The Ontario Building Code | Septic Tanks

8.2.2.3. Septic Tanks

(1) The minimum working capacity of a septic tank shall be the greater of 3 600 L and,

(a) in residential occupancies, twice the daily design sanitary sewageflow, or

(b) in non-residential occupancies, three times the daily design sanitary sewage flow.

(2) Every septic tank shall be constructed in such a manner that any sanitary sewage flowing through the tank will pass through at least 2 compartments.

(3) The working capacity of the compartments required in Sentence (2) shall be sized such that,

(a) the first compartment is at least 1.3 times the daily design sanitary sewage flow but in no case less than 2 400 L, and

(b) each subsequent compartment shall be at least 50% of the first compartment.

(4) Where multiple tanks are to be used to meet the requirements of Sentences (2) and (3), the tanks shall be connected in series such that,

(a) the first tank in the series shall have at least a capacity as calculated in Clause (3)(a), however at no time shall a tank having a working capacity of less than 3 600 L be used,

(b) all additional tanks after the first tank, excluding pump or dosing tanks shall have at least a working capacity equal to the volume required by Clause (3)(b),

(c) the pipe between the outlet of one tank and the inlet of the next tank in the series shall have a minimum slope of 2 per cent,

(d) there shall be no partitions in the tank except where a partition is required to maintain the structural integrity of the tank, in which case openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings within the partition shall be provided to allow the free movement of sanitary sewagethroughout the tank, and

(e) all piping between tanks shall be continuous and shall be connected to the tank through the use of flexible watertight seals that will permit differential movement between the tanks.

(5) Partitions separating the septic tankinto compartments shall extend at least 150 mm above the liquid level at the outlet, and there shall be one or more openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings through or above the partition.

(6) The openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings required between compartments referred to in Sentence (2) shall have a total cross-sectional area of at least three times the area of the inlet pipe and be located between the top and a level 150 mm above the liquid level at the outlet to provide for the free flow of air between compartments.

(7) sanitary sewageshall pass from one compartment to another of the septic tank as follows:

(a) by means of a device similar to that described in CSA B66, "design, Material, and Manufacturing Requirements for Prefabricated Septic Tanks and Sewage Holding Tanks" for outlet devices, or

(b) through two or more openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings through the partition located in a horizontal line, and evenly spaced across the width of the partition, centred at approximately 40% of the liquid depth below the surface of the liquid, and having a total area of between three and five times that of the cross-sectional area of the inlet pipe.

(8) A septic tank shall be of such design and construction as will permit the collection and holding of sanitary sewage in it to a depth of not less than 1 000 mm, except that a depth of not less than 900 mm is permitted where the excavation is in rock, or to avoid rupture or displacement of the tank due to ground water pressure.

(9) Except as provided in Sentences (10) and (11), every septic tank shall be installed in such a manner that the access openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings are located not more than 300 mm below the ground surface.

(10) Where the top of the septic tank is located more than 300 mm below the ground surface, it shall be equipped with risers that extend from the access opening of the septic tank to within 300 mm of the ground surface.

(11) Where risers are used they shall conform to the requirements of CSA B66, "design, Material, and Manufacturing Requirements for Prefabricated Septic Tanks and Sewage Holding Tanks", and shall have adequate access openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings to allow for regular maintenance of the septic tank.