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At least 523 records · Page 29Linked to original sources

USGS1994

Remote sensing and airborne geophysics in the assessment of natural aggregate resources

Natural aggregate made from crushed stone and deposits of sand and gravel is a vital element of the construction industry in the United States. Although natural aggregate is a high volume/low value commodity that is relatively abundant, new sources of aggregate are becoming increasingly difficult to find and develop because of rigid industry specifications, political considerations, development and transporation costs, and environmental concerns, especially in urban growth centers where much of the aggregate is used. As the demand for natural aggregate increases in response to urban growth and the repair and expansion of the national infrastructure, new sources of natural aggregate will be required. The USGS has recognized the necessity of developing the capability to assess the potential for natural aggregate sources on Federal lands; at present, no methodology exists for systematically describing and evaluating potential sources of natural aggregate. Because remote sensing and airborne geophysics can detect surface and nearsurface phenomena, these tools may useful for detecting and mapping potential sources of natural aggregate; however, before a methodology for applying these tools can be developed, it is necessary to understand the type, distribution, physical properties, and characteristics of natural aggregate deposits, as well as the problems that will be encountered in assessing their potential value. There are two primary sources of natural aggregate: (1) exposed or near-surface igneous, metamorphic, and sedimentary bedrock that can be crushed, and (2) deposits of sand and gravel that may be used directly or crushed and sized to meet specifications. In any particular area, the availability of bedrock suitable for crushing is a function of the geologic history of the area - the processes that formed, deformed, eroded and exposed the bedrock. Deposits of sand and gravel are primarily surficial deposits formed by the erosion, transportation by water and ice, and deposition of bedrock fragments. Consequently, most sand and gravel deposits are Tertiary or Quaternary in age and are most common in glaciated areas, alluvial basins, and along rivers and streams. The distribution of potential sources of natural aggregate in the United States is closely tied to physiography and the type of bedrock that occurs in an area. Using these criteria, the United States can be divided into 12 regions: western mountain ranges, alluvial basins, Columbia Plateau, Colorado Plateau and Wyoming basin, High Plains, nonglaciated central region, glaciated central region, Piedmont Blue Ridge region, glaciated northeastern and Superior uplands, Atlantic and Gulf coastal plain, Hawaiian Islands, and Alaska. Each region has similar types of natural aggregate sources within its boundary, although there may be wide variations in specific physical and chemical characteristics of the aggregates within a region. Conventional exploration for natural aggregate deposits has been largely a ground-based operation (field mapping, sampling, trenching and augering, resistivity), although aerial photos and topographic maps have been extensively used to target possible deposits for sampling and testing. Today, the exploration process also considers other factors such as the availability of the land, space and water supply for processing purposes, political and environmental factors, and distance from the market; exploration and planning cannot be separated. There are many physical properties and characteristics by which aggregate material is judged to be acceptable or unacceptable for specific applications; most of these properties and characteristics pertain only to individual aggregate particles and not to the bulk deposit. For example, properties of crushed stone aggregate particles such as thermal volume change, solubility, oxidation and hydration reactivity, and particle strength, among many others, are important consi

Open-File Report↗

USGS1995

Results of geophysical surveys of glacial deposits near a former waste-disposal site, Nashua, New Hampshire

Geophysical investigations were done near a former waste-disposal site in Nashua, New Hampshire to determine the thickness and infer hydraulic characteristics of the glacial sediments that underlie the area. Approximately 5 miles of ground- penetrating radar (GPR) data were collected in the study area by use of dual-80 Megahertz antennas. Three distinct radar-reflection signatures were evident from the data and are interpreted to represent (1) glacial lake-bottom sediments, (2) coarse sand and gravel and (or) sandy glacial till, and (3) bedrock. The GPR signal penetrated as much as 70 feet of sediment in coarse-grained areas, but penetration depth was generally less than 40 feet in extensive areas of fine-grained deposits. Geologic features were evident in many of the profiles. Glacial-lake-bottom sediments were the most common features identified. Other features include deltas deposited in glacial Lake Nashua and lobate fans of sediment deposited subaqueously at the distal end of deltaic sediments. Cross-bedded sands were often identifiable in the deltaic sediments. Seismic-refraction data were also collected at five of the GPR data sites. In most cases, depths to the water table and to the till and (or) bedrock surface indicated by the seismic-refraction data compared favorably with depths calculated from the GPR data. Test holes were drilled at three locations to determine the true depths to radar reflectors and to determine the types of geologic material represented by the various reflectors.

Open-File Report↗

USGS1997

Stratigraphy and geophysical logs from a corehole drilled to bedrock at Robins Point, J-Field, Edgewood area, Aberdeen Proving Ground, Maryland

A continuous core was recovered from a 961-foot- deep stratigraphic corehole at Robins Point, located at the southeastern tip of the Gunpowder Neck Peninsula, Harford County, Maryland. A 2-inch- diameter ground-water-quality observation well was installed with the screen set at a depth of 392 to 402 feet (ft). Geophysical logs obtained from thecorehole include: natural gamma, multipoint normal resistivity (16-inch and 64-inch), 4-ft-guard focused resistivity, acoustic (sonic) velocity, and caliper. Pollen analysis of 34 samples provided relativestratigraphic ages. Lithologies encountered in ascending order (surface elevation 4 ft above mean sea level), include: 72.4 ft of weatheredmetamorphic rock and saprolie, 711.4 ft of lower and upper Cretaceous fluvio-deltaic deposits, and 145.9 ft of Pleistocene and 31.3 ft of Holocene(?) fluvial and estuarine deposits. Aquifers and confining units identified include, in descending order: 41.8 ft of surficial aquifer, 90.9 ft of upper paleochannel confining unit, 28.8 ft of paleochannel confined aquifer, 15.7 ft of lower paleochannel confining unit, 123.7 ft of Upper Patapsco aquifer, 44.6 ft of Upper Patapsco confining unit, 92.8 ft of Middle Patapsco aquifer, 57.3 ft of Lower Patapsco confining unit, 151.7 ft of Lower Patapsco aquifer, 115.4 ft of Potomac confining unit, 126.4 ft of Patuxent aquifer, an aquifer of 23.4 ft of saprolite, and 48.7 ft of weathered-rock/saprolite confining unit.

Open-File Report↗

USGS1999

Geological and geophysical setting of the gold-silver vein systems of Unga Island, southwestern Alaska

The topic of this CD-ROM is the geologic framework of gold-silver vein deposits on Unga Island, in the Shumagin Islands, southwestern Alaska. The core of the publication is a new geologic map at a scale of 1:63,360 and aeromagnetic and electromagnetic survey data acquired by industry over the area of mineralization. Both the geologic map as well as a preliminary interpretation of the geophysical data - which are included by permission of the owner - are aimed towards deciphering the relations among volcanism, tectonism, and mineralization. Data and discussions are organized in seven chapters, titles of which are outlined in the table of contents. The chapters consist of viewable text and figure images; postscript versions of the frontispiece figures and all chapter figures are included on the CD-ROM as well. The geologic map is a large viewable figure (Plate 1) that accompanies chapter 2. The map was constructed in ARC and its component coverages are provided in the folder 'Geology' for users who may wish to modify the geologic data or add their own data.

Alaska↗

USGS2009

Geophysical Interpretations of the Southern Espanola Basin, New Mexico, That Contribute to Understanding Its Hydrogeologic Framework

The southern Espanola basin consists of a westward- and northward-thickening wedge of rift fill, composed primarily of Santa Fe Group sediments, that serves as an important aquifer for the city of Santa Fe and surrounding areas. Detailed aeromagnetic surveys were flown to better understand ground-water resources in this aquifer. This report presents a synthesis of these data with gravity data and other constraints. The interpretations were accomplished using qualitative interpretation, state-of-art data analysis techniques, and two- and three-dimensional modeling. The results depict the presence of and depth to many geologic features that have hydrogeologic significance, including shallow faults, different types of igneous units, and basement rocks. The results are presented as map interpretations, geophysical profile models, and a digital surface that represents the base and thickness of Santa Fe Group sediments, as well as vector files of some volcanic features and faults.

Professional Paper↗

USGS2008

Maps showing geology, structure, and geophysics of the central Black Hills, South Dakota

This 1:100,000-scale digital geologic map details the complex Early Proterozoic granitic rocks, Early Proterozoic supracrustal metamorphic rocks, and Archean crystalline basement of the Black Hills. The granitic rocks host pegmatite deposits renowned for their feldspar, mica, spodumene, and beryl. The supracrustal rocks host the Homestake gold mine, which produced more than 40 million ounces of gold over a 125-year lifetime. The map documents the Laramide deformation of Paleozoic and Mesozoic cover rocks; and shows the distribution of Laramide plutonic rocks associated with precious-metals deposits. Four 1:300,000-scale maps summarize Laramide structures; Early Proterozoic structures; aeromagnetic anomalies; and gravity anomalies. Three 1:500,000-scale maps show geophysical interpretations of buried Early Proterozoic to Archean rocks in western South Dakota and eastern Wyoming.

South Dakota↗

USGS2008

Well Inventory and Geophysical Logging of Selected Wells in Troup County, Georgia, 2007-2008

The U.S. Geological Survey (USGS) - in cooperation with the Troup County Board of Commissioners - conducted a well inventory to provide information to help evaluate ground-water resources for Troup County, Georgia. In addition, borehole geophysical logs were collected in selected wells to provide a better understanding of the subsurface geologic and water-bearing characteristics in specific areas of interest. This investigation provides information to help guide future ground-water development and water-management decisions for Troup County while enhancing understanding of the hydrogeology of fractured rocks in the Piedmont physiographic province. This report presents well data compiled from USGS files and from site visits to wells during November and December 2007. Data were entered into the USGS National Water Information System (NWIS) and made available on the Web at http://waterdata.usgs.gov/ga/nwis/inventory. Previous studies of ground-water resources have been conducted in the vicinity, but did not include Troup County. The ground-water resources of Heard and Coweta Counties, located north and northeast, respectively, of Troup County were part of a larger study by Cressler and others (1983) that encompassed the Greater Atlanta Region. That study evaluated the quantity and quality of ground water in the Atlanta region and described the methods that could be used for locating high-yielding wells in the Piedmont Province. The geology underlying the Atlanta area is similar to that underlying Troup County. Clarke and Peck (1990) conducted a similar investigation that included Meriwether and Coweta Counties, located to the east and northeast of Troup County.

Georgia↗

USGS2021

Geologic and geophysical maps of the Santa Maria and part of the Point Conception 30'×60' quadrangles, California

This report presents digital geologic, gravity, and aeromagnetic maps for the onshore parts of the Santa Maria and Point Conception 30'x60' quadrangles at a compilation scale of 1:100,000. The map depicts the distribution of bedrock units, surficial deposits, paleontological data, geophysical data and structural features in the Santa Maria basin and the Santa Ynez Mountains to the south, an area corresponding to 26 contiguous 7.5-minute quadrangles. The map also includes offshore faults from the Hosgri fault, a major structural feature, east to the shoreline. This new map revises and supersedes two earlier versions of the 30'x60' Santa Maria quadrangle that were produced as part of the U.S. Geological Survey’s investigations of onshore oil and gas resources of the Santa Maria province (Keller, 1995). The first map was released as a scanned black-and-white image of hand-drawn compilation (Tennyson, 1992); the second map was a digital release that is no longer available (Tennyson and others, 1995). This new map also includes the geology of the onshore part of the adjacent Point Conception 30'x60' quadrangle that encompasses the Santa Ynez Mountains of the western Transverse Ranges. The digital database also contains magnetic and gravity data for the entire region, paleontological data, and interpretation of major offshore structural features that bear on the continuity and connection of the mapped onshore structures.

California↗

USGS2006

A cyclostratigraphic and borehole-geophysical approach to development of a three-dimensional conceptual hydrogeologic model of the karstic Biscayne aquifer, southeastern Florida

A fundamental problem in the simulation of karst ground-water flow and solute transport is how best to represent aquifer heterogeneity as defined by the spatial distribution of porosity, permeability, and storage. Combined analyses of cyclostratigraphy, including lithofacies and depositional environments, and borehole-geophysical logs, has improved the conceptualization of porosity, permeability, and storage within the triple-porosity karstic Biscayne aquifer in an approximately 95-square-mile study area of Miami-Dade County in southeastern Florida. The triple porosity of the Biscayne aquifer is principally: (1) matrix of interparticle and separate-vug porosity, providing much of the storage, and under dynamic conditions, diffuse-carbonate flow; (2) touching-vug porosity creating stratiform ground-water flow passageways; and (3) less common conduit porosity composed mainly of bedding-plane vugs, thin solution pipes, and cavernous vugs. These three conduit porosity types are all pathways for conduit ground-water flow. To develop an accurate three-dimensional conceptual hydrogeologic model of the Biscayne aquifer in the study area, a detailed analysis of data was conducted that include continuously drilled cores, digital borehole images, borehole-fluid conductivity and temperature logs, and borehole-flowmeter measurements from 25 wells that fully penetrate the Biscayne aquifer. Six depositional environments for major lithologic components of the Biscayne aquifer--the Tamiami Formation, Fort Thompson Formation, and Miami Limestone--include: (1) middle ramp, (2) platform margin-to-outer platform, (3) open-marine platform interior, (4) restricted platform interior, (5) brackish platform interior, and (6) freshwater terrestrial environments. High-frequency cycles form the fundamental building blocks of the rocks composing the Biscayne aquifer. Vertical lithofacies successions, which have stacking patterns that reoccur, fit within the high-frequency cycles. Upward-shallowing subtidal cycles, upward-shallowing paralic cycles, and aggradational subtidal cycles define three types of ideal high-frequency cycles that occur within the Fort Thompson Formation and Miami Limestone. Based on vertical cycle patterns, high-frequency cycles group into two cycle sets: an older progradational cycle set and an overlying younger aggradational cycle. A primary observation is that a predictable vertical pattern of porosity and permeability commonly exists within the three ideal cycles because the porosity and permeability relate directly to lithofacies. Sixteen major lithofacies of the Fort Thompson Formation and Miami Limestone have been assigned to one of three pore classes (I, II, and III). Touching-vug porosity and conduit porosity characterize pore class I, which commonly comprises the lower part of upward-shallowing cycles within the Fort Thompson Formation and an upper aggradational cycle of the Miami Limestone. Matrix porosity distinguishes pore class II, which commonly occurs in the upper part of the upward-shallowing subtidal cycles and middle part of the upward-shallowing paralic cycles. Micrite-dominated, leaky, low-permeability lithologies are characteristic of pore class III, which commonly caps upward-shallowing paralic cycles and occurs throughout much of a lower aggradational cycle of the Miami Limestone. These relations among lithofacies, cyclicity, and aquifer attributes (porosity, permeability, and storage) are crucial features of the architecture of a three-dimensional conceptual hydrogeologic model of the karstic Biscayne aquifer. This study shows that development of these relations is critical to producing a realistic cycle-based karstic aquifer framework for the Biscayne aquifer and for karst aquifers within other platform carbonates.

Florida↗

USGS2007

Geophysical delineation of the freshwater/saline-water transition zone in the Barton Springs segment of the Edwards Aquifer, Travis and Hays Counties, Texas, September 2006

During September 2006, the U.S. Geological Survey, in cooperation with the Barton Springs/Edwards Aquifer Conservation District, conducted a geophysical pilot study to determine whether time-domain electromagnetic (TDEM) sounding could be used to delineate the freshwater/saline-water transition zone in the Barton Springs segment of the Edwards aquifer in Travis and Hays Counties, Texas. There was uncertainty regarding the application of TDEM sounding for this purpose because of the depth of the aquifer (200-500 feet to the top of the aquifer) and the relatively low-resistivity clayey units in the upper confining unit. Twenty-five TDEM soundings were made along four 2-3-mile-long profiles in a study area overlying the transition zone near the Travis-Hays County boundary. The soundings yield measurements of subsurface electrical resistivity, the variations in which were correlated with hydrogeologic and stratigraphic units, and then with dissolved solids concentrations in the aquifer. Geonics Protem 47 and 57 systems with 492-foot and 328-foot transmitter-loop sizes were used to collect the TDEM soundings. A smooth model (vertical delineation of calculated apparent resistivity that represents an estimate [non-unique] of the true resistivity) for each sounding site was created using an iterative software program for inverse modeling. The effectiveness of using TDEM soundings to delineate the transition zone was indicated by comparing the distribution of resistivity in the aquifer with the distribution of dissolved solids concentrations in the aquifer along the profiles. TDEM sounding data show that, in general, the Edwards aquifer in the study area is characterized by a sharp change in resistivity from west to east. The western part of the Edwards aquifer in the study area shows higher resistivity than the eastern part. The higher resistivity regions correspond to lower dissolved solids concentrations (freshwater), and the lower resistivity regions correspond to higher dissolved solids concentrations (saline water). On the basis of reasonably close matches between the inferred locations of the freshwater/saline-water transition zone in the Edwards aquifer in the study area from resistivities and from dissolved solids concentrations in three of the four profiles, TDEM sounding appears to be a suitable tool for delineating the transition zone.

Texas↗

USGS2009

Integrated Geophysical Investigation of Preferential Flow Paths at the Former Tyson Valley Powder Farm near Eureka, Missouri, May 2006

In May 2006, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, conducted surface and borehole geophysical surveys at the former Tyson Valley Powder Farm near Eureka, Mo., to identify preferential pathways for potential contaminant transport along the bedrock surface and into dissolution-enhanced fractures. The Tyson Valley Powder Farm was formerly used as a munitions storage and disposal facility in the 1940s and 1950s, and the site at which the surveys were performed was a disposal area for munitions and waste solvents such as trichloroethylene and dichloroethylene. Direct-current resistivity and seismic refraction data were acquired on the surface; gamma, electromagnetic induction, and full waveform sonic logs were acquired in accessible boreholes. Through the combined interpretation of the seismic refraction tomographic and resistivity inversion results and borehole logs, inconsistencies in the bedrock surface were identified that may provide horizontal preferential flow paths for dense nonaqueous phase liquid contaminants. These results, interpreted and displayed in georeferenced three-dimensional space, should help to establish more effective monitoring and remediation strategies.

Scientific Investigations Report↗

USGS2013

Geophysical and hydrologic analysis of an earthen dam site in southern Westchester County, New York

Ninety percent of the drinking water for New York City passes through the Hillview Reservoir facility in the City of Yonkers, Westchester County, New York. In the past, several seeps located downslope from the reservoir have flowed out from the side of the steepest slope at the southern end of the earthen embankment. One seep that has been flowing continuously was discovered during an inspection of the embankment in 1999. Efforts were made in 2001 to locate the potential sources of the continuous flowing seep. In 2005, the U.S. Geological Survey, in cooperation with the New York City Department of Environmental Protection, began a cooperative study to investigate the relevant hydrogeologic framework to characterize the local groundwater-flow system and to determine possible sources of the seeps. The two agencies used hydrologic and surface geophysical techniques to assess the earthen embankment of the Hillview Reservoir. Between April 1, 2005 and March 1, 2008, water levels were measured manually each month at 46 wells surrounding the reservoir, and flow was measured monthly at three of the five seeps on the embankment. Water levels were measured hourly in the East Basin of the reservoir, at 24 of 46 wells, and discharge was measured hourly at two of the five seeps. Slug tests were performed at 16 wells to determine the hydraulic conductivity of the geologic material surrounding the screened zone. Estimated hydraulic conductivities for 25 wells on the southern embankment ranged from 0.0063 to 1.2 feet per day and averaged 0.17 foot per day. The two-dimensional resistivity surveys indicate a subsurface mound of electrically conductive material (low-resistivity zone) beneath the terrace area (top of dam) surrounding the reservoir with a distinct elevation increase closer to the crest. Two-dimensional shear wave velocity surveys indicate a similar structure of the high shear wave velocity materials (high-velocity zone), increasing in elevation toward the crest and decreasing toward the reservoir and toward the northern part of the study area. Water-quality samples collected from 12 wells, downtake chamber 1 of the reservoir, and two seeps detected the presence of arsenic, toluene, and two trihalomethanes. Water-quality samples collected at the two seeps detected fluoride, indicating a connection with reservoir water. Shallow wells on the southern embankment exhibited the largest seasonal water-level fluctuations ranging between 6 feet and 12 feet. The embankment is constructed from reworked low-permeability glacial deposits at the site. Water-level responses in observation wells within the embankment indicate that there is a shallow (approximately the upper 45 feet of the embankment) and a deep water-bearing unit within the embankment with a large downward vertical gradient between the shallow and deep water-bearing units. Precipitation strongly affected water levels in shallow wells, whereas the basin appears to be the main control on water levels in the deep wells. Seeps on the embankment slope appear to be caused by above-average precipitation that increases water levels in the shallow water-bearing unit, but does not easily recharge the deep water-bearing unit. Based on the data that have been analyzed, source water to the seeps appears to be primarily groundwater and, to a lesser extent, water from the East Basin of the reservoir.

New York↗

USGS2016

Geologic and geophysical models for Osage County, Oklahoma, with implications for groundwater resources

This report summarizes a three-dimensional (3-D) geologic model that was constructed to provide a framework to investigate groundwater resources of the Osage Nation in northeastern Oklahoma. This report also presents an analysis of an airborne electromagnetic (AEM) survey that assessed the spatial variation of electrical resistivity to depths as great as 300 meters in the subsurface. The report and model provide support for a countywide assessment of groundwater resources, emphasizing the Upper Pennsylvanian rock units in the shallow subsurface of central and eastern Osage County having electrical resistivity properties that may indicate aquifers. Surface outcrops and subsurface stratigraphic picks on wire-line geophysical logs of Upper Pennsylvanian–Lower Permian sedimentary rock were used to construct a 3-D model of the geologic subsurface as an aid for evaluating groundwater resources in Osage County. Quaternary alluvium and terraces along major streams and the Arkansas River are included in the geologic framework model. Data from the AEM survey were subjected to quality-control procedures, truncated at depth of investigation (DOI), and then used to build a 3-D electrical resistivity model making use of secondary and tertiary interpolation profiles between primary data profiles. The AEM data highlight westward-inclined resistivity gradients that parallel the shallow dip of bedrock strata; bodies have resistivity >30 ohm-meters, and extend as much as 10 kilometers (km) down the dip of host geologic units. Volume analysis and internal imaging of an integrated 3-D geology and electrical resistivity model give a proxy for likely aquifer units with large relative volumes of high resistivity: Quaternary alluvium, Elgin Sandstone Lentil in the upper part of the Vamoosa Group, Tallant Formation, and parts of a combined Wann-Iola-Chanute Formation. Less voluminous, high-resistivity bodies correspond to intervals in the lower part of the Vamoosa Group in the east-central part of the county and probable limestone intervals in the upper part of the Vanoss Group in the northwest part of the county. Northwestern and eastern troughs of potable water previously defined for central Osage County generally correspond to down-dip projections of high-resistivity bodies associated with the Elgin Sandstone Lentil of the Vamoosa Group and Tallant Formation, respectively.

Oklahoma↗

USGS2020

Geophysical surveys, hydrogeologic characterization, and groundwater flow model for the Truxton basin and Hualapai Plateau, northwestern Arizona

This is the third and final report in a series that describe the groundwater resources of the Hualapai Indian Reservation. These reports document the findings of a comprehensive groundwater study conducted on the reservation and adjacent areas from 2015 through 2018 by the U.S. Geological Survey in cooperation with the Bureau of Reclamation. The first report described the hydrologic framework and characterization of the Truxton aquifer on the Hualapai Indian Reservation (Bills and Macy, 2016). The second report described the hydrogeologic characterization of the Hualapai Plateau part of the reservation (Mason, Macy, and others, 2020). This report includes five chapters. Chapter A (Mason, Knight, and others, 2020) is a summary of this multichapter volume and briefly describes the study area. Chapter B (Mason, Bills, and Macy, 2020) describes the geology and hydrology of the Truxton basin and Hualapai Plateau. Chapter C (Kennedy, 2020) describes the results of a gravity geophysical survey of the Truxton basin. Chapter D (Ball, 2020) describes the findings of an airborne electromagnetic survey of the Truxton aquifer and Hualapai Plateau. Chapter E (Knight, 2020) describes the results of a transient groundwater model created for the entire Truxton aquifer both on and off the reservation. The groundwater-flow model is used to estimate projected groundwater levels based on future groundwater withdrawal scenarios.

Arizona↗

USGS2018

PDEPTH—A computer program for the geophysical interpretation of magnetic and gravity profiles through Fourier filtering, source-depth analysis, and forward modeling

PDEPTH is an interactive, graphical computer program used to construct interpreted geological source models for observed potential-field geophysical profile data. The current version of PDEPTH has been adapted to the Windows platform from an earlier DOS-based version. The input total-field magnetic anomaly and vertical gravity anomaly profiles can be filtered to produce derivative products such as reduced-to-pole magnetic profiles, pseudogravity profiles, pseudomagnetic profiles, and upward-or-downward-continued profiles. A variety of source-location methods can be applied to the original and filtered profiles to estimate (and display on a cross section) the locations and physical properties of contacts, sheet edges, horizontal line sources, point sources, and interface surfaces. Two-and-a-half-dimensional source bodies having polygonal cross sections can be constructed using a mouse and keyboard. These bodies can then be adjusted until the calculated gravity and magnetic fields of the source bodies are close to the observed profiles. Auxiliary information such as the topographic surface, bathymetric surface, seismic basement, and geologic contact locations can be displayed on the cross section using optional input files. Test data files, used to demonstrate the source location methods in the report, and several utility programs are included.

Techniques and Methods↗

USGS2001

Surface-geophysical characterization of ground-water systems of the Caloosahatchee River basin, southern Florida

The Caloosahatchee River Basin, located in southwestern Florida, includes about 1,200 square miles of land. The Caloosahatchee River receives water from Lake Okeechobee, runoff from the watershed, and seepage from the underlying ground-water systems; the river loses water through drainage to the Gulf of Mexico and withdrawals for public-water supply and agricultural and natural needs. Water-use demands in the Caloosahatchee River Basin have increased dramatically, and the Caloosahatchee could be further stressed if river water is used to accommodate restoration of the Everglades. Water managers and planners need to know how much water will be used within the river basin and how much water is contributed by Lake Okeechobee, runoff, and ground water. In this study, marine seismic-reflection and ground-penetrating radar techniques were used as a means to evaluate the potential for flow between the river and ground-water systems. Seven test coreholes were drilled to calibrate lithostratigraphic units, their stratal geometries, and estimated hydraulic conductivities to surface-geophysical profiles. A continuous marine seismic-reflection survey was conducted over the entire length of the Caloosahatchee River and extending into San Carlos Bay. Lithostratigraphic units that intersect the river bottom and their characteristic stratal geometries were identified. Results show that subhorizontal reflections assigned to the Tamiami Formation intersect the river bottom between Moore Haven and about 9 miles westward. Oblique and sigmoidal progradational reflections assigned to the upper Peace River Formation probably crop out at the floor of the river in the Ortona area between the western side of Lake Hicpochee and La Belle. These reflections image a regional-scale progradational deltaic depositional system containing quartz sands with low to moderate estimated hydraulic conductivities. In an approximate 6-mile length of the river between La Belle and Franklin Lock, deeper karstic collapse structures are postulated. These structures influence the geometries of parallel reflections that intersect the river channel. Here, reflections assigned to the Buckingham Limestone Member of the Tamiami Formation (a confining unit) and reflections assigned to the clastic zone of the sandstone aquifer likely crop out at the river bottom. Beneath these shallow reflections, relatively higher amplitude parallel reflections of the carbonate zone of the sandstone aquifer are well displayed in the seismic-reflection profiles. In San Carlos Bay, oblique progradational reflections assigned to the upper Peace River Formation are shown beneath the bay. Almost everywhere beneath the river, a diffuse ground-water flow system is in contact with the channel bottom. Ground-penetrating radar profiles of an area about 2 miles north of the depositional axis of the deltaic depositional system in the Ortona area show that progradational clinoforms imaged on seismic reflection profiles in the Caloosahatchee River are present within about 17 feet of the ground surface. Ground-penetrating radar profiles show southward dipping, oblique progradational reflections assigned to the upper Peace River Formation that are terminated at their tops by a toplapping or erosional discontinuity. These clinoformal reflections image clean quartz sand that is probably characterized by moderate hydraulic conductivity. This sand could be mapped using ground-penetrating radar methods.

Water-Resources Investigations Report↗

USGS1987

Surface-geophysical investigations in Melton Valley, Oak Ridge Reservation, Tennessee

Surface geophysical methods were found to be valuable for refining knowledge of the geohydrology of Melton Valley, an area used for burial of low-level radioactive waste at the Oak Ridge Reservation in Tennessee. The valley is characterized by locally complex geologic structures in lithologies of interbedded shale and limestone. Radionuclides have been transported away from the burial areas by groundwater along paths that are, in part, controlled by geologic structures and rock type. Direct current resistivity soundings were used to determine the depth to bedrock and to aid in the delineation of subsurface stratigraphy. Depth to bedrock, as indicated by an increase in resistivity in the interpreted geoelectric layering, was compared to auger-hole data at five sites, where bedrock depths ranged from 1 to 14 ft and were within 3 ft at four sites. The subsurface contact between shale and limestone was indicated by an increase in model calculated resistivity from < 100 to > 150 ohm-meters at four different sites. Terrain conductivity profiles were used to aid in mapping surficial geologic contacts between shale and limestone units. Terrain conductivity for shale at 33-ft coil separation was generally greater than 15 millimhos/m and ranged from about 10 to 40 millimhos/m. Conductivity for limestone was generally < 15 millimhos/m and ranged from 5 to 25 millimhos/m. Azimuthal conductivity surveys indicated that conductivity was generally greatest when the transmitter and receiver coils were oriented parallel to strike. This anisotropy in terrain conductivity shows the need to keep the coil orientation consistent throughout the length of a profile. (Author 's abstract)

Tennessee↗

USGS1993

Techniques for estimating specific yield and specific retention from grain-size data and geophysical logs from clastic bedrock aquifers

Specific yield and specific retention are aquifer characteristics that are important in determining the volume of water in storage in an aquifer. These characteristics can be determined by laboratory analyses of undisturbed samples of aquifer material. However. quicker, less costly alternatives to these laboratory analyses are needed. This report presents techniques for estimating specific yield and specific retention based on grain-size analyses, and based on interpretation of borehole geophysical logs.

Water-Resources Investigations Report↗