area. Recharge to these aquifers occurs from infiltration of precipitation upon the outcrops and, in some cases, from infiltration of streamflow (Hortness and Driscoll, 1998). Artesian conditions generally exist within these aquifers where an upper confining layer is present. Flowing wells and artesian springs that originate from confined aquifers are common around the periphery of the Black Hills. The purpose of this map is to show the altitude of the top (structure contours) of the Deadwood Formation within the area of the Black Hills Hydrology Study. The depth to the top of the Deadwood Formation can be estimated at a specific site by subtracting the altitude of the top of the formation from the topographic elevation, However, caution is urged in determining the depth to the top of the formation in areas on the map where the contours are approximately located.

South Dakota↗