Consists of a settling or septic tank and a soil absorption field. The traditional system accepts both grey water (wastewater from showers, sinks, and laundry) and black water (wastewater from toilets). These systems are typically restricted in that the bottom invert of the absorption field should be at least 90 cm above the seasonally high-water table or impermeable layer (separation distance) and the permeation rate of the soil should be between 20 and 50 minutes per cm. Also, to ensure proper operation, the tank should be pumped every 3 to 5 years. Nitrogen removal of these systems is minimal and somewhat dependent on temperature. The most common type of failure of these systems is from clogging of the absorption field, insufficient separation distance to the water table, insufficient permeation capacity of the soil, and overloading of water.