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.
Underground storage tank
Petroleum USTs are used throughout North America at automobile filling stations and by the US military. Many have leaked, allowing petroleum to contaminate the soil and groundwater and enter as vapor into buildings, ending up as brownfields or Superfund sites. Many USTs installed before 1980 consisted of bare steel pipes, which corrode over time. Faulty installation can also cause structural failure of the tank or piping, causing leaks.