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Thomas J. Mack

Publications and source records attributed to Thomas J. Mack.

At least 37 records · Page 2Linked to original sources
USGS2005

Hydrogeologic framework and water quality of the Vermont Army National Guard Ethan Allen Firing Range, northern Vermont, October 2002 through December 2003

The Ethan Allen Firing Range of the Vermont Army National Guard is a weapons-testing and training facility in a mountainous region of Vermont that has been in operation for about 80 years. The hydrologic framework and water quality of the facility were assessed between October 2002 and December 2003. As part of the study, streamflow was continuously measured in the Lee River and 24 observation wells were installed at 19 locations in the stratified drift and bedrock aquifers to examine the hydrogeology. Chemical analyses of surface water, ground water, streambed sediment, and fish tissue were collected to assess major ions, trace elements, nutrients, and volatile and semivolatile compounds. Sampling included 5 surface-water sites sampled during moderate and low-flow conditions; streambed-sediment samples collected at the 5 surface-water sites; fish-tissue samples collected at 3 of the 5 surface-water sites; macroinvertebrates collected at 4 of the 5 surface-water sites; and ground-water samples collected from 10 observation wells, and samples collected at all surface- and ground-water sites. The hydrogeologic framework at the Ethan Allen Firing Range is dominated by the upland mountain and valley setting of the site. Bedrock wells yield low to moderate amounts of water (0 to 23 liters per minute). In the narrow river valleys, layered stratified-drift deposits of sand and gravel of up to 18 meters thick fill the Lee River and Mill Brook Valleys. In these deposits, the water table is generally within 3 meters below the land surface and overall ground-water flow is from east to west. Streamflow in the Lee River averaged 0.72 cubic meters per second (25.4 cubic feet per second) between December 2002 and December 2003. Streams are highly responsive to precipitation events in this mountainous environment and a comparison with other nearby watersheds shows that Lee River maintains relatively high streamflow during dry periods. Concentrations of trace elements and nutrients in surface-water samples are well below freshwater-quality guidelines for the protection of aquatic life. Brook-trout samples collected in 1992 and 2003 show trace-metal concentrations have decreased over the past 11 years. concentrations in water samples are well below levels that restrict swimming at all five stream sites at moderate and low-flow conditions and in all observation wells. Comparisons among surface-water, streambed-sediment, and biological samples collected in 2003 to earlier studies at the Ethan Allen Firing Range indicate water-quality conditions are similar or have improved over the past 15 years. Ground water in the stratified-drift aquifers at the facility is well buffered with relatively high alkalinities and pH greater than 6. Concentrations of arsenic, cadmium, chromium, lead, nickel, uranium, and zinc were below detection levels in ground-water samples. Barium, cobalt, copper, iron, manganese, molybdenum, and strontium were the only trace elements detected in ground-water samples. Cobalt and iron were detected at low levels in two wells near Mill Brook, and copper was detected at the detection limit in one of these wells. These same two wells had concentrations of barium and manganese 2 to 10 times greater than other ground-water samples. Concentrations of nutrients are at or below detection levels in most ground-water samples. Volatile organic compounds and semivolatile organic compounds were not detected in any water samples from the Ethan Allen Firing Range.

Scientific Investigations Report↗
USGS2003

Geophysical characterization of fractured bedrock at Site 8, former Pease Air Force Base, Newington, New Hampshire

Borehole-geophysical logs collected from eight wells and direct-current resistivity data from three survey lines were analyzed to characterize the fractured bedrock and identify transmissive fractures beneath the former Pease Air Force Base, Newington, N.H. The following logs were used: caliper, fluid temperature and conductivity, natural gamma radiation, electromagnetic conductivity, optical and acoustic televiewer, and heat-pulse flowmeter. The logs indicate several foliation and fracture trends in the bedrock. Two fracture-correlated lineaments trending 28? and 29?, identified with low-altitude aerial photography, are coincident with the dominant structural trend. The eight boreholes logged at Site 8 generally have few fractures and have yields ranging from 0 to 40 gallons per minute. The fractures that probably resulted in high well yields (20?40 gallons per minute) strike northeast-southwest or by the right hand rule, have an orientation of 215?, 47?, and 51?. Two-dimensional direct-current resistivity methods were used to collect detailed subsurface information about the overburden, bedrock-fracture zone depths, and apparent-dip directions. Analysis of data inversions from data collected with dipole-dipole and Schlumberger arrays indicated electrically conductive zones in the bedrock that are probably caused by fractured rock. These zones are coincident with extensions of fracture-correlated lineaments. The fracture-correlated lineaments and geophysical-survey results indicate a possible northeast-southwest anisotropy to the fractured rock.

Open-File Report↗
USGS2003

Approximate potentiometric surface of the bedrock aquifer at Great Bay, southeastern New Hampshire, 2001

Ground-water elevations (heads) in 265 wells were used to map the potentiometric-head surface in the fractured-bedrock aquifer adjacent to Great Bay, N.H. Remotely sensed data, spring-water temperatures and specific conductances, land-surface elevations, and simulated heads were also used to guide construction of the potentiometric surface. Heads in the bedrock aquifer locally varied more than 20 ft (feet) between adjacent wells as little as 200 ft apart. The depth to water below land surface was greater on the western and northwestern sides of the bay (about 20 ft) than on the southern and eastern sides (about 8 ft). Topography has a greater effect on heads than does temporal variation or measurement accuracy. Head gradients are steeper at the southern side of Great Bay, where the topographic relief is greatest, than at the northwestern and northeastern sides.

Open-File Report↗
USGS2001

Geophysical investigations of well fields to characterize fractured-bedrock aquifers in southern New Hampshire

Bedrock-fracture zones near high-yield bedrock wells in southern New Hampshire well fields were located and characterized using seven surface and six borehole geophysical survey methods. Detailed surveys of six sites with various methods provide an opportunity to integrate and compare survey results. Borehole geophysical surveys were conducted at three of the sites to confirm subsurface features. Hydrogeologic settings, including a variety of bedrock and surface geologic materials, were sought to gain an insight into the usefulness of the methods in varied terrains. Results from 15 survey lines, 8 arrays, and 3 boreholes were processed and interpreted from the 6 sites. The surface geophysical methods used provided physical properties of fractured bedrock. Seismic refraction and ground-penetrating radar (GPR) primarily were used to characterize the overburden materials, but in a few cases indicated bedrock-fracture zones. Magnetometer surveys were used to obtain background information about the bedrock to compare with other results, and to search for magnetic lows, which may result from weathered fractured rock. Electromagnetic terrain conductivity surveys (EM) and very-low-frequency electromagnetic surveys (VLF) were used as rapid reconnaissance techniques with the primary purpose of identifying electrical anomalies, indicating potential fracture zones in bedrock. Direct-current (dc) resistivity methods were used to gather detailed subsurface information about fracture depth and orientation. Two-dimensional (2-D) dc-resistivity surveys using dipole-dipole and Schlumberger arrays located and characterized the overburden, bedrock, and bedrock-fracture zones through analysis of data inversions. Azimuthal square array dc-resistivity survey results indicated orientations of conductive steep-dipping bedrock-fracture zones that were located and characterized by previously applied geophysical methods. Various available data sets were used for site selection, characterizations, and interpretations. Lineament data, developed as a part of a statewide and regional scale investigation of the bedrock aquifer, were available to identify potential near-vertical fracture zones. Geophysical surveys indicated fracture zones coincident with lineaments at 4 of the sites. Geologic data collected as a part of the regional scale investigation provided outcrop fracture measurements, ductile fabric, and contact information. Dominant fracture trends correspond to the trends of geophysical anomalies at 4 of the sites. Water-well drillers’ logs from water supply and environmental data sets also were used where available to characterize sites. Regional overburden information was compiled from stratified-drift aquifer maps and surficial-geological maps.

New Hampshire↗
USGS2001

Simulated Ground-Water-Flow Responses to Geohydrologic Characteristics, Corinna, Maine

Ground-water-flow simulations of an idealization of surficial and bedrock aquifers of the East Branch Sebasticook River Valley, in Corinna, Maine, were done to test the effects of known or hypothesized geohydrologic characteristics on the local and regional ground-water-flow system. The purpose of the simulations was to develop a better understanding of the aquifer system to aid in planning for the eventual removal of contaminants. The effects of eight individual geohydrologic characteristics on simulated ground-water flow were compared with a base simulation. The eight geohydrologic characteristics simulated were (1) a northeast-southwest transmissive bedding- plane fracture system, (2) a northwest-southeast valley floor transmissive fracture zone, (3) an upper weathered bedrock transmissive zone, (4) river- and pond-stage changes, (5) river- and pondbottom conductivity changes, (6) multiple withdrawals, (7) a combination of some of these characteristics, and (8) relocation of a pond-outlet stream. The effects of many of the analyzed characteristics are slight or relatively minor with respect to a simulated bedrock aquifer. The simulated ground-water flow through the bedrock aquifer is a small percentage (about 1 percent) of the total flow to the system; therefore, the effects of most geohydrologic characteristics simulated are minimal in the aquifer. Some characteristics, for example, anisotropy imparted on the bedrock system by a northeast-southwest transmissive bedding-plane fracture system, strongly affect flow patterns in the bedrock aquifer but not in the surficial aquifer. Individually, most of the geohydrologic characteristics evaluated only slightly affect the groundwater flow in the bedrock; however, in combination, these characteristics significantly affected the entire simulated ground-water-flow system. Domestic or remedial withdrawal wells generally had little effect on the regional ground-water-flow system but did affect the local ground-water-flow patterns, which could affect the extent and movement of contaminants.

Water-Resources Investigations Report↗
USGS1999

Borehole-geophysical characterization of a fractured-bedrock aquifer, Rye, New Hampshire

Borehole geophysical logs collected from six wells were analyzed to characterize a high-yield bedrock aquifer in the Town of Rye, New Hampshire. Video camera, caliper, fluid temperature and conductivity, natural gamma, and deviation logs were used to identify and characterize the fractured bedrock. More advanced geophysical tools included acoustic televiewer and borehole radar, which were used to determine the orientation of fractures and fracture zones that intersect and surround each of the six wells. Borehole-radar surveys included single-hole directional-reflection surveys. The borehole radar logs indicate that the bedrock aquifer is highly fractured. Zones of low velocity and high attenuation in the radar logs correlated with the fractures and fracture zones observed in the standard geophysical logs of the six wells. The strikes of the fracture sets, as determined by the acoustic televiewer, coincide with photolineaments identified on high-altitude and low-altitude aerial photography and side-looking airborne radar (SLAR). The coincident fracture sets and lineaments trend N100°E, N140°E, N170°E, and N40°E.

New Hampshire↗
USGS1995

Design of monitor wells, hydrogeology, and ground-water quality beneath Country Pond, Kingston, New Hampshire

Ten monitoring well were installed in May 1993 to collect data on the hydrogeology and ground-water quality beneath Country Pond, in Kingston, New Hampshire. Monitoring wells were installed 4 to 48 feet beneath the pond surface in stratified drift that was up to 40 feet thick. The stratified drift is overlain by up to 35 feet of fine-grained, predominantly organic, lake-bottom sediment. The potentiometric head in the aquifer was at or above the pond surface and up to 0.8 foot above the pond surface at one location. Water-quality analyses detected numerous volatile organic compounds including chloroethane, benzene, dichlorobenzenes, and 1,1-dichloroethane at maximum concentrations of 110, 43, 54, and 92 mg/L, respectively. The maximum concentration of total volatile organic compounds detected in ground water from a monitoring well was 550 mg/L in November 1993. Ground-water samples with high concentrations of volatile organic compounds also had elevated specific conductances indicating the presence of other non-organic contaminants. Water-quality analyses indicate that a plume of contaminated ground water extends at least 300 feet in a northeast direction beneath the pond.

Open-File Report↗
USGS1995

Hydrogeology, simulated ground-water flow, and ground-water quality at two landfills in Bristol, Vermont

A study was done to describe the hydrogeology of unconsolidated deposits, simulated ground-water flow, and ground-water quality at two landfills in Bristol, Vermont. The study area is characterized by a glacial delta greater than 200 feet thick on the west flank of the Green Mountains. An upper unconfined, coarse-grained glacial aquifer and a lower fine-grained glacial aquifer are separated throughout most of the study area by a sand, silt, and clay confining unit. A two-layer ground-water flow model was designed and calibrated to estimate ground-water-flow paths form the aquifers beneath the landfills. Large upward head gradients of 0.03 to 0.30 foot per foot are the result of ground water leaking from the underlying bedrock aquifer, which caused ground-water flow to concentrate in the upper aquifer. Most simulated ground-water-flow paths in the lower glacial aquifer beneath the landfills crossed into the upper aquifer. Simulated ground- water-flow paths in the upper aquifer, beneath the landfills, remained in the upper aquifer. Ground water characterized as landfill leachate, or influenced by landfill leachate, has a median specific conductance of 700 microseimens per centimeter at 25 degrees Celsius. Landfill leachate contained mean concentrations 1.5 to 10 times the background concentrations of common constituents and metals, including calcium, potassium, sodium, chloride, iron, magnesium, and manganese. Trace metals detected in the leachate included copper, nickel, zinc, cobalt, lead, and arsenic. Ten volatile organic compounds were found at four observation wells associated with one landfill and three volatile organic compounds were found at two observation wells associated with the record landfill. No one volatile organic compound was consistently found and detections were generally at or near detection limits.

Water-Resources Investigations Report↗
USGS1992

Geohydrology of, and simulation of ground-water flow in, the Milford-Souhegan glacial-drift aquifer, Milford, New Hampshire

Hydrogeologic data collected since 1990 were assessed and a ground-water-flow model was refined in this study of the Milford-Souhegan glacial-drift aquifer in Milford, New Hampshire. The hydrogeologic data collected were used to refine estimates of hydraulic conductivity and saturated thickness of the aquifer, which were previously calculated during 1988-90. In October 1990, water levels were measured at 124 wells and piezometers, and at 45 stream-seepage sites on the main stem of the Souhegan River, and on small tributary streams overlying the aquifer to improve an understanding of ground-water-flow patterns and stream-seepage gains and losses. Refinement of the ground-water-flow model included a reduction in the number of active cells in layer 2 in the central part of the aquifer, a revision of simulated hydraulic conductivity in model layers 2 and representing the aquifer, incorporation of a new block-centered finite-difference ground-water-flow model, and incorporation of a new solution algorithm and solver (a preconditioned conjugate-gradient algorithm). Refinements to the model resulted in decreases in the difference between calculated and measured heads at 22 wells. The distribution of gains and losses of stream seepage calculated in simulation with the refined model is similar to that calculated in the previous model simulation. The contributing area to the Savage well, under average pumping conditions, decreased by 0.021 square miles from the area calculated in the previous model simulation. The small difference in the contrib- uting recharge area indicates that the additional data did not enhance model simulation and that the conceptual framework for the previous model is accurate.

Water-Resources Investigations Report↗