Septic Systems in Bastrop County: What Buyers Need to Know About OSSF

Many homes outside city sewer service in Bastrop County use septic — formally, an On-Site Sewage Facility, or OSSF. If you are coming from a city where sewer was simply a line item on the utility bill, septic permitting, condition, capacity, and maintenance are important ownership differences to understand before the option period is underway.

I am a REALTOR®, not a licensed site evaluator, installer or inspector. This page is here so you know what to ask and who to ask. Verify specifics with Bastrop County Development Services at (512) 581-7176.

Who is in charge

Bastrop County is the authorized agent for the Texas Commission on Environmental Quality, which means the county — not the state — reviews plans, issues permits and inspects systems in unincorporated areas. That work lives in Development Services, Environmental and Sanitation Services, 211 Jackson Street, Bastrop, (512) 581-7176, open weekdays 8 to 4.

If the property is inside the City of Bastrop limits, the city maintains its own OSSF checklist — worth checking which set of rules applies before you assume.

When a permit is required

Broadly: any time you construct, install, alter, extend or repair a system. The county puts it bluntly — all septic installation and modifications require a permit, regardless of acreage. The narrow exception is emergency repairs like replacing tank lids or inlet and outlet devices, which still must be reported to the county within 72 hours of starting work.

This matters to buyers in a specific way. If a seller added a bedroom, converted a garage or put in a guest cabin without updating the septic permit, you may be inheriting an unpermitted modification and an undersized system. Ask.

The soil decides everything

There is no such thing as a standard Bastrop County septic system, because there is no standard Bastrop County soil. What you can install is determined by a site evaluation performed by a licensed site evaluator or a professional engineer — not by the builder, and not by what the neighbor has. If you are buying a new build on acreage or a custom lot, put this on the checklist in my guide to new construction homes in Bastrop County.

State rules require the evaluator to drill two soil borings or dig two backhoe pits at opposite ends of the proposed disposal area, examine the profile for restrictive horizons — clay subsoils, rock, plugged laminar soils — and check for groundwater within 24 inches of the bottom of the excavation.

The county’s own summary is the clearest version of what that means for you:

If the evaluator finds Class 1b, Class II or Class III soils to at least 42 inches with no restrictive horizons and no restrictive surface features, any type of system is usually an option.
If there are Class 1a or Class IV soils, restrictive horizons, or other restrictive site features, your options may be limited.

When soils are unsuitable for a conventional subsurface drainfield, the alternatives include evapotranspiration systems, pumped or low-pressure dosed drainfields, mound systems where soil is shallow or the water table is high, soil substitution, drip irrigation — which state rule allows in all soil classes, including Class IV — and surface application, where treated effluent is disinfected and sprayed.

Those alternatives cost more to install and more to run. That is the real reason two similar-looking ten-acre tracts can be thousands of dollars apart before you have poured a slab.

A few Bastrop-specific rules worth knowing

Surface irrigation systems may not be designed with overlapping spray patterns.
The minimum sizing factor for any structure up to 1,500 square feet is 180 gallons per day.
For a system serving more than one occupied structure, Bastrop County states that a minimum 750-gallon septic tank is required for each home, preceding the required treatment and disposal components. Confirm the design for the proposed structures with the county and the licensed designer.
All proposed and existing structures must be shown on the septic design. That workshop you are planning counts.

Lot size

State rule sets the floor, and Bastrop County restates it: a single-family lot served by a public water supply using an individual septic system must be at least half an acre. A lot not served by a public water system must be at least one acre.

But acreage alone guarantees nothing. The county is explicit that the lot must be large enough for the system to meet every required setback — from property lines, water wells, buildings, easements and bodies of water. On lots under half an acre, the system must be designed by a registered sanitarian or professional engineer regardless of type. And properties partly or wholly in a regulated floodplain carry further restrictions.

Aerobic systems and the maintenance contract

If the property has an aerobic treatment unit — the kind with a control panel, an air pump and usually spray heads in the yard — there is an ongoing legal obligation attached to it, and it transfers to you.

A new aerobic system requires a mandatory two-year initial maintenance contract with a licensed maintenance provider. After those first two years, the county allows a homeowner to maintain certain system types themselves — but Bastrop County requires homeowner training first. Otherwise you keep a contract with a licensed provider.

Either way, the county’s language is unambiguous: maintenance of an aerobic system is required for the life of the system. Licensed providers must inspect, tag the system and report to the county and the owner at least every four months, reducible to every six months with electronic monitoring.

Budget for the continuing maintenance obligation on an aerobic system. During the initial two-year service period, the required service policy is a real recurring ownership cost. After that period, an eligible trained homeowner may maintain certain systems under Bastrop County rules; otherwise, the owner continues with a licensed maintenance provider. Ask for the current agreement, service reports, renewal date, and cost before closing.

What transfers at closing — and what to ask for

Two documents matter.

The License to Operate is the county’s approval of the finished system. It lasts for the life of the system unless there is a modification or a significant change in water usage. The Permit to Construct has a one-year term, which is the window to get a new system installed, inspected and finally approved.

For aerobic systems, Bastrop County also requires an Affidavit to the Public recorded in the county deed records, disclosing the system and its continuous-service requirement. On sale or transfer, the permit transfers to the new owner.

Your option-period checklist

Pull the county file. Ask Development Services for the permit, the site evaluation, the as-built design and the inspection history for the address. This is public and it is the most useful hour you will spend.
Confirm the system matches the house. Compare the bedroom count and square footage on the permit against the house you are buying. A three-bedroom permit under a five-bedroom house is a problem.
Arrange a dedicated OSSF evaluation with a qualified septic professional whose scope is acceptable to you and, when applicable, your lender. TCEQ does not require or regulate resale OSSF evaluations, so ask exactly what will be inspected, tested, opened, and documented; also review the exclusions in the general home inspection.
Ask for the maintenance records if it is aerobic — the last few reports tell you far more than a visual look at the lid.
Check the deed records for the recorded affidavit when the system type requires one.
Notify Bastrop County after closing that you are the new OSSF owner and ask whether any ownership, maintenance, or startup records must be updated. TCEQ specifically advises buyers to notify the local permitting authority after purchase.
If you are buying raw land, make your contract contingent on a satisfactory site evaluation. Do not assume a tract is buildable because it is for sale.

What it costs

The county’s Development Services fee schedule adopted June 20, 2025 lists a standard residential OSSF permit at $600, a non-standard or aerobic residential permit at $700, and re-inspections at $200 each. It also lists a single-family development permit at $225, or $300 in a floodplain. Fees can change, so confirm the current amount with Bastrop County before applying.

Installation cost varies substantially with soil class, system type, terrain, required setbacks, design, and the distance between the home and disposal area. A visual property tour cannot determine soil suitability or system cost. For raw land or a questionable existing system, obtain a licensed site evaluation or engineering input and a written installation or repair quote within the applicable contract contingency period.

Finding a licensed professional

TCEQ maintains a public occupational-license search. Bastrop County instructs users to search for OSSF professionals in Bastrop County using ZIP code 78602. You will need a licensed site evaluator or professional engineer for the site evaluation, a properly licensed installer unless a valid owner-installation exception applies, and a licensed maintenance provider when the system is maintained under contract. Review TCEQ’s current OSSF permitting guidance and confirm local requirements with Bastrop County.

Frequently Asked Questions About Septic Systems in Bastrop County

Does Bastrop County require a permit for a septic system?

Yes. Bastrop County states that septic-system installations and modifications require a permit regardless of acreage. Most construction, installation, alteration, extension, and repair work requires approval; limited emergency-repair exceptions must be reported to the county. Confirm the planned work with Bastrop County Development Services before starting.

What determines which septic system can be installed?

The site evaluation, soil class, restrictive soil horizons, groundwater, slopes, floodplain considerations, setbacks, available disposal area, planned structures, and expected wastewater flow affect the design. A buyer should not assume that acreage alone guarantees approval for a particular system or building plan.

Does an aerobic septic system require a maintenance contract in Bastrop County?

A newly installed aerobic OSSF requires an initial two-year maintenance contract with a licensed maintenance provider, and the system must be maintained for its lifetime. After the initial two years, an eligible homeowner may perform maintenance after completing Bastrop County’s required training, or may continue using a licensed maintenance provider. Confirm the current requirements with the county for the specific system.

What septic records should a buyer request before closing?

Request the permit and license to operate, approved design or as-built documents, site evaluation, inspection records, maintenance contract and service reports, pumping and repair history, alarm or component information, and any required transfer paperwork. Ask Bastrop County and a qualified licensed professional to confirm what is available and whether additional evaluation is appropriate for the property.

Thinking about acreage here?

Septic is one of three things I check on every rural Bastrop County property before my clients get emotionally attached — the other two are water and floodplain. Let us walk a tract together and find out what it will actually take to build on it.

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Written by Bre Meador, REALTOR® — All City Real Estate, Bastrop County, TX · U.S. Army veteran and former nurse · TREC #0835116
Read client reviews. Last updated October 18, 2026. This page is general information from a licensed REALTOR®, not tax, legal, engineering or insurance advice.