Water-Quality Characteristics Indicative of Wastewater in Selected Streams in the Upper Neuse River Basin, Durham and Orange Counties, North Carolina, from 2004 to 2013

Abstract

Data were collected during three time periods to assess the effects of wastewater treatment and disposal practices on the occurrence of selected contaminants indicative of wastewater in the upper Neuse River Basin, North Carolina. The first phase of data collection, December 2004 to June 2005, and the second phase, April to October 2008, addressed the effects of point and nonpoint sources of wastewater effluent on stream quality during baseflow conditions. Point-source effects were assessed by sampling a municipal wastewater treatment plant outfall and sites on the Eno River upstream and downstream from the outfall. Water-quality data suggest that the wastewater treatment plant effluent contributed to increases in concentrations of nitrogen and carbamazepine at the downstream site. Nonpoint source effects were assessed by sampling seven small streams that drained an undeveloped area and residential areas served by either centralized or onsite wastewater treatment systems. Samples were analyzed for inorganic constituents, including nutrients, ions, and metals; organic compounds considered indicative of wastewater contamination; antibiotics, optical brighteners, and fecal coliform bacteria. Hypothesized differences in water quality between the sites with primarily centralized and onsite wastewater treatment were not apparent, likely due to the relatively large heterogeneity of the sites within each category.

During the third phase of data collection, May 2012 to January 2013, data were collected to address the suitability of optical brighteners as tracers of wastewater in small streams during streamflow recession. Samples were collected at five small streams following periods of rainfall and analyzed for optical brighteners, specific conductance nutrients, and selected hormones. Optical brighteners were absent in the undeveloped catchment but were present in the recession period after rainfall events in catchments with centralized though possibly leaky sewage treatment and areas with onsite treatment. Sand filter systems in areas with onsite treatment appear to change the effluent flow and retention characteristics such that optical brighteners were present both before and after rainfall events. Nitrate plus nitrite, as nitrogen concentrations in samples from this last study phase generally were larger than those collected during baseflow conditions in the previous phases of this study.

First posted October 30, 2014