Triangle Area Water Supply Monitoring

Cane Creek Reservoir, Aug. 15, 2003

Background

The Research Triangle area, located within the upper Cape Fear and Neuse River basins, is one of the most rapidly developing areas of North Carolina. Growth has increased demand for water from public suppliers, the majority of which draw water from streams and lakes in the region. Growth also brings the threat of greater loads of contaminants and new contaminant sources that, if not properly managed, could adversely affect water quality.

In 1988, several local governments, with assistance from Triangle J Council of Governments (TJCOG), formed the Triangle Area Water Supply Monitoring Project. With cooperative assistance from the U.S. Geological Survey (USGS), the Project has tracked water-quality conditions and trends in many of the area's water-supply reservoirs, rivers, and selected tributaries since October 1988.

Concerns about water quality of the area's water supplies and the effects of development on reservoir eutrophication and contaminant concentrations have remained prominent since the project began, although specific concerns have evolved over time. The initial focus of the project was on measuring synthetic organic compounds in the water column and sediments. Later efforts focused on analyzing nutrient and sediment loads and trends. Issues such as the occurrence of disinfection by-products, microbial pathogens, and U.S. Environmental Protection Agency (USEPA) priority pollutants, emerging contaminants, and mercury also have been addressed during different phases of the project.

Objectives

The project currently is in Phase VI, which spans the period July 2007-June 2012. Specific objectives for this phase are to:

1. Extend the existing water-quality database for major ions, nutrients, sediment, and trace elements to track spatial variations in water quality, loads to reservoirs, and long-term water-quality trends.
2. Continue collection of water-quality data at tributary sites during high-flow events to increase the understanding of constituent concentrations and mass loading during extreme hydrologic conditions.
3. Investigate the occurrence of mercury in water and sediment.
4. Maintain a network of continuous streamflow gaging stations in the study area.
5. Publish an analysis of water-quality trends for data collected through 2007.

Approach

The USGS routinely samples 19 stream and reservoir sites in the study area; 11 additional sites are sampled by the North Carolina Division of Water Quality (DWQ) as part of the North Carolina Ambient Monitoring Network and(or) by the USGS during selected storm events. As part of this project, the USGS operates continuous-record streamflow gaging stations at 10 stream sites.

Fifteen reservoir sites are sampled by the USGS four to six times per year for alkalinity, nutrients, major ions, iron, manganese, and chlorophyll, and twice per year for metals and trace elements. Four stream sites are sampled by the USGS bimonthly for nutrients, major ions, and suspended sediment, and twice per year for trace elements. Runoff samples are collected at additional stream sites.

Appropriate quality-control samples, including equipment blanks, field blanks, and replicate environmental samples, are collected and reviewed to ensure that project data-quality objectives are being met.

An analysis of water-quality trends in the study area will be published in a USGS Scientific Investigations Report. Water-quality constituents that will be analyzed for trends include nitrogen and phosphorus species, suspended sediment and solids, and selected major ions and trace elements.

Mercury has been monitored in Triangle Area streams and reservoirs since the beginning of the TAWSMP in 1988. After a new laboratory method was adopted in 2001, several TAWSMP samples were shown to contain concentrations of total recoverable mercury that exceeded the North Carolina water-quality standard. To better understand the occurrence and distribution of mercury in the TAWSMP study area, the USGS is conducting a special investigation of mercury in water and bed sediment during Phase VI. Findings will be published in an interpretive report.