Quality of surface-water supplies in the Triangle area of North Carolina, water years 2010-11

Abstract

Surface-water supplies are important sources of drinking water for residents in the Triangle area of North Carolina, which is located within the upper Cape Fear and Neuse River Basins. Since 1988, the U.S. Geological Survey and a consortium of local governments have tracked water-quality conditions and trends in several of the area’s water-supply lakes and streams. This report summarizes data collected through this cooperative effort, known as the Triangle Area Water Supply Monitoring Project, during October 2009 through September 2010 (water year 2010) and October 2010 through September 2011 (water year 2011). Major findings for this data-collection effort include Annual precipitation was approximately 4 percent above the long-term mean (average) annual precipitation in 2010 and approximately 6 percent below the long-term mean in 2011. In water year 2010, streamflow was near the long-term mean for most of the period for the 10 project streamflow gaging stations. Streamflow was near or below the long-term mean at the same streamflow gaging stations during the 2011 water year. More than 13,000 individual measurements of water quality were made at a total of 28 sites—17 in the Neuse River Basin and 11 in the Cape Fear River Basin. Forty-three water-quality properties or constituents were measured; North Carolina water-quality standards exist for 21 of these. All observations met State water-quality standards for water temperature, hardness, chloride, fluoride, sulfate, nitrate plus nitrite, arsenic, cadmium, chromium, lead, nickel, and selenium. State water-quality standards were exceeded one or more times for dissolved oxygen, dissolved oxygen percent saturation, pH, copper, iron, manganese, mercury, silver, and zinc. Exceedances occurred at 27 sites—17 in the Neuse River Basin and 10 in the Cape Fear River Basin. Stream samples collected during storm events contained elevated concentrations of 25 water-quality constituents relative to non-storm events.