Septic tank
A septic tank is an underground chamber made of concrete, fiberglass or plastic through which domestic wastewater (sewage) flows for basic treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment"). Septic tank systems are a type of simple onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field which provides further treatment. However, groundwater pollution may occur and can be a problem.
Acton, Massachusetts
Most homes and businesses in Acton (approximately 80%) use private on-site sewage systems (i.e. septic tanks). Higher density developments such as condominiums and apartment buildings (approximately 10% of the town) use private sewers which go to small-scale private treatment plants.