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Research about Virginia

Source-linked reports with geographic coverage including Virginia.

At least 451 records · Page 25Linked to original sources
USGS1991

Low-flow characteristics of streams in Virginia

Streamflow data were collected and low-flow characteristics computed for 715 gaged sites in Virginia Annual minimum average 7-consecutive-day flows range from 0 to 2,195 cubic feet per second for a 2-year recurrence interval and from 0 to 1,423 cubic feet per second for a 10-year recurrence interval. Drainage areas range from 0.17 to 7,320 square miles. Existing and discontinued gaged sites are separated into three types: long-term continuous-record sites, short-term continuous-record sites, and partial-record sites. Low-flow characteristics for long-term continuous-record sites are determined from frequency curves of annual minimum average 7-consecutive-day flows . Low-flow characteristics for short-term continuous-record sites are estimated by relating daily mean base-flow discharge values at a short-term site to concurrent daily mean discharge values at nearby long-term continuous-record sites having similar basin characteristics . Low-flow characteristics for partial-record sites are estimated by relating base-flow measurements to daily mean discharge values at long-term continuous-record sites. Information from the continuous-record sites and partial-record sites in Virginia are used to develop two techniques for estimating low-flow characteristics at ungaged sites. A flow-routing method is developed to estimate low-flow values at ungaged sites on gaged streams. A flow-routing method is developed to estimate low-flow values at ungaged sites on gaged streams. Regional regression equations are developed for estimating low-flow values at ungaged sites on ungaged streams. The flow-routing method consists of transferring low-flow characteristics from a gaged site, either upstream or downstream, to a desired ungaged site. A simple drainage-area proration is used to transfer values when there are no major tributaries between the gaged and ungaged sites. Standard errors of estimate for108 test sites are 19 percent of the mean for estimates of low-flow characteristics having a 2-year recurrence interval and 52 percent of the mean for estimates of low-flow characteristics having a 10-year recurrence interval . A more complex transfer method must be used when major tributaries enter the stream between the gaged and ungaged sites. Twenty-four stream networks are analyzed, and predictions are made for 84 sites. Standard errors of estimate are 15 percent of the mean for estimates of low-flow characteristics having a 2-year recurrence interval and 22 percent of the mean for estimates of low-flow characteristics having a 10-year recurrence interval. Regional regression equations were developed for estimating low-flow values at ungaged sites on ungaged streams. The State was divided into eight regions on the basis of physiography and geographic grouping of the residuals computed in regression analyses . Basin characteristics that were significant in the regression analysis were drainage area, rock type, and strip-mined area. Standard errors of prediction range from 60 to139 percent for estimates of low-flow characteristics having a 2-year recurrence interval and 90 percent to 172 percent for estimates of low-flow characteristics having a 10-year recurrence interval.

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USGS1991

Fishes

No abstract available.

Virginia↗
USGS1990

Estimates of ion sources in deciduous and coniferous throughfall

Estimates of external and internal sources of ions in net througfall deposition were derived for a deciduous and coniferous canopy by use of multiple regression. The external source component appears to be dominated by dry deposition of Ca 2+ , SO 2 and NO 3 − during dormant and growing seasons for the two canopy types. Increases in the leaching rates of K + and Mg 2+ during the growing season reflect the presence of leaves in the deciduous canopy and increased physiological activity in both canopies. Internal leaching rates for SO 4 2− doubled during the growing season presumably caused by increased physiological activity and uptake of SO 2 through stomates. Net deposition of SO 4 2− in throughfall during the growing season appears highly dependent on stomatal uptake of SO 2 . Estimates of SO 2 deposition velocities were 0.06 cm s −1 and 0.13 cm s −1 for the deciduous and coniferous canopies, respectively, during the dormant seasons, and 0.30 cm s −1 and 0.43 cm s −1 for the deciduous and coniferous canopies, respectively, during the growing season. For the ions of major interest with respect to ecosystem effects, namely H + , NO 3 − and SO 4 2− , precipitation inputs generally outweighed estimates of dry deposition input. However, net throughfall deposition of NO 3 − and SO 4 2− accounted for 20–47 and 34–50 per cent, respectively, of total deposition of those ions. Error estimates of ion sources were at least 50–100 per cent and the method is subject to several assumptions and limitations.

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USGS1990

Preliminary investigation of soil and ground-water contamination at a U.S. Army Petroleum Training Facility, Fort Lee, Virginia, September-October 1989

Fuel-oil constituents in the soil and groundwater at the Fort Lee Petroleum Training Facility near Petersburg, Virginia, were studied by the U.S. Geological Survey (USGS) in cooperation with the Department of Defense, U.S. Army. The study included installation of 25 groundwater monitoring wells and description of groundwater flow patterns of the shallow-aquifer system underlying the facility. Soil and groundwater samples were collected to determine the concentrations of fuel-oil constituents and to determine the potential for off-site migration of the constituents. Total petroleum hydrocarbon concentrations up to 18,400 mg/km were reported in soil samples. Concentrations of benzene in water from wells at the facility were up to 130 micrograms per liter (ug/L), and concentrations of ethylbenzene and xylene were up to 54 and 120 ug/L, respectively. Potential exists for off-site migration of the contaminants and migration of contaminants downward to deeper aquifers. Further investigations of these potential contamination-migration pathways are warranted. Risk identification at the Petroleum Training Facility cannot be properly addressed because the distribution of the fuel-oil constituents has not been fully characterized. Preliminary identification of risk, however is presented by an examination of toxicity data for the chemical constituents reported in the groundwater at the facility. Concentrations of constituents were compared to the maximum contaminant levels (MCLs) for drinking water established by the U.S. Environmental Protection Agency (USEPA). Concentrations of benzene in water from wells at the facility exceed the USEPA 's 5 ug/L MCL by as much as 26 times. Sufficient data are not available to fully design the remedial-action plan for the facility; however, general responses to contamination of the type associated with the facility include no-action, monitoring, institutional controls, removal, and treatment.

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USGS1989

Vegetation alteration along trails in Shenandoah National Park, Virginia

Most studies in the USA of vegetation alteration and human impact along trails have been located in large western wilderness areas. The objective of this study was to determine vegetation changes occurring along trails in an eastern ecosystem supporting second-growth deciduous forest. The location of this study was Shenandoah National Park in Virginia, which has a long history of trail use by humans. Located in different sections of the park, ten trails were chosen as study areas. In each, transects were established to measure ground flora in trailside, transition, and undisturbed areas perpendicular to the trail. Field data were collected on frequency, life-form, and percent cover for ground flora of 25 cm or less in height. Cover and species diversity increased toward the trail in eight out often cases. Competition for light and resistance to trampling were thought to influence the occurrence of plants along the transect. Plants found along the trail border were represented by low growthforms, early blooming, or graminoid characteristics, and hemicryptophyte, therophyte, or chamaephyte life-forms. Plants found in the undisturbed zone were represented by scattered cover and frequency, woody growth forms or delicate herbaceous forms, and phanerophyte or geophyte life-forms.

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USGS1989

The structural geometry and evolution of foreland thrust systems, northern Virginia

Seismic reflection data reveal that the structural geometry of the central Appalachians of northern Virginia consists of three distinct thrust systems. Each thrust system is characterized by a unique internal geometry.The Blue Ridge thrust sheet is a composite thrust sheet composed primarily of imbricated Precambrian crystalline rocks. It over-rode Cambrian-Ordovician carbonates and formed a sheared, basement-cored fault-bend fold. Thrusts within the sheet may be Taconic and earliest Alleghanian, whereas final thrusting and emplacement of the sheet were probably slightly younger but still early Alleghanian. The North Mountain thrust sheet is characterized by imbricated Cambrian-Ordovician carbonates that are deformed into large-amplitude mode II fault-bend folds and fault-propagation folds. Rocks of this sheet were transported more than 60 km across a similar section of carbonates. The leading edge of the North Mountain thrust sheet was deformed into a fold with a mode II fault-bend fold geometry and was juxtaposed against middle Paleozoic rocks. The middle Paleozoic rocks occur in a ramp across which displacement along the North Mountain thrust was transferred to a higher detachment. More than 60 km of cover rocks displaced during the emplacement of the North Mountain thrust sheet either were transported across this ramp and thrust over a similar section in the western Valley and Ridge province or were backthrust above the sheet. The timing for imbrication and emplacement of the North Mountain thrust sheet is probably Main Phase Alleghanian. The Lower Carbonate duplex extends from beneath the Blue Ridge and North Mountain thrust sheets, westward across the western Valley and Ridge province. The Lower Carbonate duplex is characterized by imbricated Cambrian-Ordovician carbonates that form low-amplitude fault-bend folds. This thrust system also probably formed during Main Phase Alleghanian deformation.

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USGS1988

Map showing radon potential of rocks and soils in Fairfax County, Virginia

Since 1984, indoor radon has gained national attention as a significant health hazard in the United States. Radon is a colorless, odorless, radioactive gas derived from uranium by radioactive decay. The U.S. Environmental Protection Agency (EPA) now projects that 5,000 to 20,000 lung-cancer deaths per year may be attributed to the long-term exposure to indoor radon and its radioactive decay products. Indoor radon has been previously recognized as a health hazard associated with uranium-bearing mill tailings or building materials, but it was not until December 1984 that some natural soils and rocks were found to be sources of indoor radon at levels comparable to those in uranium mines. It is now suspected that elevated indoor radon levels are far more widespread than initially though. The EPA considers 4 picoCuries of radon per liter of air (pCi/L) as the level (in a year-round measurement) at which actions ought to be taken to lower the concentration of indoor radon. All soils and rocks contain measurable amounts of uranium, which generate measurable amounts of radon. Certain soils and rocks, however, have a greater potential to cause indoor radon problems than others because (1) they have a higher uranium content and thus can generate higher levels of radon in soil gas (gas that occupies the pores of the soil), and (2) the permeability of the sol or rack is sufficiently high that radon-bearing soil gas can flow freely and move indoors through the foundation of the structure. This study was designed to demonstrate the correlation between the geologic environment and indoor radon levels and to demonstrate a method of assessment that could be used by other informed workers in areas of their interest. A parallel study by Gundersen and others (1988) of the radon potential of rocks and soils in Montgomery County, Md., used somewhat different methods of assessment because the data available for and assessment of Montgomery County differed.

Virginia↗
USGS1988

Runoff for selected sites in Shenandoah National Park, Virginia, July 18, 1981, through July 17, 1982

Estimates of runoff for 56 sites within the Shenandoah National Park were made by the U.S. Geological Survey for the Direct/Delayed Response Project that is being conducted by the U.S. Environmental Protection Agency. The purpose of that project is to determine the long-term effects of acidic deposition on surface-water chemistry. Runoff was estimated for the period July 18,1981, through July 17,1982 during which periodic water-quality samples were collected for a study by the U.S. Geological Survey to determine the sensitivity of the area to the current input of acid deposition. The runoff values and waterquality samples will be used by the U.S. Environmental Protection Agency (EPA) to determine chemical budgets for 56 watersheds in the Park. The runoff estimates were determined by a graphical-correlation procedure. Six discharge measurements at each site were made when waterquality samples were collected; these were then correlated with the concurrent recorded discharges at one of 13 nearby streamflow-gaging stations. The mean discharge at the gaging station for the subject period was transferred through the relation line to estimate the mean discharge and runoff at the waterquality sampling site. The runoff estimates during the study period ranged from 10.9 to 38.7 inches. The accuracy of the method was evaluated by treating 13 nearby gaging stations as if they were water-quality sampling sites. A comparison of estimated and recorded runoff for the same period showed differences ranging from 28.2 to 49.5 percent, with an absolute average of 14.7 percent.

Virginia↗
USGS1988

Hydrogeologic framework of the Virginia coastal plain

This report defines the hydrogeologic framework of the Virginia Coastal Plain and is a product of a comprehensive regional study to define the geology, hydrology, and geochemistry of the northern Atlantic Coastal Plain aquifer system extending from North Carolina to Long Island, New York. The Virginia Coastal Plain consists of an eastward-thickening wedge of generally unconsolidated, interbedded sands and clays, ranging in age from Early Cretaceous to Holocene. These sediments range in thickness from more than 6,000 feet beneath the northeastern part of the Eastern Shore Peninsula to nearly 0 feet along the Fall Line. Eight confined aquifers, eight confining units, and an uppermost water table aquifer are delineated as the hydrogeologic framework of the Coastal Plain sediments in Virginia. The nine regional aquifers, from oldest to youngest, are lower, middle, and upper Potomac, Brightseat, Aquia, Chickahominy-Piney Point, St. Marys-Choptank, Yorktown-Eastover, and Columbia. The Brightseat is a newly identified and correlated aquifer of early Paleoceneage. This study is one of other, similar studies of the Coastal Plain areas in North Carolina, Maryland-Delaware, New Jersey, and Long Island, New York. These combined studies provide a system of hydrogeologic units that can be identified and correlated throughout the northern Atlantic Coastal Plain. Data for this study were collected and analyzed from October 1979 to May 1983. The nine aquifers and eight confining units are identified and delineated by use of geophysical logs, drillers' information, and stratigraphic and paleontologic data. By correlating geophysical logs with hydrologic, stratigraphic, and paleontologic data throughout the Coastal Plain, a comprehensive multilayered framework of aquifers and confining units, each with distinct lithologic properties, was developed. Cross sections show the stratigraphic relationships of aquifers and confining units in the hydrogeologic framework of the Virginia Coastal Plain. Maps show confining-unit thicknesses and altitudes of aquifer tops, provide the basis for assigning aquifers to screened intervals of observation and production wells, and are used for the development of a comprehensive observation-well network in the Virginia Coastal Plain.

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