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George E. Harlow

Publications and source records attributed to George E. Harlow.

10 recordsLinked to original sources
USGS2015

Hydrogeology and simulation of groundwater flow in fractured-rock aquifers of the Piedmont and Blue Ridge Physiographic Provinces, Bedford County, Virginia

An annual groundwater budget was computed as part of a hydrogeologic characterization and monitoring effort of fractured-rock aquifers in Bedford County, Virginia, a growing 764-square-mile (mi 2 ) rural area between the cities of Roanoke and Lynchburg, Virginia. Data collection in Bedford County began in the 1930s when continuous stream gages were installed on Goose Creek and Big Otter River, the two major tributaries of the Roanoke River within the county. Between 2006 and 2014, an additional 2 stream gages, 3 groundwater monitoring wells, and 12 partial-record stream gages were operated. Hydrograph separation methods were used to compute base-flow recharge rates from the continuous data collected from the continuous stream gages. Mean annual base-flow recharge ranged from 8.3 inches per year (in/yr) for the period 1931–2012 at Goose Creek near Huddleston (drainage area 188 mi 2 ) to 9.3 in/yr for the period 1938–2012 at Big Otter River near Evington (drainage area 315 mi 2 ). Mean annual base-flow recharge was estimated to be 6.5 in/yr for the period 2007–2012 at Goose Creek at Route 747 near Bunker Hill (drainage area 125 mi 2 ) and 8.9 in/yr for the period 2007–2012 at Big Otter River at Route 221 near Bedford (drainage area 114 mi 2 ). Base-flow recharge computed from the partial-record data ranged from 5.0 in/yr in the headwaters of Goose Creek to 10.5 in/yr in the headwaters of Big Otter River. A steady-state groundwater-flow simulation for Bedford County was developed to test the conceptual understanding of flow in the fractured-rock aquifers and to compute a groundwater budget for the four major drainages: James River, Smith Mountain and Leesville Lakes, Goose Creek, and Big Otter River. Model results indicate that groundwater levels mimic topography and that minimal differences in aquifer properties exist between the Proterozoic basement crystalline rocks and Late Proterozoic-Cambrian cover crystalline rocks. The Big Otter River receives 40.8 percent of the total daily groundwater outflow from fractured-rock aquifers in Bedford County; Goose Creek receives 25.8 percent, the James River receives 18.2 percent, and Smith Mountain and Leesville Lakes receive 15.2 percent. The remaining percentage of outflow is attributed to pumping from the aquifer (consumptive use).

Virginia↗
USGS2008

Bedrock structural controls on the occurrence of sinkholes and springs in the Northern Great Valley Karst, Virginia and West Virginia

Recent geologic mapping at a scale of 1:24,000 has enabled a qualitative correlation of the occurrence of springs and sinkholes with bedrock structures and ground-water conditions in the northern Great Valley of Virginia and West Virginia. Sinkholes tend to be concentrated in zones of faulting, local minor folding, and clustered within susceptible bedrock units at the noses and axes of large plunging folds. Alignment of sinkholes mainly occurs along strike of bedding. Enhanced rock solution and conduit formation correlates with carbonate units of greater limestone purity and finer grain size, suggesting some lithologic control on karst formation. In addition, there is an apparent topographic correlation, with sinkholes usually formed in elevated and flat (<5 degrees slope) areas, as well as frequent sinkhole occurrence proximal to entrenched surface streams. Density of sinkhole occurrence tends to increase in areas where water-table fluctuations are large. Large perennial springs occur along faults, and may lie above base level streams indicating upward flow gradients particularly where cross-strike faults and joints intersect bedding planes and strike-parallel faults. Sinkhole formation also frequently occurs in areas proximal to entrenched surface streams, reflecting subsequent vadose-zone modification and excavation of sediment-filled conduits where downward ground-water flow gradients are most steep. Geologic evidence indicates that deep karst development may have taken place by rising fluids under confined (hypogenic) conditions in the distant geologic past in this region.

Virginia, West Virginia↗
USGS2006

Reconnaissance borehole geophysical, geological, and hydrological data from the proposed hydrodynamic compartments of the Culpeper Basin in Loudoun, Prince William, Culpeper, Orange, and Fairfax Counties, Virginia

The Culpeper basin is part of a much larger system of ancient depressions or troughs, that lie inboard of the Atlantic Coastal Plain, and largely within the Applachian Piedmont Geologic Province of eastern North America, and the transition region with the neighboring Blue Ridge Geologic Province. This basin system formed during an abortive attempt to make a great ocean basin during the Late Triassic and Early Jurassic, and the eroded remnants of the basins record major episodes of sedimentation, igneous intrusion and eruption, and pervasive contact metamorphism. Altogether, some twenty nine basins formed between what is now Nova Scotia and Georgia. Many of these basins are discontinuous along their strike, and have therefore recorded isolated environments for fluvial and lacustrine sedimentation. Several basins (including the Culpeper, Gettysburg, and Newark basins) are fault-bounded on the west, and Mesozoic crustal stretching has produced assymetrical patterns of basin subsidence resulting in a progressive basin deepening to the west, and a virtual onlap relationship with the pre-basin Proterozoic rocks to the east. A result of such a pattern of basin deepening is the development of sequences of sandstones and siltstones that systemmatically increase in dip towards the accomodating western border faults. A second major structural theme in several of the major Mesozoic basins (including the Culpeper) concerns the geometry of igneous intrusion, as discussed below. Froelich (1982, 1985) and Lee and Froelich (1989) discuss the general geology of the Culpeper basin, and Smoot (1989) discusses the sedimentation environments and sedimentary facies of the Mesozoic with respect to fluvial and shallow lacustrine deposition in the Culpeper basin. Ryan and others, 2007a, b, discuss the role of diabase-induced compartmentalization in the Culpeper basin (and other Mesozoic basins), and illustrate (using alteration mineral suites within the diabase and adjacent hornfels, among other evidence) how this process has played a role in organizing the paleo- and contemporary-flow of crustal fluids at local and regional scales. Within this report, the Newark Supergroup nomenclature of Weems and Olsen (1997) is adopted.

Virginia↗
USGS2005

Hydrogeology and ground-water availability in the carbonate aquifer system of Frederick County, Virginia

The carbonate aquifer system of the northern Shenandoah Valley provides an important water supply to local communities, including Frederick County, Va., which depends on ground water as a source of water supply. The county and surrounding area are undergoing increased urbanization, and increased demands on the carbonate aquifer system are expected. A study was conducted between October 2000 and March 2004 by the U.S. Geological Survey (USGS), in cooperation with the County of Frederick, Va., to describe the hydrogeology and ground-water availability in the carbonate aquifer system underlying the county. The study area encompasses about 25 percent (105 square miles) of the county that is underlain by carbonate bedrock. The carbonate aquifer system of Frederick County is in the Shenandoah Valley region of the Valley and Ridge Physiographic Province. Approximately 10,000 feet of folded and fractured Middle Cambrian to Upper Ordovician sedimentary rocks are exposed and are overlain by Pleistocene (?) and Holocene surficial deposits. All geologic units in the study area are considered to be aquifers. The geologic units are generally unconfined, fractured-rock aquifers that are recharged by precipitation and discharge locally to streams and springs, and by evapotranspiration. Stream density in the carbonate study area is less than in the remainder of the county, which is underlain by siliciclastic rock units. Most streams flow normal to strike (from the northwest towards the southeast) across the study area. These streams are characterized by shallow incisement and are usually limited to a single stream channel. In the southern third of the study area, streams flow parallel to strike (from the northeast towards the southwest) towards the deeply intrenched Cedar Creek. Springs are commonly located at the start of flows for all streams in the carbonate study area, and spring discharges are often a large portion of the streamflow (especially during drought conditions). The general direction of ground-water flow is from the hills in the west of the study area into and across the carbonate valley. A ground-water divide may occur north of Round Hill in the vicinity of the Apple Pie Ridge fault where the North Mountain fault zone cuts out the resistant Silurian and Devonian sandstone units and results in surface drainage from the carbonate rocks toward the west and out of the carbonate valley. Estimates of effective ground-water recharge for 2001-02 range from 5.8 to 6.2 inches in the Cedar Creek Basin, with base flow accounting for between 60 and 64 percent of streamflow, and from 3.2 to 3.8 inches in the Opequon Creek Basin, with base flow accounting for between 86 and 92 percent of streamflow. Water budgets calculated for 2001, a year of below-normal precipitation (33.1 inches), and 2002, a year of above-normal precipitation (41.2 inches), include a streamflow of 9.0 inches in 2001 and 9.2 inches in 2002 in Cedar Creek. Evapotranspiration ranged from 25.9 to 30.7 inches, and ground-water storage decreased 1.8 inches in 2001 and increased 1.3 inches in 2002. Streamflow was 3.7 inches in 2001 and 2002 in Opequon Creek. Evapotranspiration ranged from 29.8 to 37.5 inches, and ground-water storage decreased 0.4 inch in 2001 and did not change in 2002.

Scientific Investigations Report↗
USGS2003

Aquifer Susceptibility in Virginia: Data on Chemical and Isotopic Composition, Recharge Temperature, and Apparent Age of Water from Wells and Springs, 1998-2000

The determination of aquifer susceptibility to contamination from near-surface sources by the use of ground-water dating techniques is a critical part of Virginia's Source Water Assessment Program. As part of the Virginia Aquifer Susceptibility study, water samples were collected between 1998 and 2000 from 145 wells and 6 springs in various hydrogeologic settings across the Commonwealth. Samples were analyzed to determine water chemistry?including nitrate (NO3), dissolved organic carbon (DOC), and radon-222 (222Rn), major dissolved and noble gases?nitrogen (N2), argon (Ar), oxygen (O2), carbon dioxide (CO2), methane (CH4), helium (He), and neon (Ne), environmental tracers?chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), and tritium/helium-3 (3H/3He), carbon isotopes?carbon-14 (14C) and carbon-13 (d13C), and stable isotopes of oxygen (d18O) and hydrogen (d2H). The chemical and isotopic composition, recharge temperatures, and apparent ages of these water samples are presented in this report. Data collected between 1999 and 2000 from 18 wells in Virginia as part of two other studies by the U.S. Geological Survey also are presented. Most of the sites sampled serve as public water supplies and are included in the comprehensive Source Water Assessment Program for the Commonwealth.

Open-File Report↗
USGS2002

Conceptual hydrogeologic framework of the shallow aquifer system at Virginia Beach, Virginia

The hydrogeologic framework of the shallow aquifer system at Virginia Beach was revised to provide a better understanding of the distribution of fresh ground water, its potential use, and its susceptibility to contamination. The revised conceptual framework is based primarily on analyses of continuous cores and downhole geophysical logs collected at 7 sites to depths of approximately 200 ft. The shallow aquifer system at Virginia Beach is composed of the Columbia aquifer, the Yorktown confining unit, and the Yorktown-East-over aquifer. The shallow aquifer system is separated from deeper units by the continuous St. Marys confining unit. The Columbia aquifer is defined as the predominantly sandy surficial deposits above the Yorktown confining unit. The Yorktown confining unit is composed of a series of very fine sandy to silty clay units of various colors at or near the top of the Yorktown Formation. The Yorktown confining unit varies in thickness and in composition, but on a regional scale is a leaky confining unit. The Yorktown-Eastover aquifer is defined as the predominantly sandy deposits of the Yorktown Formation and the upper part of the Eastover Formation above the confining clays of the St. Marys Formation. The limited areal extent of highly permeable deposits containing freshwater in the Yorktown-Eastover aquifer precludes the installation of highly productive freshwater wells over most of the city. Some deposits of biofragmental sand or shell hashes in the Yorktown-Eastover aquifer can support high-capacity wells. A water sample was collected from each of 10 wells installed at 5 of the 7 core sites to determine the basic chemistry of the aquifer system. One shallow well and one deep well was installed at each site. Concentrations of chloride were higher in the water from the deeper well at each site. Concentrations of dissolved iron in all of the water samples were higher than the U.S. Environmental Protection Agency Secondary Drinking Water Regulations. Concentrations of manganese and chloride were higher than the Secondary Drinking Water Regulations in samples from some wells. In the humid climate of Virginia Beach, the periodic recharge of freshwater through the sand units of the shallow aquifer system occurs often enough to create a dynamic equilibrium whereby freshwater flows continually down and away from the center of the ridges to mix with and sweep brackish water and saltwater back toward the tidal rivers, bays, salt marshes, and the Atlantic Ocean. The aquifers and confining units of the shallow aquifer system at Virginia Beach are heterogeneous, discontinuous, and without exact marker beds, which makes correlations in the study area difficult. Investigations using well cuttings, spot cores, or split-spoon samples with geophysical logs are not as definitive as continuous cores for determining or correlating hydrogeologic units. Future investigations of the shallow aquifer system would benefit by collecting continuous cores.

Water-Resources Investigations Report↗
USGS2001

Apparent chlorofluorocarbon age of ground water of the shallow aquifer system, Naval Weapons Station Yorktown, Yorktown, Virginia

Apparent ages of ground water are useful in the analysis of various components of flow systems, and results of this analysis can be incorporated into investigations of potential pathways of contaminant transport. This report presents the results of a study in 1997 by the U.S. Geological Survey (USGS), in cooperation with the Naval Weapons Station Yorktown, Base Civil Engineer, Environmental Directorate, to describe the apparent age of ground water of the shallow aquifer system at the Station. Chlorofluorocarbons (CFCs), tritium ( 3 H), dissolved gases, stable isotopes, and water-quality field properties were measured in samples from 14 wells and 16 springs on the Station in March 1997. Nitrogen-argon recharge temperatures range from 5.9°C to 17.3°C with a median temperature of 10.9°C, which indicates that ground-water recharge predominantly occurs in the cold months of the year. Concentrations of excess air vary depending upon geohydrologic setting (recharge and discharge areas). Apparent ground-water ages using a CFC-based dating technique range from 1 to 48 years with a median age of 10 years. The oldest apparent CFC ages occur in the upper parts of the Yorktown-Eastover aquifer, whereas the youngest apparent ages occur in the Columbia aquifer and the upper parts of the discharge area setting, especially springs. The vertical distribution of apparent CFC ages indicates that groundwater movement between aquifers is somewhat retarded by the leaky confining units, but the elapsed time is relatively short (generally less than 35 years), as evidenced by the presence of CFCs at depth. The identification of binary mixtures by CFC-based dating indicates that convergence of flow lines occurs not only at the actual point of discharge, but also in the subsurface. The CFC-based recharge dates are consistent with expected 3 H concentrations measured in the water samples from the Station. The concentration of 3H in ground water ranges from below the USGS laboratory minimum reporting limit of 0.3 to 15.9 tritium units (TU) with a median value of 10.8 TU. Water-quality field properties are highly variable for ground water with apparent CFC ages less than 15 years because of geochemical processes within local flow systems. Ground water with apparent CFC ages greater than 15 years represents more stable conditions in subregional flow systems. The range of apparent CFC ages is slightly greater than the ranges in time of travel of ground water calculated for shallow wells (less than 60- feet deep) from flow-path analysis. Calculated travel times to springs can be up to two orders of magnitude greater than the CFC-based apparent ages. Reasonable assumptions of values for hydraulic parameters can result in substantial overestimates for time of travel to springs. Recharge rates computed from apparent CFC ages range from 0.29 to 0.89 feet per year (ft/ yr) with an average value of 0.54 ft/yr. The analysis of apparent CFC ages in conjunction with geohydrologic data indicates that young water (less than 50 years) is present at depth (nearly 120 feet) and that both local and subregional flow systems occur in the shallow aquifer system at the Station. The addition of the dimension of time to the three-dimensional framework of Brockman and others (1997) will benefit current (2001) and future remediation activities by providing estimates of advective transport rates and how these rates vary depending upon geohydrologic setting and position within the ground-water-flow system. Estimated ground-water apparent ages and recharge rates can be used as calibration criteria in simulations of ground-water flow on the Station to refine and constrain future ground-water-flow models of the shallow aquifer system.

Virginia↗
USGS1997

Base-flow characteristics of streams in the Valley and Ridge, the Blue Ridge, and the Piedmont physiographic provinces of Virginia

Growth within the Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces of Virginia has focused concern about allocation of surface-water flow and increased demands on the ground-water resources. The pur pose of this report is to (.1) describe the base-flow characteristics of streams, (2) identify the regional differences in these flow characteristics, and (3) describe, if possible, the potential surface-water and ground-water yields of basins on the basis of the base-flow characteristics. Base-flow characteristics are presented for streams in the Valley and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces of Virginia. The provinces are separated into five regions: (1) Valley and Ridge, (2) Blue Ridge, (3) Piedmont/Blue Ridge transition, (4) Piedmont northern, and (5) Piedmont southern. Different flow statistics, which represent stream flows predominantly comprised of base flow, were determined for 217 continuous-record stream flow-gaging stations from historical mean daily discharge and for 192 partial-record streamflow gaging stations by means of correlation of discharge measurements. Variability of base flow is represented by a duration ratio developed during this investigation. Effective recharge rates were also calculated. Median values for the different flow statis tics range from 0.05 cubic foot per second per square mile for the 90-percent discharge on the streamflow-duration curve to 0.61 cubic foot per second per square mile for mean base flow. An excellent estimator of mean base flow for the Piedmont/Blue Ridge transition region and Piedmont southern region is the 50-percent discharge on the streamflow-duration curve, but it tends to underestimate mean base flow for the remaining regions. The base-flow variability index ranges from 0.07 to 2.27, with a median value of 0.55. Effective recharge rates range from 0.07 to 33 .07 inches per year, with a median value of 8.32 inches per year. Differences in the base-flow characteristics exist between regions. The median discharges for the Valley and Ridge, the Blue Ridge, and the Piedmont/Blue Ridge transition regions are higher than those for the Piedmont regions. Results from statistical analysis indicate that the regions can be ranked in terms of base-flow characteristics from highest to lowest as follows: (1) Piedmont/Blue Ridge transition, (2) Valley and Ridge and Blue Ridge, (3) Piedmont south ern, and (4) Piedmont northern. The flow statis tics are consistently higher and the values for base-flow variability are lower for basins within the Piedmont/Blue Ridge transition region relative to those from the other regions, whereas the basins within the Piedmont northern region show the opposite pattern. The group rankings of the base-flow characteristics were used to designate the potential surface-water yield for the regions. In addition, an approach developed for this investigation assigns a rank for potential surface-water yield to a basin according to the quartiles in which the values for the base-flow characteristics are located. Both procedures indicate that the Valley and Ridge, the Blue Ridge, and the Piedmont/ Blue Ridge transition regions have moderate-to high potential surface-water yield and the Piedmont regions have low-to-moderate potential surface-water yield. In order to indicate potential ground-water yield from base-flow characteristics, aquifer properties for 51 streamflow-gaging stations with continuous record of streamflow data were determined by methods that use streamflow records and basin characteristics. Areal diffusivity ranges from 17,100 to 88,400 feet squared per day, with a median value of38,400 feet squared per day. Areal transmissivity ranges from 63 to 830 feet squared per day, with a median value of270 feet squared per day. Storage coefficients, which were estimated by dividing areal transmissivity by areal diffusivity, range from approximately 0.001 to 0.019 (dimensionless), with a median value of 0.007. The median value for areal diffusivity decreases as potential surface-water yield of the basins increases. The ranking of a real diffusivity does not correspond with the ranking of potential surface-water yield for either the regions or the basins. Areal transmissivity generally increases as storage coefficient increases; however, basins with low potential surface-water yield generally have high values of areal transmissivity associated with low values of storage coefficient over a narrow range relative to those from basins designated as having moderate-to-high potential surface-water yield. Although the basins with high potential surface-water yield tend to have comparatively lower values for areal transmissivity, storage coefficients generally are large when compared to those from basins with similar values of a real transmissivity but different potential surface-water yield. Aquifer properties were grouped by potential surface-water yield and were related to hydro geologic units categorized by large, medium, and small well yields for the Valley and Ridge Physio graphic Province and for the Blue Ridge and the Piedmont Physiographic Provinces. Generally, no trend is evident between areal diffusivity and the hydrogeologic units. Some of the high values of a real diffusivity are associated with basins predominantly underlain by hydrogeologic units with small well yields, especially basins with a low potential surface-water yield. Areal transmissivity and storage coefficient tend to decrease, which is the expected trend, as more ofthe basin is underlain by the hydrogeologic unit with small well yields in the Valley and Ridge Physiographic Province. A similar trend is indicated for the hydrogeologic unit with medium well yields in the Blue Ridge and the Piedmont Physiographic Provinces. Areal transmissivity and storage coefficient tend to increase, which is not the expected trend, as more of the basin is underlain by the hydrogeologic unit with small well yields in the Blue Ridge and the Piedmont Physiographic Provinces. The base-flow characteristics of a basin may provide a relative indication of the potential ground-water yield; but other factors need to be considered, such as geologic structure, lithology, precipitation, relief, and degree of hydraulic interrconnection between the regolith and bedrock.

Virginia↗
USGS1994

Hydrogeologic and water-quality data for the main site, Naval Surface Warfare Center, Dahlgren Laboratory, Dahlgren, Virginia

Hydrogeologic and water-quality data were collected at the Naval Surface Warfare Center, Dahlgren Laboratory at Dahlgren, Virginia, as part of a hydrogeologic assessment of the shallow aquifer system begun in 1992. The U.S. Geological Survey conducted this study to provide the Navy with hydrogeologic data to meet the requirements of a Spill Contingency Plan. This report describes the ground-water observation-well network, hydro- geologic, and water-quality data collected between August 1992 and September 1993. The report includes a description of the locations and con- struction of 35 observation wells on the Main Site. Hydrologic data include lithologic core samples, geophysical logs, and vertical hydraulic conductivity measurements of selected core intervals. Hydrologic data include synoptic and hourly measurements of ground-water levels, observation-well slug tests to determine horizontal hydraulic conductivity, and tide data. Water-quality data include analyses of major dissolved constituents in ground water and surface water.

Open-File Report↗