Geology topics

Research about Guilford County, North Carolina

Source-linked reports with geographic coverage including Guilford County, North Carolina.

6 recordsLinked to original sources

USGS1998

Ground-water recharge to and storage in the regolith-fractured crystalline rock aquifer system, Guilford County, North Carolina

Quantitative information concerning recharge rates to aquifers and ground water in storage is needed to manage the development of ground- water resources. The amount of ground water available from the regolith-fractured crystalline rock aquifer system in Guilford County, North Carolina, is largely unknown. If historical patterns seen throughout the Piedmont continue into the future, the number of ground- water users in the county can be expected to increase. In order to determine the maximum population that can be supplied by ground water, planners and managers of suburban development must know the amount of ground water that can be withdrawn without exceeding recharge and(or) overdrafting water in long-term storage. Results of the study described in this report help provide this information. Estimates of seasonal and long-term recharge rates were estimated for 15 selected drainage basins and subbasins using streamflow data and an anlytical technique known as hydrograph separation. Methods for determining the quantity of ground water in storage also are described. Guilford County covers approximately 658 square miles in the central part of the Piedmont Province. The population of the county in 1990 was about 347,420; approximately 21 percent of the population depends on ground water as a source of potable supplies. Ground water is obtained from wells tapping the regolith-fractured crystalline rock aquifer system that underlies all of the county. Under natural conditions, recharge to the ground-water system in the county is derived from infiltration of precipitation. Ground-water recharge from precipitation cannot be measured directly; however, an estimate of the amount of precipitation that infiltrates into the ground and ultimately reaches the streams of the region can be determined by the technique of hydrograph separation. Data from 19 gaging stations that measure streamflow within or from Guilford County were analyzed to produce daily estimates of ground-water recharge in 15 drainage basins and subbasins in the county. The recharge estimates were further analyzed to determine seasonal and long-term recharge rates, as well as recharge duration statistics. Mean annual recharge in the 15 basins and subbasins ranges from 4.03 to 9.69 inches per year, with a mean value of 6.28 inches per year for all basins. In general, recharge rates are highest for basins in the northern and northwestern parts of the county and lowest in the southern and southeastern parts of the county. Median recharge rates in the 15 basins range from 2.47 inches per year (184 gallons per day per acre) to 9.15 inches per year (681 gallons per day per acre), with a median value of 4.65 inches per year (346 gallons per day per acre) for all basins. The distribution of recharge rates in the county suggests a correlation between recharge rates and hydrogeologic units (and derived regolith). The highest recharge estimates occur in the northwestern part of Guilford County in basins unlain by felsic igneous intrusive rocks and lesser areas of metasedimentary rocks. Recharge estimates in this area range from 6.37 to 9.33 inches per year. Basins in the southwestern, central, and northeastern parts of the county are underlain primarily by metaigneous rocks of felsic and intermediate compositions, and recharge estimates range from 5.32 to 5.51 inches per year. In the extreme southern and southeastern parts of the county, the lower Deep River subbasin and the lower Haw River subbasins have the lowest estimated recharges at 4.15 and 4.03 inches per year, respectively. Although the areas of these subbasins that lie within Guilford County are underlain primarily by metaigneous rocks of felsic and intermediate compositions, the larger part of these subbasins lies south and southeast of Guilford County in areas underlain by hydrogeologic units of metavolcanic origin. The distribution of recharge rates in the study area is almost the reverse of the distributio

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USGS1997

Radon in ground water in Guilford County, North Carolina

Approximately 30 percent of the water used in Guilford County, North Carolina, is from ground-water sources. All rural supplies are from ground water; approximately 65,000 residents used ground water for their domestic water supplies in 1990. The U.S. Geological Survey (USGS), in cooperation with the Guilford County Soil and Water Conservation District and the Guilford County Department of Health, began a study in 1996 of the hydrogeology of Guilford County to update previous work. As part of this effort and according to methods presented in Koterba and others (1995), dissolved radon samples were collected from 70 wells throughout the county. Because radon in ground water poses a potential health hazard, this report presents results from this sampling effort and the implications that radon may have on ground-water use in Guilford County.

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USGS1995

Effects of agricultural land-management practices on water quality in northeastern Guilford County, North Carolina, 1985-90

The effects of selected agricultural land-management practices on water quality were assessed in a comparative study of four small basins in the Piedmont province of North Carolina. Agricultural practices, such as tillage and applications of fertilizer and pesticides, are major sources of sediment, nutrients, and pesticides in surface water, and of nutrients and pesticides in ground water. The four study basins included two adjacent row-crop fields, a mixed land-use basin, and a forested basin. One of the row-crop fields (7.4 acres) was farmed by using conservation land-management (CLM) practices, which included strip cropping, contour plowing, field borders, and grassed waterways. The other row-crop field (4.8 acres) was farmed by using standard land-management (SLM) practices, which included continuous cropping, straight-row plowing without regard to land topography, and poorly maintained waterways. The mixed land-use basin (665 acres) was monitored to compare water quality in surface water as SLM practices were converted to CLM practices during the project. The forested basin (44 acres) provided background surface-water hydrologic and chemical-quality conditions. Surface-water flow was reduced by 18 percent by CLM practices compared to surface-water flow from the SLM practices basin. The thickness of the unsaturated zone in the row-crop basins ranged from a few feet to 25 feet. Areas with thick unsaturated zones have a greater capacity to intercept and store nutrients and pesticides than do areas with thinner zones. Sediment concentrations and yields for the SLM practices basin were considerably higher than those for the other basins. The median sediment concentration in surface water for the SLM basin was 3.4 times that of the CLM basin, 8.2 times that of the mixed land-use basin, and 38.4 times that of the forested basin. The total sediment yield for the SLM basin was 2.3 times that observed for the CLM basin, 14.1 times that observed for the mixed land-use basin, and 19.5 times the yield observed for the forested basin. Nutrient concentrations in surface water from the row-crop and mixed land-use basins were higher than those measured in the forested basin and in precipitation collected near the row-crop basins. The SLM basin generally had the highest concentrations of total nitrogen, nitrite plus nitrate, total phosphorus (equivalent to the mixed land-use basin), and potassium. Nutrient concentrations in soil water and ground water were less than concentrations in surface water for the row-crop basins. Nutrient concentrations generally were at least slightly below the root zone (3-foot depth) and in ground water. Differences in nutrient yields among basins had patterns similar to those observed for nutrient concentrations. The total nitrogen yield for the SLM basin was 1.2 times the yield for the CLM basin, 1.9 times the yield for the mixed land-use basin, and 4.2 times the yield for the forested basin. The total phosphorus yield for the SLM basin was 1.7 times the yield for the CLM basin, 3.3 times the yield for the mixed land-use basin, and 7.8 times the yield for the forested basin. No significant differences in pesticide concentrations in surface water were identified between those measured in the SLM basin and those measured in the CLM basin. Significantly higher pesticide concentrations were observed at the row-crop basins compared with those observed at the mixed land-use basin probably because sampling sites for the row-crop basins were closer to the pesticide sources. No pesticides were detected in the forested basin. Comparisons of pesticide concentrations in soil from the two row-crop basins indicated some differences. Concentrations of the soil pesticides isopropalin and flumetralin were higher in the SLM basin than in the CLM basin. The surface-water quality of the mixed land-use basin generally was less affected by agricultural nonpoint sources than that of the smaller row-crop b

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USGS1991

Effects of land-management practices on sediment yields in northeastern Guilford County, North Carolina

Streamflow, precipitation, and suspended-sediment data were collected from two small agricultural basins in the Piedmont province of North Carolina. The data were used to determine the effects of land-management practices on sediment yield. One basin of 7.4 acres represents best land-management practices with strip cropping, crop rotation, contour farming, and grassed waterways. The other basin of 4.8 acres represents standard land-management practices with down-slope row orientation, unmaintained grassed waterways, and without crop rotation. Data collected during the 1985-87 water years were used to develop regression equations to describe the relation between suspended-sediment discharge and water discharge. Data sets consisting of suspended-sediment concentrations and corresponding instantaneous water-discharge data were developed. There were two data sets from each basin, one representing data collected during the growing season, May through September, and the other representing data collected during the nongrowing season, October through April. Four regression equations were developed, one for each data set, and were tested for goodness-of-fit by use of graphical analysis, influence diagnostics, significance tests, and residuals analysis. Following acceptance of the four equations, the slope of each individual line was tested to determine if season was a significant variable. Seasonally, the average sediment yields (2.7 tons per acre) from the basin having best land-management practices were only about one-seventh of those (20 tons per acre) from the basin having standard land-management practices. Comparison of annual sediment yields in the agricultural basins against the yield from a nearby forested basin, which represents a nearly undisturbed basin, indicates a 10- to 100-fold increase in sediment yields from the study basins. The forested basin sediment yield was 0.1 ton per acre in the 1987 water year. Sheet erosion, which represents soil moving from high areas to low areas in a basin but not necessarily reaching a stream, is also influenced by land-management practices. This type of erosion was estimated to be 3.6 tons per acre per year for the basin with best land-management practices and 45 tons per acre per year for the basin with standard land-management practices.

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USGS1989

Hydrologic and chemical-quality data from four rural basins in Guilford County, North Carolina, 1985-88

An investigation was begun in 1984 in Guilford County, North Carolina, to monitor water quality and soil erosion in basins with various land-management practices. Hydrologic and chemical-quality data were collected from four rural drainage basins, including two agricultural basins (7.4 and 4.8 acres) cultivated in tobacco and small grains, a mixed rural land-use basin (665 acres) currently under standard land-management practices, and a forested control basin (44 acres) characterizing background conditions. Mean concentrations of total nitrite plus nitrate were 1.0 milligrams per liter from the agricultural basin under standard land-management practices. This was nearly 10 times greater than concentrations from the forested basin. Records of streamflow discharge, chemical quality, ground-water levels, precipitation, and farming activities collected from October 1984 through September 1988 at one or more of the basins are also presented in this report.

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USGS1988

Surface-water and water-quality data from selected streams and treated waters in the Greensboro Area, North Carolina, 1986-87

Water and bottom-sediment samples were collected from April 1986 to September 1987 at 19 sites in Guilford County and the City of Greensboro, North Carolina. Sampling locations included 13 stream sites, two lakes that supply City of Greensboro drinking water, two City of Greensboro finished drinking-water filtration plants, and two municipal wastewater plants where effluents were sampled prior to outfall into the receiving streams. Water sampling consisted of six routine samplings during various stages of steady flow at all sites, and rainfall-event sampling during two storms at six sites. Bottom-sediment samples were collected at three sites during two routine samplings. Samples were analyzed for trace-element, major ion, and nutrient concentrations, as well as general water-quality indicators, such as pH, dissolved oxygen, and specific conductivity. Concentrations of acid and base/neutral extractable, volatile organic compounds, and organochlorine and organophosphorus constituents were also determined. Chromatographs from organic analyses were submitted to computerized library searches, the results of which are included in this report. Results from all analyses are presented in tabular form in the appendices.

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