Septic System Design type is determined by a soil analysis, critical area and topography. The Design of a septic system reflects the soil conditions and site characteristics of a specific lot or parcel. The design includes a scaled site plan, detailed drawings of the septic system components and all required by Washington State regulations. The Clallam County permit application is also a part of the design. The layout assistance, final inspection and as-built are included for the duration of the permit.