B-1.1, r. 2 - Construction Code

Full text
8.32. An underground tank not to be subjected to overhead vehicular traffic must be sited
(1)  at a depth of not less than 600 mm below ground level and be covered with a backfill material referred to in section 8.33; or
(2)  at a depth of not less than 400 mm, be covered with a backfill material referred to in section 8.33 and be covered with a reinforced concrete slab at least 100 mm thick.
O.C. 220-2007, s. 1.