Bacteriophage Tracer for Fecal Contamination Sources in Coastal Waters

Septic systems are designed for on-site treatment of wastewater, often for individual households with dependence on homeowner maintenance. They frequently become overloaded and fail, short-circuiting wastewater treatment within the tank, allowing untreated wastes into groundwater or surface water. Current methods for detection of such leaks rely on the use of inert dye and are often inadequate. The work described here included development and testing of bacteriophage-based tracking approaches to improve assessment of on-site sewage disposal systems and identification of leaks. The hypothesis is that a benign bacteriophage can be used to detect chronically failing septic systems with greater sensitivity and longevity than inert dye technology. Testing was conducted in both open waterway and coastal groundwater systems subject to astronomical tidal forcing. Results in open (surface) water demonstrated correlation between dye and phage presence initially, but the phage was detectable at greater distances and longer durations than the dye. Phage detection in groundwater did not correlate with dye presence, and revealed that phage moves more quickly through soils than dye. Details of the development, testing, and deployment of the bacteriophage tracer are provided, illuminating both the pros and cons of the approach. The ultimate advantage is that the use of a sentinel bacteriophage improves detectability of failing septic systems in coastal and other environments. This approach may thus be useful for establishing new science-based criteria for the installation of new septic systems in coastal areas.