Environment Ontario Legacy, Vol 11, No. 3 January 1983. Pg. 7
Filter beds requiring less than half the surface area needed for conventional absorption trench leaching beds have been approved by Environment Ontario for use in private septic and aerobic sewage treatment installations, providing certain conditions are met.
The application of filter beds is limited to septic tank systems with a daily sewage flow of less than 5,000 litres. Their functioning depends on the use of a specific type of sand as filter material. The specifications for the sand are contained, with other standards pertaining to filter beds, in Ontario Regulation 374/8 1.
In a filter bed system, a distribution pipe network is set in a continuous layer of 19 mm clear stone or clean gravel of between 19 and 53 mm size. Below this layer of stone lies the sand filter of a minimum depth of 75 cm over soil of a percolation time not exceeding 50 minutes.
The base of the special sand medium may have to be extended beyond the area of its surface to cover an area of underlying soil that will promote infiltration. The extent depends on the characteristics of the underlying soil.
A filter bed of a maximum size of 50 square metres can be used either for a new private septic tank system or for the replacement of an inadequate tile leaching bed. It is especially suitable for installation on small lots if the site conditions, primarily the soil conditions, are such that the volume of liquid introduced into the filter can be absorbed by the soil under and around the filter without breaking out at the surface or causing the ground to become spongy.
The cost of the installation will depend largely on the cost of aggregate or gravel and of the filter medium, all of which may not be available locally in all areas of the province.
All other specifications for the construction and maintenance of private
septic systems, including clearances to wells and watercourses, capacities of septic tanks and distances from dwellings, remain unchanged.
The design and construction of a private septic tank sewage treatment system is subject to approval by the Ontario Ministry of the Environment or its agencies, normally local health units. Both can be contacted for additional information.
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