Septic and OSSF guide
Septic and OSSF on Hill Country acreage: what to know before you build
On rural Hill Country land, the septic permit is usually the approval that governs your build, not a building inspection. This guide explains the on-site sewage facility (OSSF) rules in plain language, including the 10-acre exemption, why most sites need an aerobic unit, and where the counties differ.
The short version
- Most Hill Country counties do not inspect general building in unincorporated areas. The septic permit is the real gate.
- On 10+ acres a single-family home can be exempt from the permit under 30 TAC 285.3, if it meets all the conditions. Gillespie County is the exception.
- Thin soil over limestone usually means an aerobic treatment unit, not a conventional drain field.
Why septic, not a building inspector, runs the show
Texas counties have limited authority to enforce a general building code in unincorporated areas, and the Hill Country counties generally do not. That surprises people who expect a building inspector. What you do answer to is the OSSF (septic) program, run by the county or its authorized agent under state rules in 30 TAC Chapter 285. If your project generates wastewater, a home, a shop with a bathroom, a barn with a wash rack, the septic permit is usually the approval that sets your schedule.
The 10-acre exemption, and its conditions
Under 30 TAC 285.3, a single-family dwelling on a tract of 10 acres or more can be exempt from the septic permit, planning, and inspection requirements. The conditions all have to be met:
- the tract is 10 acres or larger;
- it is a single-family dwelling and the only dwelling on the tract;
- every part of the system is at least 100 feet from all property lines; and
- the effluent is disposed of on the same tract.
Two cautions. First, the exemption removes the permit and inspection step only. The system still has to meet the construction and groundwater-protection standards in Chapter 285, so build it right regardless. Second, local authorized agents can be stricter. In Gillespie County, the county requires approved wastewater disposal in all areas regardless of acreage, so treat the 10-acre exemption as unavailable there. Always confirm with your county before relying on it.
Why most Hill Country sites need an aerobic unit
A conventional septic system relies on soil to absorb and treat effluent through a drain field. Much of the Hill Country is thin soil over fractured limestone, which does not provide that, and which can let untreated effluent reach groundwater. The common answer is an aerobic treatment unit that treats the wastewater before dispersing it by spray or drip. ATUs cost more up front and require a maintenance contract, but on karst ground they are frequently the only system that will pass. Budget for one unless a site evaluation says otherwise.
The Edwards Aquifer question
People often ask whether the Edwards Aquifer adds a layer of septic review. For our five counties, almost never. None of Gillespie, Kerr, Kendall, Bandera, or Blanco is in the regulated Edwards Aquifer Protection Program. The single exception is the southeast corner of Kendall County near Boerne, where the regulated recharge zone begins at Herff Falls on Cibolo Creek, and a Water Pollution Abatement Plan can apply. If your land is in that corner, check the TCEQ Edwards map viewer. Everywhere else, design to protect groundwater as a matter of course, but there is no Edwards review on your project.
How the counties differ
The state rules are the floor, but each county runs its own program. Gillespie requires a permitted system everywhere. Kerr County Environmental Health issues an Authorization to Construct you must have before installing. Kendall folds septic into a development-permit process. Bandera runs it through the County Engineer under a county OSSF Order. Blanco ties the septic permit to subdivision platting, so an unplatted lot can stall you. Read your county page for specifics and the official contact.
Sources and where to verify
Keep reading
Frequently asked questions
Do I need a septic permit on 10 acres in the Hill Country?
Often not, under the statewide 30 TAC 285.3 exemption: a single-family home that is the only dwelling on a tract of 10 or more acres, with every part of the system at least 100 feet from the property lines and effluent kept on the property. The exemption removes the permit and inspection only; the system still has to be built to state standards. Gillespie County is the local exception, where a permitted system is required in all areas regardless of acreage.
What is an aerobic treatment unit and why do I probably need one?
An aerobic treatment unit (ATU) treats wastewater with oxygen and then disperses it, usually by spray or drip. Hill Country soils are typically thin over limestone and will not support a conventional gravity drain field, so most sites use an ATU. ATUs cost more and require an ongoing maintenance contract, but they are often the only system that works on karst ground.
Who issues the septic permit in my county?
A county office or designated authorized agent. In Kerr County it is Environmental Health, which issues an Authorization to Construct. In Gillespie it is the county Sanitation Office. Kendall, Bandera, and Blanco run their own programs as well. Each county permitting page links to the right office.
Does the Edwards Aquifer affect my septic system?
For most of our five counties, no. None are in the regulated Edwards Aquifer Protection Program except the southeast corner of Kendall County near Boerne, where the recharge zone begins at Herff Falls. There a Water Pollution Abatement Plan can apply. Elsewhere, design to protect groundwater as always, but the formal Edwards review does not apply.