The design of the individual sewage disposal system shall take into consideration topography, water table, soil characteristics, available area, the quantity and type of sewage, the cost of constructing the system, projected sewage flow based on maximum occupancy of the structure, square footage of the structure, or other acceptable methods. The type of system to be installed shall be determined on the basis of location, soil permeability, and groundwater conditions, including depth to the water table. The system shall be designed to receive and treat all sewage, including wastes from garbage grinders and automatic washing machines, from the structures. Drainage from basement footings or from roofs shall not enter the system. In addition, wastes shall not be discharged into the system when their introduction would interfere with proper operation of the system. The treated wastes from a septic tank shall be discharged into subsurface disposal systems approved by the Health Officer. The minimum distances that shall be observed in locating the various components of the individual sewage system from other structures shall be as indicated in Table 4 (Section 22-155). Under unusual circumstances, the Health Officer may approve variances to the design criteria, or may require the installation of special sewage disposal components such as alternating drainfields, low pressure distribution, diversion valves or dosing when appropriate.