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At least 1,495 records · Page 83Linked to original sources
USGS2006

Metallogeny of the Great Basin: Crustal evolution, fluid flow, and ore deposits

The Great Basin physiographic province in the Western United States contains a diverse assortment of world-class ore deposits. It currently (2006) is the world’s second leading producer of gold, contains large silver and base metal (Cu, Zn, Pb, Mo, W) deposits, a variety of other important metallic (Fe, Ni, Be, REE’s, Hg, PGE) and industrial mineral (diatomite, barite, perlite, kaolinite, gallium) resources, as well as petroleum and geothermal energy resources. Ore deposits are most numerous and largest in size in linear mineral belts with complex geology. U.S. Geological Survey (USGS) scientists are in the final year of a research project initiated in the fall of 2001 to increase understanding of relations between crustal evolution, fluid flow, and ore deposits in the Great Basin. Because of its substantial past and current mineral production, this region has been the focus of numerous investigations over the past century and is the site of ongoing research by industry, academia, and state agencies. A variety of geoinformatic tools was used to organize, reinterpret, and display, in space and time, the large amounts of geologic, geophysical, geochemical, and hydrologic information deemed pertinent to this problem. This information, in combination with concentrated research on (1) critical aspects of the geologic history, (2) an area in northern Nevada that encompasses the major mineral belts, and (3) important mining districts and deposits, is producing new insights about the interplay between key tectonic events, hydrothermal fluid flow, and ore genesis in mineral belts. The results suggest that the Archean to Holocene history of the Great Basin was punctuated by several tectonic events that caused fluids of different origins (sea water, basinal brine, meteoric water, metamorphic water, magmatic water) to move through the crust. Basement faults reactivated during these events localized deformation, sedimentation, magmatism, and hydrothermal fluid flow in overlying rocks to form mineral belts that contain ore deposits of different types and ages that are locally superimposed (demonstrating inheritance). Fluid flow in these systems also was influenced by the distribution of permeable lithologies and paleotopographic highs and lows. Hydrothermal fluids evolved from their initial chemistries towards compositions that reflect the ƒ O 2 and ƒ S 2 buffering capacity of, and the ligands and metals present in, the rocks (±older mineralization) through which they moved. In northern Nevada, where gold deposits are relatively common, carbonaceous, pyritic strata buffered fluids of diverse origins to H 2 S-rich compositions so they could transport gold repeatedly over Paleozoic-Cenozoic time (convergent evolution). Ore formed where metal-laden fluids encountered effective physicochemical traps. Maps of Neogene basin fill and erosion surfaces identify areas where preexisting ore deposits have been progressively exposed or concealed. Comparisons with analogous terrains and deposit types in other parts of the world provide global context. The initial findings and some of the databases, geologic maps, sections, reconstructions, hydrogeologic models, topical syntheses, regional overviews, short courses, field guides, and deposit comparisons produced by project staff and associated managers, contractors, and collaborators have been presented in numerous abstracts, symposia, USGS publications, and professional journals over the last 5 years (see the extensive bibliography). Notable among these was the 2005 Geological Society of Nevada symposium in Reno, Nevada, and the 2005 Geological Society of America annual meeting in Salt Lake City, Utah, where project results were presented to audiences from around the nation and world. The final results of the project will be submitted for publication in 2007 to appropriate USGS and professional journals. A special issue of GEOSPHERE, scheduled for publication in 2007, will be devoted to the results of this project and related work. This special issue will reach an international audience and be available worldwide on the internet. Much of the research for this project has concentrated on areas that will receive the focused attention of the mining industry in the future. As such, the data and interpretations generated by this project have direct use for land-use managers in Federal, State, and local agencies. Improved hydrogeologic models developed by this project will considerably enhance ongoing and future water resource investigations in the region. The increased understanding of when, where, and how hydrothermal systems produce significant economic deposits has direct uses for mineral exploration and for future USGS mineral resource assessments in the Great Basin and other parts of the world.

Great Basin↗
USGS1999

Geology of Unga Island and the northwestern part of Popof Island: Chapter 2 in A geological and geophysical study of the gold-silver vein system of Unga Island, Southwestern Alaska

The first geologic map of Unga Island was published by Atwood (1911; scale 1:250,000), who correctly inferred the middle Tertiary age of the volcanic rocks and made the important distinction between the lava flows and the intrusive domes. Although Burk's (1964) reconnaissance map of the Alaska Peninsula (scale 1:250,000) has been modified in some respects, it does correct Atwood's map by replacing the Kenai Formation on northwestern Unga Island with the Unga Conglomerate and by recognizing the older Stepovak Formation elsewhere on Unga and Popof Islands. U.S. Geological Survey (USGS) field studies that were focused on the mineral-resource potential of the Alaska Peninsula began in the late 1970's. These studies led to a geologic map of the Port Moller quadrangle--including Unga Island--at 1:250,000 scale (Wilson and others, 1995), as well as summaries of mineral occurrences and geochronological studies (Wilson and others, 1988, 1994) and a formal revision of the stratigraphic units of the Alaska Peninsula (Detterman and others, 1996). As follow-up to the regional studies, a detailed study of the vein systems on Unga Island was undertaken as a collaborative effort between USGS and private industry (White and Queen, 1989). The fieldwork leading to the present report and geologic map was started in 1978 (Riehle and others, 1982) and was completed as part of the vein study. The objective was a better understanding of the geologic setting of the vein systems: the geologic history of the host rocks, the structural controls on the veins, and the types of processes that likely caused the mineralization.

Alaska↗
USGS1992

The study of the undiscovered mineral resources of the Tongass National Forest and adjacent lands, Southeastern Alaska

The quantitative probabilistic assessment of the undiscovered mineral resources of the 17.1-million-acre Tongass National Forest (the largest in the United States) and its adjacent lands is a nonaggregated, mineral-resource-tract-oriented assessment designed for land-planning purposes. As such, it includes the renewed use of gross-in-place values (GIPV's) in dollars of the estimated amounts of metal contained in the undiscovered resources as a measure for land-use planning. Southeastern Alaska is geologically complex and contains a wide variety of known mineral deposits, some of which have produced important amounts of metals during the past 100 years. Regional geological, economic geological, geochemical, geophysical, and mineral exploration history information for the region was integrated to define 124 tracts likely to contain undiscovered mineral resources. Some tracts were judged to contain more than one type of mineral deposit. Each type of deposit may contain one or more metallic elements of economic interest. For tracts where information was sufficient, the minimum number of as-yet-undiscovered deposits of each type was estimated at probability levels of 0.95, 0.90, 0.50, 0.10, and 0.05. The undiscovered mineral resources of the individual tracts were estimated using the U.S. Geological Survey's MARK3 mineral-resource endowment simulator; those estimates were used to calculate GIPV's for the individual tracts. Those GIPV's were aggregated to estimate the value of the undiscovered mineral resources of southeastern Alaska. The aggregated GIPV of the estimates is $40.9 billion. Analysis of this study indicates that (1) there is only a crude positive correlation between the size of individual tracts and their mean GIPV's: and (2) the number of mineral-deposit types in a tract does not dominate the GIPV's of the tracts, but the inferred presence of synorogenic-synvolcanic nickel-copper, porphyry copper skarn-related, iron skarn, and porphyry copper-molybdenum deposits does. The influence of this study on the U.S. Forest Service planning process is yet to be determined. ?? 1992 Oxford University Press.

Nonrenewable Resources↗
USGS2015

Sample descriptions and geophysical logs for cored well BP-3-USGS, Great Sand Dunes National Park and Preserve, Alamosa County, Colorado

The BP-3-USGS well was drilled at the southwestern corner of Great Sand Dunes National Park in the San Luis Valley, south-central Colorado, 68 feet (ft, 20.7 meters [m]) southwest of the National Park Service’s boundary-piezometer (BP) well 3. BP-3-USGS is located at latitude 37°43ʹ18.06ʺN. and longitude 105°43ʹ39.30ʺW., at an elevation of 7,549 ft (2,301 m). The well was drilled through poorly consolidated sediments to a depth of 326 ft (99.4 m) in September 2009. Water began flowing from the well after penetrating a clay-rich layer that was first intercepted at a depth of 119 ft (36.3 m). The base of this layer, at an elevation of 7,415 ft (2,260 m) above sea level, likely marks the top of a regional confined aquifer recognized throughout much of the San Luis Valley. Approximately 69 ft (21 m) of core was recovered (about 21 percent), almost exclusively from clay-rich zones. Coarser grained fractions were collected from mud extruded from the core barrel or captured from upwelling drilling fluids. Natural gamma-ray, full waveform sonic, density, neutron, resistivity, spontaneous potential, and induction logs were acquired. The well is now plugged and abandoned. This report presents lithologic descriptions from the well samples and core, along with a compilation and basic data processing of the geophysical logs. The succession of sediments in the well can be generalized into three lithologic packages: (1) mostly sand from the surface to about 77 ft (23.5 m) depth; (2) interbedded sand, silt, and clay, decreasing in overall grain size downward, from 77 to 232 ft (23.5 to 70.7 m) depth; and (3) layers of massive clay alternating with layers of fine sand to silt from 232 to 326 ft (70.7 to 99.4 m), the total depth of the well. The topmost clay layers of the deepest package have a blue tint, prompting a correlation with the “blue clay” of the San Luis Valley that is commonly considered as the top of the confined aquifer. However, a confining clay was intercepted 113 ft (34.4 m) higher than the blue clay in BP-3-USGS. Most of the geophysical logs have good correspondence to the lithologic variations in the well. Exceptions are the gamma-ray log, which is likely affected by naturally occurring radiation from abundant volcanic detritus, and one interval within the deepest lithologic package, which appears to be abnormally electrically conductive. Resistivity logs and variations in sand versus clay content within the well are consistent with electrical resistivity models derived from time-domain electromagnetic geophysical surveys for the area. In particular, the topmost blue clay corresponds to a strong electrical conductor that is prominent in the electromagnetic geophysical data throughout the park and vicinity. BP-3-USGS was sited to test hypotheses developed from geophysical studies and to answer questions about the history and evolution of Pliocene and Pleistocene Lake Alamosa, which is represented by lacustrine deposits sampled by the well. The findings reported here represent a basis from which future studies can answer these questions and address other important scientific questions in the San Luis Valley regarding geologic history and climate change, groundwater hydrology, and geophysical interpretation.

Colorado↗
USGS2022

Revisions to the Virginia Coastal Plain hydrogeologic framework southwest of the James River

New drilling information reveals that altitudes of some hydrogeologic units of the Virginia Coastal Plain aquifer system differ by as much as 50 feet (ft) from those previously known, namely the Aquia and Potomac aquifers, the Potomac confining zone, and the Nanjemoy-Marlboro and Saint Marys confining units. In addition, the lateral margins of some hydrogeologic units are located as much as several miles from previously estimated locations. The largest revisions to unit margins were for the Aquia aquifer and the Nanjemoy-Marlboro and Saint Marys confining units. Interpretation of new geophysical logs, sediment core, and cuttings as well as revised interpretations to existing data indicate channels and embayments are also preserved on eroded top surfaces of the shallowest hydrogeologic units including the Yorktown confining zone, Yorktown-Eastover aquifer, Saint Marys confining unit, Potomac confining zone, and Potomac aquifer. Enhanced details on the configuration of part of the aquifer system southwest of the James River are provided by sediment cores and cuttings as well as geophysical logs from 36 recently drilled boreholes. These, along with reinterpretation of data from 93 preexisting boreholes, form the basis for revised top-surface altitudes and margins of hydrogeologic units beneath parts of Prince George, Surry, Sussex, Isle of Wight, and Southampton Counties and the cities of Franklin and Suffolk. Groundwater withdrawals in the Virginia Coastal Plain cause widespread water-level declines, create the potential for saltwater intrusion, and contribute to regionwide land subsidence. A description of the aquifer system, termed a hydrogeologic framework, was developed by the U.S. Geological Survey in 2006 and provides information needed to base withdrawal-permitting decisions by the Virginia Department of Environmental Quality. This revision of part of the hydrogeologic framework southwest of the James River is based on interpretations of both new and previously analyzed borehole data. The revision is strictly confined to the study area extent and hydrogeologic units not found within the study area were not revised and are not discussed in this report. The newly determined hydrogeologic-unit altitudes and margins have implications for groundwater-withdrawal permitting. New interpretations have found that the Yorktown Eastover aquifer is absent in the southwestern part of the City of Suffolk, owing to what is most likely an isolated area of sediment-texture facies change. Most notably, the top-surface altitudes of the Aquia and Potomac aquifers have been lowered by as much as 50 ft from previous interpretations. This means that wells previously believed to be screened in the top of the Potomac aquifer could, based on these new interpretations, be screened in the bottom of the Aquia aquifer. These changes to aquifers in which wells are screened means that there is potentially more room in the groundwater withdrawal permitting for the Potomac aquifer, the largest and most productive aquifer in Virginia, and overpumping occurring in the Aquia aquifer.

Virginia↗
USGS1996

Estimated depth to the water table and estimated rate of recharge in outcrops of the Chicot and Evangeline aquifers near Houston, Texas

In 1989, the U.S. Geological Survey, in cooperation with the Harris-Galveston Coastal Subsidence District, began a field study to determine the depth to the water table and to estimate the rate of recharge in outcrops of the Chicot and Evangeline aquifers near Houston, Texas. The study area comprises about 2,000 square miles of outcrops of the Chicot and Evangeline aquifers in northwest Harris County, Montgomery County, and southern Walker County. Because of the scarcity of measurable water-table wells, depth to the water table below land surface was estimated using a surface geophysical technique, seismic refraction. The water table in the study area generally ranges from about 10 to 30 foot below land surface and typically is deeper in areas of relatively high land-surface altitude than in areas of relatively low land- surface altitude. The water table has demonstrated no long-term trends since ground-water development began, with the probable exception of the water table in the Katy area: There the water table is more than 75 feet deep, probably due to ground-water pumpage from deeper zones. An estimated rate of recharge in the aquifer outcrops was computed using the interface method in which environmental tritium is a ground-water tracer. The estimated average total recharge rate in the study area is 6 inches per year. This rate is an upper bound on the average recharge rate during the 37 years 1953-90 because it is based on the deepest penetration (about 80 feet) of postnuclear-testing tritium concentrations. The rate, which represents one of several components of a complex regional hydrologic budget, is considered reasonable but is not definitive because of uncertainty regarding the assumptions and parameters used in its computation.

Texas↗
USGS2006

Spirit rover localization and topographic mapping at the landing site of Gusev crater, Mars

By sol 440, the Spirit rover has traversed a distance of 3.76 km (actual distance traveled instead of odometry). Localization of the lander and the rover along the traverse has been successfully performed at the Gusev crater landing site. We localized the lander in the Gusev crater using two-way Doppler radio positioning and cartographic triangulations through landmarks visible in both orbital and ground images. Additional high-resolution orbital images were used to verify the determined lander position. Visual odometry and bundle adjustment technologies were applied to compensate for wheel slippage, azimuthal angle drift, and other navigation errors (which were as large as 10.5% in the Husband Hill area). We generated topographic products, including 72 ortho maps and three-dimensional (3-D) digital terrain models, 11 horizontal and vertical traverse profiles, and one 3-D crater model (up to sol 440). Also discussed in this paper are uses of the data for science operations planning, geological traverse surveys, surveys of wind-related features, and other science applications.

Journal of Geophysical Research E: Planets↗
USGS1963

Natural radioactivity in Washington County, Maryland

Natural gamma- radioactivity patterns in Washington County , Maryland , reflect the principal variations in lithology. The highest radioactivity is associated with the more argillaceous parts of the geologic section and with soils derived from high-potassium carbonate rocks. Surface radiation intensity ranges from about 5 to 30 microroentgens per hour, of which the rocks contribute 30 to 90 percent. From the aerial survey data, the surface radiation intensity from extended sources can be estimated to within about three microroentgens per hour and the equivalent uranium content can be estimated to within approximately 5 ppm.

Maryland↗
USGS2007

Seismic Shear Wave Reflection Imaging at the Former Fort Ord, Monterey, California

At the former Fort Ord in Monterey County, California, contamination threatens an aquifer that provides drinking water for local communities. Assessment and remediation require accurate hydrological modeling, which in turn require a thorough understanding of aquifer stratigraphy. In order to help guide remediation efforts at the site, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, has undertaken seismic reflection surveys, testing compressional (P) and horizontally polarized shear (SH) waves. Sledgehammer-source SH data show reflections from interfaces up to approximately 60 m deep, which correspond with the major boundaries between aquifers and aquitards. In contrast, P-wave data show only the reflection from the water table at approximately 30 m depth. We collected SH data along two transects and processed these data to produce reflection images. The interpreted SH-wave images agree with available well information, constrain the geology for ground-water models, and provide guidance for future geophysical studies. These favorable results demonstrate the effectiveness of SH reflection methods for imaging unconsolidated aquifer layers at the former Fort Ord and at other sites with similar geologic conditions.

Open-File Report↗
USGS2014

Stitching the western Piedmont of Virginia: Early Paleozoic tectonic history of the Ellisville Pluton and the Potomac and Chopawamsic Terranes

The theme of the 2014 Virginia Geological Field Conference is the tectonic development, economic geology, and seismicity of the western Piedmont of Louisa County, Virginia. It is timely for the conference to turn its attention here, for during the past decade these aspects of western Piedmont geology have garnered the renewed attention of researchers. In terms of regional tectonics, it has been hypothesized that the major structure in the region, the Chopawamsic fault system, represents the most significant boundary in the Appalachian orogen, the main Iapetan suture (Hibbard et al., 2014). Economically, recent elevated market values of metals— particularly that of gold—has spurred reconsideration of the economic geology of the western Piedmont. Finally, the August 23, 2011, M5.8 earthquake, with its epicenter in our field area, startled the North American east coast and has revived awareness of the seismic potential of the region. This renewed interest in the geology of the western Piedmont of north-central Virginia has led to new detailed bedrock mapping, detailed surficial mapping, high-resolution UPb TIMS zircon geochronology, U-Pb LA-ICPMS detrital zircon geochronology, radiogenic isotope geochemistry, major/minor/REE geochemistry, and geophysical studies (e.g. Bailey et al., 2005, 2008; Bailey and Owens, 2012: Berti et al., 2012; Burton et al., 2014; Burton, in progress; Harrison, 2012; Horton et al., 2010, in press; Hughes, 2010, 2014; Hughes et al., 2013a, 2013b, 2014, in press a, in press b; Malenda, in progress; Owens et al., 2013; Spears and Gilmer 2012; Spears et al. 2013, Terblanche, 2013; Terblanche and Nance, 2012). A host of institutions have taken part in the research, including North Carolina State University, the Virginia Department of Mines, Minerals, and Energy, the U.S. Geological Survey, Virginia Tech, Lehigh University, and the College of William and Mary. Many of these investigations remain active. The majority of the data presented herein is the product of research conducted from 2010 to 2014 by geologists at North Carolina State University. This field trip guide is intended to complement a Geological Society of America field guide (Hughes et al., 2014) that covers the western Piedmont geology along strike to the northeast in the vicinity of Fredericksburg. Geologic mapping and geochronologic and geochemical sampling were coordinated between these two areas as part of a study funded in part by the National Science Foundation and the USGS EDMAP program. Some of the stops in this guide have previously been written up in past field guides (Hughes, 2010; Burton et al., 2014) and are reused here because of their ease of access for large groups and because of new data that update the context and our understanding of the outcrops.

Virginia↗
USGS2006

Applications of geophysical methods to volcano monitoring

The array of geophysical technologies used in volcano hazards studies - some developed originally only for volcano monitoring - ranges from satellite remote sensing including InSAR to leveling and EDM surveys, campaign and telemetered GPS networks, electronic tiltmeters and strainmeters, airborne magnetic and electromagnetic surveys, short-period and broadband seismic monitoring, even microphones tuned for infrasound. They include virtually every method used in resource exploration except large-scale seismic reflection. By “geophysical ” we include both active and passive methods as well as geodetic technologies. Volcano monitoring incorporates telemetry to handle high-bandwith cameras and broadband seismometers. Critical geophysical targets include the flux of magma in shallow reservoir and lava-tube systems, changes in active hydrothermal systems, volcanic edifice stability, and lahars. Since the eruption of Mount St. Helens in Washington State in 1980, and the eruption at Pu’u O’o in Hawai’i beginning in 1983 and still continuing, dramatic advances have occurred in monitoring technology such as “crisis GIS” and lahar modeling, InSAR interferograms, as well as gas emission geochemistry sampling, and hazards mapping and eruption predictions. The on-going eruption of Mount St. Helens has led to new monitoring technologies, including advances in broadband Wi-Fi and satellite telemetry as well as new instrumentation. Assessment of the gap between adequate monitoring and threat at the 169 potentially dangerous Holocene volcanoes shows where populations are dangerously exposed to volcanic catastrophes in the United States and its territories . This paper focuses primarily on Hawai’ian volcanoes and the northern Pacific and Cascades volcanoes. The US Geological Survey, the US National Park System, and the University of Utah cooperate in a program to monitor the huge Yellowstone volcanic system, and a separate observatory monitors the restive Long Valley caldera in collaboration with the US Forest Service.

Conference Paper↗
USGS2010

Western Mineral and Environmental Resources Science Center--providing comprehensive earth science for complex societal issues

Minerals in the environment and products manufactured from mineral materials are all around us and we use and come into contact with them every day. They impact our way of life and the health of all that lives. Minerals are critical to the Nation's economy and knowing where future mineral resources will come from is important for sustaining the Nation's economy and national security. The U.S. Geological Survey (USGS) Mineral Resources Program (MRP) provides scientific information for objective resource assessments and unbiased research results on mineral resource potential, production and consumption statistics, as well as environmental consequences of mining. The MRP conducts this research to provide information needed for land planners and decisionmakers about where mineral commodities are known and suspected in the earth's crust and about the environmental consequences of extracting those commodities. As part of the MRP scientists of the Western Mineral and Environmental Resources Science Center (WMERSC or 'Center' herein) coordinate the development of national, geologic, geochemical, geophysical, and mineral-resource databases and the migration of existing databases to standard models and formats that are available to both internal and external users. The unique expertise developed by Center scientists over many decades in response to mineral-resource-related issues is now in great demand to support applications such as public health research and remediation of environmental hazards that result from mining and mining-related activities. Western Mineral and Environmental Resources Science Center Results of WMERSC research provide timely and unbiased analyses of minerals and inorganic materials to (1) improve stewardship of public lands and resources; (2) support national and international economic and security policies; (3) sustain prosperity and improve our quality of life; and (4) protect and improve public health, safety, and environmental quality. The MRP supports approximately 40 USGS research specialists who utilize cooperative agreements with universities, industry, and other governmental agencies to support their collaborative research and information exchange. Scientists of the WMERSC study how and where non-fuel mineral resources form and are concentrated in the earth's crust, where mineral resources might be found in the future, and how mineral materials interact with the environment to affect human and ecosystem health. Natural systems (ecosystems) are complex - our understanding of how ecosystems operate requires collecting and synthesizing large amounts of geologic, geochemical, biologic, hydrologic, and meteorological information. Scientists in the Center strive to understand the interplay of various processes and how they affect the structure, composition, and health of ecosystems. Such understanding, which is then summarized in publicly available reports, is used to address and solve a wide variety of issues that are important to society and the economy. WMERSC scientists have extensive national and international experience in these scientific specialties and capabilities - they have collaborated with many Federal, State, and local agencies; with various private sector organizations; as well as with foreign countries and organizations. Nearly every scientific and societal challenge requires a different combination of scientific skills and capabilities. With their breadth of scientific specialties and capabilities, the scientists of the WMERSC can provide scientifically sound approaches to a wide range of societal challenges and issues. The following sections describe examples of important issues that have been addressed by scientists in the Center, the methods employed, and the relevant conclusions. New directions are inevitable as societal needs change over time. Scientists of the WMERSC have a diverse set of skills and capabilities and are proficient in the collection and integration of

Circular↗
USGS2016

Altitudes and thicknesses of hydrogeologic units of the Ozark Plateaus aquifer system in Arkansas, Kansas, Missouri, and Oklahoma

A hydrogeologic framework was constructed to represent the altitudes and thicknesses of hydrogeologic units within the Ozark Plateaus aquifer system as part of a regional groundwater-flow model supported by the U.S. Geological Survey Water Availability and Use Science Program. The Ozark Plateaus aquifer system study area is nearly 70,000 square miles and includes parts of Arkansas, Kansas, Missouri, and Oklahoma. Nine hydrogeologic units were selected for delineation within the aquifer system and include the Western Interior Plains confining system, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, which was divided into the upper, middle, and lower Ozark aquifers to better capture the spatial variation in the hydrologic properties, the St. Francois confining unit, the St. Francois aquifer, and the basement confining unit. Geophysical and well-cutting logs, along with lithologic descriptions by well drillers, were compiled and interpreted to create hydrologic altitudes for each unit. The final compiled dataset included more than 23,000 individual altitude points (excluding synthetic points) representing the nine hydrogeologic units within the Ozark Plateaus aquifer system.

Arkansas, Kansas, Missouri, Oklahoma↗
USGS2018

Analysis ready data: Enabling analysis of the Landsat archive

Data that have been processed to allow analysis with a minimum of additional user effort are often referred to as Analysis Ready Data (ARD). The ability to perform large scale Landsat analysis relies on the ability to access observations that are geometrically and radiometrically consistent, and have had non-target features (clouds) and poor quality observations flagged so that they can be excluded. The United States Geological Survey (USGS) has processed all of the Landsat 4 and 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) archive over the conterminous United States (CONUS), Alaska, and Hawaii, into Landsat ARD. The ARD are available to significantly reduce the burden of pre-processing on users of Landsat data. Provision of pre-prepared ARD is intended to make it easier for users to produce Landsat-based maps of land cover and land-cover change and other derived geophysical and biophysical products. The ARD are provided as tiled, georegistered, top of atmosphere and atmospherically corrected products defined in a common equal area projection, accompanied by spatially explicit quality assessment information, and appropriate metadata to enable further processing while retaining traceability of data provenance.

Remote Sensing↗
USGS2004

Results of Electrical Resistivity Data Collected near the Town of Guernsey, Platte County, Wyoming

As part of a study to investigate subsurface geologic conditions as they relate to ground-water flow in an abandoned landfill near the town of Guernsey, Wyoming, geophysical direct current (DC) resistivity data were collected. Eight vertical resistivity soundings and eight horizontal resistivity profiles were made using single channel and multi-channel DC instruments. Data collected in the field were converted from apparent resistivity to inverted resistivity with depth using a numerical inversion of the data. Results of the inverted resistivity data are presented as horizontal profiles and as profiles derived from the combined horizontal profile and vertical sounding data. The data sets collected using the single-channel and multi-channel DC systems provided for the resistivity investigation to extend to greater depth. Similarity of the electrical properties of the bedrock formations made interpretation of the resistivity profiles more difficult. High resistivity anomalies seen in the profiles are interpreted as quartzite lenses and as limestone or metadolomite structures in the eastern part of the study area. Terrace gravels were mapped as resistive where dry and less resistive in the saturated zone. The DC resistivity methods used in this study illustrate that multi-electrode DC resistivity surveying and more traditional methodologies can be merged and used to efficiently map anomalies of hydrologic interest in geologically complex terrain.

Open-File Report↗
USGS2015

Hexavalent and total chromium at low reporting concentrations in source-water aquifers and surface waters used for public supply in Illinois, 2013

On the basis of their recent review of the human health effects of hexavalent chromium [Cr(VI)] in public drinking water, the U.S. Environmental Protection Agency is considering the need for Federal regulation of Cr(VI). Presently, only total chromium is regulated, at a Maximum Contaminant Level (MCL) of 100 micrograms per liter (µg/L). The occurrence of Cr(VI) in groundwater and surface waters generally is attributed to industrial sources, but can be of natural origin. California’s recently established MCL for Cr(VI) of 10 µg/L illustrates the drinking-water concerns associated with Cr(VI). To improve understanding of the possible impact of a Cr(VI)-specific standard that approximates the California level on the management of Illinois’ public drinking water, the U.S. Geological Survey, in cooperation with the Illinois Environmental Protection Agency, assessed the occurrence and distribution of Cr(VI) in the State’s public-water supplies. During 2013, untreated water samples were collected to be analyzed for Cr(VI) and total chromium [Cr(T)] at 119 water-supply wells and 32 surface-water intakes; also, 32 treated surface-water samples were collected near the point of treatment and 32 near the furthest point of distribution. Public-supply sample sites were selected by a stratified random method. Samples typically were analyzed within 24 hours of collection at reporting limits of 0.02 µg/L for Cr(VI) and 0.1 µg/L for Cr(T). The occurrence of Cr(VI) was compared with selected geophysical, physical, and sampling factors that might more fully explain its distribution and magnitude of concentrations. The maximum concentration of Cr(VI) in groundwater was 2.1 µg/L. Maximum concentrations in untreated and treated surface water were 0.29 µg/L and 2.4 µg/L, respectively. All sample concentrations were below the California MCL; only 35 percent were below that State’s non-enforceable public health goal of 0.02 of µg/L. Cr(VI) was undetected in 43 percent of untreated groundwater samples, with a median of 0.06 µg/L when detected. All but two (94 percent) of untreated surface-water samples had detections. In untreated surface water, the median concentration was 0.09 µg/L, whereas in treated (tap and distributed) water the median was 0.20 µg/L. Surface waters treated with lime for softening typically had the greatest Cr(VI) concentrations (maximum, 2.4 µg/L; median, 1.2 µg/L). The maximum concentration of Cr(T) in groundwater was 1.8 µg/L. Maximum concentrations in untreated and treated surface water were 1.8 µg/L and 2.5 µg/L, respectively. All sample concentrations were below the Federal MCL. Total chromium was detected in 65 percent of untreated groundwater samples, with a median of 0.40 µg/L, when detected. All but one (97 percent) of untreated surface-water samples had detections. In untreated surface water, the median concentration was 0.40 µg/L, whereas in treated (tap and distributed) water the median was 0.30 µg/L. As with Cr(VI), surface waters treated with lime typically had the greatest Cr(T) concentrations. Examination of factors that might account for or be associated with the occurrence of Cr(VI) in public-supply source waters found few clearly evident factors. Associations in frequencies of occurrence and range of concentrations indicate that surface waters and groundwaters of shallow, unconsolidated, unconfined aquifers, particularly alluvial aquifers, are possibly most commonly affected by anthropogenic sources of Cr(VI). Groundwaters of deep (greater than 500 feet) bedrock aquifers, particularly the Cambrian-Ordovician aquifer system, are possibly most commonly affected by geologic sources of Cr(VI). Additional study, with supporting geologic and geochemical data that were not collected in this study, would be necessary to verify these associations. There was a weak positive relation (ρ = 0.23) between concentrations of Cr(VI) and Cr(T) in untreated water samples, with a much stronger positive relation (ρ = 0.86 and ρ = 0.90, respectively) in samples collected soon after treatment and near the endpoint of distribution. The stronger relation and greater similarity between Cr(VI) and Cr(T) concentrations in treated water samples indicate that Cr(VI) represents a greater proportion of the measured concentrations of Cr(T) in treated waters than in untreated waters. The analysis of spikes and other quality-assurance samples indicate uncertainties associated with obtaining or confirming consistently accurate analytical results for Cr(VI) at near the applied reporting limit of 0.02 µg/L.

Illinois↗
USGS2015

Hydrogeologic data and water-quality data from a thick unsaturated zone at a proposed wastewater-treatment facility site, Yucca Valley, San Bernardino County, California, 2008-11

The Hi-Desert Water District, in the community of Yucca Valley, California, is considering constructing a wastewater-treatment facility and using the reclaimed water to recharge the aquifer system through surface spreading. The Hi-Desert Water District is concerned with possible effects of this recharge on water quality in the underlying groundwater system; therefore, an unsaturated-zone monitoring site was constructed by the U.S. Geological Survey (USGS) to characterize the unsaturated zone, monitor a pilot-scale recharge test, and, ultimately, to monitor the flow of reclaimed water to the water table once the treatment facility is constructed. In June and July 2008, a borehole (YVUZ-5) was drilled by the USGS through the unsaturated zone in the vicinity of the proposed wastewater-treatment facility site by using an overburden drilling method. In addition to a variety of unsaturated-zone instrumentation, an observation well screened near the water table was installed in the borehole. The drilling procedures, lithologic and geophysical data, construction details, physical properties of unsaturated alluvial deposits, and instrumentation installed in YVUZ-5 are described in this report. Core material was analyzed for bulk-density, porosity, effective porosity, volumetric water content, residual water content, saturation, effective saturation, matric-potential, and saturated hydraulic conductivity. Concentrations of soluble anions, including bromide, chloride, fluoride, sulfate, nitrate, nitrite, phosphate, and orthophosphate, in unsaturated-zone sediment and dissolved in unsaturated-zone water were determined by analyzing water extracted from drill-cutting material. A 0.1-acre pilot-scale infiltration pond was constructed in the vicinity of YVUZ-5. Water was applied to the pond over a period of about 8 months and allowed to infiltrate into the underlying unsaturated zone. Data were collected on chemical and isotopic composition of the groundwater, unsaturated-zone water, and infiltration pond water before, during, and after infiltration of water from the constructed pond. Selected drill cuttings and core samples collected during drilling were analyzed for the presence or absence of denitrifying and nitrate-reducing bacteria. Water levels in the observation well ranged from about 367 to 370 feet below land surface during the period of the study. Measured saturated hydraulic conductivity of core material ranged from 2.1 to 11.0 feet per day. Average vertical infiltration rates in the pilot-scale infiltration pond ranged from 0.7 to 2.4 feet per day. Both denitrifying and nitrate-reducing bacteria were present in drill cutting material in most probable numbers ranging from below detection limits to 2,400,000 for denitrifying and to 93,000 for nitrate-reducing bacteria.

California↗
USGS2013

Borehole geophysical, fluid, and hydraulic properties within and near the freshwater/saline-water transition zone, San Antonio segment of the Edwards aquifer, south-central Texas, 2010-11

The freshwater zone of the San Antonio segment of the Edwards aquifer is used by residents of San Antonio and numerous other rapidly growing communities in south-central Texas as their primary water supply source. This freshwater zone is bounded to the south and southeast by a saline-water zone with an intermediate zone transitioning from freshwater to saline water (transition zone). As demands on this water supply increase, there is concern that the transition zone could potentially move, resulting in more saline water in current freshwater supply wells. Since 1985, the U.S. Geological Survey, San Antonio Water System, and other Federal and State agencies have conducted studies to better understand the transition zone.

Texas↗