Aerobic vs. conventional anaerobic — what decides which one my property needs?

Nothing is chosen by preference: "the type and size of an OSSF shall be determined on the basis of the soil and site information developed according to §285.30," and a standard subsurface (conventional) absorption system may be used only if all soil and site criteria are suitable — otherwise a proprietary or non-standard system such as an aerobic treatment unit must be used (30 TAC Chapter 285, §285.32). The controlling factors found in the site evaluation are soil class/texture (Class Ia gravelly sands through Class IV clays), restrictive horizons, groundwater within 24 inches of the excavation bottom, slope, floodplain, lot size, setbacks, and easements (30 TAC Chapter 285, §285.30; Northeast Texas MWD OSSF FAQs). In practice, tight clay soils, shallow seasonal water tables, rocky ground, and small lots are what push a Texas property to aerobic treatment with spray or drip dispersal (Whippoorwill Septic, East Texas — industry); aerobic units are proprietary, must be on TCEQ's approved list, and cannot be home-built (Northeast Texas MWD).

Reviewed August 2026. Links go to the sources this answer was checked against.