Each layer of Class 1 and Class 2 fills shall be compacted at optimum moisture content (plus or minus two (2) percentage points), and to a minimum of ninety-five percent (95%) and ninety percent (90%), respectively, of maximum density as determined in the laboratory by the Standard Proctor Test (AASHTO T-99, ASTM D-698). Each layer of Class 3 fills shall be compacted sufficiently to support customarily used tracked spreading equipment and upon completion to be stable and after planting to prevent erosion. Other methods of compaction that the Director deems appropriate and result in an equal or better quality of compaction for Class 1 and 2 fills may be accepted. Lower degrees of compaction may be permitted by the Director after receipt of a report by a soil engineer certifying that the soil engineer has investigated the subsoils of the site, has tested representative fill materials and that, in the opinion of the soil engineer, such lower degree of compaction will be adequate for the intended use of the fill. In-place (field) density shall be determined in accordance with the ASTM test method D-1556-82E, D-2922-91 or AASHTO T-191-86, T-238-86. All fills shall be placed in approximately horizontal layers, each layer having a loose thickness of not more than eight (8) inches for Class 1, twelve (12) inches for Class 2 and two (2) feet for Class 3 fills. If approved by the Director, thicker lifts may be permitted only upon submittal of adequate density test documentation of limited test fills.