Abstract
Wastewater contains elevated concentrations of fecal indicator bacteria (FIB). The type of wastewater treatment technology and septic system density may influence the FIB concentration and exports at the watershed scale. The goal of this study was to gain a better understanding of FIB concentrations and exports from watersheds served by conventional septic (CS) systems, sand filter (SF) septic systems, and a municipal sewer (SEW) system. Seven watersheds (3 CS, 3 SF, and 1 SEW) were monitored to quantify FIB concentration and export monthly from April 2015 to March 2016. The type of wastewater treatment did not yield significant differences in FIB concentration or exports when pooling watersheds using similar wastewater treatment. Watersheds with the highest septic densities (approximately 0.4 systems ha−1) contained greater FIB concentrations and exports than watersheds with the lowest (approximately 0.1–0.2 systems ha−1), but only FIB concentrations significantly differed. These findings suggest that when the septic system density exceeds 0.4 systems ha−1, water quality degradation from septic leachate may be observable at the watershed scale, especially in watersheds dominated by residential development. More research is recommended to determine if this density threshold is similar for other water pollutants and/or in watersheds with differing hydrogeological, land use, and wastewater characteristics.
Highlights
Elevated concentrations of pathogens in water resources are one of the most commonly cited reasons for water use impairment [1]
This study found that watersheds with septic system densities of approximately 0.4 systems ha−1 contained elevated fecal indicator bacteria (FIB) concentrations and yields (SF3 only) compared to other septic watersheds
Past research suggests that watersheds with septic system densities > 1 system ha−1 may have a significant effect on watershed FIB [16,24]
Summary
Elevated concentrations of pathogens in water resources are one of the most commonly cited reasons for water use impairment [1]. Fecal waste from humans and animals may contain various types of pathogens, including viruses, protozoa, and bacteria, that can cause infections, illnesses, or death if exposure via consumption, inhalation, or skin contact occurs [2]. Fecal indicator bacteria (FIB) are often used to assess risk associated with exposure to contaminated water, because elevated concentrations of FIB may indicate the presence of harmful pathogens [3,4]. The United States Environmental Protection Agency (US EPA) [5] recommends that geometric mean values of Escherichia coli (E. coli) and Enterococcus spp. ( called enterococcus/enterococci) should not exceed 126 and 35 most probable number (MPN) 100 mL−1 , respectively, in recreational.
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