The septic tank separates settleable solids (sludge) and floating scum from domestic raw sewage and discharges effluent to a soil treatment system. The accumulated sludge and scum together with the liquid in the tank during cleaning is known as septage. Three potential hazards are associated with land application of septage. First, nitrate concentrations may increase in the top layer of a surficial aquifer and be present in water drawn by shallow domestic wells. Second, with high application rates, pathogens may move through the soil, contaminating shallow aquifers. Third, excessive applications of phosphorus, potassium, sodium, calcium and magnesium result in an accumulation of nutrients which may be detrimental to crop growth in certain soils.
