The Ontario Building Code | Construction Requirements
220.127.116.11. Construction Requirements
(1) The bottom of the pit shall be at least 900 mm above the high ground water table.
(4) The pit shall be provided with a tight, strong cover that shall remain over the pit except when it is necessary to remove it for purposes of adding greywater to or removing greywater from the pit or for purposes of maintenance of the pit.
(5) The earth around the perimeter of the pit shall be raised or mounded to a height of at least 150 mm above ground level.
(7) The pit shall be surrounded on all sides and on its bottom by at least 600 mm of soil having a percolation time of less than 50 minutes.