Medina County authorized 376 septic systems in 2025, and 203 of them were standard trench-and-bed drainfields. Surface irrigation, the spray-field method that dominates the Hill Country counties to the north and east, accounted for 138; leaching chambers, 31. The year before, from TCEQ’s same report series, the county authorized 504, of which 231 were standard trenches and 188 spray. The count comes from TCEQ’s “Types of Systems Installed by Time Period” reports for 2024 and 2025, each re-summed row by row for this page.
That split is the county’s geography written in permits. The 1977 USDA soil survey put about 30 percent of Medina County in the Knippa-Mercedes-Castroville association, “deep, nearly level to gently sloping, loamy and clayey, calcareous soils” on the broad uplands south of the Balcones Escarpment, and about 14 percent more in the deep, loamy Duval-Miguel-Amphion soils. North of the escarpment it is a different county: the Tarrant-Real-Brackett association, about 19 percent, is “very shallow and shallow” ground “underlain by fractured limestone bedrock,” and the Speck-Pratley-Mereta soils, another 10 percent, overlie limestone and drain slowly.
A Soil Data Access query of the current NRCS survey for Medina County (TX325, 65 map units, September 2025 tabular data) rates 52 map units “Very limited” for a septic tank absorption field on their dominant soil and 12 “Somewhat limited,” with none “Not limited.” The count is this page’s own, not an NRCS-published percentage. Slow water movement is the fully limiting feature on 34 of those units, depth to bedrock on 17, and a cemented caliche pan on 9.
The somewhat limited ground is the deep southern soils: Castroville clay loam, Duval very fine sandy loam, and Atco loam are the three largest. Where a lot sits on those, a conventional field can pass. Where rock or a restrictive layer comes within two feet of the trench bottom, TCEQ’s site criteria rule a standard trench out, and the design moves to an aerobic system or another non-standard method.
The north is also Edwards Aquifer country. The U.S. Geological Survey’s atlas of the Edwards-Trinity system says the aquifer reaches its widest, about 30 miles, in Medina and Williamson Counties, and that in 1980 about 70 percent of all recharge to the Edwards came from Kinney, Uvalde and Medina Counties. On the recharge zone, 30 TAC §285.40 requires at least one acre per single-family dwelling, puts the planning in the hands of a professional engineer or registered sanitarian rather than a site evaluator, and exempts from the acre minimum only lots platted before March 26, 1974.
The county’s 2013 Order adds three rules of its own. A permit is required “regardless of size tract of land or acreage,” so the state’s 10-acre exemption does not exist here. No homeowner may install a system “unless the homeowner is a licensed installer.” And a surface-application system must keep a current contract with a licensed maintenance provider for as long as it runs, unless the owner holds that license; the state’s owner-maintenance option is closed. It all runs through one office: Medina County Environmental Health in Hondo is the sole permitting authority for every acre of the county, cities included.
The Census Bureau’s Vintage 2025 estimate puts Medina County at 56,881 residents, up 1,270 in the year and up from a 2020 base of 50,861. Fees, the inspection schedule and the Order’s full text are on the county’s Environmental Health page; the Texas permit authority table lists the office.
Every septic permit in Medina County comes from Medina County Environmental Health, 1502 Avenue K, 2nd Floor, Hondo, (830) 741-6195, whether the lot is in Hondo, Castroville, Devine, or open country.
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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
Medina County permits septic in the whole county under its own Medina County Order Adopting Rules for On-Site Sewage Facilities. Texas designates a county an authorized agent only after the commissioners court adopts such an order and TCEQ approves it (Health and Safety Code § 366.031), and § 366.032(b) makes that order prevail wherever it is stricter than the state rules in 30 TAC Chapter 285. Read the order before siting a system.
Medina County is inside the area 30 TAC Chapter 213 covers. The contributing zone takes in all of the county. On the recharge zone §285.40's siting rules apply, and where the site needs a TCEQ protection plan the San Antonio regional office must approve it before the authorized agent issues a permit. §213.5(h)(2) exempts an owner building their own single-family home at 20 percent impervious cover or less. Check the parcel on TCEQ's Edwards map viewer first.
The dominant constraint here is bedrock close to the surface (32.8% of rated soils), followed by clayey subsoil that water moves through too slowly (31.2%). NRCS rates 71.8% of rated ground very limited for a standard soil absorption field, 40.0% for subsurface drip and 19.4% for surface application with disinfection. Where a conventional field will not pass, surface application is usually the route that does.
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