Developing Novel Indicators of Sewage Collection Systems for Wet Weather Source Tracking

Despite the known human and aquatic life risks associated with raw sewage, source tracking tools for sewage in urban runoff remain challenging. Many chemical source tracking tools usually lack sensitivity to detect low-levels of sewage, microbial tools typically lack the specificity for sewage, and many novel sensors are inhibited by stormwater matrix. Source tracking tools for sewage are particularly challenging in wet weather when the myriad of pollutant sources are dynamically mixing. Finding sensitive and reliable source tracking tools are particularly important in southern California because sanitary sewer collection systems and municipal storm drainage systems are separate (e.g., no combined sewer overflows). The aim of this study was to develop unique markers of the public sanitary sewer collection system utilizing the microbial community profiles of biofilms that line the inside of pipes (sewage biofilms). If sewage biofilms are quantified in stormwater runoff, then the sewer collection system is somehow leaking and entering the storm drain system. The unique sewage biofilm marker development followed four major steps: 1) building a prototype sampling device for collecting biofilms and refining high-throughput DNA sequencing technology; 2) ensuring the microbial community profiles from sewer biofilms were consistent among pipes of different ages, materials, locations, and season; 3) confirming microbial community profiles from sewer biofilms were distinctly and consistently different from storm drain biofilms, and; 4) quantifying sewer biofilms from the storm drain system during wet weather. After sampling more than 60 sites across multiple seasons over two years, microbial communities in sewage biofilms were extremely consistent yet distinctly different than storm drain biofilms based on non-metric multi-dimensional scaling (nMDS). After sampling 13 sites over two wet seasons across a 900 sq km urban watershed, sewage biofilms were quantified during every storm at over 90% of the storm drain sites. However, concentrations of sewer biofilms in storm drains were consistently dilute, typically less than 0.1% relative to raw sewage. New research is now focusing on quantifying exfiltration from the 5,000 km of sanitary sewer collection system pipe infrastructure.