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The local health department determines the size of the septic tank and drainfield based on the number of bedrooms in the home and the soil conditions on the property. They also evaluate the seasonal high-water table, which helps determine the type of system required (such as a conventional gravity system or a mound system). In some cases, advanced treatment systems may be required, particularly on smaller lots or properties located near lakes, streams, or other sensitive environments.

A conventional gravity septic system typically starts around $10,000, while advanced treatment systems can cost $40,000 or more. The final price depends on factors such as soil conditions, groundwater levels, space constraints, and local health department requirements. In our area, most homes qualify for conventional gravity systems, which generally keeps costs on the lower end of that range. Restoration needs, such as replacing lawns, landscaping, driveways, or other disturbed areas, can add to the overall project cost and are based on site-specific conditions.

When replacing a septic system, the process generally begins with permitting and a site evaluation. Providing an accurate price before this step is difficult because each property is unique and may have different design and regulatory requirements. After the site evaluation and percolation (perc) test are completed in coordination with the local health department, a permit is issued based on those findings. At that point, an accurate project quote can be developed.

During the perc test, a 6–7-foot test hole is excavated so the sanitarian can evaluate soil characteristics and assess seasonal high groundwater levels. Soil conditions significantly influence the size and type of system required. For example, medium sand typically requires approximately 200 square feet of drainfield area per bedroom, while heavier soils such as clay or loam absorb water more slowly and may require up to 500 square feet per bedroom. Another important factor is septic tank sizing. A three-bedroom home is typically permitted with a 1,000-gallon septic tank with access riser covers to grade, and an effluent filter. For homes with more than three bedrooms, an additional 250 gallons is generally added per bedroom. If the home has a garbage disposal, an additional 250 gallons is also required. For example, a five-bedroom home with a garbage disposal would typically require a minimum 1,750-gallon septic tank.

–Ryan Carey, Carey-Sodergren Inc.