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Research about Virginia

Source-linked reports with geographic coverage including Virginia.

At least 559 records · Page 31Linked to original sources
USGS1977

Geology of the Waynesboro East and Waynesboro West Quadrangles, Virginia

The Waynesboro East and Waynesboro West Quadrangles comprise an area of approximately 117 square miles (304 sq km) in portions of Albemarle, Augusta, and Nelson counties in north-central Virginia. Included in the quadrangles are portions of the Piedmont, Blue Ridge, and Valley and Ridge physiographic provinces and two major regional structures - the Blue Ridge anticlinoriurm and the Massanutten synclinorium. The rocks of the Blue Ridge anticlorium are complexly folded and faulted and consist of five sequences, the oldest being the Precambrian gneisses that include the Lovingston and Pedlar formations. Unconformably overlying these rocks or in fault contact with them is a sequence of Precambrian(?) stratified rock units including the metamorphosed, fluvial, sedimentary, and basic volcanic strata of the Swift Run and Catoctin formations. These are overlain by a sequence of Cambrian clastic rocks that include the Weverton, Harpers, and Antietarn formations. The Massanutten synclinorium within the study area is formed from the overlying Cambrian and Ordovician carbonate sequence that includes the Shady, Waynesboro, Elbrook, Conococheague, Chepultepec, Beekmantown, New Market, and Lincolnshire formations. These carbonate rocks are overlain by the Ordovician clastic sequence of the Martinsburg Formation. Many of these rock units are locally intruded by diabase dikes of Triassic age and are IocalIy covered by alluvial Quaternary sediments. The intensity of deformation increases from northwest to southeast with recumbent folds, thrust faults, and zones of cataclastic rocks present in the southeastern half of the area. All of the rocks are altered with the metamorphic rank being somewhat greater to the southeast. Sources of agricultural limestone, limestone aggregate, and in limited quantities high-calcium Iimestone are present. Ceramic clay, crushed stone. sand and gravel, and iron and manganese have been produced in small quantities. Fourteen environmental geologic units having similar geologic factors - bedrock, residuum, and soil properties - affecting land modification have been delineated. Each is briefly evaluated with respect to slope stability, erodibility, and response to excavation or other types of land modification. Rockfall, karst. cave areas, and floodprone regions have been delineated.

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USGS1976

Detailed investigation of a coastal plain-Piedmont fault contact in northeastern Virginia

A trench across the Dumfries fault of the Stafford fault zone near Stafford, Virginia (see Mixon and Newell, 1976) exposed a high-angle reverse fault juxtaposing Paleozoic Quantico Slate and Cretaceous Potomac Group rocks. A system of subsidiary reverse faults and small scale normal faults disrupt the Coastal Plain strata adjacent to the main fault. Cross-cutting relations and stratigraphic details indicate that the subsidiary faults in the Cretaceous rocks document a history of episodic deformation, in part active during accumulation of the Coastal Plain strata. Slickensides and stereo net analysis of theorientation of subsidiary reverse faults, normal faults, and bedding indicate that, through time, faulting consistently included right lateral separation.

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USGS1976

Preliminary appraisal of ground water in the Franconia area, Virginia

A brief study of ground-water conditions in the Franconia, Virginia area was made using available data and rapid reconnaissance techniques: (1) to select optimum sites for water wells (2) to identify regionally favorable sites for recharge pits or surface-retention ponds for the disposal of excess storm-water runoff. The principal sources of ground water in the Franconia area are narrow elongate sand lenses within the Coastal Plain. The subsurface distribution of these sand lenses is unknown due to the lack of deep test drilling. However, a previous study of surface exposures suggests that the lenses are elongate in an east-west direction. Measurements of base flow and specific conductance of water in the small streams in the area were used to delineate sites most likely to be underlain by the sand lenses. A water-table contour map and shallow sub-surface geologic map can be used for preliminary selection of sites for recharge pits and retention ponds.

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USGS1976

Flood-plain delineation for Cameron Run Basin, Fairfax County-Alexandria City, Virginia

Flood-Plain Delineation for Cameron Run Basin Water-surface profiles of the 25-, 50-, and 100-year recurrence interval discharges have been computed for all streams and reaches of channels in Fairfax County, Virginia, having a drainage area greater than 1 square mile except for Dogue Creek, Little Hunting Creek, and that part of Cameron Run above Lake Barcroft. Maps having a 2-foot contour interval and a horizontal scale of 1 inch equals 100 feet have been used for a base on which flood boundaries were delineated for 25-, 50-, and 100-year floods to be expected in each basin under ultimate development conditions. Included are techniques employed in computing discharges and profiles as well as the flood profiles and maps on which flood boundaries have been delineated for that part of Cameron Run basin below Lake Barcroft in both Fairfax County and the city of Alexandria.

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USGS1976

Flood-plain delineation for Difficult Run Basin, Fairfax County, Virginia

Water-surface profiles of the 25-year and 100-year floods and maps on which the 25-, 50-, and 100-year flood boundaries are delineated for streams in the Difficult Run basin are presented in this report. The techniques used in the computation of the flood profiles and delineation of flood boundaries are presented, and specific hydraulic problems encountered within the study area are also included.

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USGS1976

Measured and simulated ground-water levels in the Franklin area, southeastern Virginia

The Lower Cretaceous aquifer is the principal source of water in Southeastern Virginia. Synoptic water-level measurements made since 1970 have been used to verify a digital model of the aquifer. Measurements made in December 1973, August and December 1974 were used to further verify the model, using updated pumpage for those periods. The close agreement of the potentiometric maps based on measured and simulated water levels indicates that the model is simulating hydrologic conditions satisfactorily. (Woodard-USGS)

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USGS1975

A predictive computer model of the Lower Cretaceous aquifer, Franklin area, southeastern Virginia

The Lower Cretaceous aquifer of Southeastern Virginia is simulated in this study. The aquifer is only a few feet thick along the Fall Line, where it is near or at the surface, but it thickens and dips to the east. At Franklin where the top of the aquifer is 220 feet (67 metres) below sea level, it is about 600 feet (180 metres) thick. Thirty five miles (56 kilometres) east of Franklin, along the eastern boundary of the model area, the top is about 900 feet (270 metres) below sea level, and the thickness is estimated to be 2,000 feet (610 metres). The aquifer consists of an alternating series of permeable and semipermeable beds, which contain various mixtures of sand, gravel, silt and clay. The sediments are continental stream deposits in the western and central parts of the area, but grade to marine deposits in the eastern part. Transmissivity is zero at or near the Fall Line, and increases eastward to 19,000 cubic feet per day per foot (1,800 cubic metres per day per metre) at Franklin. Further eastward, trans-missivity probably increases slightly, but then decreases as the marine phase is reached. The aquifer is.overlain by a semiper-meable'confining layer and is underlain by relatively impermeable rocks of the pre-Cretaceous basement. The model used is the finite-difference digital type described by Pinder (1970). Historical water levels of the aquifer were simulated from 1891 to December 1, 1972. The 1891 water-level surface was developed by running a steady-state version of the Pinder model. Simulation runs from 1891 to 1941, 1970, and 1972 are in good agreement with historical water levels. A modeling factor was used as a multiplier for varying the coefficients of transmissivity and vertical permeability of the confining layer without altering the initial (1891) surface used to start the modeling runs. This technique should be helpful in the development of other models of artesian aquifers. Predicitive runs show that, if pumpage continues to increase as it has in the past, serious dewatering of the aquifer will occur at Franklin and possibly at other centers of increased pumpage. However, a predictive run to the year 2022 shows that if pumpage does not increase, additional drawdown would be small. Other predictive runs show the effects caused by hypothetical withdrawals at other locations.

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USGS1974

Tour guide: John Wesley Powell Federal Building

Data from 5,594 samples collected from 1931 through 2006 were used to describe naturally occurring fluoride concentrations in freshwater aquifers in Louisiana. Statistical analyses were used to summarize fluoride concentrations in the aquifers.

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USGS1974

The National Center of the U.S. Geological Survey

In August of 1973, the U. S. Geological Survey moved its first group of employees into the John Wesley Powell Federal Building of its newly constructed National Center at Reston, Virginia. The move signaled the fruition of more than a decade of planning and work to consolidate the agency's widespread activities into one location which could truly serve as a National Center. The Survey's leadership in the natural resources field has been materially strengthened through the availability of the Center's outstanding research and engineering facilities. Also the Center affords important professional and administrative advantages by bringing together the 2,200 Survey employees in the Washington, D.C, metropolitan area.

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USGS1974

Summary of the ground-water resources of the James River basin, Virginia

The James River basin, in central Virginia, encompasses an area of 10,000 square miles. The river flows eastward through varied geologic settings including the Valley and Ridge, Blue Ridge, Piedmont, and Coastal Plain provinces. Springs are most abundant in the Paleozoic rocks of the Valley and Ridge province. Most of the large springs, some of which yield as much as 7,000 gallons per minute, emanate from solution channels and fractures in carbonate rock or sandstone. Well yields range from less than 10 to more than 1,000 gallons per minute; the larger yields usually are found in formations that also contain the larger springs. Wells located at the intersection of fractures also usually have large yields. Discharge of ground water to streams is estimated to be 100,000 to 300,000 gallons per day per square mile. Rocks of the Blue Ridge and Piedmont provinces are metamorphic and intrusive rocks largely of Precambrian age. They are highly fractured but in general have lower porosity and permeability than rocks of the Valley and Ridge province. Small to moderate yields (1 to 100 gallons per minute) are usually obtained from the lower part of the saprolite (weathered rock residuum) and the upper fractured part of the unweathered crystalline rock. Most wells in the Blue Ridge and Piedmont provinces obtain most of their water within a depth of 200 feet. Wells drilled indraws usually have larger yields than wells drilled on hilltops. Rocks of Triassic age are present in small isolated basins in the Piedmont. Moderate yields are obtained from sandstone or conglomerate layers. Coastal Plain sediments consist of gravel, sand, silt, and clay beds of Holocene to Early Cretaceous age. Sediments of Pleistocene age, which are usually near the surface, contain aquifers that are about 10 to 30 feet thick and that usually yield 10 gallons per minute or less of soft water. Sediments of Miocene age usually are confining beds, but in some areas they contain thin sand or shell aquifers that yield small to moderate amounts of water that is generally hard. Sediments of Eocene, Paleocene, and Late Cretaceous age are characterizedby abundant glauconitic sand that yields moderate amounts ofwater. However, the glauconitic sand often clogs wells and yields waterwith a disagreeable taste and odor. Quartz sand beds of Late Cretaceousage yield moderate amounts of water. Sediments of Early Cretaceous age consist of thick alternating bedsof sand and clay of continental origin. Quartz sand beds more than30 feet thick are common, and some are more than 100 feet thick. Somemultiscreen wells yield more than 2,000 gallons per minute. Large withdrawalsof ground water have lowered potentiometric levels as much as 200 feet near Franklin, Va. Total pumpage from aquifers within the James River basin is estimatedto have been more than 68 million gallons per day in 1971. Recharge takesplace at outcrop areas near the Fall Line and throughout the area byseepage through the overlying confining beds. The quality of the water in Lower Cretaceous sediments ranges from soft water of low mineral and bicarbonate content near the Fall Line through hard calcium bicarbonate water of moderate mineral content in the west-central part of the area to soft sodium bicarbonate water of moderate to high mineral content in the eastern parts. Salty water occurs in coastal areas and a considerable distance inland. The horizontal and vertical extent of the salty water is not known, but, becausethe hydraulic gradient is from areas of salty water toward the areas ofheavy pumping, the water must be moving toward areas of heavy pumpage.The rate of movement is unknown.

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USGS1974

Correlation between geophysical data and rock types in the Piedmont and coastal plain of northeast Virginia and related areas

Physical, chemical, and mineralogic characteristics of rock units in parts of the northeast Virginia Piedmont are reflected in the aeromagnelic, aeroradioactivity, and gravity data for this area. Magnetic anomalies show the areal distribution of rocks containing magnetite. Aeroradiometric anomalies in the Piedmont and Coastal Plain provinces are directly related to the K 2 O content of the formations. In the crystalline rocks of the Piedmont this is reflected in their muscovite and microcline content, whereas in the Coastal Plain province it is related to the glauconite content of the Aquia Formation. Locally, in the crystalline rocks of the Piedmont, uranium- and thorium-bearing mineral content is of greater importance than K 2 O-bearing mineral content in producing aeroradiometric anomalies. The region also is characterized by (1) a northern gravity high, (2) a southern gravity high presumed to be caused by mafic rocks, and (3) an intervening zone characterized by low gravity relief and underlain by schist and gneiss. Geologic and geophysical extrapolation southward toward the Arvonia area show that the Chopawamsic Formation and the volcanic rocks of the Evington group are coeval. Also, on the northwest side of these volcanic rocks is a belt of small rootless mafic and ultramafic rocks diapirically ceplaced in folded rocks of Early Cambrian (?) age.

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