accomplished from the outside of the tank, typically through one or more access points no more than 12 inches across.
As municipal sewers have become available to properties, septic tank systems were typically decommissioned by pumping out and entirely removing the tank from the property. If not completely removed, a tank left in the ground would have been filled completely with native fill or granular material to eliminate the risk of the tank collapsing or entry by a person. Due to the hazards associated with septic tanks, it would be very unusual to have an empty decommissioned septic tank located on properties in Windsor.
The design of most septic tanks makes them challenging to repurpose for rainwater collection. Residential septic tanks are not intended for human access, as their contents are toxic. In order to comply with requirements, semi-annual inspections are recommended and a Municipal Inspection is required every 5 years (OBC, Article 1.10.2.3. Division C). Further, all tanks would be require to have a minimum opening of 18” in order to allow inspectors inside (O. Reg 632/05), whereas Septic Tanks have 12” openings. Rainwater collection regulations also have particular concerns for bacterial contamination of the water they hold; therefore, any tank would have to be completely cleaned in order to meet required standards (NSF/ANSI Standard 61). Furthermore, all cleaning and modifications need to be certified by a licensed professional engineer in order to comply with regulatory and technical standards (BCA, S.O. 1992, Chapter 23, Article 15.9 (3)). The costs for cleaning, modifying and certifying an existing septic tank can easily run in the thousands of dollars; meanwhile, a new rainwater system would cost less than half the cost of repurposing an old septic tank.
Risk Analysis:
Risks associated with repurposing septic tanks relate to citizen health and well-being. Storing untreated water carries the potential for bacteria or algae to develop, presenting an opportunity for infection and disease if contaminated water is used. Existing provincial guidelines address this risk by recommending twice-yearly internal inspection of rainwater holding tanks and limiting how they are used. Further, Ontario requires a Phase 1 inspection by a qualified individual every 5 years (OBC, Article 1.10.2.3. Division C) be submitted to the Municipality.
Most septic tanks are designed to prevent a person from entering them, which makes complying with the regulations (O. Reg 350/06 & O. Reg 632/05) that address this risk challenging without significant modification. Any modification of the tank would require certification by a professional engineer to ensure the structure is still sound per O. Reg 350/06. Further, The Ontario Building Code deems rainwater catchment as a ‘greywater system’. This designation limits the uses of the water after collection to recycling (flushing toilets) and subsurface irrigation due to health concerns. Controlling for modifications or errant use of the stored water after initial construction could require a policy for requiring periodic inspections by the Municipality.
Septic tanks also carry a falling risk if they collapse or trapping someone inside. The underground chambers are subject to deterioration over time and can present a hazard.