Aerobic vs. Conventional Septic Systems
If you're building or buying in the Austin area, you'll run into two main flavors of septic system. They look different, work differently, and demand very different things from you over the next 30 years. Here's the side-by-side.
How Each System Works
Conventional Septic (Gravity Drainfield)
The simplest design. Wastewater flows from the house into a buried tank where solids settle to the bottom and grease floats to the top. The middle layer (clarified effluent) flows out through a series of perforated pipes buried in trenches — the drain field. Soil microbes finish the treatment as the effluent percolates down toward the water table.
No power, no pumps in most cases, no moving parts. Just a tank, gravity, and dirt doing the work.
Aerobic Treatment Unit (ATU)
Treats wastewater to a much higher standard before dispersing it. Air pumps inject oxygen into the tank, dramatically speeding up the bacterial breakdown of waste. A chlorine chamber disinfects the effluent. The treated water is then sprayed across your lawn through pop-up spray heads or distributed through subsurface drip lines.
The treated water is clean enough to be sprayed on the surface — which is the whole point. It also means more equipment: a tank, an aerator, a control panel with an alarm, a pump, and the spray system. Power is required.
Side-by-Side Comparison
| Factor | Conventional | Aerobic |
|---|---|---|
| Install cost (Austin) | $5,000-$10,000 | $10,000-$18,000 |
| Annual upkeep | $200-$400 (pumping every 3-5 yrs averaged out) | $300-$500 (mandatory TCEQ maintenance contract) |
| Power required? | No | Yes — air pump runs continuously |
| Soil requirements | Needs deep, well-draining soil | Works on tight lots, clay, or rocky soil |
| Lot size needed | ~1/2 acre+ for the drain field | Can fit on smaller lots |
| Distance to water | Restricted near creeks, lakes, wells | Permitted closer to water bodies |
| Lifespan (tank/field) | 30-40 yrs | 30+ yrs (tank); 8-12 yrs (pumps and spray heads) |
| Maintenance | Pump every 3-5 yrs | Inspect every 4 months (TCEQ requirement) |
| Visible above ground | Just the lids | Spray heads in the yard |
| Repair complexity | Low — tank or field work | Higher — electrical, pump, control panel |
Which One Is Right for You?
Pick a conventional system if:
- You have a lot of at least half an acre with deep, well-draining soil
- You want the lowest install cost and the simplest long-term maintenance
- You're far enough from creeks, lakes, and water wells
- You're comfortable with a 3-5 year pumping schedule and basically no other thinking about it
Pick an aerobic system if:
- Your lot is small, rocky, or has clay-heavy soil that won't percolate
- You're near a lake, creek, or water well with setback restrictions
- The local jurisdiction requires it (some Hill Country areas do)
- The water table is high seasonally
- You don't mind the maintenance contract and the equipment in your yard
TCEQ Requirements You Should Know
The Texas Commission on Environmental Quality regulates every onsite sewage facility in the state. Key things that affect your decision:
- Site evaluation is mandatory. A licensed designer has to evaluate your soil before any system can be permitted. The soil dictates the system, not your preference.
- Aerobic systems require a maintenance contract for life. No exceptions. The contract has to be with a licensed maintenance provider, with documented inspections every four months.
- You can't legally service your own aerobic system. Even if you're handy. The state wants licensed eyes on these units.
- Conventional systems have no maintenance contract requirement after install — but pumping records help if you ever sell the property.
The Real Cost Over 30 Years
People focus on the install number, but a septic system is a 30-40 year decision. Here's roughly what you spend over the system's life:
| Cost Bucket | Conventional (30-yr total) | Aerobic (30-yr total) |
|---|---|---|
| Install | $5,000-$10,000 | $10,000-$18,000 |
| Routine maintenance | $3,000-$5,000 (pumping) | $9,000-$15,000 (contract + pumping + chlorine) |
| Equipment replacement | $0 (no equipment) | $3,000-$6,000 (pumps, panel, spray heads) |
| 30-year total | $8,000-$15,000 | $22,000-$39,000 |
Conventional is cheaper across the board if your soil supports it. Aerobic is the right tool when conventional isn't an option — not the upgrade, just the alternative.
Frequently Asked Questions
Can I convert from aerobic to conventional later?
Almost never. The reason you have aerobic is usually soil or setback constraints — those don't change. You can convert from conventional to aerobic if your drain field fails and the soil isn't ready for a rebuild, but that's a one-way street.
Do aerobic systems smell?
A properly working aerobic system shouldn't smell. The aerobic bacteria don't produce the methane and hydrogen sulfide that make a conventional tank stink. If you can smell your aerobic system, something's wrong — usually the air pump.
Will my power bill go up with an aerobic?
The air pump uses about $15-25 of electricity per month. Not nothing, but not a deal-breaker.
What if I want both — a tank and aerobic treatment?
Some sites use a hybrid: a conventional tank that empties into an aerobic unit, then to a drip distribution field. It's expensive and rare. Usually only seen on commercial properties or unusual residential situations.
How long does an install take?
Conventional: 1-3 days of dig, install, and inspection. Aerobic: 2-4 days, plus startup once power is connected and the bacterial colony establishes.
Get a Real Quote, Not a Guess
The right answer depends on your soil test, your lot, your local jurisdiction, and your family's water usage. We do site evaluations, design TCEQ-permitted systems, and install both types across Greater Austin and the Texas Hill Country. We'll tell you which fits your property — and which doesn't, and why.