Search USGS⌕ Search

SEARCH · Search USGS

Results for “Water Resources Research”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
USGS2026

Decision analysis of long-term research and monitoring investments for the Upper Mississippi River Restoration program

Congressional authorization of the Water Resource Development Act of 2020 increased funding for the Upper Mississippi River Restoration (UMRR) program and its Long Term Resource Monitoring (LTRM) element. With adequate resources there is an opportunity for LTRM to expand its understanding of the Upper Mississippi River System, address unmet partner information needs, and better inform restoration and management of the Upper Mississippi River System. Additional information needs will need to be identified and prioritized in a manner that accounts for potential tradeoffs among the preferences of UMRR partners for long-term commitments of effort. In this report, we describe a decision analysis process used by UMRR partners to develop a comprehensive framework for prioritizing and selecting the information needs they would address in the event of changes in available resources. The partners of the UMRR formed a “planning team” with members representing the UMRR partner agencies to work through the decision analysis process. This team included two facilitators who led the decision analysis process. The planning team began this process by articulating a consensus understanding of the specific decisions to be made and identifying a set of decision outcomes (objectives) the UMRR partners wanted to achieve. Next, they identified information needs not being addressed by ongoing monitoring and research, developed criteria for assessing the expected benefit of addressing each information need, and estimated the costs of addressing each information need. They then used an optimization approach to identify the portfolio of information needs that would produce the most benefit for a given cost if they were effectively addressed. Originally, the planning team expected this analysis to inform a project plan that would start in 2024, but in recognition of financial uncertainties, we refer to planning dates as the number of years after resources become available (for example, “year 1,” “year 2,” and so on).

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2017

Fallow-land Algorithm based on Neighborhood and TemporalAnomalies (FANTA) to map planted versus fallowed croplands usingMODIS data to assist in drought studies leading to water and foodsecurity assessments

An important metric to monitor for optimizing water use in agricultural areas is the amount of cropland left fallowed, or unplanted. Fallowed croplands are difficult to model because they have many expressions; for example, they can be managed and remain free of vegetation or be abandoned and become weedy if the climate for that season permits. We used 250 m, 8-day composite Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to develop an algorithm that can routinely map cropland status (planted or fallowed) with over 75% user’s and producer’s accuracies. The Fallow-land Algorithm based on Neighborhood and Temporal Anomalies (FANTA) compares the current greenness of a cultivated pixel to its historical greenness and to the greenness of all cultivated pixels within a defined spatial neighborhood, and is therefore transportable across space and through time. This article introduces FANTA and applies it to California from 2001 to 2015 as a case study for use in data-poor places and for use in historical modeling. Timely and accurate knowledge of the extent of fallowing can provide decision makers with insights and knowledge to mitigate the impacts of drought and provide a scientific basis for effective management response. This study is part of the WaterSMART (Sustain and Manage America’s Resources for Tomorrow) project, an interdisciplinary and collaborative research effort focused on improving water conservation and optimizing water use.

California↗
USGS2017

Geochemical modeling for mine site characterization and remediation

Geochemical Modeling for Mine Site Characterization and Remediation is the fourth of six volumes in the Management Technologies for Metal Mining Infl uenced Water series about technologies for management of metal mine and metallurgical process drainage. This handbook describes the important components of hydrogeochemical modeling for mine environments, primarily those mines where sulfi de minerals are present—metal mines and coal mines. It provides general guidelines on the strengths and limitations of geochemical modeling and an overview of its application to the hydrogeochemistry of both unmined mineralized sites and those contaminated from mineral extraction and mineral processing. The handbook includes an overview of the models behind the codes, explains vital geochemical computations, describes several modeling processes, provides a compilation of codes, and gives examples of their application, including both successes and failures. Hydrologic modeling is also included because mining contaminants most often migrate by surface water and groundwater transport, and contaminant concentrations are a function of water residence time as well as pathways. This is an indispensable resource for mine planners and engineers, environmental managers, land managers, consultants, researchers, government regulators, nongovernmental organizations, students, stakeholders, and anyone with an interest in mining influenced water.

Book↗
USGS2012

Hydrologic, vegetation, and soil data collected in selected wetlands of the Big River Management area, Rhode Island, from 2008 through 2010

The Rhode Island Water Resources Board planned to develop public water-supply wells in the Big River Management Area in Kent County, Rhode Island. Research in the United States and abroad indicates that groundwater withdrawal has the potential to affect wetland hydrology and related processes. In May 2008, the Rhode Island Water Resources Board, the U.S. Geological Survey, and the University of Rhode Island formed a partnership to establish baseline conditions at selected Big River wetland study sites and to develop an approach for monitoring potential impacts once pumping begins. In 2008 and 2009, baseline data were collected on the hydrology, vegetation, and soil characteristics at five forested wetland study sites in the Big River Management Area. Four of the sites were located in areas of potential drawdown associated with the projected withdrawals. The fifth site was located outside the area of projected drawdown and served as a control site. The data collected during this study are presented in this report.

Rhode Island↗
USGS1995

Simulated response of the High Plains aquifer to ground-water withdrawals in the Upper Republican Natural Resources District, Nebraska

The U.S. Geological Survey, in cooperation with the National Soil Tilth Laboratory of the U.S. Department of Agriculture, Agricultural Research Service, conducted a study as part of the multi- scale, interagency Management Systems Evaluation Area (MSEA) program to evaluate the effects of agricultural management (farming) systems on water quality. Data on surface flow, tileflow, and streamflow in the Walnut Creek watershed just south of Ames, Iowa, were collected during April 1991-September 1993 at five sites with drainage areas ranging from 366 to 5,130 hectares. Precipitation, flow discharge, and concentration, loads, and yields of nitrate as nitrogen, atrazine, and metolachlor were analyzed to relate the transport of agricultural chemicals to major water-flow processes and to examine and transport differences among three subwatersheds. Antecedent conditions and basin-characteristic differences had significant effects on the flow response from the subwatersheds. Monthly streamflow-to- precipitation ratios were greater than 1.0, as a result of snowmelt, and negative when streamflow was lost to the ground-water system in the downstream subwatershed. Dry antecedent conditions resulted in ratios less than 0.3 (July 1992), whereas wet antecedent conditions resulted in ratios from 0.7 to almost 1.0 (July 1993) during months with similar large rainfall amounts. Most of the streamflow from the upland subwatersheds came from tileflow. Surface flow (surface runoff, interflow, and return flow0 was highly variable and intermittent, usually lasting for only a few days after a storm, although it could be the dominant source of flow when stormflow was large. Tileflow was less variable and much more persistent, ceasing only after prolonged dry periods. Large quantities of nitrate as nitrogen were transported in Walnut Creek, with concen- trations often greater than the Maximum Contaminant Level of 10 milligrams per liter established by the U.S. Environmental Protection Agency for finished drinking water. In the upland subwatersheds, ground-water flow from the tiles appears to have been the primary means of transport to the streams. Concentrations in tileflow and streamflow generally were 4 to 16 milligrams per liter, with the lower concen- trations often the result of dilution by surface runoff. Loss ratios, chemical yields expressed as a percentage of average application rates of nitrate as nitrogen for October 1992-September 1993, were about 10 percent for surface flow and more than 100 percent for tileflow from the 366-hectare basin and were more than 200 percent for streamflow from the downstream subwatershed. Concentrations of atrazine and metolachlor in streamflow, typically, were less than the Maximum Contaminant Level of 3.0 micrograms per liter, but were as high as 59 and 80 micrograms per liter, respectively, during stormflow. Concentrations as high as 170 micrograms per liter occurred in tileflow, but these were related to surface flow through surface inlets. The transport of herbicides was extremely variable, with most of the loads occurring during stormflow. Atrazine appeared more susceptable to transport losses to streamflow than did metolachlor. Loss ratios for streamflow from the subwatersheds for April- September periods were 0.3 to 20 percent for atrazine and 0.1 to 2.9 percent for metolachlor. Chemical loss ratios indicated differences in the transport characteristics of the three subwatersheds. The downstream subwatershed, which has steeper terrain, a more-developed natural drainage system, and fewer tiles than the two upland subwatersheds, had the largest loss rates for all three chemicals--206 percent for nitrate as nitrogen (October 1992-September 1993) and 20 percent for atrazine and 2.9 percent for metolachlor (April-September 1993). For May-July 1993, when most of the herbicides were transported, the downstream subwatershed also had the largest cumulative unit discharge and the largest streamflow-to-precipitation ra

Water-Resources Investigations Report↗
USGS2015

Hydrologic record extension of water-level data in the Everglades Depth Estimation Network (EDEN), 1991-99

The real-time Everglades Depth Estimation Network (EDEN) has been established to support a variety of scientific and water management purposes. The expansiveness of the Everglades, limited number of gaging stations, and extreme sensitivity of the ecosystem to small changes in water depth have created a need for accurate water-level and water-depth maps. The EDEN water-surface elevation model uses data from approximately 240 gages in the Everglades to create daily continuous interpolations of the water-surface elevation and water depth for the freshwater portion of the Everglades from 2000 to the present (2014). These maps provide hydrologic data previously unavailable for assessing biological and ecological studies. Ecologists working in the Everglades expressed a need to the EDEN project team for daily EDEN water-level surfaces from 1990 to 1999. The additional 10 years of surfaces will provide ecologists and resource managers with two decades (1991–2011) of surfaces to analyze hydrologic dynamics. Before 2000, many of the EDEN gages used to generate water surfaces were not in operation. These datasets were extended to provide estimations of hydrologic time-series histories. The general approach to the record extension (hindcasts) was to (1) create a database of available data from 1990 to the present; (2) use dynamic cluster analysis to group stations with similar hydrologic behaviors for subareas of the Everglades with a large number of stations; (3) use results from the cluster analysis to select candidate explanatory variables; (4) develop linear regression or artificial neural network models to extend water-level records; and (5) evaluate record extensions by using model performance statistics and comparison of water-surface maps for similar hydrologic conditions for the hindcasted period (1991–99) and measured period (2000–11). To hindcast and fill data records, 214 empirical models were developed—189 are linear regression models and 25 are artificial neural network models. The coefficient of determination (R 2 ) for 163 of the models is greater than 0.80 and the median percent model error (root mean square error divided by the range of the measured data) is 5 percent. To evaluate the performance of the hindcast models as a group, contour maps of modeled water-level surfaces at 2-centimeter (cm) intervals were generated using the hindcasted data. The 2-cm contour maps were examined for selected days to verify that water surfaces from the EDEN model are consistent with the input data. The biweekly 2-cm contour maps did show a higher number of issues during days in 1990 as compared to days after 1990. May 1990 had the lowest water levels in the Everglades of the 21-year dataset used for the hindcasting study. To hindcast these record low conditions in 1990, many of the hindcast models would require large extrapolations beyond the range of the predictive quality of the models. For these reasons, it was decided to limit the hindcasted data to the period January 1, 1991, to December 31, 1999. Overall, the hindcasted and gap-filled data are assumed to provide reasonable estimates of station-specific water-level data for an extended historical period to inform research and natural resource management in the Everglades.

Florida↗
USGS1996

Joint US Geological Survey, US Nuclear Regulatory Commission workshop on research related to low-level radioactive waste disposal, May 4-6, 1993, National Center, Reston, Virginia; Proceedings

This report contains papers presented at the "Joint U.S. Geological Survey (USGS) and U.S. Nuclear Regulatory Commission (NRC) Technical Workshop on Research Related to Low-Level Radioactive Waste (LLW) Disposal" that was held at the USGS National Center Auditorium, Reston, Virginia, May 4-6, 1993. The objective of the workshop was to provide a forum for exchange of information, ideas, and technology in the geosciences dealing with LLW disposal. This workshop was the first joint activity under the Memorandum of Understanding between the USGS and NRC's Office of Nuclear Regulatory Research signed in April 1992. Participants included invited speakers from the USGS, NRC technical contractors (U.S. Department of Energy (DOE) National Laboratories and universities) and NRC staff for presentation of research study results related to LLW disposal. Also in attendance were scientists from the DOE, DOE National Laboratories, the U.S. Environmental Protection Agency, State developmental and regulatory agencies involved in LLW disposal facility siting and licensing, Atomic Energy Canada Limited (AECL), private industry, Agricultural Research Service, universities, USGS and NRC.

Water-Resources Investigations Report↗
USGS2018

Ecosystems science: Genes to landscapes

Bountiful fisheries, healthy and resilient wildlife, flourishing forests and vibrant grasslands are coveted resources that benefit all Americans. U.S. Geological Survey (USGS) science supports the conservation and management of the Nation’s fish and wildlife, and the landscapes they inhabit. Our biological resources—ecosystems and the wild things that live in them—are the foundation of our conservation heritage and an economic asset to current and future generations of Americans. The USGS Ecosystems Mission Area, the biological research arm of the Department of the Interior (DOI), provides science to help America achieve sustainable management and conservation of its biological resources. This work is done within the broader mission of the USGS—to serve the Nation with science that advances understanding of our natural resources, informs land and water stewardship, and helps safeguard communities from natural and environmental hazards. The Ecosystems Mission Area provides research, technical assistance, and education conducted by Cooperative Research Units and Science Centers located in nearly every State. The quality of life and economic strength in America hinges on healthy ecosystems that support living things and natural processes. Ecosystem science better enables society to understand how and why ecosystems change and to guide actions that can prevent damage to, and restore and sustain ecosystems. It is through this knowledge that informed decisions are made about natural resources that can enhance our Nation’s economic and environmental well-being.

Fact Sheet↗
USGS2008

Hydrogeologic Setting, Ground-Water Flow, and Ground-Water Quality at the Langtree Peninsula Research Station, Iredell County, North Carolina, 2000-2005

A 6-year intensive field study (2000-2005) of a complex, regolith-fractured bedrock ground-water system was conducted at the Langtree Peninsula research station on the Davidson College Lake Campus in Iredell County, North Carolina. This research station was constructed as part of the Piedmont and Mountains Resource Evaluation Program, a cooperative study being conducted by the North Carolina Department of Environment and Natural Resources and the U.S. Geological Survey. Results of the study characterize the distinction and interaction of a two-component ground-water system in a quartz diorite rock type. The Langtree Peninsula research station includes 17 monitoring wells and 12 piezometers, including 2 well transects along high to low topographic settings, drilled into separate parts of the ground-water-flow system. The location of the research station is representative of a metaigneous intermediate (composition) regional hydrogeologic unit. The primary rock type is mafic quartz diorite that has steeply dipping foliation. Primary and secondary foliations are present in the quartz diorite at the site, and both have an average strike of about N. 12 degree E. and dip about 60 degree in opposite directions to the southeast (primary) and the northwest (secondary). This rock is cut by granitic dikes (intrusions) ranging in thickness from 2 to 50 feet and having an average strike of N. 20 degree W. and an average dip of 66 degree to the southwest. Depth to consolidated bedrock is considered moderate to deep, ranging from about 24 to 76 feet below land surface. The transition zone was delineated and described in each corehole near the well clusters but had a highly variable thickness ranging from about 1 to 20 feet. Thickness of the regolith (23 to 68 feet) and the transition zone do not appear to be related to topographic setting. Delineated bedrock fractures are dominantly low angle (possibly stress relief), which were observed to be open to partially open at depths of as much as 479 feet below land surface. Well yields ranged from about 3 to 50 gallons per minute. The connection of fracture zones at depth was demonstrated in three bedrock wells during a 48-hour aquifer test, and drawdown curves were similar for all three wells. General findings of this study help characterize ground-water flow in the Piedmont and Mountains ground-water systems. Ground-water flow generally is from high to low topographic settings. Ground-water flow discharges toward a surface-water boundary (Lake Norman), and vertical hydraulic gradients generally are downward in recharge areas and upward in discharge areas. Dominant water types are calcium-bicarbonate and are similar in all three zones (regolith, transition zone, and bedrock) of the ground-water system. Results of continuous ground-water-quality monitoring indicate that ground-water recharge may occur seasonally over a period of several months or after heavy rainfall periods over a shorter period of a few to several weeks.

North Carolina↗
USGS2007

Klamath Basin: A watershed approach to support habitat restoration, species recovery, and water resource planning

Water allocation among human and natural resource uses in the American West is challenging. Western rivers have been largely managed for hydropower, irrigation, drinking water, and navigation. Today land and water use practices have gained importance, particularly as aging dams are faced with re-licensing requirements and provisions of the Endangered Species and Clean Water Acts. Rising demand for scarce water heightens the need for scientific research to predict consequences of management actions on habitats, human resource use, and fish and wildlife. Climate change, introduction of invasive species, or restoration of fish passage can have large, landscape-scaled consequences - research must expand to encompass the appropriate scale and by applying multiple scientific disciplines to complex ecosystem challenges improve the adaptive management framework for decision-making.

Oregon; California↗
USGS2018

Summary of wildlife-related research on the coastal plain of the Arctic National Wildlife Refuge, Alaska, 2002–17

We summarize recent (2002–17) publicly available information from studies within the 1002 Area of the Arctic National Wildlife Refuge as well as terrestrial and coastal ecosystems elsewhere on the Arctic Coastal Plain that are relevant to the 1002 Area. This report provides an update on earlier research summaries on caribou (Rangifer tarandus), forage quality and quantity, polar bears (Ursus maritimus), muskoxen (Ovibos moschatus), and snow geese (Chen caerulescens). We also provide information on new research related to climate, migratory birds, permafrost, coastal erosion, coastal lagoons, fish, water resources, and potential effects of industrial disturbance on wildlife. From this literature review, we noted evidence for change in the status of some wildlife and their habitats, and the lack of change for others. In the 1002 Area, muskox numbers have decreased and the Porcupine Caribou Herd has exhibited variation in use of the area during the calving season. Polar bears are now more common on shore in summer and fall because of declines in sea ice in the Beaufort Sea. In a study spanning 25 years, there were no significant changes in vegetation quality and quantity, soil conditions, or permafrost thaw in the coastal plain of the 1002 Area. Based on studies from the central Arctic Coastal Plain, there are persistent and emerging uncertainties about the long-term effects of energy development for caribou. In contrast, recent studies that examined direct and indirect effects of industrial activities and infrastructure on birds in the central Arctic Coastal Plain found little effect for the species and disturbances examined, except for the possibility of increased predator activity near human developments.

Alaska↗
USGS1993

Application of a geographic information system in analyzing the occurrence of atrazine in groundwater of the mid-continental United States

The US Geological Survey, US Department of Agriculture, and US Environmental Protection Agency are conducting research and regional assessments in support of policy alternatives intended to protect water resources from agricultural chemical contamination. The mid-continent was selected because of the intense row crop agriculture and associated herbicide application in this region. An application of a geographic information system is demonstrated for analyzing and comparing the distribution of estimated atrazine use to the detection rate of atrazine in groundwater. Understanding the relations between atrazine use and detection in groundwater is important in policy deliberations to protect water resources. Relational analyses between measures of chemical use and detection rate by natural resource units may provide insight into critical factors controlling the processes that result in groundwater contamination from agricultural chemicals.

Conference Paper↗
USGS2021

Great Lakes harmful algal blooms: Current knowledge gaps

Freshwater Harmful Algal Blooms (HABs) pose serious risks throughout the world to drinking water, recreation, and ecosystem health. The Great Lakes, which contain nearly 20% of the world’s available surface freshwater, have been experiencing an increase in HABs since the 1990s. Knowledge gaps relating to HABs remain even after extensive and ongoing research efforts. These knowledge gaps are presented below for the benefit of water resource managers, state and federal agencies, legislators, and others involved in the development of policies to address HABs throughout the Great Lakes.

Great Lakes↗
USGS1972

Geological Survey research 1972, Chapter C

This collection of 37 short papers is the second published chapter of "Geological Survey Research 1972." The papers report on scientific and economic results of current work by members of the Conservation, Geologic, and Water Resources Divisions of the U.S. Geological Survey. Chapter A, to be published later in the year, will present a summary of significant results of work done ~n fiscal year 1972, together with lists of investigations in progress, cooperating agencies, and Geological Survey offices. "Geological Survey Research 1972" is the thirteenth volume of the annual series Geological Survey Research. The twelve volumes already published are listed below, with their series designations.

Professional Paper↗
USGS1972

Geological Survey research 1972

This collection of 30 short papers is the third published chapter of "Geological Survey Research 1972." The papers report on scientific and economic results of current work by members of the Geologic and Water Resources Divisions of the U.S. Geological Survey. Chapter A, to be published later in the year, will present a summary of significant results of work done in fiscal year 1972, together with lists of investigations in progress, cooperating agencies, and Geological Survey offices. "Geological Survey Research 1972" is the thirteenth and last volume of the annual series Geological Survey Research. The short-papers chapters (B, C, and D) will be replaced in 197 3 by the "Journal of Research of the U.S. Geological Survey," and the summary chapter (A) will be published as a separate professional paper. The twelve volumes already published are listed below, with their series designations.

Professional Paper↗
USGS2015

Summer of Applied Geophysical Experience (SAGE): Training for our future geoscientists

Energy and natural resources are crucial to the sustainability of worldwide economies, security, and overall well-being. However, the future workforce in the energy and natural-resources sector is at risk, and meeting the challenges of this dwindling workforce requires well-educated geoscientists in exploration and applied geophysics and related geoscience and technology disciplines. Programs such as geophysical field courses that are supported by SEG and industry, in partnership with academic institutions and government laboratories, are important approaches to maintaining and enhancing expertise in exploration geophysics. One example of a geophysical field course devoted to educating our future workforce is the Summer of Applied Geophysical Experience (SAGE), a four-week program based in Santa Fe, New Mexico, designed to actively engage students in all phases of applied geophysical research. SAGE is a unique educational experience that combines teaching and research as a partnership among universities, industry, government agencies, and professional societies. SAGE teaches the principles and applications of refraction and reflection seismology, magnetics, gravity, GPS, heat flow, several electromagnetic (EM) methods, and ground-penetrating radar (GPR) in a field-based, hands-on setting. More than 850 students and qualified professionals have attended SAGE, many of whom have gone on to become leaders in academia, industry, and government. SAGE students are exposed to the exciting challenges that face earth scientists today, and they develop skills that are necessary to address the world's growing energy demands. Examples of SAGE research projects include mapping archaeological sites and tectonic structure and investigating water and geothermal resources in the Rio Grande rift.

Leading Edge (Tulsa, OK)↗
USGS2005

Workgroup report: Drinking-water nitrate and health - Recent findings and research needs

Human alteration of the nitrogen cycle has resulted in steadily accumulating nitrate in our water resources. The U.S. maximum contaminant level and World Health Organization guidelines for nitrate in drinking water were promulgated to protect infants from developing methemoglobinemia, an acute condition. Some scientists have recently suggested that the regulatory limit for nitrate is overly conservative; however, they have not thoroughly considered chronic health outcomes. In August 2004, a symposium on drinking-water nitrate and health was held at the International Society for Environmental Epidemiology meeting to evaluate nitrate exposures and associated health effects in relation to the current regulatory limit. The contribution of drinking-water nitrate toward endogenous formation of N-nitroso compounds was evaluated with a focus toward identifying subpopulations with increased rates of nitrosation. Adverse health effects may be the result of a complex interaction of the amount of nitrate ingested, the concomitant ingestion of nitrosation cofactors and precursors, and specific medical conditions that increase nitrosation. Workshop participants concluded that more experimental studies are needed and that a particularly fruitful approach may be to conduct epidemiologic studies among susceptible subgroups with increased endogenous nitrosation. The few epidemiologic studies that have evaluated intake of nitrosation precursors and/or nitrosation inhibitors have observed elevated risks for colon cancer and neural tube defects associated with drinking-water nitrate concentrations below the regulatory limit. The role of drinking-water nitrate exposure as a risk factor for specific cancers, reproductive outcomes, and other chronic health effects must be studied more thoroughly before changes to the regulatory level for nitrate in drinking water can be considered.

Environmental Health Perspectives↗
USGS2013

Hydrogeology, groundwater seepage, nitrate distribution, and flux at the Raleigh hydrologic research station, Wake County, North Carolina, 2005-2007

rom 2005 to 2007, the U.S. Geological Survey and the North Carolina Department of Environment and Natural Resources, Division of Water Quality, conducted a study to describe the geologic framework, measure groundwater quality, characterize the groundwater-flow system, and describe the groundwater/surface-water interaction at the 60-acre Raleigh hydrogeologic research station (RHRS) located at the Neuse River Waste Water Treatment Plant in eastern Wake County, North Carolina. Previous studies have shown that the local groundwater quality of the surficial and bedrock aquifers at the RHRS had been affected by high levels of nutrients. Geologic, hydrologic, and water-quality data were collected from 3 coreholes, 12 wells, and 4 piezometers at 3 well clusters, as well as from 2 surface-water sites, 2 multiport piezometers, and 80 discrete locations in the streambed of the Neuse River. Data collected were used to evaluate the three primary zones of the Piedmont aquifer (regolith, transition zone, and fractured bedrock) and characterize the interaction of groundwater and surface water as a mechanism of nutrient transport to the Neuse River. A conceptual hydrogeologic cross section across the RHRS was constructed using new and existing data. Two previously unmapped north striking, nearly vertical diabase dikes intrude the granite beneath the site. Groundwater within the diabase dike appeared to be hydraulically isolated from the surrounding granite bedrock and regolith. A correlation exists between foliation and fracture orientation, with most fractures striking parallel to foliation. Flowmeter logging in two of the bedrock wells indicated that not all of the water-bearing fractures labeled as water bearing were hydraulically active, even when stressed by pumping. Groundwater levels measured in wells at the RHRS displayed climatic and seasonal trends, with elevated groundwater levels occurring during the late spring and declining to a low in the late fall. Vertical gradients in the groundwater discharge area near the Neuse River were complex and were affected by fluctuations in river stage, with the exception of a well completed in a diabase dike. Water-quality data from the wells and surface-water sites at the RHRS were collected continuously as well as during periodic sampling events. Surface-water samples collected from a tributary were most similar in chemical composition to groundwater found in the regolith and transition zone. Nitrate (measured as nitrite plus nitrate, as nitrogen) concentrations in the sampled wells and tributary ranged from about 5 to more than 120 milligrams per liter as nitrogen. Waterborne continuous resistivity profiling conducted on the Neuse River in the area of the RHRS measured areas of low apparent resistivity that likely represent groundwater contaminated by high concentrations of nitrate. These areas were located on either side of a diabase dike and at the outfall of two unnamed tributaries. The diabase dike preferentially directed the discharge of groundwater to the Neuse River and may isolate groundwater movement laterally. Discrete temperature measurements made within the pore water beneath the Neuse River revealed seeps of colder groundwater discharging into warmer surface water near a diabase dike. Water-quality samples collected from the pore water beneath the Neuse River indicated that nitrate was present at concentrations as high as 80 milligrams per liter as nitrogen on the RHRS side of the river. The highest concentrations of nitrate were located within pore water collected from an area near a diabase dike that was identified as a suspected seepage area. Hydraulic head was measured and pore water samples were collected from two 140-centimeter-deep (55.1-inch-deep) multiport piezometers that were installed in bed sediments on opposite sides of a diabase dike. The concentration of nitrate in pore water at a suspected seepage area ranged from 42 to 82 milligrams per liter as nitrogen with a median concentration of 79 milligrams per liter as nitrogen. On the opposite side of the dike, concentrations of nitrate in pore water samples ranged from 3 to 91 milligrams per liter as nitrogen with a median concentration of 52 milligrams per liter. At one of the multiport piezometers the vertical gradient of hydraulic head between the Neuse River and the groundwater was too small to measure. At the multiport piezometer located in the suspected seepage area, an upward gradient of about 0.1 was present and explains the occurrence of higher concentrations of nitrate near the sediment/water interface. Horizontal seepage flux from the surficial aquifer to the edge of the Neuse River was estimated for 2006. Along a 130-foot flow path, the estimated seepage flux ranged from –0.52 to 0.2 foot per day with a median of 0.09 foot per day. The estimated advective horizontal mass flux of nitrate along a 300-foot reach of the Neuse River ranged from –10.9 to 5 pounds per day with a median of 2.2 pounds per day. The total horizontal mass flux of nitrate from the surficial aquifer to the Neuse River along the 130-foot flow path was estimated to be about 750 pounds for all of 2006. Seepage meters were deployed on the bed of the Neuse River in the areas of the multiport piezometers on either side of the diabase dike to estimate rates of vertical groundwater discharge and flux of nitrate. The average estimated daily seepage flux differed by two orders of magnitude between seepage areas. The potential vertical flux of nitrate from groundwater to the Neuse River was estimated at an average of 2.5 grams per day near one of the multiport piezometers and an average of 784 grams per day at the other. These approximations suggest that under some hydrologic conditions there is the potential for substantial quantities of nitrate to discharge from the groundwater to the Neuse River.

North Carolina↗