VIRAL TRACER STUDIES INDICATE CONTAMINATION OF MARINE WATERS BY SEWAGE DISPOSAL PRACTICES IN KEY-LARGO, FLORIDA

Domestic wastewater disposal practices in the Florida Keys are primari ly limited to on-site disposal systems such as septic tanks, injection wells, and illegal cesspits. Poorly treated sewage is thus released i nto the highly porous subsurface Key Large limestone matrix. To invest igate the fate and transport of sewage in the subsurface environment a nd the potential for contamination of marine surface waters, we employ ed bacteriophages as tracers in a domestic septic system and a simulat ed injection well in Key Largo, Florida. Transport of bacteriophage Ph i HSIC-1 from the septic tank to adjacent surface canal waters and out standing marine waters occurred in as little as 11 and 23 h, respectiv ely. Transport of the Salmonella phage PRD1 from the simulated injecti on well to a canal adjacent to the injection site occurred in 11.2 h. Estimated rates of migration of viral tracers ranged from 0.57 to 24.2 m/h, over 500-fold greater than flow rates measured previously by sub surface flow meters in similar environments. These results suggest tha t current on-site disposal practices can lead to contamination of the subsurface and surface marine waters in the Keys.