Drive the subdivisions spreading out from Boerne and Fair Oaks Ranch, and you’ll spot the tell of Hill Country wastewater: purple-capped sprinkler heads misting treated effluent over limestone-country lawns. Of the 256 septic systems Kendall County authorized in 2024, 177 were surface-irrigation aerobic units, nearly seven in ten, with raised absorptive mounds a distant second at 65. That ratio isn’t fashion. Rolling Edwards Plateau terrain between 1,000 and 2,000 feet, thin alkaline soils over dolomite and limestone, and rock that starts inches down leave few sites where a conventional buried drainfield can pass a site evaluation.
The water underneath explains the caution above. Kendall County draws almost everything from the Trinity Aquifer, a formation its own groundwater district describes as “tight,” with low porosity, limited fracturing, and modest well yields. The state flagged the problem decades ago: this area was designated a critical groundwater area in 1990 and lies within today’s Hill Country Priority Groundwater Management Area. One clarification worth making, because it gets muddled online: Kendall is not one of TCEQ’s Edwards Aquifer Protection Program counties. The recharge-zone septic rules you’ll read about for Bexar or Comal don’t apply here. What applies is Trinity protection. Kendall is among the Hill Country counties documented as having adopted OSSF rules stricter than the state minimums. 2,348 systems have been permitted here over the last decade, a remarkable number for roughly 50,000 residents, and growth continues to concentrate on the county’s south end, where Boerne (population 19,109 in 2021) meets the San Antonio commute.
Practical upshots for owners: expect an engineered or aerobic design rather than a bargain trench system, keep your maintenance contract current since spray systems don’t forgive neglect, and check regional context if you’re comparing notes across county lines, because Kendall’s ground behaves like Kerr’s, not like the Blackland farm country an hour east. Buying acreage? Site evaluation results will drive your budget more than square footage will; our aerobic systems page covers what those service visits should include.
Permitting is one-stop: the county runs the entire program from Boerne. Requirements and current fees are in the Kendall County permit guide.
Kendall County office: 400 E. Blanco Rd., Boerne, (830) 331-8252, M–F 8–12 and 1–4. Permit walkthrough here.
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New installs and major repairs need a permit from the local authorized agent — usually the county, sometimes a city — and the rules that bind are the local ones.
Our permit guide covers fees, required professionals and every step.
Four things decide what you can build and what it costs: zoning, environmental protections, power for aerobic systems, and the ground itself. We publish each one only where we have checked it — and say so plainly where the answer is “same as the rest of Texas”.
Zoning & land use
Kendall County issues the septic permit for the whole county. It holds that job only because the commissioners court adopted an on-site sewage facility order and TCEQ approved it (Health and Safety Code § 366.031), and § 366.032(b) makes that order prevail wherever it is stricter than 30 TAC Chapter 285. Ask the office for its current order — Texas counties have no general zoning power, so the order, not zoning, is where a local siting rule sits.
Nothing in Kendall County changes this.
Texas adds a separate approval path over the Edwards Aquifer recharge, transition and contributing zones, where TCEQ requires an Edwards Aquifer Protection Plan under 30 TAC Chapter 213. Elsewhere the Chapter 285 rules stand on their own.
The dominant constraint here is bedrock close to the surface (84.2% of rated soils), followed by clayey subsoil that water moves through too slowly (24.6%). NRCS rates 97.0% of rated ground very limited for a standard soil absorption field, 84.8% for subsurface drip and 24.4% for surface application with disinfection. Where a conventional field will not pass, surface application is usually the route that does.
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