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USGS2000

Detection of conduit-controlled ground-water flow in northwestern Puerto Rico using aerial photograph interpretation and geophysical methods

The development potential of ground-water resources in the karst limestone of northwestern Puerto Rico, in an area extending from the Río Camuy to Aguadilla, is uncertain as a result of limited knowledge of the location of areas where a high density of cavities (interconnected fractures, conduits, and other dissolution features) might suggest the occurrence of high water yields. The presence in northwestern Puerto Rico of numerous coastal submarine springs, cavernous porosity in some of the wells, and rivers with entrenched and underground paths, indicate that it is probable that water-bearing, subterranean interconnected cavities occur in the area between the Río Camuy and Aguadilla. The number of exploratory wells needed to determine the location of these conduits or zones of enhanced secondary porosity could be substantially reduced if more information were available about the location of these subterranean features, greatly reducing the drilling costs associated with a trial-and-error exploratory process. A 3-year study was conducted by the U.S. Geological Survey, in cooperation with the Puerto Rico Aqueduct and Sewer Authority, to detect the presence of cavities that might suggest the occurrence of conduit-controlled groundwater flow. Aerial photographs, geologic and topographic maps, and field reconnaissance were used to identify such linear terrain features as ridges, entrenched canyons, and fracture traces. Natural potential and gravity geophysical methods were also used. The following sites were selected for the aerial photograph interpretation and geophysical testing: Caimital Bajo uplands and former Ramey Air Force Base in Aguadilla; Quebrada de los Cedros between Aguadilla and Isabela; the University of Puerto Rico Agricultural Experiment Station, Otilio dairy farm, and Pozo Brujo in Isabela; the Monte Encantado area in Moca and Isabela; and the Rio Camuy cave system in Hatillo and Camuy. In general, the degree of success varied with site and the geophysical method used. At some sites such as Pozo Brujo, the University of Puerto Rico Agricultural Experiment Station, and Monte Encantado area, natural potential anomalies strongly suggest the existence of conduits with flowing water. At most sites, however, the results obtained did not clearly reveal the presence of subsurface cavities that might be associated with the occurrence of conduit-controlled ground-water flow. Sites such as the University of Puerto Rico Agricultural Experiment Station, Pozo Brujo, and Quebrada de los Cedros warrant a more detailed analysis, including a test well drilling phase to confirm the presence of suspected high-yield water-bearing zones.

Water-Resources Investigations Report↗

USGS2000

Hydrogeology and simulation of ground-water flow at the Gettysburg Elevator Plant Superfund Site, Adams County, Pennsylvania

Ground water in Triassic-age sedimentary fractured-rock aquifers in the area of Gettysburg, Pa., is used as drinking water and for industrial and commercial supply. In 1983, ground water at the Gettysburg Elevator Plant was found by the Pennsylvania Department of Environmental Resources to be contaminated with trichloroethene, 1,1,1-trichloroethane, and other synthetic organic compounds. As part of the U.S. Environmental Protection Agency?s Comprehensive Environmental Response, Compensation, and Liability Act, 1980 process, a Remedial Investigation was completed in July 1991, a method of site remediation was issued in the Record of Decision dated June 1992, and a Final Design Report was completed in May 1997. In cooperation with the U.S. Environmental Protection Agency in the hydrogeologic assessment of the site remediation, the U.S. Geological Survey began a study in 1997 to determine the effects of the onsite and offsite extraction wells on ground-water flow and contaminant migration from the Gettysburg Elevator Plant. This determination is based on hydrologic and geophysical data collected from 1991 to 1998 and on results of numerical model simulations of the local ground-water flow-system. The Gettysburg Elevator Site is underlain by red, green, gray, and black shales of the Heidlersburg Member of the Gettysburg Formation. Correlation of natural-gamma logs indicates the sedimentary rock strike about N. 23 degrees E. and dip about 23 degrees NW. Depth to bedrock onsite commonly is about 6 feet but offsite may be as deep as 40 feet. The ground-water system consists of two zones?a thin, shallow zone composed of soil, clay, and highly weathered bedrock and a thicker, nonweathered or fractured bedrock zone. The shallow zone overlies the bedrock zone and truncates the dipping beds parallel to land surface. Diabase dikes are barriers to ground-water flow in the bedrock zone. The ground-water system is generally confined or semi-confined, even at shallow depths. Depth to water can range from flowing at land surface to more than 71 feet below land surface. Potentiometric maps based on measured water levels at the Gettysburg Elevator Plant indicate ground water flows from west to east, towards Rock Creek. Multiple-well aquifer tests indicate the system is heterogeneous and flow is primarily in dipping beds that contain discrete secondary openings separated by less permeable beds. Water levels in wells open to the pumped bed, as projected along the dipping stratigraphy, are drawn down more than water levels in wells not open to the pumped bed. Ground-water flow was simulated for steady-state conditions prior to pumping and long-term average pumping conditions. The three-dimensional numerical flow model (MODFLOW) was calibrated by use of a parameter estimation program (MODFLOWP). Steady-state conditions were assumed for the calibration period of 1996. An effective areal recharge rate of 7 inches was used in model calibration. The calibrated flow model was used to evaluate the effectiveness of the current onsite and offsite extraction well system. The simulation results generally indicate that the extraction system effectively captures much of the ground-water recharge at the Gettysburg Elevator Plant and, hence, contaminated ground-water migrating from the site. Some of the extraction wells pump at low rates and have very small contributing areas. Results indicate some areal recharge onsite will move to offsite extraction wells.

Pennsylvania↗

USGS2001

Use of advanced borehole geophysical techniques to delineate fractured-rock ground-water flow and fractures along water-tunnel facilities in northern Queens County, New York

Advanced borehole geophysical methods were used to assess the geohydrology of crystalline bedrock along the course of a new water tunnel for New York City. The logging methods include natural gamma, spontaneous potential, single-point resistance, mechanical and acoustic caliper, focused electromagnetic induction, electromagnetic resistivity, magnetic susceptibility, borehole-fluid temperature and conductance, differential temperature, heat-pulse flowmeter, acoustic televiewer, borehole deviation, optical televiewer, and borehole radar. Integrated interpretation of the geophysical logs from an 825-foot borehole (1) provided information on the extent, orientation, and structure (foliation and fractures) within the entire borehole, including intensely fractured intervals from which core recovery may be poor; (2) delineated transmissive fracture zones intersected by the borehole and provided estimates of their transmissivity and hydraulic head; and (3) enabled mapping of the location and orientation of structures at distances as much as 100 ft from the borehole. Analyses of the borehole-wall image and the geophysical logs from the borehole on Crescent Street, in northern Queens County, are presented here to illustrate the application of the methods. The borehole penetrates gneiss and other crystalline bedrock that has predominantly southeastward dipping foliation and nearly horizontal and southeastward-dipping fractures. The heat-pulse flowmeter logs obtained under pumping and nonpumping conditions, together with the other geophysical logs, indicate five transmissive fracture zones. More than 90 percent of the open-hole transmissivity is associated with a fracture zone 272 feet BLS (below land surface). A transmissive zone at 787 feet BLS that consists of nearly parallel fractures lies within the projected tunnel path; here the hydraulic head is 12 to 15 feet lower than that of transmissive zones above the 315-foot depth. The 60-megahertz directional borehole radar logs indicate the location and orientation of two closely spaced radar reflectors that would intersect the projection of the borehole below its drilled depth. Subsequent excavation of the tunnel past the borehole allowed comparison of the log analysis with conditions observed in the tunnel. The tunnel was found to intersect gneiss with southeastward dipping foliation; many nearly horizontal fractures; and a southeastward dipping fracture zone whose location, character, and orientation was consistent with that of the mapped radar reflectors. The fracture zone produced inflow to the tunnel at a rate of 50 to 100 gallons per minute. All conditions indicated by the logging methods were consistent with those observed within the tunnel.

New York↗

USGS2002

Hydrogeological investigation at Site 5, Willow Grove Naval Air Station/Joint Reserve Base, Horsham Township, Montgomery County, Pennsylvania

The U.S. Geological Survey conducted borehole geophysical logging, collected and analyzed water-level data, and sampled sections of a rock core to determine the concentration of volatile organic compounds in the aquifer matrix of the Stockton Formation. Borehole geophysical logs were run in three monitor wells. At well 05MW04I, the vertical gradient was upward at depths above 42 feet below land surface (ft bls), downward between 42 and 82 ft bls, and upward below 82 ft bls. At well 05MW05I, a downward vertical gradient was present. At well 05MW12I, the vertical gradient was downward above 112 ft bls and upward below 112 ft bls. Three water-bearing fractures in a 17-foot long rock core from 23.5 to 40.5 ft bls were identified and sampled. Three samples were analyzed from each water-bearing fracture—at the fracture face, 2 centimeters (cm) below the fracture, and 4 cm below the fracture. Fifteen compounds were detected; however, concentrations of seven compounds were less than 1 microgram per kilogram (mg/kg) when detected. Concentrations of benzene (from 0.39 to 3.3 mg/kg), 1,1-dichloroethene (1,1-DCE) (from 0.15 to 13 mg/kg), 1,1,1-trichloroethane (TCA) (from 0.17 to 22 mg/kg), and trichloroethylene (TCE) (from 0.092 to 9.6 mg/kg) were detected in all samples. The highest concentrations detected were for toluene, which was detected at a concentration of 32 and 86 mg/kg in the samples from unweathered sandstone at 2 and 4 cm below the fracture, respectively. Concentrations generally decreased with distance below the fracture in the mudstone samples. Concentrations of benzene and toluene increased with distance below the fractures in the unweathered sandstone samples. Concentrations of 1,1-DCE, TCA, and TCE were higher in the mudstone samples than in the samples from sandstone. Toluene concentrations were higher in unweathered sandstone than in weathered sandstone or mudstone. The effect of the pumping of Horsham Water and Sewer Authority public supply well 26 (HWSA-26), 0.2 mile southwest of the base boundary, on groundwater levels on the base was determined by shutting the well down for 6 days to allow water levels to recover. Water levels in 22 nearby wells were measured. The only well (02MW01I) that showed an unambiguous response to the shutdown of well HWSA-26 is 1,350 feet directly along strike from well HWSA-26. The recovery of well 05MW11I in response to the shutdown of well HWSA-26 is masked by recharge from snowmelt but probably does not exceed about 0.2 feet on the basis of the water level in well 05MW11I, which showed a response to the pumping of well HWSA-26 that ranged from 0.5 to 0.15 foot. Horizontal gradients differ with depth, and the rate and direction of ground-water ﬂow and contaminant movement is depth dependent. The potentiometric-surface map for water levels measured in wells screened between 5 and 44 ft bls in the aquifer shows a ground-water mound that is the high point on a regional ground-water divide. From this divide, ground water ﬂows both northwest toward Park Creek and southeast toward Pennypack Creek. The hydraulic gradient around this mound is relatively ﬂat to the southeast and particularly ﬂat to the northwest. The potentiometric-surface map for water levels measured in wells screened between 40 and 100 ft bls in the aquifer shows a very ﬂat hydraulic gradient. Differences in the elevation of the potentiometric surface are less than 2 feet. The potentiometric-surface map for water levels measured in wells screened between 105 and 179 ft bls in the aquifer shows a steep hydraulic gradient between Sites 5 and 2 and a relatively ﬂat hydraulic gradient between Sites 5 and 3. Water levels measured on October 7, 1999, showed downward vertical head gradients for all well clusters at Site 5. Vertical gradients ranged from 0.01 at well cluster 05MW10 to 0.2 at cluster 05MW11. Most gradients were between 0.01 and 0.026. Vertical head gradients vary with time. The variability is caused by a difference in the magnitude of water-level ﬂuctuations between shallow and the deep fractures. The difference in the magnitude of water-level ﬂuctuations is because of differences in lithology and aquifer storativity.

Pennsylvania↗

USGS2014

Latest Quaternary paleoseismology and evidence of distributed dextral shear along the Mohawk Valley fault zone, northern Walker Lane, California

The dextral-slip Mohawk Valley fault zone (MVFZ) strikes northwestward along the eastern margin of the Sierra Nevada in the northern Walker Lane. Geodetic block modeling indicates that the MVFZ may accommodate ~3 mm/yr of regional dextral strain, implying that it is the highest slip-rate strike-slip fault in the region; however, only limited geologic data are available to constrain the system’s slip rate and earthquake history. We mapped the MVFZ using airborne lidar data and field observations and identified a site near Sulphur Creek for paleoseismic investigation. At this site, oblique dextral-normal faulting on the steep valley margin has created a closed depression that floods annually during spring snowmelt to form an ephemeral pond. We excavated three fault-perpendicular trenches at the site and exposed pond sediment that interfingers with multiple colluvial packages eroded from the scarp that bounds the eastern side of the pond. We documented evidence for four surface-rupturing earthquakes on this strand of the MVFZ. OxCal modeling of radiocarbon and luminescence ages indicates that these earthquakes occurred at 14.0 ka, 12.8 ka, 5.7 ka, and 1.9 ka. The mean ~4 kyr recurrence interval is inconsistent with slip rates of ~3 mm/yr; these rates imply surface ruptures of more than 10 m per event, which is geologically implausible for the subdued geomorphic expression and 60 km length of the MVFZ. We propose that unidentified structures not yet incorporated into geodetic models may accommodate significant dextral shear across the northern Walker Lane, highlighting the role of distributed deformation in this region.

California↗

USGS2011

Field Reconnaissance Geologic Mapping of the Columbia Hills, Mars: Results from MER Spirit and MRO HiRISE Observations

Chemical, mineralogic, and lithologic ground truth was acquired for the first time on Mars in terrain units mapped using orbital Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (MRO HiRISE) image data. Examination of several dozen outcrops shows that Mars is geologically complex at meter length scales, the record of its geologic history is well exposed, stratigraphic units may be identified and correlated across significant areas on the ground, and outcrops and geologic relationships between materials may be analyzed with techniques commonly employed in terrestrial field geology. Despite their burial during the course of Martian geologic time by widespread epiclastic materials, mobile fines, and fall deposits, the selective exhumation of deep and well-preserved geologic units has exposed undisturbed outcrops, stratigraphic sections, and structural information much as they are preserved and exposed on Earth. A rich geologic record awaits skilled future field investigators on Mars. The correlation of ground observations and orbital images enables construction of a corresponding geologic reconnaissance map. Most of the outcrops visited are interpreted to be pyroclastic, impactite, and epiclastic deposits overlying an unexposed substrate, probably related to a modified Gusev crater central peak. Fluids have altered chemistry and mineralogy of these protoliths in degrees that vary substantially within the same map unit. Examination of the rocks exposed above and below the major unconformity between the plains lavas and the Columbia Hills directly confirms the general conclusion from remote sensing in previous studies over past years that the early history of Mars was a time of more intense deposition and modification of the surface. Although the availability of fluids and the chemical and mineral activity declined from this early period, significant later volcanism and fluid convection enabled additional, if localized, chemical activity.

Journal of Geophysical Research E: Planets↗

USGS2024

Geologic map of Scoggins Dam, Henry Hagg Lake, and Scoggins Valley, Washington County, Oregon

New geologic mapping (Wells and others, 2020b) and geophysical mapping (Blakely and others, 2000; McPhee and others, 2014; Wells and others, 2020a) document kilometers of Cenozoic right-lateral offset along the Gales Creek Fault Zone, a major, northwest-striking fault zone forming the boundary between the Tualatin Valley and the Coast Range. The Bureau of Reclamation’s (Reclamation) Scoggins Dam (fig. 1), in the Coast Range foothills west of Forest Grove, Oregon, lies within the Gales Creek Fault Zone as mapped by Wells and others (2020a, 2020b; fig. 2). Active faults of the Gales Creek Fault Zone defined by paleoseismic trenching (Redwine and others, 2017, 2019b, Horst and others, 2018, 2019, 2021, and Wells and others, 2020a) are presently mapped as projecting through the existing dam. The Pacific Northwest Region of Reclamation requested assistance with geologic studies around Scoggins Dam to provide better understanding of fault locations and their activity, which are needed to design a modification of the dam (Maguire, 2019a, b). The scope of this project includes detailed geology of the existing Scoggins Dam site, Henry Hagg Lake, the reservoir behind the dam, and Scoggins Valley downstream of the existing dam, particularly around a potential new dam site, where Scoggins Creek cuts through a narrow gap formed by a resistant felsic tuff bed that crosses the valley.

Oregon↗

USGS2012

Airborne electromagnetic mapping of the base of aquifer in areas of western Nebraska

Airborne geophysical surveys of selected areas of the North and South Platte River valleys of Nebraska, including Lodgepole Creek valley, collected data to map aquifers and bedrock topography and thus improve the understanding of groundwater - surface-water relationships to be used in water-management decisions. Frequency-domain helicopter electromagnetic surveys, using a unique survey flight-line design, collected resistivity data that can be related to lithologic information for refinement of groundwater model inputs. To make the geophysical data useful to multidimensional groundwater models, numerical inversion converted measured data into a depth-dependent subsurface resistivity model. The inverted resistivity model, along with sensitivity analyses and test-hole information, is used to identify hydrogeologic features such as bedrock highs and paleochannels, to improve estimates of groundwater storage. The two- and three-dimensional interpretations provide the groundwater modeler with a high-resolution hydrogeologic framework and a quantitative estimate of framework uncertainty. The new hydrogeologic frameworks improve understanding of the flow-path orientation by refining the location of paleochannels and associated base of aquifer highs. These interpretations provide resource managers high-resolution hydrogeologic frameworks and quantitative estimates of framework uncertainty. The improved base of aquifer configuration represents the hydrogeology at a level of detail not achievable with previously available data.

Nebraska↗

USGS2014

A multiphased approach to groundwater investigations for the Edwards-Trinity and related aquifers in the Pecos County region, Texas

The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and public supply uses in the Pecos County region of western Texas. Resource managers would like to understand the future availability of water in the Edwards-Trinity aquifer in the Pecos County region and the effects of the possible increase or temporal redistribution of groundwater withdrawals. To provide resource managers with that information, the U.S. Geological Survey (USGS), in cooperation with the Middle Pecos Groundwater Conservation District, Pecos County, City of Fort Stockton, Brewster County, and Pecos County Water Control and Improvement District No. 1, completed a three-phase study of the Edwards-Trinity and related aquifers in parts of Brewster, Jeff Davis, Pecos, and Reeves Counties. The first phase was to collect groundwater, surface-water, geochemical, geophysical, and geologic data in the study area and develop a geodatabase of historical and collected data. Data compiled in the first phase of the study were used to develop the conceptual model in the second phase of the study. The third phase of the study involved the development and calibration of a numerical groundwater-flow model of the Edwards-Trinity aquifer to simulate groundwater conditions based on various groundwater-withdrawal scenarios. Analysis of well, geophysical, geochemical, and hydrologic data contributed to the development of the conceptual model in phase 1. Lithologic information obtained from well reports and geophysical data was used to describe the hydrostratigraphy and structural features of the groundwater-flow system, and aquifer-test data were used to estimate aquifer hydraulic properties. Geochemical data were used to evaluate groundwater-flow paths, water-rock interaction, aquifer interaction, and the mixing of water from different sources in phase 2. Groundwater-level data also were used to evaluate aquifer interaction, as well as to develop a potentiometric-surface map, delineate regional groundwater divides, and describe regional groundwater-flow paths. During phase 3, the data collected and compiled along with the conceptual information in the study area were incorporated into a numerical groundwater-flow model to evaluate the sustainability of recent (2008) and projected water-use demands on groundwater resources in the study area.

Texas↗

USGS2006

Geophysical Investigations of the Smoke Creek Desert and their Geologic Implications, Northwest Nevada and Northeast California

The Smoke Creek Desert is a large basin about 100 km (60 mi) north of Reno near the California-Nevada border, situated along the northernmost parts of the Walker Lane Belt, a physiographic region defined by diverse topographic expression consisting of northweststriking topographic features and strike-slip faulting. Because geologic and geophysical framework studies play an important role in understanding the hydrogeology of the Smoke Creek Desert, a geophysical effort was undertaken to help determine basin geometry, infer structural features, and estimate depth to basement. In the northernmost parts of the Smoke Creek Desert basin, along Squaw Creek Valley, geophysical data indicate that the basin is shallow and that granitic rocks are buried at shallow depths throughout the valley. These granitic rocks are faulted and fractured and presumably permeable, and thus may influence ground-water resources in this area. The Smoke Creek Desert basin itself is composed of three large oval sub-basins, all of which reach depths to basement of up to about 2 km (1.2 mi). In the central and southern parts of the Smoke Creek Desert basin, magnetic anomalies form three separate and narrow EW-striking features. These features consist of high-amplitude short-wavelength magnetic anomalies and probably reflect Tertiary basalt buried at shallow depth. In the central part of the Smoke Creek Desert basin a prominent EW-striking gravity and magnetic prominence extends from the western margin of the basin to the central part of the basin. Along this ridge, probably composed of Tertiary basalt, overlying unconsolidated basin-fill deposits are relatively thin (< 400 m). The central part of the Smoke Creek Desert basin is also characterized by the Mid-valley fault, a continuous geologic and geophysical feature striking NS and at least 18-km long, possibly connecting with faults mapped in the Terraced Hills and continuing southward to Pyramid Lake. The Mid-valley fault may represent a lateral (east-west) barrier to ground-water flow. In addition, the Mid-valley fault may also be a conduit for along-strike (north-south) ground-water flow, channeling flow to the southernmost parts of the basin and the discharge areas north of Sand Pass.

Open-File Report↗

USGS1984

Map showing outcrops of granitic rocks, Basin and Range Province, Nevada

This map report is one of a series of geologic and hydrologic maps covering all or parts of States within the Basin and Range province of the western United States. The map reports contain information on subjects that characterize the geohydrology of the province, including the ground-water hydrology, ground-water quality, surface distribution of selected rock types, tectonic conditions, areal geophysics, Pleistocene lakes and marshes, and mineral and energy resources. This work is a part of the U.S. Geological Survey's program for geologic and hydrologic evaluation of the Basin and Range province to identify potentially suitable regions for further study relative to isolation of high-level nuclear waste (Bedinger, Sargent, and Reed, 1984). Data for this report were taken largely from Spengler and others (1979), supplemented by data from individual geologic maps and reports, following the project guidelines as defined in Sargent and Bedinger (1984). As used in this report, granitic rocks include granodiorite, quartz monzonite, and granite, and locally associated mafic rocks such as diorite and gabbro. In the Snake Range and Ruby Mountains, Stewart (1980) has recognized large areas as metamorphic core complexes, and in these complexes some plutonic masses may not extend to great depth because of lateral displacement along low-angle faults subsequent to intrusion. The Description of Map Units includes the sources of data, the geologic, and if available, the radiometric age, lithologic character, type of intrusive body and relation to rock units, where known, for the granitic rocks within outlined and numbered areas in each county of the study area. The radiometric ages of the rock units are only those which are available and do not necessarily represent the entire age range of the geologic units.

Nevada↗

USGS2006

Geologic Map of the Mylitta Fluctus Quadrangle (V-61), Venus

INTRODUCTION The Magellan Mission The Magellan spacecraft orbited Venus from August 10, 1990, until it plunged into the Venusian atmosphere on October 12, 1994. Magellan Mission objectives included: (1) improving knowledge of the geological processes, surface properties, and geologic history of Venus by analysis of surface radar characteristics, topography, and morphology, and (2) improving the knowledge of the geophysics of Venus by analysis of Venusian gravity. The Magellan spacecraft carried a 12.6-cm radar system to map the surface of Venus. The transmitter and receiver systems were used to collect three data sets: (1) synthetic aperture radar (SAR) images of the surface, (2) passive microwave thermal emission observations, and (3) measurements of the backscattered power at small angles of incidence, which were processed to yield altimetric data. Radar imaging, altimetric, and radiometric mapping of the Venusian surface was done in mission cycles 1, 2, and 3 from September 1990 until September 1992. Ninety-eight percent of the surface was mapped with radar resolution on the order of 120 meters. The SAR observations were projected to a 75-m nominal horizontal resolution, and these full-resolution data compose the image base used in geologic mapping. The primary polarization mode was horizontal-transmit, horizontal-receive (HH), but additional data for selected areas were collected for the vertical polarization sense. Incidence angles varied between about 20? and 45?. High resolution Doppler tracking of the spacecraft took place from September 1992 through October 1994 (mission cycles 4, 5, 6). Approximately 950 orbits of high-resolution gravity observations were obtained between September 1992 and May 1993 while Magellan was in an elliptical orbit with a periapsis near 175 km and an apoapsis near 8,000 km. An additional 1,500 orbits were obtained following orbit-circularization in mid-1993. These data exist as a 75? by 75? harmonic field.

Scientific Investigations Map↗

USGS2015

Seismic-sequence stratigraphy and geologic structure of the Floridan aquifer system near "Boulder Zone" deep wells in Miami-Dade County, Florida

The U.S. Geological Survey, in cooperation with the Miami-Dade Water and Sewer Department, acquired, processed, and interpreted seismic-reflection data near the North and South District “Boulder Zone” Well Fields to determine if geologic factors may contribute to the upward migration of injected effluent into that upper part of the Floridan aquifer system designated by the U.S. Environmental Protection Agency as an underground source of drinking water. The depth of the Boulder Zone at the North and South District “Boulder Zone” Well Fields ranges from about 2,750 to 3,300 feet below land surface (ft bls), whereas overlying permeable zones used as alternative drinking water supply range in depth from about 825 to 1,580 ft bls at the North and South District “Boulder Zone” Well Fields. Seismic-sequence stratigraphy and geologic structures imaged on seismic-reflection profiles created for the study describe the part of the Floridan aquifer system overlying and within the Boulder Zone. Features of the Floridan aquifer system underlying the Boulder Zone were not studied because seismic-reflection profiles acquired near the North and South District “Boulder Zone” Well Fields lacked adequate resolution at such depths. Stratigraphic analysis of seismic-reflection data collected from the study area was mainly applied to the Floridan aquifer system and used to identify four provisional seismic sequences, which extend vertically from near the base of the Floridan aquifer system upward to the lower part of the intermediate confining unit. These four seismic sequences compose a framework in which each sequence includes a major permeable unit of the Floridan aquifer system; from shallowest to deepest, these units are the Upper Floridan aquifer, Avon Park permeable zone, uppermost major permeable zone of the Lower Floridan aquifer, and Boulder Zone. The relations between seismic-sequence stratigraphy and hydrostratigraphy allow for detailed mapping of permeable zones and semiconfining units of the Floridan aquifer system at a level of resolution never before accomplished using well data alone. In addition to the preceding seismic-reflection analysis, interpretation of geophysical well log data from four effluent injection wells at the North District “Boulder Zone” Well Field delineated a narrow karst collapse structure beneath the injection facility that extends upward about 900 ft from the top of the Boulder Zone to about 125 ft above the top of the uppermost major permeable zone of the Lower Floridan aquifer. No karst collapse structures were identified in the seismic-reflection profiles acquired near the North District “Boulder Zone” Well Field. However, karst collapse structures at the level of the lowermost major permeable zone of the Lower Floridan aquifer at the South District “Boulder Zone” Well Field are present at three locations, as indicated by seismic-reflection data acquired in the C–1 Canal bordering the south side of the injection facility. Results from the North District “Boulder Zone” Well Field well data indicate that a plausible hydraulic connection between faults and stratiform permeability zones may contribute to the upward transport of effluent, terminating above the base of the deepest U.S. Environmental Protection Agency designated underground source of drinking water at the North District “Boulder Zone” Well Field.

Florida↗

USGS2018

Investigating the origin of continual radio frequency impulses during explosive volcanic eruptions

Volcanic lightning studies have revealed that there is a relatively long‐lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning. This very high frequency signal is referred to as “continual radio frequency (CRF)” due to its long‐lasting nature. The discharge mechanism producing this signal was previously hypothesized to be caused by numerous, small (10–100 m) leader‐forming discharges near the vent of the volcano. To test this hypothesis, a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of Sakurajima Volcano in Japan was collected from May to June 2015. Our observations show that a single CRF impulse has a duration on the order of 160 ns (giving an upper limit on discharge length of 10 m) and is distinct from near‐vent lightning discharges that were on the order of 30 m in length. CRF impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field. Lightning mapping data and infrared video observations of the eruption column showed that CRF impulses originated from the gas thrust region of the column. These observations indicate that CRF impulses are not produced by small, leader‐forming discharges but rather are more similar to a streamer discharge, likely on the order of a few meters in length.

Sakurajima Volcano↗

USGS2021

California deepwater investigations and groundtruthing (Cal DIG) I: Fault and shallow geohazard analysis offshore Morro Bay

The California Deepwater Investigations and Groundtruthing (Cal DIG) I project focuses on the potential seafloor hazards and impacts of alternative energy infrastructure in the outer continental shelf region offshore of south-central California. This is one of three reports covering a single study area located between Monterey and Point Conception, California in federal waters outside of the State of California three nautical mile limit and in water depths of 400 to 1500 meters. The goal of this report is to provide baseline geologic interpretations of the area for the purpose of improving regional models of shallow geologic hazards and sedimentary processes. Geophysical and geological data from this project will help to address important issues associated with marine spatial planning and potential offshore infrastructure development, such as offshore floating wind turbines. Datasets covered in this report include comprehensive high-resolution sub-bottom (multi-channel and Chirp seismic reflection profiles), seafloor (bathymetry), and sampling (piston, gravity, and vibracore) data collected in 2018-2019 during a series of seven seagoing geological and geophysical surveys. Specifically, this report outlines interpretation of subsurface geologic structure from the geophysical data, details preliminary core analysis results related to fluid, gas, and sediment transport activity, provides interpretations of the current geohazards in the area, and suggests next steps for improving interpretations of geohazard processes. Specific targets of geohazard interest in the study area are geological structures such as faults and folds, seafloor pockmarks within a large field (the Big Sur pockmark field), submarine channels, and mass wasting (slope failure) features. The vast majority of faults and other structures in the study occur within sediment and rock formations we interpret to be pre-Quaternary (older than 2.58 Myr BP), and thus we interpret that these structures are unlikely to present significant current hazard to seabed infrastructure, although we note that the numerous structures mapped in the study area may have the potential to become reactivated. Similarly, we find no new evidence of Holocene (younger than 11,650 years BP) fluid or gas advection in the Big Sur pockmark field. However, such fluid and gas hazards are currently difficult to assess, as additional analyses and sampling of existing core data is needed to better understand pockmark formation processes and potential gas accumulations we have mapped in the subsurface. Mass wasting along the eastern and western edges of the Santa Lucia Bank during earthquakes, as well as sediment transport down the Lucia Chica and San Simeon channels, are among the most significant, although still likely infrequent during the Holocene, hazards to seabed stability in the study area. Further analyses of the existing cores, including radiocarbon dating, stable isotope, and compositional analyses, are again needed to better understand the timing and sources of the numerous sand deposits found throughout the study area, which may have been transported downslope due to mass wasting and/or earthquake shaking processes.

California↗

USGS1996

Hydrogeology of the surficial and intermediate aquifer systems in Sarasota and adjacent counties, Florida

From 1991 to 1995, the hydrogeology of the surficial aquifer system and the major permeable zones and confining units of the intermediate aquifer system in southwest Florida was studied. The study area is a 1,400-square-mile area that includes Sarasota County and parts of Manatee, De Soto, Charlotte, and Lee Counties. Lithologic, geophysical, hydraulic property, and water-level data were used to correlate the hydrogeology and map the extent of the aquifer systems. Water chemistry was evaluated in southwest Sarasota County to determine salinity of the surficial and intermediate aquifer systems. The surficial aquifer is an unconfined aquifer system that overlies the intermediate aquifer system and ranges from a few feet to over 60 feet in thickness in the study area. Hydraulic properties of the surficial aquifer system determined from aquifer and laboratory tests, and model simulations vary considerably across the study area. The intermediate aquifer system, a confined aquifer system that lies between the surficial and the Upper Floridan aquifers, is composed of alternating confining units and permeable zones. The intermediate aquifer system has three major permeable zones that exhibit a wide range of hydraulic properties. Horizontal flow in the intermediate aquifer system is northeast to southwest. Most of the study area is in a discharge area of the intermediate aquifer system. Water ranges naturally from fresh in the surficial aquifer system and upper permeable zones of the intermediate aquifer system to moderately saline in the lower permeable zone. Water-quality data collected in coastal southwest Sarasota County indicate that ground-water withdrawals from major pumping centers have resulted in lateral seawater intrusion and upconing into the surficial and intermediate aquifer systems.

Florida↗

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↗

USGS2000

On the modified Mercalli intensities and magnitudes of the 1811-1812 New Madrid earthquakes

We reexamine original felt reports from the 1811–1812 New Madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks. In many cases we interpret lower values than those assigned by earlier studies. In some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues. Additionally, earlier studies had assigned modified Mercalli intensity (MMI) values of V-VII to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high. We investigate several approaches to contouring the MMI values using both analytical and subjective methods. For the first mainshock on 02∶15 LT December 16, 1811, our preferred contouring yields M ω7.2–7.3 using the area-moment regressions of Johnston [1996]. For the 08∶00 LT on January 23, 1812, and 03∶45 LT on February 7, 1812, mainshocks, we obtain M ω7.0 and M ω7.4–7.5, respectively. Our magnitude for the February mainshock is consistent with the established geometry of the Reelfoot fault, which all evidence suggests to have been the causative structure for this event. We note that the inference of lower magnitudes for the New Madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern United States. We also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811–1812 sequence.

Arkansas, Illinois, Kentucky, Missouri, Tennessee↗