The provisions of this Chapter apply to projects which have been conditionally approved and which involve grading in excess of five thousand (5,000) cubic yards and when grading will occur on or adjacent to 1) Natural pregraded slopes of fifteen percent (15%) or greater, or 2) property required for natural open space retention. The provisions and conditions of this chapter are in addition to the provisions of the Uniform Building Code and the recommendations of any site-specific geotechnical investigation report on file with the Planning Department.