INFLUENCE OF ARTIFICIAL-DRAINAGE ON PENETRATION OF COLIFORM BACTERIA FROM SEPTIC TANK EFFLUENTS INTO WET TILE DRAINED SOILS

The penetration of total and fecal coliform bacteria from septic tank drainage fields into wet tile drained soils classified as Typic and Aeric Ochraquults was studied during 1974, 1975, and 1976. These bacteria were monitored in ground waters at selected distances from the septic tank drainage fields in the direction of ground water flow and were compared to coliform densities in control wells and in tile outfalls. Fecal coliform densities of the outfall from the study area were some tenfold less than the bacterial quality of the receiving stream. Coliform densities in ground waters decreased as a logarithmic function of distance. In these soils, artificial drainage systems apparently lowered the seasonal fluctuating water tables to such a degree that individual waste water treatment systems did not fail as a result of untreated or partially treated effluent coming to the surface.