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.
Bon Secours Mother and Baby Home
Corless's original research noted that the site was also the location of a septic tank when overlaid with maps of the period of use as a workhouse. The 2017 report by an Expert Technical Group, commissioned by the Department of Children and Youth Affairs, confirmed that the vault was a sewage tank after reviewing historical records and conducting a magnetometer survey; it concluded, "The combination of an institutional boarding home and commingled interments of juvenile remains in a sewage treatment system is a unique situation, with no directly comparable domestic or international cases."