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USGS2007

Selected Hydrogeologic Data for the High Plains Aquifer in Southwestern Laramie County, Wyoming, 1931-2006

The U.S. Geological Survey, in cooperation with the Wyoming State Engineer's Office, created a hydrogeologic database for southwestern Laramie County, Wyoming. The database contains records from 166 wells and test holes drilled during 1931-2006. Several types of information, including well construction; well or test hole locations; lithologic logs; gamma, neutron, spontaneous-potential, and single-point resistivity logs; water levels; and transmissivities and storativities estimated from aquifer tests, are available in the database. Most wells and test holes in the database have records containing information about construction, location, and lithology; 77 wells and test holes have geophysical logs; 70 wells have tabulated water-level data; and 60 wells have records of aquifer-test results.

Open-File Report↗

USGS2011

Kirschenmann Road multi-well monitoring site, Cuyama Valley, Santa Barbara County, California

The U.S. Geological Survey (USGS), in cooperation with the Water Agency Division of the Santa Barbara County Department of Public Works, is evaluating the geohydrology and water availability of the Cuyama Valley, California (fig. 1). As part of this evaluation, the USGS installed the Cuyama Valley Kirschenmann Road multiple-well monitoring site (CVKR) in the South-Main subregion of the Cuyama Valley (fig. 1). The CVKR well site is designed to allow for the collection of depth-specific water-level and water-quality data. Data collected at this site provides information about the geology, hydrology, geophysics, and geochemistry of the local aquifer system, thus, enhancing the understanding of the geohydrologic framework of the Cuyama Valley. This report presents the construction information and initial geohydrologic data collected from the CVKR monitoring site, along with a brief comparison to selected supply and irrigation wells from the major subregions of the Cuyama Valley (fig. 1).

California↗

USGS2014

Time-domain electromagnetic surveys at Fort Irwin, San Bernardino County, California, 2010–12

Between 2010 and 2012, a total of 79 time-domain electromagnetic (TEM) soundings were collected in 12 groundwater basins in the U.S. Army Fort Irwin National Training Center (NTC) study area to help improve the understanding of the hydrogeology of the NTC. The TEM data are discussed in this chapter in the context of geologic observations of the study area, the details of which are provided in the other chapters of this volume. Selection of locations for TEM soundings in unexplored basins was guided by gravity data that estimated depth to pre-Tertiary basement complex of crystalline rock and alluvial thickness. Some TEM data were collected near boreholes with geophysical logs. The TEM response at locations near boreholes was used to evaluate sounding data for areas without boreholes. TEM models also were used to guide site selection of subsequent boreholes drilled as part of this study. Following borehole completion, geophysical logs were used to ground-truth and reinterpret previously collected TEM data. This iterative process was used to site subsequent TEM soundings and borehole locations as the study progressed. Although each groundwater subbasin within the NTC boundaries was explored using the TEM method, collection of TEM data was focused in those basins identified as best suited for development of water resources. At the NTC, TEM estimates of some lithologic thicknesses and electrical properties in the unsaturated zone are in good accordance with borehole data; however, water-table elevations were not easily identifiable from TEM data.

California↗

USGS1979

An experimental ground-magnetic and VLF-EM traverse over a buried paleochannel near Salisbury, Maryland

Since, 1963, the Maryland Geological Survey and the U.S. Geological Survey have been engaged in a study of the Pleistocene Series beneath a 230 square kilometer area around Salisbury, Maryland. (Hansen, 1966; Weigle, 1972; Zohdy and others, 1974, p.56) North of Salisbury a deep Pleistocene paleochannel was discovered; this channel was carved into an erosional plain at the top of the Miocene deposit, was filled and blanketed subsequently with deposits (mostly sand and gravel) of Pleistocene age. The channel is a prolific source of ground water, and has been outlined for a least 15 kilometers by means of power-augering and gamma-logging. A geophysical survey using ground magnetics and VLF-EM was made over the channel in an attempt to see if a more efficient method than augering could be developed to map the paleochannel at depth; the survey traverse was made over one of the better defined parts of the paleochannel (see figure 1.) where airborne magnetics and VLF studies could easily be done as a potential follow-up. We hoped to be able to map resistivity changes between aquifer and aquiclude facies with the VLF-EM, and perhaps identify other facies changes in black-sand concentrations with ground magnetics. The data is presented in Table 1 and plotted in figure 2. The traverse extended from north to south, with station spacing of 100 meters, for an over all length of 4.5 kilometers.

Maryland↗

USGS2021

Hydrogeology and gain/loss assessment of two lakes contaminated with per- and polyfluoroalkyl substances, vicinity of Joint Base McGuire-Dix-Lakehurst, New Jersey, 2020–21

Per- and polyfluoroalkyl substances (PFAS) have been identified in two lakes near Joint Base McGuire-Dix-Lakehurst (JBMDL) in New Jersey—Little Pine Lake in Pemberton Township and Pine Lake in Manchester Township. The streams that enter these lakes begin in or near JBMDL where sources of PFAS contamination are located. The U.S. Geological Survey, in cooperation with the U.S. Air Force Civil Engineer Center, performed a study of the hydrogeology and the gaining or losing conditions associated with these lakes. Hydrogeologic characteristics in the vicinity of both lakes were assessed using qualitative vertical hydraulic profiling of the subsurface. Groundwater was pumped from test intervals at various depths below land surface, then groundwater levels were measured until they recovered to static conditions. Low permeability aquifer intervals were identified within the aquifer underlying both lakes, consistent with silty and (or) clayey subunits of the Kirkwood-Cohansey aquifer system indicated on geophysical and lithologic logs. Gaining or losing conditions between groundwater and lake surface water were assessed with continuous monitoring of water levels and temperature in the lakes and in three piezometers per lake screened at different depths in the underlying aquifer from August 2020 through May 2021. At Little Pine Lake, surface water levels were consistently lower than groundwater levels, which is indicative of a gaining condition with groundwater flowing into the lake. Gaining conditions also support the lack of diurnal temperature fluctuations observed in groundwater, but poor response of surface-water temperature prevents complete analysis. The potential for losing conditions at other locations around Little Pine Lake necessitates further assessment in regard to possible PFAS contamination of groundwater in the underlying aquifer. Temperature results were inconclusive at Pine Lake, but surface water levels were consistently higher than groundwater levels throughout the monitoring period, which indicates a losing condition with lake water flowing into the underlying aquifer. Because of the downward vertical hydraulic gradient identified at Pine Lake, there is a strong possibility that PFAS in the lake water has also contaminated groundwater in its vicinity.

New Jersey↗

USGS2014

Methane hydrates in nature - Current knowledge and challenges

Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

Journal of Chemical and Engineering Data↗

USGS2008

Digital surfaces and thicknesses of selected hydrogeologic units within the Mississippi Embayment Regional Aquifer Study (MERAS)

Digital surfaces of selected Tertiary and younger age hydrogeologic units within the Mississippi embayment aquifer system were created using more than 2,600 geophysical logs for an area that covers approximately 70,000 square miles and encompasses parts of eight states. The digital surfaces were developed to define and display the hydrogeologic framework for the Mississippi Embayment Regional Aquifer Study (MERAS). The digital surfaces also provide a foundation of the selected hydrogeologic units for development of a steady-state and transient regional ground-water flow model of the Mississippi embayment aquifer system from the top of the Midway confining unit upwards to land surface. The ground-water flow model is under development as part of the U.S. Geological Survey Ground-Water Resources Program. Using a Geographic Information System, nine digital surfaces of the tops of selected hydrogeologic units were created using the Australian National University Digital Elevation Model method as an interpolation scheme. Thickness maps also were constructed using the Geographic Information System by calculating the difference between the altitude of the interpreted base of an overlying unit and the altitude of the interpreted top of an underlying unit. In general, the highest hydrogeologic unit altitudes are located along the eastern edge of the study area in the outcrop, and the lowest altitudes, in general, are located along the southern edge of the study area along the axis of the embayment. The Mississippi River Valley alluvial aquifer and the lower Claiborne aquifer are the thinnest aquifers of importance in the study area; the thickest aquifer of importance is the middle Claiborne aquifer.

Mississippi Embayment Regional Aquifer↗

USGS2004

Hydrogeologic characteristics of four public drinking-water supply springs in northern Arkansas

In October 2000, a study was undertaken by the U.S. Geological Survey (USGS) in cooperation with the Arkansas Department of Health to determine the hydrogeologic characteristics, including the extent of the recharge areas, for Hughes Spring, Stark Spring, Evening Shade Spring, and Roaring Spring, which are used for public-water supply in northern Arkansas. Information pertaining to each spring can be used to enable development of effective management plans to protect these water resources and public health. An integrated approach to determine the ground-water characteristics and the extent of the local recharge areas of the four springs incorporated tools and methods of hydrology, structural geology, geomorphology, geophysics, and geochemistry. Analyses of discharge, temperature, and water quality were completed to describe ground-water flow characteristics, source-water characteristics, and connectivity of the ground-water system with surface runoff. Water-level contour maps were constructed to determine ground-water flow directions and ground-water tracer tests were conducted to determine the extent of the recharge areas and ground-water flow velocities. Hughes Spring supplies water for the city of Marshall, Arkansas, and the surrounding area. The mean annual discharge for Hughes Spring was 2.9 and 5.2 cubic feet per second for water years 2001 and 2002, respectively. Recharge to the spring occurs mainly from the Boone Formation (Springfield Plateau aquifer). Ground-water tracer tests indicate the recharge area for Hughes Spring generally coincides with the surface drainage area (15.8 square miles) and that Hughes Spring is connected directly to the surface flow in Brush Creek. The geochemistry of Hughes Spring demonstrated variations with flow conditions and the influence of surface-runoff in the recharge area. Calcite saturation indices, total dissolved solids concentrations, and hardness demonstrate noticeable differences with flow conditions reflecting the reduced residence time and interaction of water with the source rock within the ground-water system at higher discharges for Hughes Spring. Concentrations of fecal indicator bacteria also demonstrated a substantial increase during high-flow conditions, suggesting that a non-point source of bacteria possibly from livestock may enter the system. Conversely, nutrient concentrations did not vary with flow and were similar to concentrations reported for undeveloped sites in the Springfield Plateau and Ozark aquifers in northern Arkansas and southern Missouri. Deuterium and oxygen-18 data show that the Hughes Spring discharge is representative of direct precipitation and not influenced by water enriched in oxygen-18 through evaporation. Discharge data show that Hughes Spring is dominated by conduit type ground-water flow, but a considerable component of diffuse flow also exists in the ground-water system. Carbon-13 data indicate a substantial component of the recharge water interacts with the surface material (soil and regolith) in the recharge area before entering the ground-water system for Hughes Spring. Tritium data for Hughes Spring indicate that the discharge water is a mixture of recent recharge and sub-modern water (recharged prior to 1952). Stark Spring supplies water for the city of Cushman, Arkansas, and the surrounding area. 2 Hydrogeologic Characteristics of Four Public Drinking-Water Supply Springs in Northern Arkansas The mean annual discharge for Stark Spring was 0.5 and 1.5 cubic feet per second for water years 2001 and 2002, respectively. The discharge and water-quality data show the ground-water system for Stark Spring is dominated by rapid recharge from surface runoff and mainly consists of a conduit- type flow system with little diffuse-type flow. Analyses of discharge data show that the estimated recharge area (0.79 square mile) is larger than the surface drainage area (0.34 square mile). Ground-water tracer tests and the outcrop of the

Water-Resources Investigations Report↗

USGS2000

New 40Ar/39Ar age of the Bishop Tuff from multiple sites and sediment rate calibration for the Matuyama-Brunhes boundary

Precise dating of sanidine from proximal ash flow Bishop Tuff and air fall Bishop pumice and ash, California, can be used to derive an absolute age of the Matuyama Reversed-Brunhes Normal (M-B) paleomagnetic transition, identified stratigraphically close beneath the Bishop Tuff and ash at many sites in the western United States. An average age of 758.9±1.8 ka, standard error of the mean (SEM), was obtained for individual sanidine crystals or groups of several crystals, determined from ∼70 individual analyses of sanidine separates from 11 sample groups obtained at five localities. The basal air fall pumice (757.7±1.8 ka) and overlying ash flow tuff (762.2±4.7 ka) from near the source yield essentially the same dates within errors of analysis, suggesting that the two units were emplaced close in time. A date on distal Bishop air fall ash bed at Priant, California, ∼100 km to the west of the source area, is younger, 750.1±4.3 ka, but not significantly different within analytical error (±1 standard deviation). Previous dates of the Bishop Tuff, obtained by others using conventional K-Ar and the fission track method on zircons, ranged from ∼650 ka to ∼1.0 Ma. The most recent, generally accepted date by the K-Ar method on sanidine was 738±3 ka. We infer, as others before, that many K-Ar dates on sanidine feldspar are too young owing to incomplete degassing of radiogenic Ar during fusion in the K-Ar technique and that many older K-Ar dates are too old owing to detrital or xenocrystic contamination in the larger samples that are necessary for the technique. The new dates are similar to recent 40Ar/39Ar ages of the Bishop Tuff determined on individual samples by others but are derived from a larger proximal sample population and from multiple analysis of each sample. The results provide a definitive and precise age calibration of this widespread chronostratigraphic marker in the western United States and northeastern Pacific Ocean. We calculated the age of the M-B transition at five sites, assuming constant sedimentation rates, the age of the Bishop ash bed and one or more well-dated chronostratigraphic horizons above and below the Bishop Tuff ash bed and M-B transition, and stratigraphic separations between these datum levels. The age of the M-B transition is 774.2±2.8 ka, based on the average of eight such calculations, close to other recent determinations, and similar to that determined from the astronomically tuned polarity timescale. Our approach provides an alternative and surprisingly precise method for determining the age of the M-B and other chronostratigraphic levels. The above dates, calculated using U.S. Geological Survey values of 27.92 Ma for the Taylor Creek (TC) sanidine can be recalculated to other widely used values for these monitors. For example, using recently published values of 28.34 Ma (TC) and 523.1 Ma (McLure Mountain hornblende, MMhb-1), the resulting ages are ∼774 ka for the Bishop Tuff and ash bed and ∼789 ka for the M-B transition.

California↗

USGS2005

Generation and verification of theoretical rating curves in the Whitewater River basin, Kansas

[1] A new method for generating stage-discharge relations (rating curves) for geomorphically stable channels is presented and applied to two streams in the Whitewater River basin, Kansas. The approach converts measurements of stage into discharge using a fluid mechanically based model. The model does not use empirical roughness coefficients, such as Manning coefficients, but rather determines channel roughness from field measurements of the (1) channel geometry, (2) the physical roughness of the bed, banks, and floodplain, and (3) the vegetation density on the banks and floodplain. These measurements are used to calculate explicitly the drag on the small-scale topographic features on the boundary, the drag on the stems and branches of woody vegetation, and the friction on the bed, banks, and floodplain. The theoretical rating curves produced by the model for two study reaches, which are near U.S. Geological Survey (USGS) streamflow-gauging stations, are in good agreement with direct measurements of discharge made by the USGS. Our method has the potential of providing accurate estimates of stream flows less expensively than conventional gauging methods. In addition, the method can be used to obtain more accurate discharge estimates than conventional indirect methods for determining discharge, which are based on estimates of Manning's coefficient.

Journal of Geophysical Research F: Earth Surface↗

USGS2007

Mount St. Helens Petrology Workshop

Following seismic activity in late September 2004, the current eruption of Mount St. Helens began with an explosive steam and ash emission on 1 October 2004, with hot dacite emerging from the crater floor on 11 October 2004. Nearly two years later, with more than 80 million cubic meters of erupted dacite, accompanied by rare explosions and predominantly shallow seismicity questions still remain about what initiated and what is sustaining the eruption. The U.S. Geological Survey's (USGS) Cascade Volcano Observatory (CVO) hosted the 2006 Mount St. Helens Petrology Workshop in Vancouver, Wash., on 27–30 August 2006. With many of the more than 40 workshop participants finalizing contributions to a USGS Professional Paper on the current Mount St. Helens eruption, the workshop was a timely opportunity to share results, reconcile interpretations, and plan future research.

Washington↗

USGS2014

Porphyry copper assessment of eastern Australia

The U.S. Geological Survey (USGS) conducts national and global assessments of resources (mineral, energy, water, and biologic) to provide science in support of decision making. Mineral resource assessments provide syntheses of available information about where mineral deposits are known and suspected to occur in the Earth’s crust and which commodities may be present, together with estimates of amounts of resources that may be present in undiscovered deposits. The USGS collaborated with geologists of the Geological Survey of New South Wales and Geoscience Australia (formerly the Australian Geological Survey Organisation) on an assessment of Phanerozoic-age porphyry copper resources in Australia. Porphyry copper deposits contain about 11 percent of the identified copper resources in Australia. This study addresses resources of known porphyry copper deposits and expected resources of undiscovered porphyry copper deposits in eastern Australia. A three-part form of assessment was used for estimation of undiscovered resources. Using this method, four tracts were delineated that are permissive for porphyry copper deposits. A probabilistic estimate of the expected number of deposits in each tract was prepared on the basis of existing information about geology, geochemistry, geophysics, exploration history, and mineral occurrences. Monte Carlo simulation was used to combine the estimated number of deposits with an appropriate model of grade and tonnage for porphyry copper deposits to provide a probabilistic estimate of metal content and total tonnage for undiscovered deposits. The Delamerian permissive tract comprises igneous rocks of Cambrian age in the Delamerian Orogen, which borders the western margin of the Tasmanides. The Delamerian tract contains no known porphyry copper deposits, but the Adelaide sub-tract, one of three sub-tracts that compose the Delamerian tract, contains four porphyry copper prospects. The Adelaide sub-tract is estimated to contain 2.5±2.2 undiscovered deposits in an area of about 50,700 square kilometers. The Macquarie permissive tract comprises volcanic, volcaniclastic, and minor exposed intrusive igneous rocks of the Macquarie Arc. The nine known deposits in this tract are now estimated to contain a total of about 13.5 million metric tons of copper and 1,700 metric tons of gold. This tract is estimated to contain 6.9±3.5 undiscovered deposits for a total of about 16 deposits in an area of about 41,500 square kilometers. The Yeoval permissive tract includes subequal areas of permissive volcanic and intrusive rocks of Silurian to Devonian age exposed in and around the Cowra-Buchan Rift System, which overlaps the previously accreted Macquarie Arc. The Yeoval tract contains one porphyry copper deposit and several porphyry copper prospects. This tract is estimated to contain 1.3±0.75 undiscovered porphyry copper deposits, for a total of about 2 expected deposits in an area of about 53,200 square kilometers. The East Tasmanide permissive tract includes a semi-continuous belt of plutonic and subordinate volcanic rocks along the eastern margins of Queensland and northeastern New South Wales. The East Tasmanide tract contains 14 known porphyry copper deposits and many porphyry copper prospects, which are all in the Central sub-tract. This sub-tract is expected to contain 4.8±3.3 undiscovered porphyry copper deposits, for a total of about 19 deposits in an area of about 291,000 square kilometers. This assessment estimates that 15 undiscovered deposits contain an arithmetic mean of ~21 million metric tons or more of copper in four tracts, in addition to the 24 known porphyry copper deposits that contain identified resources of ~16 million metric tons of copper. In addition to copper, the mean expected amount of undiscovered byproduct gold predicted by the simulation is ~1,500 metric tons. The probability associated with these arithmetic means is on the order of 30 percent. Median expected amounts of metals predicted by the simulations may be ~50 percent lower than mean estimates.

Scientific Investigations Report↗

USGS1984

U. S. GEOLOGICAL SURVEY'S RESEARCH PROGRAM IN THE NEWLY PROCLAIMED EXCLUSIVE ECONOMIC ZONE.

The U. S. Geological Survey (USGS) has been developing a program which would emphasize broad-scale surveys of the continental margin and intensive studies of 'baseline corridors' in various areas of the U. S. EEZ to gather energy and mining information in this new frontier as quickly as possible. Of twelve baseline corridors identified to date along the east and west coasts and the Gulf of Mexico, the highest priority would be placed on areas off the west coast, including Juan De Fuca and Gorda Ridges and off Hawaii. Each corridor assessment will involve collection of multi-channel and high resolution geophysical data, bottom relief and sampling, and production of reports and cartographic products displaying the scientific findings of the assessments.

Conference Paper↗

USGS2011

Challenges of using electrical resistivity method to locate karst conduits-A field case in the Inner Bluegrass Region, Kentucky

Conduits serve as major pathways for groundwater flow in karst aquifers. Locating them from the surface, however, is one of the most challenging tasks in karst research. Geophysical methods are often deployed to help locate voids by mapping variations of physical properties of the subsurface. Conduits can cause significant contrasts of some physical properties that can be detected; other subsurface features such as water-bearing fractures often yield similar contrasts, which are difficult to distinguish from the effects of the conduits. This study used electrical resistivity method to search for an unmapped karst conduit that recharges Royal Spring in the Inner Bluegrass karst region, Kentucky, USA. Three types of resistivity techniques (surface 2D survey, quasi-3D survey, and time-lapse survey) were used to map and characterize resistivity anomalies. Some of the major anomalies were selected as drilling targets to verify the existence of the conduits. Drilling near an anomaly identified by an electrical resistivity profile resulted in successful penetration of a major water-filled conduit. The drilling results also suggest that, in this study area, low resistivity anomalies in general are associated with water-bearing features. However, differences in the anomaly signals between the water-filled conduit and other water-bearing features such as water-filled fracture zones were undistinguishable. The electrical resistivity method is useful in conduit detection by providing potential drilling targets. Knowledge of geology and hydrogeology about the site and professional judgment also played important roles in locating the major conduit. ?? 2011 Elsevier B.V.

Journal of Applied Geophysics↗

USGS2024

Hydrologic investigations and a preliminary conceptual model of the groundwater system at North Penn Area 1 Superfund Site, Souderton, Montgomery County, Pennsylvania

The U.S. Geological Survey (USGS) conducted hydrogeologic investigations, reviewed existing data, and developed a preliminary conceptual model of the groundwater system as part of technical support of the U.S. Environmental Protection Agency (EPA) at the North Penn Area 1 Superfund Site (hereafter, the NP1 Site) located within the Borough of Souderton in Montgomery County, Pennsylvania. Field work and monitoring took place during 2012–18. The area is underlain by sedimentary formations that form a fractured-rock aquifer used for drinking water and industrial supply. The EPA placed the Site on the National Priorities List in 1989, identifying tetrachloroethylene (PCE) and trichloroethylene (TCE) as contaminants of concern. During 2012–18, the USGS conducted field activities that included drilling an 82-foot (ft)-deep monitoring well (MG 2220) in 2016, reconstructing a 208-ft-deep former industrial production well (MG 668 [Granite Knitting Mill]), and collecting borehole geophysical and video logs and water levels from those and five additional wells, which ranged in depth from about 50 to 200 ft below land surface. Continuous water levels were collected during 2014–17, and a synoptic set of water levels were measured in April 2018 in the seven wells. The borehole geophysical logs (caliper, acoustic televiewer, natural gamma, single-point resistance, vertical flow, and fluid temperature and resistivity) and borehole video logs in the seven wells were evaluated to assess potential for lithologic correlation and to identify and describe water-bearing features, which included both low- and high-angle fractures and other openings oriented along dipping bedding planes, joints, or possible faults. Borehole geophysical logs collected by USGS in 1992 in a 300-ft-deep former production well near the Site were also evaluated. Few to no distinctive features were identified on geophysical logs (natural gamma and single-point resistance) that could be used for correlation, thus limiting this approach to determining local geologic structure. Extensive fracturing in the upper 62 ft of monitoring well MG 2220 indicates that the well was likely drilled through a zone of faulting, and other evidence of faulting is present in the area near the Site. Assessment of continuous water levels showed hydraulic connections among some wells as indicated by rising or falling water levels in response to changes in pumping rates at nearby wells. A map of water levels measured in April 2018 indicates potential for groundwater flow generally toward the stream to the south and southwest of the Site, but the limited water-level data are insufficient to describe vertical groundwater gradients or lateral gradients in any detail. Review of 1999–2022 volatile organic compound (VOC) monitoring data collected by the Pennsylvania Department of Environmental Protection for five monitoring wells indicates that the highest groundwater concentrations of PCE and TCE were found in samples from extraction well MG 2201 (S-1) downgradient from, and nearest to, the previously identified Site contaminant source area, and these concentrations fluctuated through time. PCE concentrations were higher than TCE concentrations in samples from all five monitoring wells and were much higher than TCE concentrations in samples from extraction well MG 2201 (S-1). Temporally variable recharge is a possible factor affecting observed fluctuations in PCE concentrations in groundwater samples from well extraction MG 2201 (S-1), as indicated by a general inverse relation between PCE concentrations and water levels in a nearby long-term observation well. The PCE concentration of 1,830 micrograms per liter (μg/L) in a May 2018 water sample from monitoring well MG 2220 was more than four times the PCE concentration of 444 μg/L in a December 2017 sample from the nearby extraction well MG 2201 (S-1), which is open to fewer fractures. Low concentrations of VOCs were measured in surface water at two stream sites downgradient from wells with the highest groundwater VOC concentrations at the Site, indicating that discharge of contaminated groundwater to the stream is likely. Development of a conceptual model of the groundwater system was constrained by limited data. In areas with no pumping, groundwater-flow directions generally are thought to be controlled by topography and geologic structure (bedding orientation) and likely to the south and southwest of the Site, with local flow directions affected by orientations of fractures, joints, and local faults. Additional investigations that could help improve the conceptual model of the groundwater system and help delineate the extent of groundwater contamination and its transport are discussed.

Pennsylvania↗

USGS2014

Coefficients of storage and transmissibility obtained from pumping tests in the Houston District, Texas

An investigation of the ground‐water supply of the Houston District, in Texas, has been in progress since December, 1930, under the general direction of O. E. Meinzer, Geologist‐in‐Charge of the Division of Ground Water of the Geological Survey. The Houston District, as the term is used here, comprises all of Harris County and parts of Montgomery, Waller, and Fort Bend counties, lying between the Trinity and Brazos rivers. The investigation in this area has consisted primarily of inventorying well‐logs and pumpage‐records, of obtaining water‐level data and information regarding the chemical character of the ground‐water, and wherever possible of correlating these data.

Texas↗

USGS2016

Seasonal electrical resistivity surveys of a coastal bluff, Barter Island, North Slope Alaska

Select coastal regions of the North Slope of Alaska are experiencing high erosion rates that can be attributed in part to recent warming trends and associated increased storm intensity and frequency. The upper sediment column of the coastal North Slope of Alaska can be described as continuous permafrost underlying a thin (typically less than 1–2 m) active layer that responds variably to seasonal thaw cycles. Assessing the temporal and spatial variability of the active layer and underlying permafrost is essential to better constrain how heightened erosion may impact material fluxes to the atmosphere and the coastal ocean, and how enhanced thaw cycles may impact the stability of the coastal bluffs. In this study, multi-channel electrical resistivity tomography (ERT) was used to image shallow subsurface features of a coastal bluff west of Kaktovik, on Barter Island, northeast Alaska. A comparison of a suite of paired resistivity surveys conducted in early and late summer 2014 provided detailed information on how the active layer and permafrost are impacted during the short Arctic summer. Such results are useful in the development of coastal resilience models that tie together fluvial, terrestrial, climatic, geologic, and oceanographic forcings on shoreline stability.

Alaska↗

USGS2002

Crustal structure of the coastal and marine San Francisco Bay region, California

As of the time of this writing, the San Francisco Bay region is home to about 6.8 million people, ranking fifth among population centers in the United States. Most of these people live on the coastal lands along San Francisco Bay, the Sacramento River delta, and the Pacific coast. The region straddles the tectonic boundary between the Pacific and North American Plates and is crossed by several strands of the San Andreas Fault system. These faults, which are stressed by about 4 cm of relative plate motion each year, pose an obvious seismic hazard. We have many ways to study earthquake faults. Where faults break the land surface, we may learn valuable information needed for hazard assessment, such as cumulative offset, slip rate, and earthquake history. However, many of the major faults in the region are partly submerged beneath San Francisco and Monterey Bays. Although this situation poses problems in gathering observational data for hazard assessment, bay-region waterways provide an opportunity to study faultzone structure by using marine subsurface-imaging techniques, which are easier and cheaper than equivalent studies on land. In 1993, the U.S. Geological Survey (USGS) launched a 5-year project aimed at unearthing the basic science of the submerged San Andreas strike-slip fault system in the San Francisco Bay region with its many interacting strands. Primary project goals were structural, such as to discover how the San Andreas and Hayward Faults are connected or related at depth, to learn how the complex of faults in the San Andreas stepover zone on the Golden Gate platform functions, and to locate previously unknown faults. This volume thus contains mostly structural information about the San Francisco Bay region, much of it gathered through exploratory geophysical experiments. The volume is organized “top down,” from studies in the shallowest crust to the base of the crust. The first three chapters are linked through their use of novel geophysical techniques to study earthquake effects, coseismic slip, and shallow stratigraphy. Kayen and others examine crustal structure at very high resolution and demonstrate the use of ground-penetrating-radar tomography to measure the liquefaction potential of coastal sedimentary deposits. McGann and others use microfossils from drill cores along the San Francisco-Oakland Bay Bridge to determine a more detailed late Pleistocene stratigraphy of San Francisco Bay than was previously available. Geist and Zoback use the historical record of a small local tsunami generated by the great 1906 San Francisco earthquake to model the rupture process of that earthquake. The last four chapters are dedicated to studies of fault related structure of the seismogenic crust in and around the San Andreas Fault system in the San Francisco Bay region. Jachens and others compile an aeromagnetic anomaly map from new high-resolution flights across the bay region. Some of these anomalies mark the positions of offshore faults, and others are offset by faults, providing constraints on cumulative slip. Hart and others concisely summarize the marine seismic data recorded in and around San Francisco Bay, map the coverage, and provide archival information for those interested in acquiring data. The last two chapters present the results of the seismic data that have been analyzed. Bruns and others present their analysis of high-quality intermediate-resolution (~5-km penetration) seismic-reflection data gathered over the complex San Andreas-San Gregorio Fault junction. This junction, which is thought to be where the 1906 San Francisco earthquake originated (see Geist and Zoback, this volume), contains an apparent extensional right stepover in the San Andreas Fault. Finally, Parsons and others review and summarize the results of deep-crustal seismic-reflection experiments and local-earthquake tomographic studies, including previously unpublished data, and provide additional support and discussion for already-published studies. In summary, these studies were carried out in an environment where background information on faults in the San Francisco Bay region was sought. Much of the structural information presented here comes from experiments of a style unlikely to be conducted by the USGS in the near future. Together, the chapters in this volume provide a structural framework for a major part of a complex strike-slip fault system.

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