Soils engineering report regarding the nature, distribution and strength of existing soils, conclusions and recommendations for grading procedures, and design criteria for corrective measures when necessary, and opinion and recommendations covering adequacy of the sites to be developed by the proposed grading. The report shall also discuss expansion of the soils and the recommended measures for foundations and slabs on grade to resist volumatic changes in soil. If a public sewer system will not be used, a detailed engineering data and test report including a percolation test setting forth soil porosity and ground water level, and recommending procedures and design criteria for private sewage disposal shall also be provided;