Background Storm water outfalls that flow into coastal waters can have significant potential impacts on human and environmental health. Elevated levels of pathogenic bacteria and viruses have been found in beach waters close to coastal storm water outfalls the world over, leading to closures of recreational beaches and shellfish harvesting areas as well as causing a variety of human illnesses. The areas adjacent to these outfalls are a cause of concern regarding human fecal contamination and the USEPA has identified this research focus to be one of the highest priorities relating to water quality.
The pipes and ditches of storm water drainage systems force polluted water to bypass natural filtration processes provided by soil and vegetation. Storm water drainage networks are believed to be conduits for pollution from residential development (sewage and septic systems, pet waste), industry (toxins and hydrocarbons) and agriculture (livestock waste, bio-solids and antibiotics). Storm water outfalls in coastal NC are poorly studied, but are a cause for concern given the sheer volume of precipitation that is received during annual and episodic (e.g. hurricanes, Nor'easters) timescales.
Funded by the North Carolina Department of Environment and Natural Resources (NCDENR), this is a joint project between UNC Chapel Hill Institute of Marine Science (IMS) and the UNC Coastal Studies Institute. This project proposes to identify the key microbial constituents of storm water in these ocean outfalls, determine concentrations and likely sources of indicator and tracer microorganisms in the storm water, and provide measures of patterns of loading in storm and ambient conditions, in Dare County, North Carolina.
Project Description The study will consist of two phases. Phase I begins with a preliminary study including pilot scale monitoring on nine storm water outfalls in Dare County that will last approximately six months. The outfalls will be prioritized in terms of likely impact on recreational waters. During the first phase, water will be sampled from multiple stations within the watershed of each outfall. Sampling will be conducted during storm events producing at least one inch of precipitation. Up to three storms will be sampled as well as one period with no precipitation. During each sampling event more than 100 water samples will be processed and tested for Enterococcus sp., E. Coli and total coliforms using IDEXX lab procedures.
Next, samples will be pumped through individual filters and frozen for transport to UNC-IMS for Quantitative Polymerase Chain Reaction (QPCR) based analyses for tracers of human fecal contamination and other human pathogens. Further molecular analyses will be conducted to identify the potential source of the microbial contamination. In addition, samples at each station will be tested for temperature, pH, turbidity, dissolved oxygen, chlorophyll a and salinity while Doppler flow meters measure the amount and velocity of water that passes through the system. Combining bacteria concentrations with flow measurements will provide the total amount of pathogenic bacteria passing through the system.
Phase II incorporates a comprehensive monitoring project for all nine outfalls after the installation of Best Management Practices (BMPs). This phase will consist of a sampling protocol used in Phase I. A storm water BMP is a broad term that refers to a practice or method that effectively reduces sources of pollution. The engineering firm Moffatt and Nichol will explore the use of BMPs including but not limited to bioretention areas and marshland buffers. These BMPs can provide wildlife habitat, increased evapotranspiration and infiltration rates while decreasing the amount of sediment and nutrients in storm water run off. Other possible BMPs include filters installed into the outfall catch basins, UV disinfection and hydrodynamic separators.
During Phase II, dye studies will be conducted at outfalls determined to be a significant public health risk. During periods of flow, Rhodamine dye will be released into catch basins and tracked along the beach with fluorometers. The information gathered will provide an idea of how far and how fast viruses and bacteria travel from outfalls.
This research should provide us with a better understanding of the levels of bacteria and viruses in stormwater, as well as an idea of the possible sources. In addition, the dye studies will show how far along the beach the health risk to the public extends during times when the outfalls are flowing. The data will also aid the development of predictive models to better foresee potential public health risks in the presence of stormwater.