Septic Design Services

Septic system design is the engineering process of planning an onsite wastewater treatment system that is properly sized, correctly positioned, and compliant with local regulations for a specific property. A well-designed system protects public health, preserves groundwater quality, and provides decades of reliable service.

The design process begins with a thorough site evaluation. A licensed soil scientist or professional engineer conducts percolation tests (perc tests) to measure how quickly water drains through the soil at various depths. They also evaluate the soil profile by digging test pits to identify soil layers, depth to bedrock, depth to the seasonal high water table, and the presence of restrictive layers like clay or hardpan. These factors determine what type of system the site can support.

Based on the site evaluation, the designer selects the appropriate system type — conventional gravity, pressure-dosed, mound, drip irrigation, or advanced treatment unit — and calculates the required tank size and drain field area. Tank sizing depends on the number of bedrooms (which determines expected daily wastewater flow), while drain field sizing depends on both the flow rate and the soil's measured percolation rate. A designer must also account for setback distances from wells, property lines, water bodies, and structures, which vary by local jurisdiction.

The completed design is submitted to the local health department or environmental agency as part of the septic permit application. Most jurisdictions require designs to be prepared or reviewed by a licensed professional engineer (PE) or a state-certified septic designer. Review and approval typically takes 2 to 6 weeks.

Design costs range from $1,000 to $5,000 depending on the complexity of the site and system type. Simple conventional designs on ideal sites cost less, while complex engineered systems on challenging sites (high water tables, steep slopes, poor soils) require more extensive testing and engineering and cost more. The design fee is separate from and in addition to the permit fees and installation costs.