U.S. Department of the Interior
US Geological Survey
WRI 87-4075

Two septic tank test sites, one in sand and one in limestone, in Broward county, Florida, were analyzed for effluent migration. Ground water from shallow wells, both in background areas and hydraulically downgradient of the septic tank system, was sampled during a 16- month period from April 1983 through August 1984. Water-quality indicators were used to determine the effluent affected zone near the septic tank systems.

Specific conductance levels and concentrations of chloride, sulfate, ammonium, and nitrate indicated effluent movement primarily in a vertical direction with abrupt dilution as it moved downgradient. Effluent was detected in the sand to a depth more than 20 feet below the septic tank outlet, but was diluted to near background conditions 50 feet downgradient from the tank. Effluent in the limestone was detected in all three observation wells to depths exceeding 25 feet below the septic tank outlet and was diluted, but still detectable, 40 feet downgradient.

The primary controls on effluent movement from septic tank systems in Broward County are the lithology and layering of the geologic materials, hydraulic gradients, and the volume and type of use the system receives.

Information about on-line reading and printing of historic documents