Soil contamination by septic tank effluent

Abstract

A survey of literature relating to septic tanks and the movement of micro-organisms through soil was made. The septic tank still appears to be the most satisfactory method of treating household wastes. Little experimental evidence is available concerning the movement of microorganisms through soil, but work which has been done indicates that soils vary greatly in their filtering ability. Furthermore soils appear to change in capacity to retain micro-organisms which subsequently die at different rates depending on the nature of the soil. The travel of viruses through ~oil has received negligible attention. Investigations undertaken at two sites in the Tai Tapu Area, near Christchurch, indicated that pollution of the soil by faecal organisms can take place from septic tanks and can extend over quite a wide area. The bacteria may remain viable in the soil for some months, both near the surface and at depth. From samples obtained by drilling holes in the soil it was found that bacteria could apparently move laterally through the soil at 2.0 to 3.0 m depth for considerable distances. Two main conclusions can be drawn from this work. First, soil can become contaminated by septic tank effluent over a wide area. Second, once the soil is contaminated the micro-organisms can persist for long periods.