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At least 1,027 records · Page 57Linked to original sources
USGS2011

Borehole geophysical investigation of a formerly used defense site, Machiasport, Maine, 2003-2006

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, collected borehole geophysical logs in 18 boreholes and interpreted the data along with logs from 19 additional boreholes as part of an ongoing, collaborative investigation at three environmental restoration sites in Machiasport, Maine. These sites, located on hilltops overlooking the seacoast, formerly were used for military defense. At each of the sites, chlorinated solvents, used as part of defense-site operations, have contaminated the fractured-rock aquifer. Borehole geophysical techniques and hydraulic methods were used to characterize bedrock lithology, fractures, and hydraulic properties. In addition, each geophysical method was evaluated for effectiveness for site characterization and for potential application for further aquifer characterization and (or) evaluation of remediation efforts. Results of borehole geophysical logging indicate the subsurface is highly fractured, metavolcanic, intrusive, metasedimentary bedrock. Selected geophysical logs were cross-plotted to assess correlations between rock properties. These plots included combinations of gamma, acoustic reflectivity, electromagnetic induction conductivity, normal resistivity, and single-point resistance. The combined use of acoustic televiewer (ATV) imaging and natural gamma logs proved to be effective for delineating rock types. Each of the rock units in the study area could be mapped in the boreholes, on the basis of the gamma and ATV reflectivity signatures. The gamma and mean ATV reflectivity data were used along with the other geophysical logs for an integrated interpretation, yielding a determination of quartz monzonite, rhyolite, metasedimentary units, or diabase/gabbro rock types. The interpretation of rock types on the basis of the geophysical logs compared well to drilling logs and geologic mapping. These results may be helpful for refining the geologic framework at depth. A stereoplot of all fractures intersecting the boreholes indicates numerous fractures, a high proportion of steeply dipping fractures, and considerable variation in fracture orientation. Low-dip-angle fractures associated with unloading and exfoliation are also present, especially at a depth of less than 100 feet below the top of casing. These sub-horizontal fractures help to connect the steeply dipping fractures, making this a highly connected fracture network. The high variability in the fracture orientations also increases the connectivity of the fracture network. A preliminary comparison of all fracture data from all the boreholes suggests fracturing decreases with depth. Because all the boreholes were not drilled to the same depth, however, there is a clear sampling bias. Hence, the deepest boreholes are analyzed separately for fracture density. For the deepest boreholes in the study, the intensity of fracturing does not decline significantly with depth. It is possible the fractures observed in these boreholes become progressively tighter or closed with depth, but this is difficult to verify with the borehole methods used in this investigation. The fact that there are more sealed fractures at depth (observed in optical televiewer logs in some of the boreholes) may indicate less opening of the sealed fractures, less water moving through the rock, and less weathering of the fracture infilling minerals. Although the fracture orientation remained fairly constant with depth, differences in the fracture patterns for the three restoration sites indicate the orientation of fractures varies across the study area. The fractures in boreholes on Miller Mountain predominantly strike northwest-southeast, and to a lesser degree they strike northeast. The fractures on or near the summit of Howard Mountain strike predominantly east-west and dip north and south, and the fractures near the Transmitter Site strike northeast-southwest and dip northwest and southeast. The fracture populations for the boreholes on or near the summit of Howard Mountain show more variation than at the other two sites. This variation may be related to the proximity of the fault, which is northeast of the summit of Howard Mountain. In a side-by-side comparison of stereoplots from selected boreholes, there was no clear correspondence between fracture orientation and proximity to the fault. There is, however, a difference in the total populations of fractures for the boreholes on or near the summit of Howard Mountain and the boreholes near the Transmitter Site. Further to the southwest and further away from the fault, the fractures at the Transmitter Site predominantly strike northeast-southwest and northwest-southeast.Heat-pulse flowmeter (HPFM) logging was used to identify transmissive fractures and to estimate the hydraulic properties along the boreholes. Ambient downflow was measured in 13 boreholes and ambient upflow was measured in 9 boreholes. In nine other bedrock boreholes, the HPFM did not detect measurable vertical flow. The observed direction of vertical flow in the boreholes generally was consistent with the conceptual flow model of downward movement in recharge locations and upward flow in discharge locations or at breaks in the slope of land surface. Under low-rate pumping or injection rates [0.25 to 1 gallon per minute (gal/min)], one to three inflow zones were identified in each borehole. Two limitations of HPFM methods are (1) the HPFM can only identify zones within 1.5 to 2 orders of magnitude of the most transmissive zone in each borehole, and (2) the HPFM cannot detect flow rates less than 0.010 + or - 0.005 gal/min, which corresponds to a transmissivity of about 1 foot squared per day (ft2/d). Consequently, the HPFM is considered an effective tool for identifying the most transmissive fractures in a borehole, down to its detection level. Transmissivities below that cut-off must be measured with another method, such as packer testing or fluid-replacement logging. Where sufficient water-level and flowmeter data were available, HPFM results were numerically modeled. For each borehole model, the fracture location and measured flow rates were specified, and the head and transmissivity of each fracture zone were adjusted until a model fit was achieved with the interpreted ambient and stressed flow profiles. The transmissivities calculated by this method are similar to the results of an open-hole slug test; with the added information from the flowmeter, however, the head and transmissivity of discrete zones also can be determined. The discrete-interval transmissivities ranged from 0.16 to 330 ft2/d. The flowmeter-derived open-hole transmissivity, which is the combined total of each of the transmissive zones, ranged from 1 to 511 ft2/d. The whole-well open-hole transmissivity values determined with HPFM methods were compared to the results of open-hole hydraulic tests. Despite the fact that the flowmeter-derived transmissivities consistently were lower than the estimates derived from open-hole hydraulic tests alone, the correlation was very strong (with a coefficient of determination, R2, of 0.9866), indicating the HPFM method provides a reasonable estimate of transmissivities for the most transmissive fractures in the borehole. Geologic framework, fracture characterization, and estimates of hydraulic properties were interpreted together to characterize the fracture network. The data and interpretation presented in this report should provide information useful for site investigators as the conceptual site groundwater flow model is refined. Collectively, the results and the conceptual site model are important for evaluating remediation options and planning or implementing the design of a well field and borehole completions that will be adequate for monitoring flow, remediation efforts, groundwater levels, and (or) water quality. Similar kinds of borehole geophysical logging (specifically the borehole imaging, gamma, fluid logs, and HPFM) should be conducted in any newly installed boreholes and integrated with interpretations of any nearby boreholes. If boreholes are installed close to existing or other new boreholes, cross-hole flowmeter surveys may be appropriate and may help characterize the aquifer properties and connections between the boreholes.

Maine↗
USGS2004

Mapping saline groundwater beneath the Sea Galilee and its vicinity using time domain electromagnetic (TDEM) geophysical technique

An extensive time domain electromagnetic (TDEM) survey covering the Sea of Galilee with a dense grid of points has been recently carried out. A total of 269 offshore and 33 supplementary onshore TDEM soundings were performed along six N-S and ten W-E profiles and at selected points both offshore and onshore along the whole coastal line. The interpreted resistivities were calibrated with the direct salinity measurements in the Haon-2 borehole and relatively deep (5 m) cores taken from the lake bottom. It was found that resistivities below 1 ohm-m are solely indicative of groundwater salinity exceeding 10,000 mg Cl/l. Such low resistivities (high salinities) were detected at depths greater than 15 m below almost the entire bottom of the lake. At some parts of the lake, particularly in the south, the saline water was detected at shallower depths, sometimes at a few meters below the bottom. Relatively high resistivity (fresh groundwater) was found along the margins of the lake down to roughly 100 m, the maximum exploration depth of the system. The detected sharp lateral contrasts at the lake margin between high and low resistivities coincide with the faults separating the carbonate and clastic units, respectively. The geometry of the fresh/saline groundwater interface below the central part of the lake is very similar to the shape of the lake bottom, probably due to the diffusive salt transport from the bottom sediments to the lake water. The above geophysical observations suggest differentsalt transport mechanisms from the sediments to the central part of the lake (diffusion) and from regional aquifers to the margins of the lake (advection). ?? 2004 Science From Israel/LPPLtd.

Israel Journal of Earth Sciences↗
USGS1979

Mineral resources of the Minarets Wilderness and adjacent areas, Madera and Mono counties, California

A mineral survey of the Minarets Wilderness area and adjacent areas in the central Sierra Nevada, Calif., was conducted during 1973 through 1975. The total area covers about 620 km 2 (237 sq mi) in the Sierra and Inyo National Forests, of which about 440 km 2 (170 sq mi) are within the officially designated Minarets Wilderness. The mineral resource potential was evaluated by geological, geochemical, and geophysical studies by the U.S. Geological Survey, and by examination of mineralized rocks, prospects, and mining claims by the U.S. Bureau of Mines. The results of the survey indicate that the study area has small to moderate submarginal to paramarginal resources of copper, silver, zinc, lead, iron, and tungsten and an unevaluated potential for molybdenum resources. Limestone is present, but not of commercial quantity or quality. No other industrial minerals have been recognized in quantity. Granitic rocks have potential use as decorative stone and sand and gravel could be produced from either alluvial deposits or glacial drift. However, these commodities are more accessible elsewhere at localities closer to markets. The study area has no potential for fossil fuels, and, because of the general geologic environment, the potential for nuclear fuel minerals is considered to be low. The study area has low geothermal potential, even though it is on the western edge of the Mono-Long Valley "Known Geothermal Resource Area" (KGRA). The area is underlain by metavolcanic and metasedimentary rocks that have been intruded by granitic rocks of the Sierra Nevada batholith. Pliocene volcanic rocks are present locally. With few exceptions, the known occurrences of mineralized rock are confined to the metamorphic rocks, and the exceptions appear to be confined to plutonic rocks that are older than the Late Cretaceous granitic rocks that make up the bulk of the batholithic rocks in the study area. Although no mineral production has been recorded from prospects within the study area, mines adjacent to it have produced significant amounts of gold and tungsten. Production figures are incomplete, but mines in the Mammoth mining district (fig. 1) may have produced as much as $1 million worth of gold, silver, and other metals at the then-existing prices. The Monte Cristo mine in the Mammoth district was in production during 1978.

California↗
USGS2018

Geophysical and geologic maps of Mountain Pass and vicinity, California and Nevada

U.S. Geological Survey Scientific Investigations Map 3412 is a series of products that consists of geophysical and geologic maps of Mountain Pass and vicinity, California. Maps A and B (red outline in above map image) are gravity and aeromagnetic maps, respectively. The map series was begun as part of an effort to study regional crustal structures as an aid to understanding the geologic framework and mineral resources of the southeast Mojave Desert. Mountain Pass resides within the southeast Mojave Desert, and it is host to a one of the world’s largest rare earth element carbonatite deposits. The deposit is found along a north-northwest- trending, fault-bounded block that extends along the eastern parts of the Clark Mountain Range, Mescal Range, and Ivanpah Mountains. This Paleoproterozoic block is composed of a 1.7-Ga metamorphic complex of gneiss and schist that underwent widespread metamorphism and associated plutonism during the Ivanpah orogeny. The Paleoproterozoic rocks were intruded by a Mesoproterozoic (1.4 Ga) ultrapotassic alkaline intrusive suite and carbonatite body. The intrusive rocks include, from oldest to youngest, shonkinite, mesosyenite, syenite, quartz syenite, potassic granite, carbonatite, carbonatite dikes, and late shonkinite dikes. Each map in the series provides the basis for geophysical and geologic interpretations of the Mountain Pass carbonatite terrane. Combined, they provide a comprehensive framework of the regional subsurface geologic structure of the area. Together, they form the first publicly available series of geophysical and geologic maps of this part of the southeast Mojave Desert.

California, Nevada↗
USGS1952

Preliminary report on the Passamaquoddy bedrock survey, July-August, 1951

In order to understand the results of the Passamaquoddy bedrock survey and the details of the method of obtaining them, it is desirable to have, in outline, a general idea of the methods and their application. In this part of the report a general account of the operation will be developed. The details will be found in subsequent parts of the report. At this point a statement of the general objective and some mention of the plans for reaching it are in order. The purpose of the Passamaquoddy survey was to determine the submarine geology in certain areas of Passamaquoddy and Cobscook Bays--the sea-bottom topography, the bedrock topography, the thickness of sediment overlying the bedrock beneath the sea, and the type of sediment. The information is needed for the planning of major engineering structures that may be built in the area. It developed in planning the study that detailed surveys could be limited to several areas where dams may be located. To determine bottom or bedrock topography, elevations of each were determined by sonic methods at a number of closely spaced locations (about 400 feet apart), evenly distributed on range lines 1,000 or 800 feet apart, in each of eight areas. Contour lines were then drawn to produce the desired topographic maps. Sonic soundings are necessarily referred to the existing water surface. To ascertain specific elevations in an area of large tidal variations is a complex problem. The details are discussed in the section on Vertical Control by Charles E. Knox (part 8). The basic datum is mean low water as determined by the U. S. Coast and Geodetic Survey. Equally important is the accurate positioning horizontally of each sounding location or fix. All such positioning was by the use of the standard three point fix procedure, using sextants. A net of shore points tied to the first-order control net of the Coast and Geodetic Survey was set up for this purpose, and all positions were thus accurately located. These problems are discussed in a section on Horizontal Control by Norman Duckworth (part 7). The general planning was done in conferences held in May 1951 at the Boston office of the Corps of Engineers, and in Eastport, Maine, after a brief reconnaissance of the area. A detailed account of the conferences is given in a memorandum by Herman J. Kropper of the New England Division, Corps of Engineers, reproduced in this report as part 4. Detailed survey procedures were developed on May 18, 1951, at a conference attended by P. J. A. Scott and Norman Duckworth of the Corps of Engineers and W. O. Smith of the Geological Survey. In order to make the necessary geophysical interpretation of the sound records, adequate geologic control had to be established. A preliminary field study of the geology was made by G. G. Parker of the Geological Survey during the period May 15-17, 1951. Subsequently Dr. T. E. Upson of the Geological Survey made the detailed geologic study required for the project. Two sonar units were used for the survey. One was a low-frequency high-power sonar unit developed by the Edo Corp. to meet specifications established by the Geological Survey. It was used to collect the bulk of the bedrock and bottom data. The other, of higher frequency and lower power, was manufactured by Bludworth Marine, Inc., end was required for adequate determination of water depths in shoal areas. The Edo equipment is described by Dr. Charles E. Mongan, Jr., in part 6 of this report.

Maine↗
USGS1971

Aeromagnetic map of the Bopolu quadrangle, Liberia

Aeromagnetic and total-count gamma radiation surveys were flown simultaneously during the 1967-68 dry season over the entire country and consist of approximately 140,000 km of traverse, mostly along north-south lines 0.8 km apart over land and 4 km apart over the continental shelf. Continuous photography and Doppler navigation provided horizontal control. Flight altitude was 150 m above terrain. Time variations in the magnetic field measured with a fluxgatc magnetometer were removed by adjustment at crossings of east-west control lines. Variable contour intervals of 10, 50, 250, and 1000 gammas were used depending on horizontal gradient. The airborne geophysical data obtained during the Liberian survey are being prepared in a series of maps at 1:250,000 scale showing aeromagnetic and total-count gamma radiation data for each. The index map shows the location of the quadrangles.The radioactivity map of the Bopolu quadrangle should be used with this report (Behrendt and Wotorson, 1971). The surveys were flown by Lockwood, Kessler, and Bartlett, under contract to the Liberian Geological Survey. The purpose of both surveys was to assist in the geologic mapping program undertaken cooperatively by the Liberian Geological Survey and the U. S. Geological Survey under the auspices of the Liberian Government and the Agency for International Development, U. S. Department of State. The entire country is heavily forested, access is difficult, outcrops are sparse, and thick laterite is a characteristic feature. Consequently, it was hoped that; the surveys would be useful in interpolating and extrapolating from the known geologic information and in locating potential targets for mineral exploration.

Open-File Report↗
USGS1971

Aeromagnetic map of the Buchanan quadrangle, Liberia

Aeromagnetic and total-gamma radiation surveys were flown simultaneously during the 1967-68 dry season over the entire country and consist of approximately 140,000 km of traverse, mostly along north-south lines 0.8 km apart over the land and 4 km apart over the continental shelf. Continuous photography and Doppler navigation provided horizontal control. Flight altitude was 150 m above terrain. Time variations in the magnetic field measured with a fluxgate magnetometer were removed by adjustment at crossings of east-west control lines. Variable contour intervals of 10, 50, 250, and 1000 gammas were used depending on horizontal gradient. The airborne geophysical data obtained during the Liberian survey are being prepared in a series of maps at 1:250,000 scale showing aero-magnetic and total-count gamma,radiation data for each of ten quadrangles.The index map shows the location of the quadrangles. The radioactivity map of this quadrangle should be used with this report (Behrendt and Wotorson,1971). The surveys were flown by Lockwood, Kessler, and Bartlett, undercontract to the Liberian Geological Survey. The purpose of both surveys was to assist in the geologic mapping program undertaken cooperatively by the Liberian Geological Survey and the U. S. Geological Survey under the auspices of the Liberian Government and the Agency for International Development, U. S. Department of State. The entire country is heavily forested, access is difficult, outcrops are sparse, and thick laterite is a characteristic feature. Consequently, it was hoped that the surveys would be useful in interpolating and extrapolating from the known geologic information and in locating potential targets for mineral exploration. Figure 1 shows the tectonic interpretation for sheets 1 and 2 of the map based on available geologic information (White and Leo, 1969; unpub. data in files of Liberian Geol. Survey). Figure 2 is part of the residual total magnetic intensity map of Liberia obtained by digitizing the data of the map on a one-minute grid, tying to an absolute survey (Lowrieand Escowitz, 1969) by a constant of ±25,980 It 35 gammas and, removing Cain's "Field G" (Cain and others, 1965).

Open-File Report↗
USGS1977

Chemical analysis, physical property tests, and lithologic description of cores and cuttings of lignite and overburden rocks from an area near Watkins, Colorado

The data presented in this report represents analytical and testing information from cores drilled by the Geophysics Department, Colorado School of Mines, assisted by the U.S. Geological Survey. The drilling was done in conjunction with the establishment of a geophysical testing facility by the Colorado School of Mines. Location of the study area and drill holes is shown in Figure 1. A total of 15 holes were drilled and geophysically logged; holes 9-1 and 7-11 were cored, and attempts to core hole 3-1 were made, but the lignite was very incompetent due to weathering and oxidation and recovery was very poor. Lithologic descriptions of the cores and cuttings for holes 9-1, 7-11, and 3-1 are listed on pages 13-21. Calculationdbased on hole 9-1 indicate that of the total lignite zone, 56 percent consists of partings and 44 percent is lignite. These percentages were obtained by statistical analysis of the core description and natural gamma logs of the hole. The total thickness of the lignite zone in hole 9-1 is approximately 18 m.

Colorado↗
USGS2008

Borehole Geophysical Logging Program: Incorporating New and Existing Techniques in Hydrologic Studies

The borehole geophysical logging program at the U.S. Geological Survey (USGS)-Florida Integrated Science Center (FISC) provides subsurface information needed to resolve geologic, hydrologic, and environmental issues in Florida. The program includes the acquisition, processing, display, interpretation, and archiving of borehole geophysical logs. The borehole geophysical logging program is a critical component of many FISC investigations, including hydrogeologic framework studies, aquifer flow-zone characterization, and freshwater-saltwater interface delineation.

Fact Sheet↗
USGS2013

Acquiring marine data in the Canada Basin, Arctic Ocean

This article describes the logistical challenges and initial data sets from geophysical seismic reflection, seismic refraction, and hydrographic surveys in the Canada Basin conducted by scientists with U.S. and Canadian government agencies (Figure 1a) to fulfill the requirements of the United Nations Convention on the Law of the Sea to determine sediment thickness, geological origin, and basin evolution in this unexplored part of the world. Some of these data were collected using a single ship, but the heaviest ice conditions necessitated using two icebreakers, similar to other recent Arctic surveys [e.g., Jokat, 2003].

Eos, Transactions, American Geophysical Union↗
USGS2023

Maps of elevation of top of Pierre Shale and surficial deposit thickness with hydraulic properties from borehole geophysics and aquifers tests within and near Ellsworth Air Force Base, South Dakota, 2020–21

The U.S. Geological Survey, in cooperation with the U.S. Air Force Civil Engineer Center, collected borehole geophysical data and completed simple aquifer tests to estimate the thickness and hydraulic properties of surficial deposits. The purpose of data collection was to create generalized contour maps of Pierre Shale elevation and surficial deposit thickness within and near Ellsworth Air Force Base (study area). Natural gamma and electromagnetic induction data were collected to refine or determine surficial deposit thickness at selected wells. Additionally, data from previous geophysical studies and driller logs were compiled and combined with results from natural gamma and electromagnetic induction data to provide a more spatially complete image of the subsurface. Borehole nuclear magnetic resonance (bNMR) data were collected to estimate hydraulic conductivity and water content of surficial deposits overlying Pierre Shale. Simple aquifer tests using water slugs (slug tests) were completed to estimate hydraulic conductivity of surficial deposits, and results were compared to hydraulic conductivity estimates from bNMR data. All data used to construct maps and estimate hydraulic properties are provided in an accompanying U.S. Geological Survey data release (available at https://doi.org/10.5066/P9FLR79F ). Generalized contour maps were constructed using results from 26 borehole geophysical logs, 35 geophysical transects from previous studies, and 304 wells with driller logs. Pierre Shale elevation generally followed land-surface topography, sloping from high elevations in the north to lower elevations in the south. Topographic highs of Pierre Shale, where present, could act as groundwater divides that potentially affect groundwater flow direction. Surficial deposit thickness varied spatially and ranged from 0 to 86 feet. Surficial deposits generally were thickest in higher elevation areas near ephemeral streams in the northern part of the study area. Hydraulic conductivity estimated from bNMR results using two analytical methods ranged from 0.1 to 2,314 feet per day, whereas hydraulic conductivity estimated from slug tests ranged from 0.001 to 193 feet per day. Hydraulic conductivity estimates from slug tests were plotted with surficial deposit thickness contours instead of bNMR estimates because bNMR estimates were determined to overestimate hydraulic conductivity. Hydraulic conductivity values generally were greater in the southwestern part of study area than the northeastern part.

South Dakota↗
USGS2011

Hydrogeologic setting and simulation of groundwater flow near the Canterbury and Leadville Mine Drainage Tunnels, Leadville, Colorado

The Leadville mining district is historically one of the most heavily mined regions in the world producing large quantities of gold, silver, lead, zinc, copper, and manganese since the 1860s. A multidisciplinary investigation was conducted by the U.S. Geological Survey, in cooperation with the Colorado Department of Public Health and Environment, to characterize large-scale groundwater flow in a 13 square-kilometer region encompassing the Canterbury Tunnel and the Leadville Mine Drainage Tunnel near Leadville, Colorado. The primary objective of the investigation was to evaluate whether a substantial hydraulic connection is present between the Canterbury Tunnel and Leadville Mine Drainage Tunnel for current (2008) hydrologic conditions. Altitude in the Leadville area ranges from about 3,018 m (9,900 ft) along the Arkansas River valley to about 4,270 m (14,000 ft) along the Continental Divide east of Leadville, and the high altitude of the area results in a moderate subpolar climate. Winter precipitation as snow was about three times greater than summer precipitation as rain, and in general, both winter and summer precipitation were greatest at higher altitudes. Winter and summer precipitation have increased since 2002 coinciding with the observed water-level rise near the Leadville Mine Drainage Tunnel that began in 2003. The weather patterns and hydrology exhibit strong seasonality with an annual cycle of cold winters with large snowfall, followed by spring snowmelt, runoff, and recharge (high-flow) conditions, and then base-flow (low-flow) conditions in the fall prior to the next winter. Groundwater occurs in the Paleozoic and Precambrian fractured-rock aquifers and in a Quaternary alluvial aquifer along the East Fork Arkansas River, and groundwater levels also exhibit seasonal, although delayed, patterns in response to the annual hydrologic cycle. A three-dimensional digital representation of the extensively faulted bedrock was developed and a geophysical direct-current resistivity field survey was performed to evaluate the geologic structure of the study area. The results show that the Canterbury Tunnel is located in a downthrown structural block that is not in direct physical connection with the Leadville Mine Drainage Tunnel. The presence of this structural discontinuity implies there is no direct groundwater pathway between the tunnels along a laterally continuous bedrock unit. Water-quality results for pH and major-ion concentrations near the Canterbury Tunnel showed that acid mine drainage has not affected groundwater quality. Stable-isotope ratios of hydrogen and oxygen in water indicate that snowmelt is the primary source of groundwater recharge. On the basis of chlorofluorocarbon and tritium concentrations and mixing ratios for groundwater samples, young groundwater (groundwater recharged after 1953) was indicated at well locations upgradient from and in a fault block separate from the Canterbury Tunnel. Samples from sites downgradient from the Canterbury Tunnel were mixtures of young and old (pre-1953) groundwater and likely represent snowmelt recharge mixed with older regional groundwater that discharges from the bedrock units to the Arkansas River valley. Discharge from the Canterbury Tunnel contained the greatest percentage of old (pre-1953) groundwater with a mixture of about 25 percent young water and about 75 percent old water. A calibrated three-dimensional groundwater model representing high-flow conditions was used to evaluate large-scale flow characteristics of the groundwater and to assess whether a substantial hydraulic connection was present between the Canterbury Tunnel and Leadville Mine Drainage Tunnel. As simulated, the faults restrict local flow in many areas, but the fracture-damage zones adjacent to the faults allow groundwater to move along faults. Water-budget results indicate that groundwater flow across the lateral edges of the model controlled the majority of flow in and out of the aquifer (79 percent and 63 percent of the total water budget, respectively). The largest contributions to the water budget were groundwater entering from the upper reaches of the watershed and the hydrologic interaction of the groundwater with the East Fork Arkansas River. Potentiometric surface maps of the simulated model results were generated for depths of 50, 100, and 250 m. The surfaces revealed a positive trend in hydraulic head with land-surface altitude and evidence of increased control on fluid movement by the fault network structure at progressively greater depths in the aquifer. Results of advective particle-tracking simulations indicate that the sets of simulated flow paths for the Canterbury Tunnel and the Leadville Mine Drainage Tunnel were mutually exclusive of one another, which also suggested that no major hydraulic connection was present between the tunnels. Particle-tracking simulations also revealed that although the fault network generally restricted groundwater movement locally, hydrologic conditions were such that groundwater did cross the fault network at many locations. This cross-fault movement indicates that the fault network controls regional groundwater flow to some degree but is not a complete barrier to flow. The cumulative distributions of adjusted age results for the watershed indicate that approximately 30 percent of the flow pathways transmit groundwater that was younger than 68 years old (post-1941) and that about 70 percent of the flow pathways transmit old groundwater. The particle-tracking results are consistent with the apparent ages and mixing ratios developed from the chlorofluorocarbon and tritium results. The model simulations also indicate that approximately 50 percent of the groundwater flowing through the study area was less than 200 years old and about 50 percent of the groundwater flowing through the study area is old water stored in low-permeability geologic units and fault blocks. As a final examination of model response, the conductance parameters of the Canterbury Tunnel and Leadville Mine Drainage Tunnel were manually adjusted from the calibrated values to determine if altering the flow discharge in one tunnel affects the hydraulic behavior in the other tunnel. The examination showed no substantial hydraulic connection. The multidisciplinary investigation yielded an improved understanding of groundwater characteristics near the Canterbury Tunnel and the Leadville Mine Drainage Tunnel. Movement of groundwater between the Canterbury Tunnel and Leadville Mine Drainage Tunnel that was central to this investigation could not be evaluated with strong certainty owing to the structural complexity of the region, study simplifications, and the absence of observation data within the upper sections of the Canterbury Tunnel and between the Canterbury Tunnel and the Leadville Mine Drainage Tunnel. There was, however, collaborative agreement between all of the analyses performed during this investigation that a substantial hydraulic connection did not exist between the Canterbury Tunnel and the Leadville Mine Drainage Tunnel under natural flow conditions near the time of this investigation.

Colorado↗
USGS1964

Preliminary report on tests of the application of geophysical methods to Arctic ground water problems

Seismic refraction and electrical resistivity surveys were made during the summer and fall of 1952 in the Tanana Valley near Fairbanks, Alaska, as part of the studies of the application of geophysical techniques to ground-water problems in Alaska instigated in 1951 by the U.S. Army Engineer Research and Development Laboratories. Work centered around the highway junctions at Fairbanks, Big Delta, and Tok. It was found that both survey methods defined the horizontal extent of the frozen ground and both were capable of determining the depth to the top of the permafrost but neither regularly yielded reliable information on the material beneath the top of the permafrost. The greatest need at present is for a thorough examination of data obtained in the field seasons of 1948 and 1952. Two fundamental theoretical investigations are desirable: (1) examination of the attenuation of longitudinal waves traveling through a thin layer, and (2) further development of the theoretical multilayer resistivity interpretation of problems in which the second layer has a very high resistivity. Further field work should include: (1) tests of the U.S. Geological Survey's new shallow-reflection seismograph; (2) a brief test of electromagnetic equipment; (3) additional resistivity measurements with commutated current; and (4) both seismic and resistivity measurements in areas where the bedrock possesses different physical properties from the schist usually found in interior Alaska. It is doubtful that geophysical techniques are sufficiently developed to be valuable for use by Army personnel in prospecting for ground water in areas of thick permafrost.

Alaska↗
USGS1983

Hydrogeologic data from the US Geological Survey test wells near Waycross, Ware County, Georgia

Two wells were constructed near Waycross, Ware County, Georgia, from July 1980 to May 1981 to collect stratigraphic, structural, geophysical, hydrologic, hydraulic, and geochemical information for the U.S. Geological Survey Tertiary Limestone Regional Aquifer-System Analysis. Data collection included geologic sampling and coring, borehole geophysical logging, packer testing, water-level measuring, water-quality sampling, and aquifer testing. In the study area, the Tertiary limestone aquifer system is about 1,300 feet thick and is confined and overlain by about 610 feet of clastic sediments. The aquifer system consists of limestone, dolomite, and minor evaporites and has high porosity and permeability. A 4-day continuous discharge aquifer test was conducted, from which a transmissivity of about 1 million feet squared per day and a storage coefficient of 0.0001 were calculated. Water from the upper part of the aquifer is of a calcium bicarbonate type. The deeper highly mineralized zone produces a sodium bicarbonate type water in which concentrations of magnesium, sulfate, chloride, sodium, and some trace metals increase with depth. (USGS)

Georgia↗
USGS2007

Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

Personnel from the U.S. Geological Survey and Martin Marietta Aggregates, Inc., conducted field demonstrations of five different geophysical methods to show how these methods could be used to characterize deposits of alluvial aggregate. The methods were time-domain electromagnetic sounding, electrical resistivity profiling, S-wave reflection profiling, S-wave refraction profiling, and P-wave refraction profiling. All demonstrations were conducted at one site within a river valley in central Indiana, where the stratigraphy consisted of 1 to 2 meters of clay-rich soil, 20 to 35 meters of alluvial sand and gravel, 1 to 6 meters of clay, and multiple layers of limestone and dolomite bedrock. All geophysical methods, except time-domain electromagnetic sounding, provided information about the alluvial aggregate that was consistent with the known geology. Although time-domain electromagnetic sounding did not work well at this site, it has worked well at other sites with different geology. All of these geophysical methods complement traditional methods of geologic characterization such as drilling.

Scientific Investigations Report↗
USGS1974

Preliminary report on geology along Atlantic continental margin of northeastern United States

The U.S. Geological Survey is conducting a geologic and geophysical study of the northeastern United States outer continental shelf and the adjacent slope from Georges Bank to Cape Hatteras. The study also includes the adjacent coastal plain because it is a more accessible extension of the shelf. The total study area is about 324,000 sq km, of which the shelf and slope constitute about 181,000 sq km and the coastal plain constitutes 143,000 sq km. The shelf width ranges from about 30 km at Cape Hatteras to about 195 km off Raritan Bay and on Georges Bank. Analyses of bottom samples make if possible to construct a preliminary geologic map of the shelf and slope to a water depth of 2,000 m. The oldest beds cropping out in the submarine canyons and on the slope are of early Late Cretaceous age. Beds of Early Cretaceous and Jurassic age are present in deep wells onshore and probably are present beneath the shelf in the area of this study. Such beds are reported beneath the Scotian shelf on the northeast where they include limestone, salt, and anhydrite. Preliminary conclusions suggest a considerably thicker Mesozoic sedimentary sequence than has been described previously. The region is large; the sedimentary wedge is thick; structures seem favorable; and the hydrocarbon potential may be considerable.

Atlantic continental margin↗
USGS1998

Use of Microgravity to Assess the Effects of El Nino on Ground-Water Storage in Southern Arizona

The availability of ground water is of extreme importance in areas, such as southern Arizona, where it is the main supply for agricultural, industrial, or domestic purposes. Where ground-water use exceeds recharge, monitoring is critical for managing water supplies. Typically, monitoring has been done by measuring water levels in wells; however, this technique only partially describes ground-water conditions in a basin. A new application of geophysical technology is enabling U.S. Geological Survey (USGS) scientists to measure changes in the amount of water in an aquifer using a network of microgravity stations. This technique enables a direct measurement of ground-water depletion and recharge. In Tucson, Arizona, residents have relied solely upon ground water for most of their needs since the 19th century. Water levels in some wells in the Tucson area have declined more than 200 ft in the past 50 years. Similar drops in water levels have occurred elsewhere in Arizona. In response to the overdrafting of ground water, the State of Arizona passed legislation designed to attain 'safe yield,' which is defined as a balance between ground-water withdrawals and annual recharge of aquifers. To monitor progress in complying with the legislation, ground-water withdrawals are measured and estimated, and annual recharge is estimated. The Tucson Basin and Avra Valley are two ground-water basins that form the Tucson Active Management Area (TAMA), which by State statute must attain 'safe yield' by the year 2025.

Fact Sheet↗