Enterococci Populations in Conventional, Manufactured, and LID Stormwater Treatment Systems

Pathogenic microoganisms can cause disease in humans exposed to contaminated recreational waters. New Hampshire uses enterococci as the fecal indicator in estuarine and marine recreational waters. Stormwater runoff is the most significant source of bacterial pollution in NH, and several types of routinely installed stormwater control systems are ineffective for removing enteroocci. This study addresses the performance of eleven treatment system designs on enterococci populations during storms. Water samples were collected during storms from eleven treatment systems under controlled conditions and enterococci were enumerated using EPA method 1101.6. Some systems appeared to be sources while others appeared to remove enterococci from runoff. Enterococci concentrations exhibited marked seasonal trends, peaking in August. These results suggest elevated enterococci concentrations are present in wet treatment systems between storms, resulting in increased concentrations being discharged into receiving waters with runoff from storms. Ongoing studies are designed to better characterize enterococci dynamics between storm events.