Septic system type is not really a choice of preference; it follows from what the site’s soil evaluation finds. A designer starts from a conventional gravity system as the default and only moves to a pressure-dosed, mound, sand filter, aerobic, or drip system when soil, water table, slope, or lot size specifically rule the simpler option out.
The soil evaluation is the actual decision point: adequate depth to the seasonal high water table and to any restrictive layer, an acceptable application rate, and enough usable slope together clear the way for a conventional gravity system, which is simpler and typically cheaper to install and maintain than every alternative.
Where the water table or a restrictive layer sits too shallow, a mound system raises the field above the problem. Where soil is too tight or a smaller footprint is needed, pretreatment through a sand filter or aerobic unit lets a smaller or more forgiving drainfield work. Where the lot is irregular or space-constrained, drip dispersal can be fit into shapes a trench layout cannot use.
Cost generally rises with mechanical complexity: conventional gravity is cheapest, pressure dosing and chambers add modest cost, and mound, sand filter, ATU, and drip systems cost progressively more due to imported material, pumps, controls, and required maintenance contracts. The right system for a given lot is the least complex one the soil evaluation actually allows, not the cheapest one on paper.
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Not really; the site's soil evaluation determines what's viable. A designer starts with a conventional gravity system and only moves to an alternative when soil, water table, slope, or lot size specifically rule it out.
Conventional gravity systems are typically the least expensive to install and maintain, since they need no pump or imported fill; alternatives cost more roughly in proportion to their added mechanical complexity.
The soil and site evaluation, since it establishes application rate, depth to seasonal high water table, depth to any restrictive layer, and slope, all of which determine which system types are even viable.
Guide last reviewed 2026-08-31.