Onsite Wastewater Treatment Systems and Their Impact On Surface Water Quality in Eastern North Carolina.

On-site wastewater treatment (septic) systems are thought to be one of the major contributors of fecal contaminants to coastal and estuarine systems. Material leaking from failing systems could potentially represent a significant public health risk to those using nearby waters for shellfish harvesting and recreation. This potential problem is exacerbated along the Eastern NC coast by the high density of septic systems, combined with episodic heavy precipitation and large-scale climatic events. In this study we examined the performance of septic systems using a combination of techniques for tracing fecal contaminants.  We identified two working and two failing systems in Carteret county. Monitoring wells were installed within 2 ft. of lateral lines to study material flowing from the systems. Additional sampling sites were set up in nearby surface waters and ditches. Samples were analyzed for total coliforms, E. coli and Enterococci. Dye release and tracer studies were done with Rhodamine, non pathogenic virus (MS2) and antibiotic resistant E. coli strain to understand the fate and transport of contaminants through the systems.  E. coli and Enterococci numbers were higher around failing than working systems. Storm events increased E. coli and Enterococci numbers around failing systems while the impact was not obvious in properly working systems. Higher E. coli and Enterococci numbers in nearby ditches, creeks, or marinas suggest that failing systems were not the only sources (e.g., wild and domestic animals). MS2 and E. coli persisted in the distribution box of the septic system for greater than a month and were detected in some wells, mainly around failing systems. Dye and biological tracer studies have not conclusively shown failing systems to be major sources of fecal pollution, however this might have to do with the degree of “failure”. Conclusions drawn from the dye studies are limited due to adsorption to sediments.