Geology Reports⌕ Search

Geology topics

John T. Wilson

Publications and source records attributed to John T. Wilson.

15 recordsLinked to original sources
USGS2022

Populations using public-supply groundwater in the conterminous U.S. 2010; Identifying the wells, hydrogeologic regions, and hydrogeologic mapping units

Most Americans receive their drinking water from publicly supplied sources, a large portion of it from groundwater. Mapping these populations consistently and at a high resolution is important for understanding where the resource is used and needs to be protected. The results show that 269 million people are supplied by public supply, 107 million are supplied by groundwater and 162 million are supplied by surface water. The population using public supply drinking water was mapped in two ways: the census enhanced method (CEM) evenly distributes the population across populated census blocks, and the urban land-use enhanced method (ULUEM) distributes the population only to certain urban land use designations. In addition, a two-dimensional polygon dataset was created for the conterminous U.S. that identifies 177 unique Hydrogeologic Mapping Units (HMUs) with similar hydrogeologic characteristics. The HMUs do not overlap, but they can delineate areas where stacked hydrogeologic regions (HRs) contribute drinking water from below the surface. HRs are waterbearing geologic regions identified as either a principal aquifers (PA) or secondary hydrogeologic regions (SHR). Within each HMU, the wells were used to determine the proportion of each HR that is providing groundwater to the HMU. In 63% of the HMUs, a single HR is providing water to the public supply wells located within it, while the rest of the HMUs show that the wells are tapping up to a maximum of four stacked HRs. In total, groundwater from 108 HRs provide drinking water for public supply, six of which provide more than 50% of the groundwater used for public supply drinking water. The aquifer serving the largest number of equivalent people (>17 million) is the glacial aquifer. The HR providing the greatest number of people per km 2 is the Biscayne aquifer in Florida at nearly 453 people per km 2 .

Science of the Total Environment↗
USGS2019

Drinking water quality in the glacial aquifer system, northern USA

Groundwater supplies 50% of drinking water worldwide, but compromised water quality from anthropogenic and geogenic contaminants can limit usage of groundwater as a drinking water source. Groundwater quality in the glacial aquifer system, USA (GLAC), is presented in the context of a hydrogeologic framework that divides the study area into 17 hydrogeologic terranes. Results are reported at aquifer-system scale and regional (terrane) scale. This paper presents a quantitative assessment of groundwater quality in the GLAC using data from numerous sources for samples collected 2005–2013, compared to health-based and aesthetic (non-health) benchmarks, and evaluated with areal and population metrics. Concentrations above a benchmark are considered high. Trace elements are widespread across the study area, with an estimated 5.7 million people relying on groundwater with high concentrations of one or more trace elements; manganese and arsenic are most often at high concentration. Nitrate is found at high concentration in 4.0% of the study area, serving about 740 thousand people. Organic compounds including pesticides and volatile organic compounds are high in 2.0% of the assessed study area, with about 870 thousand people relying on groundwater with high concentrations of an organic compound. High arsenic and manganese concentrations occur primarily in the terranes with thick, stratigraphically complex, fine-grained glacial sediment, coincident with groundwater under reducing conditions (indicated by iron concentrations >100 μg/L); high nitrate is uncommon in those same terranes. When nitrate is high in thick, fine-grained, complex terranes, though, it is much more commonly associated with groundwater under more oxidizing conditions. Common geogenic trace elements occur at high concentration due to characteristic geologic and geochemical conditions. Conversely, anthropogenic nitrate and organic compounds are introduced at or near the land surface. High concentrations of nitrate or organic compounds are generally limited to areas in proximity where people live and use the chemicals.

Science of Total Environment↗
USGS2015

The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed

The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO 3 ) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO 3 concentrations were used to predict temporal variations in streambed NO 3 removal in response to dynamic SW-GW exchange. NO 3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO 3 .

Indiana↗
USGS2015

Low-flow characteristics for selected streams in Indiana

The management and availability of Indiana’s water resources increase in importance every year. Specifically, information on low-flow characteristics of streams is essential to State water-management agencies. These agencies need low-flow information when working with issues related to irrigation, municipal and industrial water supplies, fish and wildlife protection, and the dilution of waste. Industrial, municipal, and other facilities must obtain National Pollutant Discharge Elimination System (NPDES) permits if their discharges go directly to surface waters. The Indiana Department of Environmental Management (IDEM) requires low-flow statistics in order to administer the NPDES permit program. Low-flow-frequency characteristics were computed for 272 continuous-record stations. The information includes low-flow-frequency analysis, flow-duration analysis, and harmonic mean for the continuous-record stations. For those stations affected by some form of regulation, low-flow frequency curves are based on the longest period of homogeneous record under current conditions. Low-flow-frequency values and harmonic mean flow (if sufficient data were available) were estimated for the 166 partial-record stations. Partial-record stations are ungaged sites where streamflow measurements were made at base flow.

Indiana↗
USGS2013

Impacts of an ethanol-blended fuel release on groundwater and fate of produced methane: simulation of field observations

In a field experiment at Vandenberg Air Force Base (VAFB) designed to mimic the impact of a small-volume release of E10 (10% ethanol and 90% conventional gasoline), two plumes were created by injecting extracted groundwater spiked with benzene, toluene, and o-xylene, abbreviated BToX (No-Ethanol Lane) and BToX plus ethanol (With-Ethanol Lane) for 283 days. We developed a reactive transport model to understand processes controlling the fate of ethanol and BToX. The model was calibrated to the extensive field dataset and accounted for concentrations of sulfate, iron, acetate, and methane along with iron-reducing bacteria, sulfate-reducing bacteria, fermentative bacteria, and methanogenic archaea. The benzene plume was about 4.5 times longer in the With-Ethanol Lane than in the No-Ethanol Lane. Matching this different behavior in the two lanes required inhibiting benzene degradation in the presence of ethanol. Inclusion of iron reduction with negligible growth of iron-reducers was required to reproduce the observed constant degradation rate of benzene. Modeling suggested that vertical dispersion and diffusion of sulfate from an adjacent aquitard were important sources of sulfate in the aquifer. Matching of methane data required incorporating initial fermentation of ethanol to acetate, methane loss by outgassing, and methane oxidation coupled to sulfate and iron reduction. Simulation of microbial growth using dual Monod kinetics, and including inhibition by more favorable electron acceptors, generally resulted in reasonable yields for microbial growth of 0.01-0.05.

California↗
USGS2012

Water-quality assessment of the Cambrian-Ordovician aquifer system in the northern Midwest, United States

This report provides a regional assessment of groundwater quality of the Cambrian-Ordovician aquifer system, based primarily on raw water samples collected by the NAWQA Program during 1995 through 2007. The NAWQA Program has published findings in local study-unit reports encompassing parts of the Cambrian-Ordovician aquifer system. Data collected from the aquifer system were used in national synthesis reports on selected topics such as specific water-quality constituent classes, well type, or aquifer material; however, a synthesis of groundwater quality at the principal aquifer scale has not been completed and is therefore the major purpose of this report. Water samples collected by the NAWQA Program were analyzed for various classes of characteristics including physical properties, major ions, trace elements, nutrients and dissolved organic carbon, radionuclides (tritium, radon, and radium), pesticides, and volatile organic compounds. Subsequent sections of this report provide discussions on these classes of characteristics. The assessment objectives of this report are to (1) summarize constituent concentrations and compare them to human-health benchmarks and non-health guidelines; (2) determine the geographic distribution of constituent concentrations and relate them to various factors such as confining conditions, well type, land use, and groundwater age; and (3) evaluate near-decadal-scale changes in nitrate concentrations and pesticide detections. The most recent sample collected from each well by the NAWQA Program was used for most analyses. Near-decadal-scale changes in nitrate concentrations and pesticide detections were evaluated for selected well networks by using the most recent sample from each well and comparing it to the results from a sample collected 7 or 11 years earlier. Because some of the NAWQA well networks provide a limited areal coverage of the aquifer system, data for raw water samples from other USGS sources and state agencies were included to expand the data coverage into areas between the NAWQA well networks and into northeastern Missouri. Many of the maps in this report that show concentrations of selected constituents include data from other sources to expand on the geographic area covered by the NAWQA data.

Midwest;Cambrian-ordovician Aquifer System↗
USGS2008

Methods and sources of data used to develop selected water-quality indicators for streams and ground water for EPA's 2007 Report on the Environment: Science report

The U.S. Geological Survey (USGS) was one of numerous governmental agencies, private organizations, and the academic community that provided data and interpretations for the U.S. Environmental Protection Agency’s (USEPA) 2007 Report on the Environment: Science Report . This report documents the sources of data and methods used to develop selected water–quality indicators for the 2007 edition of the report compiled by USEPA. Stream and ground–water–quality data collected nationally in a consistent manner as part of the USGS’s National Water–Quality Assessment Program (NAWQA) were provided for several water–quality indicators, including Nitrogen and Phosphorus in Streams in Agricultural Watersheds; Pesticides in Streams in Agricultural Watersheds; and Nitrate and Pesticides in Shallow Ground Water in Agricultural Watersheds . In addition, the USGS provided nitrate (nitrate plus nitrite) and phosphorus riverine load estimates calculated from water–quality and streamflow data collected as part of its National Stream Water Quality Accounting Network (NASQAN) and its Federal–State Cooperative Program for the Nitrogen and Phosphorus Discharge from Large Rivers indicator.

Open-File Report↗
USGS2008

Methods and Sources of Data Used to Develop Selected Water-Quality Indicators for Streams and Ground Water for the 2007 Edition of The State of the Nation's Ecosystems Report with Comparisons to the 2002 Edition

The U.S. Geological Survey (USGS) was one of numerous governmental, private, and academic entities that provided input to the report The State of the Nation?s Ecosystems published periodically by the Heinz Center. This report describes the sources of data and methods used by the USGS to develop selected water?quality indicators for the 2007 edition of the Heinz Center report and documents modifications in the data sources and interpretations between the 2002 and 2007 editions of the Heinz Center report. Stream and ground?water quality data collected nationally as part of the USGS National Water-Quality Assessment Program were used to develop the ecosystem indicators for the Heinz Center report, including Core National indicators for the Movement of Nitrogen and Chemical Contamination and for selected ecosystems classified as Farmlands, Forest, Grasslands and Shrublands, Freshwater, and Urban and Suburban. In addition, the USGS provided water?quality and streamflow data collected as part of the National Stream Water Quality Accounting Network and the Federal?State Cooperative Program. The documentation provided herein serves not only as a reference for current and future editions of The State of the Nation?s Ecosystems but also provides critical information for future assessments of changes in contaminant occurrence in streams and ground water of the United States.

Open-File Report↗
USGS2007

Water and agricultural-chemical transport in a Midwestern, tile-drained watershed: Implications for conservation practices

The study of agricultural chemicals is one of five national priority topics being addressed by the National Water-Quality Assessment (NAWQA) Program in its second decade of studies, which began in 2001. Seven watersheds across the Nation were selected for the NAWQA agricultural-chemical topical study. The watersheds selected represent a range of agricultural settings - with varying crop types and agricultural practices related to tillage, irrigation, artificial drainage, and chemical use - as well as a range of landscapes with different geology, soils, topography, climate, and hydrology (Capel and others, 2004). Chemicals selected for study include nutrients (nitrogen and phosphorus) and about 50 commonly used pesticides. This study design leads to an improved understanding of many factors that can affect the movement of water and chemicals in different agricultural settings. Information from these studies will help with decision making related to chemical use, conservation, and other farming practices that are used to reduce runoff of agricultural chemicals and sediment from fields (Capel and others, 2004). This Fact Sheet highlights the results of the NAWQA agricultural chemical study in the Leary Weber Ditch Watershed in Hancock County, Indiana. This watershed was selected to represent a tile-drained, corn and soybean, humid area typical in the Midwest.

Indiana↗
USGS2006

Occurrence and transport of agricultural chemicals in Leary Weber Ditch Basin, Hancock County, Indiana, 2003-04

Leary Weber Ditch Basin, Hancock County, Indiana, is one of seven first-order basins selected from across the United States as part of the Agricultural Chemicals: Source, Transport, and Fate study conducted by the National Water-Quality Assessment Program of the U.S. Geological Survey. The nationwide study was designed to increase the understanding of the links between the sources of water and agricultural chemicals (nutrients and pesticides) and the transport and fate of these chemicals through the environment. Agricultural chemicals were detected in Leary Weber Ditch and in every associated hydrologic compartment sampled during 2003 and 2004. Pesticides were detected more frequently in samples collected from overland flow and from the ditch itself and less frequently in ground-water samples. The lowest concentrations of pesticides and nutrients were detected in samples of rain, soil water, and ground water. The highest concentrations of pesticides and nutrients were detected in samples of tile-drain water, overland flow, and water from Leary Weber Ditch. Samples collected from the tile drain, overland flow and Leary Weber Ditch soon after chemical applications to the fields and coincident with rainfall and increased streamflow had higher concentrations of pesticides and nutrients than samples collected a longer time after the chemicals were applied. A mass-balance mixing analysis based on potassium concentrations indicated that tile drains are the primary contributor of water to Leary Weber Ditch, but overland flow is also an important contributor during periods of high-intensity rainfall. When maximum rainfall intensity was 0.5 inches per hour or lower, overland flow contributed about 10 percent and tile drains contributed about 90 percent of the flow to Leary Weber Ditch. When maximum rainfall intensity was 0.75 inches per hour or greater, overland flow contributed about 40 percent and tile drains contributed about 60 percent of the flow to the ditch. Ground-water flow to Leary Weber Ditch was negligible. Tile drains are an important agricultural-chemical transport path to Leary Weber Ditch, based on the hydrologic contributions of overland flow and tile drains to the ditch. Overland flow is also an important agricultural-chemical transport pathway during high-intensity rainfall; however, storms with high-intensity rainfall are sporadic throughout the year. Tile drains and the soil water moving to the tile drains are the primary transport pathway for agricultural-chemical transport to Leary Weber Ditch during most storms as well as between storms.

Indiana↗
USGS2002

Geohydrology, water quality, and simulation of ground-water flow in the vicinity of a former waste-oil refinery near Westville, Indiana, 1997–2000

Geohydrologic and water-quality data collected during 1997 through 2000 in the vicinity of a former waste-oil refinery near Westville, Indiana, define a plume of 1,4-dioxane in ground water that extends to the southwest approximately 0.8 miles from the refinery site. Concentrations of 1,4-dioxane in the plume ranged from 3 to 31,000 micrograms per liter. Ground water containing 1,4-dioxane is discharged to Crumpacker Ditch, approximately one-half mile west of the refinery site. Concentrations of 1,4-dioxane detected in surface water ranged from 8 to 140 micrograms per liter; 1,4-dioxane also is transported in ground water beneath the ditch. The study area is underlain by glacial deposits of sand and gravel that overlie lacustrine clay and shale. The sand and gravel deposits form an extensive aquifer ranging from 148 to 215 feet thick in the study area. Ground water generally flows from northeast to southwest and the depth to water ranges from about 3 to 36 feet below land surface. The average horizontal hydraulic conductivity of the aquifer, determined from a multiple-well aquifer test, was 121 feet per day, and the transmissivity was 18,600 feet squared per day. Vertical hydraulic conductivity ranged from 24 to 36 feet per day and specific yield ranged from 0.05 to 0.08. Analysis of single-well aquifer tests indicated that horizontal hydraulic conductivity ranged from 0.6 to 127 feet per day and was largest in the lower part of the aquifer. Horizontal gradients averaged about 0.001 feet per foot; estimated ground-water- flow velocities averaged about 0.1 feet per day in the upper and middle parts of the glacial aquifer and about 0.4 feet per day near the bottom of the aquifer. Analytical results of water samples indicate the ground water generally is a calcium-bicarbonate type with a nearly neutral pH. Specific conductivity ranged from 437 to 1,030 microsiemens per centimeter at 25 degrees Celsius in water from wells upgradient from the refinery site and 330 to 3,780 microsiemens per centimeter at 25 degrees Celsius in water from downgradient wells. Barium, iron, manganese, nickel, and zinc commonly were detected in samples of ground water. Volatile organic compounds (including chlorinated solvents and aromatic hydrocarbons) were consistently detected in samples from shallow wells near the boundaries of the former refinery site. Concentrations of 1,4-dioxane were detected in water from wells screened in the upper, middle, and lower parts of the aquifer downgradient from the site and in samples of surface water collected approximately 5 miles downstream from where the plume intersects Crumpacker Ditch. A three-dimensional, four layer groundwater- flow model was constructed and calibrated to match ground-water levels and streamflow measured during December 1997. The model was used to simulate possible mechanisms of contaminant release, the effect of increased pumpage from water-supply wells, and pumping at the leading edge of the plume as a possible means of remediation. Based on simulation of three waste-oil lagoons, a vertical hydraulic conductivity of 0.2 feet per day was required to move contaminants into the bottom layer of the model at a constant leakage rate of about 98 gallons per minute. Simulations of a disposal well in layer 3 of the model indicated an injection rate of 50 gallons per minute was necessary to spread contaminants vertically in the aquifer. Simulated pumping rates of about 300 and 1,000 gallons per minute were required for water supply wells at the Town of Westville and the Westville Correctional Facility to draw water from the plume of 1,4-dioxane. Simulated pumping from hypothetical wells at the leading edge of the plume indicated that three wells, each pumping 25 gallons per minute from model layer 3, would capture the plume of 1,4-dioxane.

Indiana↗
USGS2002

Effects of highway-deicer application on ground-water quality in a part of the Calumet Aquifer, northwestern Indiana

The effects of highway-deicer application on ground-water quality were studied at a site in northwestern Indiana using a variety of geochemical indicators. Site characteristics such as high snowfall rates; large quantities of applied deicers; presence of a high-traffic highway; a homogeneous, permeable, and unconfined aquifer; a shallow water table; a known ground-water-flow direction; and minimal potential for other sources of chloride and sodium to complicate source interpretation were used to select a study area where ground water was likely to be affected by deicer application. Forty-three monitoring wells were installed in an unconfined sand aquifer (the Calumet aquifer) near Beverly Shores in northwestern Indiana. Wells were installed along two transects that approximately paralleled groundwater flow in the Calumet aquifer and crossed US–12. US–12 is a highway that receives Indiana’s highest level of maintenance to maintain safe driving conditions. Ground-water quality and water-level data were collected from the monitoring wells, and precipitation and salt-application data were compiled from 1994 through 1997. The water-quality data indicated that chloride was the most easily traced indicator of highway deicers in ground water. Concentration ratios of chloride to iodide and chloride to bromide and Stiff diagrams of major element concentrations indicated that the principal source of chloride and sodium in ground water from the uppermost one-third to one-half of the Calumet aquifer and downgradient from US–12 was from a halite highway-deicer source. Borehole logs of relative electromagnetic conductivity defined a distinct plume of deicer-affected water in the uppermost 8 feet of aquifer at about 9 feet horizontally from the paved roadway edge and a zone of higher conductivity than background in the lower one-third of the aquifer. Chloride and sodium in the deep parts of the aquifer originated from natural sources. Chloride and sodium from highway deicers were present in the aquifer throughout the year. The highest concentrations of chloride and sodium in ground water were determined in samples collected during the spring and summer from wells open to the water table within about 9 feet of the highway. Chloride concentrations in ground water that were attributable to highway deicers also were found in tested wells about 400 feet downgradient from US–12 during the fall and winter and at greater depths than in wells closer to US–12. Chloride concentrations exceeded the U.S. Environmental Protection Agency’s (USEPA) secondary maximum contaminant level of 250 milligrams per liter for drinking water at seven wells downgradient from the highway during late winter, spring, and summer samplings. The chloride standard was exceeded only in water from wells with total depths that are less than about 10 feet below land surface. Sodium concentrations in water periodically exceeded the USEPA drinking-water equivalency level of 20 milligrams per liter in both the uppermost (deicer 2 Effects of Highway-Deicer Application on Ground-Water Quality in a Part of the Calumet Aquifer, Northwestern Indiana affected) and lower one-thirds of the aquifer. Sodium concentrations in ground water downgradient from US–12 and in the upper 5 feet of the aquifer also occasionally exceeded drinking-water standards for sodium (160 milligrams per liter) as set by the State of Florida and a standard for taste (200 milligrams per liter) as set by the World Health Organization. Dispersion was identified by analysis of aquifer-test data, isotopic dating of ground water, and water-quality data to be the process most responsible for reducing concentrations of highway deicers in the aquifer. Chemical analyses of the sand composing the aquifer indicated that cation exchange decreased the mass of deicerrelated sodium in ground water, although the sand has a limited capacity to sustain the process. Automated daily measurements of specific conductance, correlated to chloride concentrations, indicated that some deicer is retained in the aquifer near the highway throughout the entire year and acts as a continuous chloride source for ground water. Peak concentrations of deicerrelated constituents occasionally were detected by the daily, automated measurements of specific conductance that were made between the monthly samplings of ground water. Data analysis indicated that more frequent sampling than monthly intervals would be necessary if maximum chloride concentrations were to be measured. Some deicer may be retained in the aquifer and unsaturated zone between annual salt-application periods. Chloride concentrations at wells 1-DG-WT and 2-DG-WT remained greater than background through much or all of the year. The estimated masses of chloride transported in ground water past 2-DG in 1995 and 1996 were either slightly greater than (1995) or less than (1996) the masses of chloride applied to US–12 during the study.

Indiana↗
USGS2001

An evaluation of borehole flowmeters used to measure horizontal ground-water flow in limestones of Indiana, Kentucky, and Tennessee, 1999

Three borehole flowmeters and hydrophysical logging were used to measure ground-water flow in carbonate bedrock at sites in southeastern Indiana and on the west-central border of Kentucky and Tennessee. The three flowmeters make point measurements of the direction and magnitude of horizontal flow, and hydrophysical logging measures the magnitude of horizontal flowover an interval. The directional flowmeters evaluated include a horizontal heat-pulse flowmeter, an acoustic Doppler velocimeter, and a colloidal borescope flowmeter. Each method was used to measure flow in selected zones where previous geophysical logging had indicated water-producing beds, bedding planes, or other permeable features that made conditions favorable for horizontal-flow measurements. Background geophysical logging indicated that ground-water production from the Indiana test wells was characterized by inflow from a single, 20-foot-thick limestone bed. The Kentucky/Tennessee test wells produced water from one or more bedding planes where geophysical logs indicated the bedding planes had been enlarged by dissolution. Two of the three test wells at the latter site contained measurable vertical flow between two or more bedding planes under ambient hydraulic head conditions. Field measurements and data analyses for each flow-measurement technique were completed by a developer of the technology or by a contractor with extensive experience in the application of that specific technology. Comparison of the horizontal-flow measurements indicated that the three point-measurement techniques rarely measured the same velocities and flow directions at the same measurement stations. Repeat measurements at selected depth stations also failed to consistently reproduce either flow direction, flow magnitude, or both. At a few test stations, two of the techniques provided similar flow magnitude or direction but usually not both. Some of this variability may be attributed to naturally occurring changes in hydraulic conditions during the 1-month study period in August and September 1999. The actual velocities and flow directions are unknown; therefore, it is uncertain which technique provided the most accurate measurements of horizontal flow in the boreholes and which measurements were most representative of flow in the aquifers. The horizontal heat-pulse flowmeter consistently yielded flow magnitudes considerably less than those provided by the acoustic Doppler velocimeter and colloidal borescope. The design of the horizontal heat-pulse flowmeter compensates for the local acceleration of ground-water velocity in the open borehole. The magnitude of the velocities estimated from the hydrophysical logging were comparable to those of the horizontal heat-pulse flowmeter, presumably because the hydrophysical logging also effectively compensates for the effect of the borehole on the flow field and averages velocity over a length of borehole rather than at a point. The acoustic Doppler velocimeter and colloidal borescope have discrete sampling points that allow for measuring preferential flow velocities that can be substantially higher than the average velocity through a length of borehole. The acoustic Doppler velocimeter and colloidal borescope also measure flow at the center of the borehole where the acceleration of the flow field should be greatest. Of the three techniques capable of measuring direction and magnitude of horizontal flow, only the acoustic Doppler velocimeter measured vertical flow. The acoustic Doppler velocimeter consistently measured downward velocity in all test wells. This apparent downward flow was attributed, in part, to particles falling through the water column as a result of mechanical disturbance during logging. Hydrophysical logging yielded estimates of vertical flow in the Kentucky/Tennessee test wells. In two of the test wells, the hydrophysical logging involved deliberate isolation of water-producing bedding planes with a packer to ensure that small horizontal flow could be quantified without the presence of vertical flow. The presence of vertical flow in the Kentucky/Tennessee test wells may preclude the definitive measurement of horizontal flow without the use of effective packer devices. None of the point-measurement techniques used a packer, but each technique used baffle devices to help suppress the vertical flow. The effectiveness of these baffle devices is not known; therefore, the effect of vertical flow on the measurements cannot be quantified. The general lack of agreement among the point-measurement techniques in this study highlights the difficulty of using measurements at a single depth point in a borehole to characterize the average horizontal flow in a heterogeneous aquifer. The effective measurement of horizontal flow may depend on the precise depth at which measurements are made, and the measurements at a given depth may vary over time as hydraulic head conditions change. The various measurements also demonstrate that the magnitude and possibly the direction of horizontal flow are affected by the presence of the open borehole. Although there is a lack of agreement among the measurement techniques, these results could mean that effective characterization of horizontal flow in heterogeneous aquifers might be possible if data from many depth stations and from repeat measurements can be averaged over an extended time period. Complications related to vertical flow in the borehole highlights the importance of using background logging methods like vertical flowmeters or hydrophysical logging to characterize the borehole environment before horizontal-flow measurements are attempted. If vertical flow is present, a packer device may be needed to acquire definitive measurements of horizontal flow. Because hydrophysical logging provides a complete depth profile of the borehole, a strength of this technique is in identifying horizontal- and vertical-flow zones in a well. Hydrophysical logging may be most applicable as a screening method. Horizontal- flow zones identified with the hydrophysical logging then could be evaluated with one of the point-measurement techniques for quantifying preferential flow zones and flow directions. Additional research is needed to determine how measurements of flow in boreholes relate to flow in bedrock aquifers. The flowmeters may need to be evaluated under controlled laboratory conditions to determine which of the methods accurately measure ground-water velocities and flow directions. Additional research also is needed to investigate variations in flow direction with time, daily changes in velocity, velocity corrections for fractured bedrock aquifers and unconsolidated aquifers, and directional differences in individual wells for hydraulically separated flow zones.

Indiana, Kentucky, Tennessee↗