OSSF vs. Centralized Sewer: Choosing Between Travis County Septic Permitting and TCEQ Wastewater Permits for Exurban Sites

What counts as an OSSF, and who permits it in Travis County?

A small system that treats and disposes of sewage on the site it serves. Under 30 TAC §285.2, an on-site sewage facility treats or disposes of no more than 5,000 gallons of sewage a day, produced on a site where part of the system sits. A local authorized agent, delegated by TCEQ under Health and Safety Code Chapter 366, runs the permit program.

In Travis County that agent is the county. Its rules, Travis County Code Chapter 448, were last amended November 28, 2023 and took effect July 16, 2024. They cover:

• unincorporated Travis County, except areas under another local entity's OSSF order and areas Austin annexed for the limited purpose of public health;
• the corporate limits of Webberville, Manor, Mustang Ridge and San Leanna, and the Travis County part of Leander;
• other authorized agents that have an interlocal agreement with the county.

A Permit to Construct comes before any OSSF is built or changed. A system above 5,000 gallons per day is not an OSSF at all; it needs a TCEQ wastewater permit.

How big does a lot need to be for an OSSF in Travis County?

At least one acre for each home, even with public water. The state minimum in 30 TAC §285.4 is half an acre with a public water supply and one acre with private wells. Travis County's stricter rule (§448.032) sets one acre regardless of public water, and counts each residential unit separately.

That one rule caps density. A subdivision planned at two or three homes per acre cannot be served by individual OSSFs in the county's jurisdiction, whatever the soils look like.

On the Edwards Aquifer recharge zone in southwest Travis County, 30 TAC §285.40 also applies. It requires one acre per single-family dwelling for new systems and keeps soil absorption systems 150 feet from any recharge feature, and tanks 50 feet.

What do soils and drainage decide?

Whether a conventional system works, or the site needs a more demanding one. Every property using an OSSF is evaluated for overall site suitability (§285.4(a)), by a licensed site evaluator or a professional engineer.

Shallow soil over rock, restrictive layers, high groundwater or poor drainage can rule out a conventional drainfield. The alternatives, such as aerobic treatment units, carry more upkeep. Travis County's maintenance affidavit requires a continuous service policy for the first two years. After that, the owner of an aerobic system for a home either signs a maintenance contract or maintains it personally.

When does density push a project to centralized sewer?

When the lot yield you need is below an acre per home, or a single site's flow passes 5,000 gallons per day. Commercial and mixed-use programs reach that flow fastest.

Developments face a review step before any OSSF application. Under §448.032(d), single-family subdivisions, condominium and multi-unit developments, manufactured housing communities and commercial developments served by OSSFs submit planning materials to the county and get written approval first. A professional engineer or professional sanitarian prepares them.

Run the flow for the actual program before you choose. If the numbers only work at OSSF densities, the land price should reflect that.

Why can OSSFs become the wrong answer for a phased project?

Because lot-by-lot systems do not convert into a collection system later. If the first phase is one-acre lots on OSSFs and later phases are denser, those later phases need a plant and a collection system anyway, and the first phase's systems do not become part of it.

Plan on the full build-out. Where later phases are denser, compare a centralized system sized and phased from the start against OSSFs for phase one plus a plant later.

What are the centralized options?

A sewer extension where a provider has capacity, or a private plant. A private plant needs a TCEQ permit: a TPDES permit to discharge, or a TLAP to apply effluent to land.

Each brings duties an OSSF does not. The permit holder must employ or contract licensed operators under 30 TAC §30.350, which our post on package plant operator staffing explains. On the recharge zone, 30 TAC §213.6 prohibits a new discharge that adds pollutant loading.

Where the project has irrigation demand, reuse can serve it. Under 30 TAC §210.2(e), a producer of domestic reclaimed water still needs a TPDES permit, a TLAP or a Chapter 321, Subchapter P authorization before it builds the plant. Our post on Chapter 210 reclaimed water covers the reuse rules.

What can endangered species review add?

Time and routing limits, where a utility corridor or building area crosses habitat. Western Travis County has a regional permit for this, the Balcones Canyonlands Conservation Plan, held by Travis County and the City of Austin. It covers the golden-cheeked warbler and six cave invertebrates.

Check its status first. The county's BCCP annual report for fiscal 2025 said the permit's original 30-year term would end May 2, 2026, and that renewal with the U.S. Fish and Wildlife Service was under way. Confirm the permit's current status with the county before you count on it. A landowner who does not use the plan can seek an individual permit from the Service, a longer path.

Before you lock in the wastewater path, check these. Every answer should be yes:

1. Have you run the wastewater flow for the full build-out program, not just phase one?
2. Does every planned home have at least one acre if it will use an OSSF?
3. Does each OSSF stay at or under 5,000 gallons per day for its site?
4. Has a site evaluator or engineer confirmed the soils and drainage?
5. Do you know whether the site is on the Edwards recharge zone?
6. Have you asked the nearest provider in writing about sewer capacity?
7. Have you checked utility corridors against habitat and the BCCP's status?

Any no is a question for your engineer before the site plan is fixed.

This post is general education on TCEQ's Chapter 285 and related rules and Travis County's Chapter 448 as published in October 2026. Your permitting authority decides each application, so confirm the current rules with it and your engineer.

Frequently asked questions

Can we start with OSSFs for phase one and switch to centralized treatment later?

You can, but the OSSFs usually do not carry over into the later system. Compare both paths against the full build-out before you commit.

Who permits septic systems in Travis County?

Travis County, as TCEQ's authorized agent, in unincorporated areas and the cities its rules list. Where another local entity has its own OSSF order, that entity does.

I'm subdividing land in unincorporated Travis County with public water available. How small can lots be if each home uses a septic system?

One acre per residential unit under Travis County's Chapter 448, even with public water, unless an exemption applies. Planning materials must be approved before any OSSF application.

I'm planning a small retail center outside city limits in Travis County. When does our wastewater stop being an OSSF?

When the system would treat or dispose of more than 5,000 gallons per day, or take sewage from beyond its site. Then it needs a TCEQ permit instead. A commercial OSSF still needs approved planning materials.

Does a site near the Edwards Aquifer rule out an OSSF?

No. Licensed on-site systems are the exception to Chapter 213's ban on percolation disposal, but §285.40 requires an acre per home and keeps drainfields 150 feet from recharge features.

Related resources

• Edwards Aquifer Recharge Zone Development: What Austin Area Developers Must Do Differently for Wastewater
• Permit-by-Rule vs. Standard Permit: When Each Path Applies to Your Development
• Building a Private WWTP in Texas: What Developers Need to Know Before They Commit
• Decentralized Wastewater Clusters: Designing Multiple Small Package Plants Across a Phased Development

Choosing between septic and sewer for an exurban Travis County site?

We compare the OSSF path and the centralized options against your full build-out during due diligence, so the wastewater plan fits the project you will actually build.

We specialize in:

• Site feasibility and due diligence
• Septic system and on-site wastewater design
• Wastewater treatment plant design and TCEQ permitting
• Land application and reuse system design
• Collection system and lift station design
• Construction administration

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com