All Class 1 and 2 fills shall consist of readily compactable soils meeting the following minimum requirements: No inclusions of ice or snow, organic or other deleterious materials subject to decay and high shrink-swell soils shall be permitted. No rock or similar irreducible material with a maximum dimension greater than eighteen (18) inches shall be buried or placed in any portion of the fill, with the top two and one-half (2½) feet below finished grade, foundations and utility service connections having nothing larger than eight (8) inches in any dimension, unless permitted by the Director after receipt of a report by a soil engineer certifying that he has investigated the property and the fill materials, and that a fill including oversized materials may be constructed to meet the intent of this Division. Class 3 fills may include the more difficult to compact soils, at other than optimum moisture content; rock and similar irreducible materials without limit as to size provided no detectable voids are formed, into which overlying soils may later be displaced; and top soil, intermittently layered with nonorganic soil. In other than rock gardens, at least twelve (12) inches of top soil must cover all rock or irreducible materials with a maximum dimension greater than eight (8) inches. The material must be free of contamination levels of any pollutant which is, or may be considered to represent, a possible health hazard to the public or may be detrimental to surface or ground water quality, or may cause damage to property or the drainage system.