Geology topics

Research about Orange County, North Carolina

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

5 recordsLinked to original sources

USGS2026

Integrating fecal DNA and telemetry to estimate wildlife densities in anthropogenic landscapes

Density estimation is central to wildlife management efforts but can be challenging in anthropogenically-dominated landscapes due to small parcel sizes, access restrictions, and limited green space. Reliable density estimates are especially important for managing white-tailed deer ( Odocoileus virginianus ), whose high abundance in urbanized areas increases the need for accurate population assessments to guide management and reduce negative human–wildlife interactions. Herein, we evaluated (a) the use of a plot-based spatial capture-recapture sampling design to estimate deer density in developed landscapes and (b) if integrating telemetry data improved the precision or biological inferences of density estimates. We conducted fecal sampling at 2 study areas reflecting different characteristics of the urbanization gradient in Durham and eastern Orange counties, North Carolina: (1) rural (i.e., forested, large parcels) and (2) suburban (i.e., small parcels, limited continuous access, diversity of landscape features). We collected 223 fecal samples during a 3-week sampling period in July and September 2022, resulting in 157 individual deer detected (112 F:45 M). Rural densities were estimated at 54 deer/km 2 (95% CI = 35–84) and suburban densities at 75 deer/km 2 (95% CI = 48–117). Integrating telemetry data allowed estimation of sex-specific space use and densities, which were not possible from fecal data alone; however, precision of total density estimates was similar across integrated and fecal-only analyses. Overall, our results highlighted key trade-offs inherent to plot-based spatial capture-recapture in suburban landscapes, most notably low recapture rates, accessibility challenges to maintain optimal trap spacing, and the importance of considering auxiliary data streams as part of the study design.

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USGS2015

Effect of land-applied biosolids on surface-water nutrient yields and groundwater quality in Orange County, North Carolina

Land application of municipal wastewater biosolids is the most common method of biosolids management used in North Carolina and the United States. Biosolids have characteristics that may be beneficial to soil and plants. Land application can take advantage of these beneficial qualities, whereas disposal in landfills or incineration poses no beneficial use of the waste. Some independent studies and laboratory analysis, however, have shown that land-applied biosolids can pose a threat to human health and surface-water and groundwater quality. The effect of municipal biosolids applied to agriculture fields is largely unknown in relation to the delivery of nutrients, bacteria, metals, and contaminants of emerging concern to surface-water and groundwater resources. Therefore, the North Carolina Department of Environment and Natural Resources (NCDENR) collaborated with the U.S. Geological Survey (USGS) through the 319 Nonpoint Source Program to better understand the transport of nutrients and bacteria from biosolids application fields to groundwater and surface water and to provide a scientific basis for evaluating the effectiveness of the current regulations. The USGS conducted a paired agricultural watershed study in the Collins Creek and Cane Creek Reservoir watersheds in Orange County, North Carolina. Field activities were conducted from March 2011 through May 2013 at two field study sites, including biosolids field application sites owned by Orange County Water and Sewer Authority (OWASA) in the Collins Creek watershed and a background study site in the Cane Creek watershed that has no fields receiving biosolids applications. Samples of biosolids source material and soil were collected from the land-application fields for laboratory analyses. Soil samples were also collected from a background agricultural field in the Cane Creek watershed that has never received land-applied municipal biosolids. Shallow groundwater samples were collected quarterly from new monitoring wells installed by NCDENR along the edge of the biosolids land-application fields and a background agricultural field for laboratory analyses. Two surface-water monitoring sites were established on Collins Creek to compute continuous streamflow and collect discrete baseflow and stormwater runoff water-quality data upstream and downstream from the biosolids land-application fields. Surface water-quality samples were also collected for baseflow and stormwater runoff conditions at an existing USGS streamgage on Cane Creek to monitor water-quality conditions in the background study watershed. The study primarily focused on nutrients and bacteria; however, data for field properties and water-quality constituents, including metals, major ions, and contaminants of emerging concern (household-, industrial-, and agricultural-use compounds, pharmaceutical compounds, hormones, and antibiotics) also were collected and used in the analyses. There were no exceedances of the 10 elements with designated U.S. Environmental Protection Agency (EPA) ceiling concentrations for land-applied biosolids in any of the biosolids samples. Treatment processes and storage techniques used by OWASA are effective in eliminating Escherichia coli and fecal coliform bacteria from biosolids. Copper, molybdenum, total Kjeldahl nitrogen, and total phosphorus were elevated in the soil from biosolids land-application fields relative to the background field. The relative richness of these constituents in the biosolids land-application fields is consistent with biosolids being the source of the elevated concentrations given the relatively high concentrations of these constituents in the biosolids samples that were collected. Shallow groundwater in the transitional zone wells, which were located adjacent to and topographically downgradient from all the biosolids land-application fields, were found to be statistically different and had higher nitrate concentrations (medians greater than 12 milligrams per liter) than all the other wells sampled as part of the study. Surface-water nutrient concentrations and yields, primarily nitrate, were higher at the monitoring site on Collins Creek downstream from the biosolids land-application fields than the other study sites that drained watersheds without biosolids land application. The largest differences in concentrations between sites were measured at baseflow conditions, which indicate that the main cause of these differences, particularly between Cane Creek and the Collins Creek site downstream from the OWASA application fields, is related to nitrate contribution from the shallow groundwater. Contaminants of emerging concern were detected in approximately 40 percent of the laboratory analyses of the biosolids samples and more frequently in soil samples from the biosolids land-application fields (approximately 40 percent of laboratory analyses) relative to the soil samples from the background field (approximately 12 percent of laboratory analyses). However, contaminants of emerging concern detected in the laboratory analysis for this study do not appear to be good indicators of human-waste contaminants derived from land-applied biosolids in groundwater or surface-water because the number of detections and concentrations at the background wells and surface-water monitoring sites are similar to or higher than those at wells and monitoring sites adjacent to or downstream from the biosolids land-application fields. The data, analysis, and conclusions associated with this study can be used by regulatory agencies, resource managers, and wastewater-treatment operators to (1) better understand the quantity and characteristics of nutrients, bacteria, metals, and contaminants of emerging concern that are transported away from biosolids land-application fields to surface water and groundwater under current regulations for the purposes of establishing effective total maximum daily loads (TMDLs) and restoring impaired water resources, (2) assess how well existing regulations protect waters of the State and potentially recommend effective changes to regulations or land-application procedures, and (3) establish a framework for developing guidance on effective techniques for monitoring and regulatory enforcement of permitted biosolids land-application fields.

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USGS2001

Investigation of Ground-Water Availability and Quality in Orange County, North Carolina

A countywide inventory was conducted of 649 wells in nine hydrogeologic units in Orange County, North Carolina. As a result of this inventory, estimates of ground-water availability and use were calculated, and water-quality results were obtained from 51 wells sampled throughout the County from December 1998 through January 1999. The typical well in Orange County has an average depth of 208 feet, an average casing length of 53.6 feet, a static water level of 26.6 feet, a yield of 17.6 gallons per minute, and a well casing diameter of 6.25 inches. The saturated thickness of the regolith averages 27.0 feet and the yield per foot of total well depth averages 0.119 gallon per minute per foot. Two areas of the County are more favorable for high-yield wells—a west-southwest to east-northeast trending area in the northwestern part of the County, and a southwest to northeast trending area in the southwestern part of the County. Well yields in Orange County show little correlation with topographic or hydrogeologic setting. Fifty-one sampling locations were selected based on (a) countywide areal distribution, (b) weighted distribution among hydrogeologic units, and (c) permission from homeowners. The list of analytes for the sampling program consisted of common anions and cations, metals and trace elements, nutrients, organic compounds, and radon. Samples were screened for the presence of fuel compounds and pesticides by using immuno-assay techniques. Dissolved oxygen, pH, temperature, specific conductance, and alkalinity were measured in the field. The median pH was 6.9, which is nearly neutral, and the median hardness was 75 milligrams per liter calcium carbonate. The median dissolved solids concentration was 125 milligrams per liter, and the median specific conductance was 175 microsiemens per centimeter at 25 degrees Celsius. Orange County ground water is classified as a calcium-bicarbonate type. High nutrient concentrations were not found in samples collected for this study. Nitrate was detected in 82 percent of the samples at concentrations ranging up to 7.2 milligrams per liter, although the median concentration was 0.49 milligram per liter; all other samples had a concentration of 2.9 milligrams per liter or less. In general, trace elements were detected infrequently or at concentrations less than State drinking-water standards. However, exceedances of North Carolina drinking-water standards were observed for iron (3 exceedances of 51 analyses, detection up to 1,100 micrograms per liter), manganese (12 exceedances of 51 analyses, detection up to 890 micrograms per liter), and zinc (4 exceedances of 31 analyses, detection up to 4,900 micrograms per liter). Lead was detected in 8 of 31 samples with a concentration up to 3.5 micrograms per liter. Zinc, manganese, iron, and copper were the most frequently detected trace metals at 100, 94, 80, and 61 percent, respectively. Lead, arsenic, bromide, alum inum, and selenium were detected in 13 to 26 percent of the analyses. No benzene, toluene, ethylbenzene, and xylene (BTEX) or atrazine compounds were detected in any of the samples. Radon activities in ground water can be high because of the rock units present in Orange County. Radon activity ranged from 38 to 4,462 picocuries per liter countywide, with a median activity of 405 picocuries per liter. Median radon activities in Orange County were highest in felsic rocks (487 picocuries per liter) and lowest in mafic rocks (357 picocuries per liter). When evaluated by individual hydrogeologic units, the median radon activity was highest in the phyllite unit (1,080 picocuries per liter in 2 samples) and the felsic metaigneous unit (571 picocuries per liter in 13 samples). Overall, water-quality data in Orange County indicate few drinking-water concerns. No organic contaminants analyzed (total BTEX and atrazine) or excessive nutrient concentrations were detected, and few exceedances of North Carolina drinking- water standards were detected.

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USGS1999

Susceptibility of ground water to surface and shallow sources of contamination, Orange County, North Carolina

In 1998, the relative susceptibility of ground water in Orange County, North Carolina,to contamination from surface and shallow sources was evaluated. A geographic information system was used to build three county-wide layers--soil permeability, land use/land cover, and land-surface slope. The harmonic mean permeability of soil layers was used to estimate a location's capacity to transmit water through the soil. Values for each of these three factors were categorized and ranked from 1 to 10 according to relative potential for contamination. Each factor was weighted to reflect its relative potential contribution to ground-water contamination, then the factors were combined to create a relative susceptibility index. The relative susceptibility index was categorized to reflect lowest, low, moderate, high, and highest potential for ground-water contamination. The relative susceptibility index for about 12 percent of the area in Orange County was categorized as high or highest. The high and highest range areas have highly permeable soils, land cover or land-use activities that have a high contamination potential, and low to moderate slopes. Most of the county is within the moderate category of relative susceptibility to ground-water contamination. About 21 percent of the county is ranked as low or lowest relative susceptibility to ground-water contamination.

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USGS1996

Ground-water recharge to the regolith-fractured crystalline rock aquifer system, Orange 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 Orange 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 12 selected drainage basins and subbasins using streamflow data and an analytical technique known as hydrograph separation. Methods for determining the quality of ground water in storage also are described. Orange County covers approximately 401 square miles in the eastern part of the Piedmont Province. The population of the county in 1990 was about 93,850; approximately 41 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 most of the county. Ground water also is obtained from Triassic age sedimentary rocks that occur in a small area in southeastern Orange County. Under natural conditions, recharge to the county's ground-water system is derived from the 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 17 gaging stations that measure streamflow within or from Orange County were analyzed to produce daily estimates of ground-water recharge in 12 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 12 basins and subbasins ranges from 4.15 to 6.40 inches per year, with a mean value of 4.90 inches per year for all basins. In general, recharge rates are highest for basins along a north- south zone extending down the center of the county, and lowest in the western and southeastern parts of the county. Median recharge rates in the 12 basins range from 1.08 inches per year (80.7 gallons per day per acre) to 4.97 inches per year (370 gallons per day per acre), with a median value of 3.06 inches per year (228 gallons per day per acre) for all basins. Recharge estimates for the Morgan Creek Basin upstream from White Cross and upstream from Chapel Hill are higher than any other basin or subbasin in Orange County. Ground water also constitutes a higher percentage of total streamflow in Morgan Creek (44.4 percent upstream from White Cross; 47.9 percent upstream from Chapel Hill) than in any other stream in the county. Greater topographic relief and depth of channel incision may explain the high recharge estimates (base-flow rates) in the Morgan Creek Basin. The presence of large areas of regolith derived from the metaigneous, felsic hydrogeologic unit may magnify the effects of topographic relief and channel incision. Base flow in the New Hope River subbasin, as a percentage of total streamflow, at 32.2 percent, is the lowest of the 12 basins and subbasins. Much of the New Hope River subbasin is underlain by the Triassic sedimentary rock hydrogeologic unit that occurs within a rift basin of Triassic age. These data suggest that in areas underlain by Triassic sedimentary rock, there is less recharge to the ground-water syst

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