Evaluation of Fecal Indicator Bacteria Concentrations in Watersheds Served by Varying Densities of Onsite Wastewater Systems in the North Carolina Piedmont

Abstract

Onsite wastewater systems (OWS) are commonly used in North Carolina for wastewater treatment. Wastewater contains elevated concentrations of pathogens. If OWS do not efficiently treat wastewater then high concentrations of microorganisms may be contributed to water resources. The fecal indicator bacteria (FIB) Escherichia (E.) coli and enterococci are often used to assess the environmental health risks associated with microbial contamination. The goal of this study was to gain a better understanding of the influence that onsite system density have on FIB concentrations in piedmont streams. The studied streams included segments of Lick Creek, Laurel Creek, and Little Lick Creek and all are tributaries of Falls Lake, a water supply and recreation source for central North Carolina. Stream sampling occurred approximately monthly between January 2015 to December 2016 at 13 sample locations in the watersheds. Monitoring included the analyses of stream samples for E. coli and enterococci and, physical and chemical parameters including: pH, temperature, dissolved oxygen, oxygen-reduction potential, specific conductivity, stream discharge, and turbidity. The geometric mean of E. coli and enterococci concentrations in streams were typically elevated in smaller watersheds (<250 ha) with high densities of conventional-style OWS. The geometric mean FIB concentrations were lower in a forested watershed, centralized sewer watershed, and larger watersheds (> 500 ha) with lower densities of OWS. These data suggest that the density of OWS and watershed size may influence FIB concentrations in streams.