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At least 109 records · Page 6Linked to original sources
USGS2009

Water-Resources Data and Hydrogeologic Setting at the Raleigh Hydrogeologic Research Station, Wake County, North Carolina, 2005-2007

Water-resources data were collected to describe the hydrologic conditions at the Raleigh hydrogeologic research station, located in the Piedmont Physiographic Province of North Carolina. Data collected by the U.S. Geological Survey and the North Carolina Department of Environment and Natural Resources, Division of Water Quality, from May 2005 through September 2007 are presented in this report. Three well clusters and four piezometers were installed at the Raleigh hydrogeologic research station along an assumed flow path from recharge to discharge areas. Each well cluster includes four wells to monitor the regolith, transition zone, and shallow and deep bedrock. Borehole, surface, and waterborne geophysics were conducted to examine the lithology and physical properties of the bedrock and to determine the aerial extent of near vertical diabase dikes. Slug tests were conducted in the wells at each cluster to determine the hydraulic conductivity of the formation tapped by each well. Periodic water-level altitudes were measured in all wells and in four piezometers. Continuous hourly water levels were measured in wells for variable periods of time during the study, and a surface-water gage collected 15-minute stage data from April to June 2006. In October 2005 and April 2006, water-quality samples were collected from a tributary and in all wells at the Raleigh hydrogeologic research station. Continuous water-quality data were collected hourly in three wells from December 2005 through January 2007 and every 15 minutes in the tributary from May to June 2006. In August 2006, streambed temperatures and drive-point ground-water samples were collected across lines of section spanning the Neuse River.

Open-File Report↗
USGS2011

Mars atmospheric surface interactions and the CO2 cycle

Mars' northern and southern seasonal polar caps are formed during their respective autumn and winter seasons both by condensation of atmospheric carbon dioxide (CO 2 ) directly onto the surface, and through atmospheric precipitation in the form of CO 2 snow. During the polar spring and summer, the seasonal ice sublimes, returning CO 2 to the atmosphere. Roughly 25% of the atmosphere, which is 95% CO 2 by volume, is cycled through the seasonal caps annually. This CO 2 cycle dominates atmospheric circulation on Mars and must be thoroughly understood before the fundamental questions about Mars' climate history and the global distribution of near‐surface water can be addressed.

Eos, Transactions, American Geophysical Union↗
USGS1993

Geological and technological assessment of artificial reef sites, Louisiana outer continental shelf

This paper describes the general procedures used to select sites for obsolete oil and gas platforms as artificial reefs on the Louisiana outer continental shelf (OCS). The methods employed incorporate six basic steps designed to resolve multiple-use conflicts that might otherwise arise with daily industry and commercial fishery operations, and to identify and assess both geological and technological constraints that could affect placement of the structures. These steps include: (1) exclusion mapping; (2) establishment of artificial reef planning areas; (3) database compilation; (4) assessment and interpretation of database; (5) mapping of geological and man-made features within each proposed reef site; and (6) site selection. Nautical charts, bathymetric maps, and offshore oil and gas maps were used for exclusion mapping, and to select nine regional planning areas. Pipeline maps were acquired from federal agencies and private industry to determine their general locations within each planning area, and to establish exclusion fairways along each pipeline route. Approximately 1600 line kilometers of high-resolution geophysical data collected by federal agencies and private industry was acquired for the nine planning areas. These data were interpreted to determine the nature and extent of near-surface geologic features that could affect placement of the structures. Seismic reflection patterns were also characterized to evaluate near-bottom sedimentation processes in the vicinity of each reef site. Geotechnical borings were used to determine the lithological and physical properties of the sediment, and for correlation with the geophysical data. Since 1987, five sites containing 10 obsolete production platforms have been selected on the Louisiana OCS using these procedures. Industry participants have realized a total savings of approximately US $1 500 000 in salvaging costs by converting these structures into artificial reefs. ?? 1993.

Ocean and Coastal Management↗
USGS1985

Remotely sensed limonite anomaly on Lordsburg Mesa, New Mexico: Possible implications for uranium deposits

We have identified a large, anomalously limonitic area in Cenozoic gravels on Lordsburg Mesa near Lordsburg, New Mexico, using Landsat images. Our interpretation of the geophysical and geochemical data suggests the exploration hypothesis that the Lordsburg Mesa limonite anomaly is the surface expression of a chemical trap that may contain concentrations of uranium similar to calcrete-uranium deposits. Ground water originating in the Big Burro Mountains, where uranium vein deposits are known, drains through the Lordsburg Mesa area. This ground water is apparently forced near the surface by a buried bed-rock ridge along the west side of the limonite anomaly. The resulting changes in ground-water chemistry may be precipitating uranium along the eastern margin of the limonite anomaly.

Economic Geology↗
USGS2026

Understanding the resource potential of natural hydrogen on Earth: Scientific gaps, uncertainties and recommendations

A comprehensive scientific research roadmap is essential to bridge knowledge gaps and deepen the understanding of key geological, geochemical, and geophysical aspects of natural hydrogen (H 2 ) as a potential new energy resource. This paper reviews major scientific uncertainties on natural H 2 , suggesting research priorities, as a guide for defining exploration strategies, techniques, and data interpretation. The uncertainties concern all phases of the natural H 2 cycle, from generation (source rocks) through migration (advection and diffusion) and accumulation (reservoir and cap rocks) to the application and interpretation of subsurface and surface geochemical and geophysical exploration techniques. Understanding H 2 sources and generation rates (the amount of H 2 generated by a given volume of rock over time) is crucial for determining whether a geological H 2 system operates as a short-term dynamic system with rapid H 2 production and release, or as a conventional gas system with long-term accumulations, analogous to petroleum reservoirs. Preliminary estimates for serpentinisation, radiolysis, and organic matter degradation suggest that H 2 generation is not inherently fast, especially for non-hydrothermal continental systems (crystalline basement of shields, ophiolites, peridotite massifs, sedimentary basins), and long-term accumulations, like those of fossil natural gas systems, represent the most likely scenario. The mechanisms of H 2 migration through geological formations require application of fundamental principles of fluid-flow physics, distinguishing advection and diffusion, as well as their forms (from gas-phase, bubble flows to aqueous solutions). Additional studies of H 2 accumulation and retention in subsurface reservoirs could improve understanding of mechanisms of H 2 migration by focusing on the rock fluid-bearing properties and the factors affecting H 2 preservation, such as the presence of cap rocks impermeable to H 2 , pressure conditions, residence times, and microbial or abiotic consumption. Advanced techniques, including reservoir modelling, flow simulations, 3D imaging (micro-CT) of H 2 -bearing rocks, and extraction and analysis of gas occluded in rocks, can provide insights into the stability and potential recoverability of H 2 accumulations. The interpretation of surface exploration techniques, including gas geochemistry, geophysics, and remote sensing, long employed in mineral and energy resource exploration, is now being adapted for natural H 2 studies, but challenges remain in the data interpretation. Distinguishing H 2 seepage due to geological degassing from H 2 produced near the surface by modern microbial processes or artificial sources, such as hammering or drilling for soil-gas sampling, drilling into aquifers, and corrosion in boreholes, is an essential step in exploration. The simple detection of H 2 in soils, even in morphological structures like sub-circular depressions or “fairy circles”, cannot be cursorily interpreted as a signal of natural H 2 seepage from a deep source. A holistic geochemical approach, including isotopic analyses of gases associated with H 2 , is recommended to distinguish among the variety of possible H 2 origins. Observations of H 2 in wells should be interrogated to rule out possible artifacts such as corrosion and drill bit metamorphism. The integration of multiple geophysical methods, including seismic, gravimetric, magnetic, and electro-magnetic surveys, is recommended to mitigate interpretation ambiguities regarding the structure of a subsurface H 2 system (source and reservoir rocks, including fluid and gas storage), due to the non-uniqueness of rock-specific physical properties.

Earth-Science Reviews↗
USGS1999

Deformation and quaternary faulting in southeast Missouri across the Commerce geophysical lineament

High-resolution seismic-reflection data acquired at three sites along the surface projection of the Commerce geophysical lineament in southeast Missouri reveal a complex history of post-Cretaceous faulting that has continued into the Quaternary. Near Qulin, Missouri, approximately 20 m of apparent vertical fault displacement has occurred in the Quaternary. Reflection data collected at Idalia Hill, about 45 km to the northeast, reveal a series of reverse and possibly right-lateral strike-slip faults with Quaternary displacement. In the Benton Hills, 45 km northeast of Idalia Hill, seismic data image a complicated series of anticlinal and synclinal fault-bounded blocks immediately north of the Commerce fault. We infer that most of the deformation imaged in the upper 400 m of these three data sets occurred since post-Cretaceous time, and a significant portion of it occurred during Quaternary time. Collectively, these seismic data along with geomorphic and surface-geologic evidence suggest (1) the existence of at least one potential seismogenic structure in southeastern Missouri outside the main zones of New Madrid seismicity, and (2) these structures have been active during the Quaternary. The geographic location of the imaged deformation suggests it is related to structures along with the Commerce geophysical lineament.

Missouri↗
USGS1997

Evaluation of geophysical logs, Phase I, at Willow Grove Naval Air Station, Montgomery County, Pennsylvania

Between April and June 1997, the U.S. Navy contracted Brown and Root Environmental, Inc., to drill 20 monitor wells at the Willow Grove Naval Air Station in Horsham Township, Montgomery County, Pa. The wells were installed to monitor water levels and allow collection of water samples from shallow, intermediate, and deep water-bearing zones. Analysis of the samples will determine the horizontal and vertical distribution of any contaminated ground water migrating from known contaminant sources. Eight wells were drilled near the Fire Training Area (Site 5), five wells near the 9th Street Landfill (Site 3), four wells at the Antenna Field Landfill (Site 2), and three wells near Privet Road Compound (Site 1). Depths range from 73 to 167 feet below land surface. The U.S. Geological Survey conducted borehole-geophysical and borehole-video logging to identify water-bearing zones so that appropriate intervals could be screened in each monitor well. Geophysical logs were run on the 20 monitor wells and 1 existing well. Video logs were run on 16 wells. Caliper and video logs were used to locate fractures, inflections on fluid-temperature and fluid-resistivity logs were used to locate possible water-bearing fractures, and flowmeter measurements verified these locations. Single-point-resistance and natural-gamma logs provided information on stratigraphy. After interpretation of geophysical logs, video logs, and driller's notes, all wells were screened such that water-level fluctuations could be monitored and discrete water samples collected from one or more shallow and intermediate water-bearing zones in each borehole.

Open-File Report↗
USGS1997

Results of the application of seismic-reflection and electromagnetic techniques for near-surface hydrogeologic and environmental investigations at Fort Bragg, North Carolina

As part of the U.S. Geological Survey's Resource Conservation and Recovery Act, Facilities Investigations at Fort Bragg, North Carolina, selected geophysical techniques were evaluated for their usefulness as assessment tools for determining subsurface geology, delineating the areal extent of potentially contaminated landfill sites, and locating buried objects and debris of potential environmental concern. Two shallow seismic-reflection techniques (compression and shear wave) and two electromagnetic techniques (ground-penetrating radar and terrain conductivity) were evaluated at several sites at the U.S. Army Base. The electromagnetic techniques also were tested for tolerance to cultural noise, such as nearby fences, vehicles, and power lines. For the terrain conductivity tests, two instruments were used--the EM31 and EM34, which have variable depths of exploration. The shallowest reflection event was 70 feet below land surface observed in common-depth point, stacked compression-wave data from 24- and 12-fold shallow-seismic-reflection surveys. Several reflection events consistent with clay-sand interfaces between 70 and 120 feet below land surface, along with basement-saprolite surfaces, were imaged in the 24-fold, common- depth-point stacked data. 12-fold, common-depth-point stacked data set contained considerably more noise than the 24-fold, common-depth-point data, due to reduced shot-to-receiver redundancy. Coherent stacked reflection events were not observed in the 24-fold, common-depth-point stacked shear-wave data because of the partial decoupling of the shear- wave generator from the ground. At one site, ground-penetrating radar effectively delineated a shallow, 2- to 5-foot thick sand unit bounded by thin (less than 1 foot) clay layers. The radar signal was completely attenuated where the overlying and underlying clay units thickened and the sand unit thinned. The pene- tration depth of the radar signal was less than 10 feet below land surface. A slight increase in electromagnetic conductivity across shallow sampling EM31 and EM34 profiles provided corroborative evidence of the shallow, thickening clay units. Plots of raw EM31 and EM34 data provided no direct interpretable information to delineate sand and clay units in the shallow subsurface. At two sites, the ground-penetrating radar effectively delineated the lateral continuity of surficial sand units 5 to 25 feet in thickness and the tops of their underlying clay units. The effective exploration depth of the ground-penetrating radar was limited by the proximity of clay units to the subsurface and their thickness. The ground-penetrating radar delineated the areal extent and depth of cover at a previously unrecognized extension of a trench-like landfill underlying a vehicle salvage yard. Attenuation of the radar signal beneath the landfill cover and the adjacent subsurface clays made these two mediums indistinguishable by ground-penetrating radar; however, EM31 data indicated that the electrical conductivity of the landfill was higher than the subsurface material adjacent to the landfill. The EM31 and EM34 conductivity surveys defined the areal extent of a landfill whose boundaries were inaccurately mapped, and also identified the locations of an old dumpsite and waste incinerator site at another landfill. A follow-up ground-penetrating radar survey of the abandoned dumpsite showed incongruities in some of the shallow radar reflections interpreted as buried refuse dispersed throughout the landfill. The ground-penetrating radar and EM31 effectively delineated a shallow buried fuel-oil tank. Of the three electromagnetic instruments, the ground-penetrating radar with the shielded 100-megahertz antenna was the least affected by cultural noise followed, in order, by the EM31 and EM34. The combination of terrain- conductivity and ground-penetrating radar for the site assessment of the landfill provided a powerful means to identify the areal extent of the landfill, potenti

Water-Resources Investigations Report↗
USGS2014

Magnetic studies by the Geophysical Section of the United States Geological Survey

Continued progress has been made in magnetic surveys over large sectional areas by G. R. MacCarthy. Beginning in Florida south of the Okeefenokee Swamp, magnetic traverses were measured and continued through the southern part of Georgia. The most northerly traverses crossed regions where they contacted the crystallines near the surface of the ground. All traverses were run in an east‐west direction. It is planned to continue the magnetic relief‐map described in the Transactions of 1939 of the American Geophysical Union by adding to it this portion of the State of Georgia.

Eos, Transactions, American Geophysical Union↗
USGS2017

Stratigraphic cross sections of the Niobrara interval of the Cody Shale and associated rocks in the Wind River Basin, central Wyoming

The Wind River Basin in Wyoming is one of many structural and sedimentary basins that formed in the Rocky Mountain foreland during the Laramide orogeny. The basin is nearly 200 miles long, 70 miles wide, and encompasses about 7,400 square miles in central Wyoming. The basin is bounded by the Washakie Range, Owl Creek uplift, and southern Bighorn Mountains on the north, the Casper arch on the east, the Granite Mountains on the south, and Wind River Range on the west. Many important conventional oil and gas fields producing from reservoirs ranging in age from Mississippian through Tertiary have been discovered in this basin. In addition, an extensive unconventional overpressured basin-centered gas accumulation has been identified in Cretaceous and Tertiary strata in the deeper parts of the basin. It has long been suggested that various Upper Cretaceous marine shales, including the Cody Shale, are the principal hydrocarbon source rocks for many of these accumulations. With recent advances and success in horizontal drilling and multistage fracture stimulation, there has been an increase in exploration and completion of wells in these marine shales in other Rocky Mountain Laramide basins that were traditionally thought of only as hydrocarbon source rocks. The two stratigraphic cross sections presented in this report were constructed as part of a project carried out by the U.S. Geological Survey to characterize and evaluate the undiscovered continuous (unconventional) oil and gas resources of the Niobrara interval of the Upper Cretaceous Cody Shale in the Wind River Basin in central Wyoming. The primary purpose of the cross sections is to show the stratigraphic relationship of the Niobrara equivalent strata and associated rocks in the lower part of the Cody Shale in the Wind River Basin. These two cross sections were constructed using borehole geophysical logs from 37 wells drilled for oil and gas exploration and production, and one surface section along East Sheep Creek near Shotgun Butte in the northwestern part of the basin. Both lines originate at the East Sheep Creek surface section and end near Clarkson Hill in the extreme southeastern part of the basin. The stratigraphic interval extends from the upper part of the Frontier Formation to the middle part of the Cody Shale. The datum is the base of the “chalk kick” marker bed, a distinctive resistivity peak or zone in the lower part of the Cody Shale. A gamma ray and (or) spontaneous potential (SP) log was used in combination with a resistivity log to identify and correlate units. Marine molluscan index fossils collected from nearby outcrop sections were projected into the subsurface to help determine the relative ages of the strata and aid in correlation.

Wyoming↗
USGS1972

Geological and geophysical investigations of an Apollo 9 photo anomaly near Point of Pines, Arizona

An infrared photograph of southeastern Arizona, taken during the Apollo 9 multispectral terrain photography experiment in 1969, reveals a ringlike feature, some 3-4 miles (5-6 kin) in diameter, on the Natanes Plateau, 35 miles (56 kin) north of the town of Safford. Because the feature occurs in an area of nearly flat lying Tertiary volcanic rocks, the possibilities of its being a small collapse caldera or an exposed circular intrusive body were considered. Geological and geophysical studies of the area were made to test these hypotheses. The local stratigraphic section consists of approximately 1,500 feet (457 m) of Oligocene and perhaps older volcanic rocks, resting on a moderately irregular basement surface carved from nearly flat lying trending Basin-and-Range faults define a broad horst within which two arcuate cross faults, with 300-600 feet (91-183 m) of displacement, bound a downdropped area. Deep erosion along these faults has created a polygonal network of canyons which constitutes the 'ring' seen on the photograph. A mild arching of the volcanic rocks within the ring is suggested by structure contours on the base of the youngest flows. A sharp 350-gamma positive aeromagnetic anomaly is centered within the ring. In its southwest quadrant the anomaly has an elongate extension that trends northwest along an adjoining Basin-and-Range fault. Associated with both is a subtle gravity low. The geophysical data thus suggest the presence of a small blind silicic pluton, possibly of middle Tertiary or younger age. Although it can be argued that the arcuate faults and mild arching of the volcanic pile are related to this postulated pluton, no evidence of hydrothermal alteration or thermal metamorphism of the country rocks was seen. Thus if a pluton is present and of postvolcanic age, it must have been emplaced as a relatively cool dry body; or alternatively, it is older than the surface volcanic rocks. In either instance, its magnetic expression contrasts with that of the known mineralized Laramide porphyry intrusive bodies of the region.

Arizona↗
USGS1998

Freshwater resources and saline water near the Sac and Fox Nation tribal lands, eastern Lincoln County, Oklahoma

The purpose of this project was to evaluate the freshwater resources and possible sources of high-chloride and high-sulfate concentrations in parts of the aquifer near the Sac and Fox Nation tribal land in eastern Lincoln County, Oklahoma. Water-quality sampling and borehole geophysical data indicate the potential for fresh ground water on tribal land generally is greatest in the Vanoss Formation, in the SE1/4 sec. 21, T. 14 N., R. 06 E. and in the NE1/4 sec. 22, T. 14 N., R. 06 E. These locations avoid the flood-prone areas and borehole geophysical resistivity logs indicate the altitude of the base of fresh ground water is below 650 ft. The altitude of the base of fresh ground water is indicated to be generally near the surface under the W1/2 sec. 22, T. 14 N., R. 06 E., the SE1/4 sec. 22, SE1/4 SE1/4 NE1/4 sec. 21, and NE1/4 NW1/4 NW1/4 sec. 27. Conditions are more favorable for placement of fresh ground-water wells in sec. 34, T. 14 N., R. 06 E., where the tribe has leased water rights, than on tribal land in secs. 15, 16, 21, and 22, T. 14 N., R. 06 E. Sandstones overlain by or enclosed in thick clay and shale sequences are likely to be somewhat isolated from the flow system and retain some of the residual brine. Borehole geophysical logs suggest that sandstones near CH1, CM1, and WT1 have more clay and shale content than the sandstones near L2. Greater amounts of clay in the sandstones will retard the flushing of residual brines from the sandstones and could result in a shallow base of fresh water near CH1, CM1, and WT1. For these reasons and because circulation of fresh ground water is limited by discharge to the Deep Fork, general water quality under tribal land would probably be poorer than in the area where the tribe has leased water rights. Samples have chloride or sulfate concentrations greater than 250 milligrams per liter in the W1/2 sec. 22, T. 14 N., R. 06 E. Six cluster well samples from tribal land have chloride or sulfate concentrations above the suggested maximum contaminant levels set by U.S. Environmental Protection Agency. Water-quality data indicate there may be more than one source for the salinity in the very saline and briny samples near the tribal land. Two possible sources for chloride and sulfate in water-quality samples are shallow brines and deep oil brines. Probable sources of shallow brines in the study area are: 1) solution of minerals by fresh water moving through the aquifer and 2) residual brines deposited with the sediment. There are no salt or gypsum beds in the Vanoss, Ada, or Vamoosa Formations, but there may be nodules and finely disseminated minerals present in the formations. Residual brines could remain in sand stones and shales that have low hydraulic conductivity and have not been diluted by freshwater recharge. Data suggest both sources have mixed with the fresh ground water from the Vanoss Formation. This is indicated by the relations of the bromide/chloride concentration ratio to chloride concentration, delta deuterium to delta 18oxygen, and by delta 18oxygen to chloride molality relation.

Water-Resources Investigations Report↗
USGS2012

Short-period strain (0.1–105 s): Near-source strain field for an earthquake (ML 3.2) near San Juan Bautista, California

Measurements of dilational earth strain in the frequency band 25–10 −5 Hz have been made on a deep borehole strainmeter installed near the San Andreas fault. These data are used to determine seismic radiation fields during nuclear explosions, teleseisms, local earthquakes, and ground noise during seismically quiet times. Strains of less than 10 −10 on these instruments can be clearly resolved at short periods (< 10 s) and are recorded with wide dynamic range digital recorders. This permits measurement of the static and dynamic strain variations in the near field of local earthquakes. Noise spectra for earth strain referenced to 1 (strain) 2 /Hz show that strain resolution decreases at about 10 dB per decade of frequency from −150 dB at 10 −4 Hz to −223 dB at 10 Hz. Exact expressions are derived to relate the volumetric strain and displacement field for a homogeneous P wave in a general viscoelastic solid as observed on colocated dilatometers and seismometers. A rare near-field recording of strain and seismic velocity was obtained on May 26, 1984, from an earthquake ( M L 3.2) at a hypocentral distance of 3.2 km near the San Andreas fault at San Juan Bautista, California. While the data indicate no precursory strain release at the 5 × 10 −11 strain level, a coseismic strain release of 1.86 nanostrain was observed. This change in strain is consistent with that calculated from a simple dislocation model of the event. Ground displacement spectra, determined from the downhole strain data and instrument-corrected surface seismic data, suggest that source parameters estimated from surface recordings may be contaminated by amplification effects in near-surface low-velocity materials.

California↗
USGS1999

Evaluation of geophysical logs, Phase II, at Willow Grove Naval Air Station Joint Reserve Base, Montgomery County, Pennsylvania

Between March and April 1998, the U.S. Navy contracted Tetra Tech NUS Inc., to drill two monitor wells in the Stockton Formation at the Willow Grove Naval Air Station Joint Reserve Base, Horsham Township, Montgomery County, Pa. The wells MG-1634 and MG-1635 were installed to monitor water levels and sample contaminants in the shallow, intermediate, and deep water-producing zones of the fractured bedrock. Chemical analyses of the samples will help determine the horizontal and vertical distribution of any contaminated ground water migrating from known contaminant sources. Wells were drilled near the Fire Training Area (Site 5). Depths of all boreholes range from 69 to 149 feet below land surface. The U.S. Geological Survey conducted borehole geophysical logging and video surveys to identify water-producing zones in newly drilled monitor wells MG-1634 and MG-1635 and in wells MG-1675 and MG-1676. The logging was conducted from March 5, 1998, to April 16, 1998. This work is a continuation of the Phase I work. Caliper logs and video surveys were used to locate fractures; inflections on fluid-temperature and fluid-resistivity logs were used to locate possible water-producing fractures. Heatpulse-flowmeter measurements were used to verify the locations of water-producing or water-receiving zones and to measure rates of flow between water-bearing fractures. Single-point-resistance and natural-gamma logs provided information on stratigraphy. After interpretation of geophysical logs, video surveys, and driller's notes, wells MG-1634 and MG-1635 were screened such that water-levels fluctuations could be monitored and discrete water samples collected from one or more water-producing zones in each borehole.

Pennsylvania↗
USGS2021

Time-domain electromagnetic soundings and passive-seismic measurements for delineation of saline groundwater in the Genesee Valley-fill aquifer system, western New York, 2016–17

The U.S. Geological Survey, in cooperation with the New York State Department of Environmental Conservation, used noninvasive surface geophysics in the investigation of the distribution of saline groundwater in the valley-fill aquifer system of the Genesee River Valley near the former Retsof salt mine in western New York. In 1994, the Retsof salt mine, the largest of its kind in the western hemisphere, underwent a catastrophic roof collapse that resulted in groundwater inflow from the valley-fill aquifer system and bedrock fracture zones into the mine through two bedrock-rubble chimneys and the subsequent dissolution and filling of the mine with saturated brine. Since the early 2000s, except for a period of remedial pumping in 2006 to 2013, high-salinity water has migrated upward through the rubble chimneys into the basal part the aquifer system. The extent of saline-water migration within the aquifer system had not been evaluated since the end of remedial pumping when all the monitoring wells were grouted shut and abandoned. Installation of a monitoring-well network would be expensive and difficult given the thickness and heterogeneous character of valley fill. An investigation of the current extent of saline water in the aquifer system was warranted because the basal part of the aquifer is shallow to the north and it is used for water supply. In fall 2016 and fall 2017, the U.S. Geological Survey collected time-domain electromagnetic soundings at 105 sites along 13 cross-valley transects north and south of the mine-collapse area, east of Piffard, and on the Fowlerville Moraine. The time-domain electromagnetic soundings were colocated with passive-seismic measurements to estimate the bedrock-surface elevation through use of a regression equation developed from measurements at well sites with reported bedrock depths in the study area. An integrated analysis of the time-domain electromagnetic soundings with the depth-to-bedrock estimates, well logs, and past chloride-monitoring data suggests the presence of a zone of high electrical conductivity associated with saline water in the confined lower part of the valley-fill aquifer system. This high-salinity zone delineated in the lower confined aquifer extends from the mine-collapse area northward for more than 2.5 miles (4.0 kilometers). The chloride concentration in groundwater within this high-conductivity zone may be about 20,000 milligrams per liter. Saline water flowing upward through the bedrock-rubble chimneys and mixing with northward groundwater flow in the lower confined aquifer likely is a major source of chlorides for this high-conductivity zone. The northern extent of the zone is unclear because of the presence of highly saline water zones that were delineated by time-domain electromagnetic soundings in the lower confined aquifer and uppermost bedrock and are probably associated with historic salt-solution wells in Piffard or possibly sourced from natural brine pools.

New York↗
USGS2012

Seismic refraction analysis: the path forward

Seismic Refraction Methods: Unleashing the Potential and Understanding the Limitations; Tucson, Arizona, 29 March 2012 A workshop focused on seismic refraction methods took place on 29 May 2012, associated with the 2012 Symposium on the Application of Geophysics to Engineering and Environmental Problems. This workshop was convened to assess the current state of the science and discuss paths forward, with a primary focus on near-surface problems but with an eye on all applications. The agenda included talks on these topics from a number of experts interspersed with discussion and a dedicated discussion period to finish the day. Discussion proved lively at times, and workshop participants delved into many topics central to seismic refraction work.

Eos, Transactions, American Geophysical Union↗
USGS2005

Use of discrete-zone monitoring systems for hydraulic characterization of a fractured-rock aquifer at the University of Connecticut Landfill, Storrs, Connecticut, 1999 to 2002

The U.S. Geological Survey, in cooperation with the University of Connecticut, used a suite of hydraulic methods to characterize the hydrogeology of a fractured-rock aquifer near the former landfill and chemical-waste disposal pits at the University of Connecticut, Storrs, Connecticut. Multiple methods were used to determine head, driving potential, and transmissivity, including manual open-hole water-level and discretezone water-level measurements from 11 boreholes; continuous discrete-zone water-level measurements from 6 of the boreholes; estimated head and transmissivity for 11 boreholes using heat-pulse flowmeter profiles and pumping records; and differential head testing using a straddle-packer apparatus from 4 boreholes. These data were analyzed to identify and characterize relations between long-term water-level patterns and precipitation, topographic setting, contaminant distribution at the site, and a conceptual ground-water flow model. Data collected using the heat-pulse flowmeter, the straddle-packer apparatus, and discrete-zone monitoring (DZM) systems helped to establish, refine, and verify a conceptual model of ground-water flow in the study area. Monitoring of DZM systems installed in 11 boreholes provided a method for longterm monitoring of hydraulic head and water quality of the aquifer at fracture zones of different depths. These data were used to help define the conceptual site model for ground-water flow and to determine and explain the distribution of contamination. Hydrographs constructed for discretely isolated zones in the boreholes showed the magnitude of seasonal changes of water levels and driving potential in response to precipitation and drought. Heads in discrete zones and in different boreholes varied both in magnitude of response and in timing of response to precipitation. Water levels in open boreholes and in DZM systems showed a semi-diurnal pattern that coincides with gravimetric tidal plots generated for this area. No fluctuations that might indicate pumping were identified in the continuous water-level records. Lack of hydraulic response between boreholes during cross-hole testing in the area of the former chemical-waste disposal pits indicates poor hydraulic connection between the boreholes that were tested. In general, data indicated the presence of downward driving potentials in the recharge areas and in the area of the ground-water divide, and upward driving potentials in discharge areas north and south of the landfill. The results of this study illustrate the importance of discrete-zone isolation and monitoring in fractured-rock aquifers to prevent cross contamination while permitting head measurements and water-quality sampling that can be used to identify and characterize contamination or pathways for contaminant migration in a fractured-rock aquifer. Without DZM systems installed in the boreholes, only open-hole heads can be measured. The open-hole heads may be misleading when determining potential flow directions at contamination sites, because they are a composite of the heads associated with each of the fractures intersecting the borehole. The flowmeter tool and straddle-packer apparatus are effective screening tools for generating a snapshot of the hydraulic conditions, including vertical flow, transmissivity, and heads; however, they cannot prevent flow and potential cross-contamination and cannot easily be used to monitor long-term conditions. This work was conducted as part of a larger multidisciplinary investigation to characterize the nature and extent of contamination in the soil, surface water, and ground water in the overburden and fractured bedrock in the area of the landfill and former chemical-waste disposal pits near the University of Connecticut. The methods and hydraulic data presented in this report were used along with surface- and borehole-geophysical data and geochemical data to understand and characterize the ground-water flow in overburden and fractured bedrock; to assess possible chemical migration; to develop a site conceptual ground-water flow model; and to assess remediation alternatives.

Connecticut↗
USGS2011

Analysis of group-velocity dispersion of high-frequency Rayleigh waves for near-surface applications

The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave velocity profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-velocity dispersion for S-wave velocity estimation with a few exceptions applying Rayleigh-wave group-velocity dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase velocities with group velocities with three four-layer models including a low-velocity layer or a high-velocity layer. Then synthetic data are simulated by a finite difference method. Images of group-velocity dispersive energy of the synthetic data are generated using the Multiple Filter Analysis (MFA) method. Finally we invert a high-frequency surface-wave group-velocity dispersion curve of a real-world example. Results demonstrate that (1) the sensitivities of group velocities are higher than those of phase velocities and usable frequency ranges are wider than that of phase velocities, which is very helpful in improving inversion stability because for a stable inversion system, small changes in phase velocities do not result in a large fluctuation in inverted S-wave velocities; (2) group-velocity dispersive energy can be measured using single-trace data if Rayleigh-wave fundamental-mode energy is dominant, which suggests that the number of shots required in data acquisition can be dramatically reduced and the horizontal resolution can be greatly improved using analysis of group-velocity dispersion; and (3) the suspension logging results of the real-world example demonstrate that inversion of group velocities generated by the MFA method can successfully estimate near-surface S-wave velocities.

Journal of Applied Geophysics↗