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Geology topics

E. R. McFarland

Publications and source records attributed to E. R. McFarland.

7 recordsLinked to original sources
USGS1998

Design, revisions, and considerations for continued use of a ground-water-flow model of the coastal plain aquifer system in Virginia

A digital numerical model of the ground-water-flow system in the Virginia Coastal Plain was constructed as part of the Regional Aquifer System Analysis program of the U.S. Geological Survey and subsequently revised based on reinterpretations of the hydrogeologic framework. The revised model has been incorporated by the Virginia Department of Environmental Quality as a means to evaluate the effects of existing and proposed ground-water withdrawals. The revised model, which is documented here, includes many design features of the original model. Principal modifications are (1) reassignment of some model layers to represent different aquifers, (2) replacement of applied recharge and the uppermost surface-water layer by constant-head cells to represent the unconfined aquifer, and (3) revision of the lateral extents and transmissivity and vertical leakance values assigned to model layers. Ground-water levels simulated by the revised model under steady-state conditions, using withdrawal rates representing the period 1978-80, generally are similar to the water levels simulated by the original model under transient conditions using the same withdrawal rates. Differences probably result largely from changes in transmissivity and vertical leakance values. T he revised model enables the continued evaluation of development of the large and complex aquifer system. Improved information on parts of some aquifers has been incorporated. Only large, regional-scale trends in ground-water water levels, flow directions, and flow rates are simulated, however, and not local trends and (or) short-term changes in water level and flow. Changing hydraulic stresses, knowledge of hydrogeologic conditions, and resource-management needs require periodic revision of the model to maintain its usefulness for the management of ground-water resources in the Virginia Coastal Plain.

Virginia↗
USGS1995

Relation of land use to nitrogen concentration in ground water in the Patuxent River basin, Maryland

A decrease in nitrogen inputs could improve water quality in the Chesapeake Bay. In order to provide information about nitrogen transport to the bay, the U.S. Geological Survey examined historical land use associated with nonpoint sources of nitrogen and nitrogen concentrations in ground water in the Patuxent River Basin, Maryland; The Patuxent River is a major tributary to the bay. Most nitrogen in ground water was present as nitrate. In the Piedmont Physiographic Province part of the Patuxent River basin, nitrate concentrations in ground water were higher in agricultural areas than in forested and urban areas. Nitrate concentrations were related to land use at well sites because wells yielded water that infiltrated within the same contributing area where the wells are located. Agricultural activities possibly were a source for the transport of large amounts of nitrogen to ground water and probably also to base flow in nearby streams. The high nitrate concentrations were not attributed to sampling bias. In the Coastal Plain Physiographic Province, most nitrate concentrations were low and were unrelated to land use at the well site because the wells were screened in deep, regional aquifers. Ground water in a few shallow wells had high nitrate concentrations, possibly related to nearby agricultural and urban land use. Increased nitrate concentrations in shallow ground water could increase concentrations in stream base flow and eventually could increase concentrations in regional aquifers and ground water that discharges directly to the Chesapeake Bay.

Water-Resources Investigations Report↗
USGS1994

Potentiometric surface of the Brightseat-upper Potomac Aquifer in Virginia, 1993

Ground-water level measurements from 30 wells in the Brightseat-upper Potomac aquifer in the Coastal Plain Physiographic Province of Virginia in 1993 were used to prepare a map of the potentiometric surface of the aquifer. The map shows the potentiometric surface of the Brightseat-upper Potomac aquifer indicating a regional trend toward the Chesapeake Bay and Atlantic Ocean. The potentiometric-surface data indicate that cones of depression are apparent around West Point and in southeastern Isle of Wight County near Franklin, Virginia. The highest ground-water-level measurement was 4 feet above sea level in northern Accomack County, and the lowest ground-water-level measurement was 117 feet below sea level in Franklin, Virginia.

Virginia↗
USGS1994

Potentiometric surface of the middle Potomac Aquifer in Virginia, 1993

Ground-water level measurements from 50 wells in the middle Potomac aquifer in the Coastal Plain Physiographic Province of Virginia in 1993 were used to prepare a map of the potentiometric surface of the aquifer. The map shows the potentiometric surface of the middle Potomac aquifer sharply declining eastward from nearly 100 feet above sear level near the western boundary of the aquifer to 20 feet below sea level, and continues declining gradually toward the Chesapeake Bay and Atlantic Ocean. A cone of depression is apparent around well fields in Franklin, Virginia. The potentiometric surface also appears to be affected by pumping in the area of Henrico County and Hanover County, Virginia. The highest ground-water-level measurement was 89 feet above sea level in Chesterfield County near Richmond, and the lowest ground-water-level measurement was 179 feet below sea level in southeastern Isle of Wight County, Virginia.

Virginia↗
USGS1994

Potentiometric surface of the lower Potomac Aquifer in Virginia, 1993

Ground-water level measurements from 17 wells in the lower Potomac aquifer in the Coastal Plain Physiographic Province of Virginia in 1993 were used to prepare a map of the potentiometric surface of the aquifer. The map shows the potentiometric surface of the lower Potomac aquifer indicating a regional trend toward the Chesapeake Bay and Atlantic Ocean. The potentiometric-surface data indicate that there are two cones of depression, one around well fields in Henrico County and the other around large well fields in Isle of Wight County and Franklin, Virginia. The highest ground-water-level measurement was 47 feet above sea level in southeast Southampton County, and the lowest ground-water-level measurement was 161 feet below sea level in the southeast area of Isle of Wight County near Franklin, Virginia.

Virginia↗