Fills shall be constructed in layers. The loose thickness of each layer of fill material before compaction shall not exceed 12 inches. Completed fills shall be stable masses of well-integrated material bonded to adjacent materials and to the materials on which they rest. Fills shall be competent to support anticipated loads and be stable at the design slopes shown on the plans. Proper surface and subsurface drainage and other appropriate measures shall be taken to ensure the continuing integrity of fills. Earth materials shall be used which have no more than minor amounts of organic substances and have no rock or similar irreducible material with a maximum dimension greater than 12 inches. Larger material may be used with the approval of the Planning Department and the geotechnical engineer.