Updated September 16, 2026
Short answer
30 TAC Chapter 285 is the Texas Commission on Environmental Quality's rulebook for on-site sewage facilities (OSSFs) — every septic system in Texas. It requires a permit from your county before construction, a site evaluation with two soil borings by a licensed evaluator or engineer, and it decides which system your lot can have: a conventional gravity drainfield only in suitable soil (Classes Ib–III) with two feet of separation to groundwater or rock, and an aerobic unit with spray or drip dispersal where the soil is clay (Class IV) or too shallow. It also sets the design flow that sizes your tank and field, and it requires aerobic systems to stay under a maintenance contract. Here is what each part means for a homeowner.
What Chapter 285 is, and who enforces it
Chapter 285 of Title 30 of the Texas Administrative Code is written by the TCEQ, but you will rarely deal with the TCEQ directly. The rules are enforced by your county (or a regional authority) acting as the TCEQ's authorized agent: the county reviews your application, issues the permit, inspects the installation, and charges its own permit fee. The state licenses the people involved — site evaluators, designers, installers, and maintenance providers — so every step of a Texas septic project is done by someone holding a TCEQ license.
The permit comes before the shovel (§285.3)
A new on-site sewage facility must be permitted by the county's authorized agent before construction starts. The application carries the site evaluation and the system design; once the system is installed, the county inspects it and authorizes it to operate. Homeowners can technically apply themselves, but because the package needs a licensed evaluation and design, the installer normally files it — we file every permit as part of the installation.
The site evaluation: two borings decide everything (§285.30)
Every tract that will get a septic system must have a site evaluation performed by a licensed site evaluator or a professional engineer. The evaluator drills two soil borings, or digs two backhoe pits, at opposite ends of the proposed disposal area, down to two feet below the planned excavation or to a restrictive layer, whichever comes first. They classify the soil texture, note any restrictive horizon (rock, cemented layers), and look for the mottling that signals a seasonal water table. In Texas this evaluation is what people call the 'perc test' — the rule classifies the soil rather than timing a hole draining.
Soil classes and what they allow (§285.31, Table V)
Chapter 285 sorts soil into classes by texture: Class Ia is gravel and coarse sand (drains too fast to treat effluent), Class Ib sandy loam and loamy sand, Class II loam and sandy clay loam, Class III clay loam and silty clay loam, and Class IV clay, silty clay, and sandy clay (drains too slowly). A conventional absorptive drainfield is allowed only in suitable soil — Classes Ib through III — and only with two feet of suitable soil between the bottom of the excavation and groundwater or a restrictive layer (§285.33(b)(1)). Class IV clay and Class Ia gravel do not qualify, which is why so many lots in the Houston region end up with an aerobic system: the rule leaves no conventional option on tight clay.
Design flow: the house sizes the system (Table III)
Everything is sized from a design flow in gallons per day set by the home's bedroom count and living area — the house, not the number of people living in it today. With water-saving fixtures a one- or two-bedroom home is designed at 180 GPD, three bedrooms at 240, four at 300, five at 360, and six at 420; the rule also steps the flow up by square footage, and the higher of the two counts applies. Homes without water-saving fixtures use higher figures (225, 300, 375, 450, 525). The table below shows both.
Tank and treatment-unit sizing (§285.91 tables)
The design flow sets the minimum septic or trash tank: 750 gallons up to 250 GPD, 1,000 gallons up to 350 GPD, and 1,250 gallons up to 500 GPD. For aerobic systems, Table II sets the minimum treatment capacity of the aerobic unit — 360 GPD through three bedrooms, 480 for four, 600 for five, 720 for six — so a larger home needs a larger-rated unit. Our sizing calculator runs exactly these tables.
Dispersal: drainfield, spray, or drip (§285.33)
The treated water has to go into the ground, and how much land that takes depends on the soil loading rate: a conventional field's area is the design flow divided by the rate for your soil class (Table I: roughly 0.38 gallons per square foot per day for Class Ib, 0.25 for Class II, 0.20 for Class III, 0.10 for Class IV). Surface application — the spray heads on an aerobic system — requires secondary treatment plus disinfection (§285.32(c)), ground with 15% slope or less, and a grass, shrub, or landscaped cover; bare ground and food crops are not acceptable (§285.33(d)(2)). Drip dispersal is the subsurface option Chapter 285 allows in Class IV clay, laid out at one emitter per four square feet (§285.33(d)(3)). Table X then sets minimum separation distances from water wells, property lines, foundations, and water bodies, which the evaluator lays out on your lot; in a mapped floodplain tanks are sealed and anchored, spray is not permitted in a regulatory floodway, and the county floodplain administrator reviews the permit.
Aerobic systems must stay under a maintenance contract
An aerobic treatment unit has an aerator, a pump, a control panel, and a disinfection step, so Chapter 285 requires it to be kept under a maintenance contract with a licensed maintenance provider. A two-year contract is typically included with a new installation; after that the owner keeps the system on an ongoing contract, and in many counties the provider reports the system's status to the county. Letting the contract lapse is one of the most common ways a system falls out of compliance.
Who has to be licensed, and what we handle
The site evaluation is done by a licensed site evaluator or a professional engineer; the design of an aerobic or other non-standard system is sealed by a professional engineer or a registered sanitarian; the installation is done by a TCEQ-licensed installer; and the ongoing service by a licensed maintenance provider. Quick Flow Septic carries the project through all of it — evaluation, design, county permit, installation, and final inspection — inside one flat installed price: $9,000 for a conventional system where the soil allows it, $13,500 for aerobic with spray, $15,500 for aerobic with drip.
What this means for your lot
Before you buy land or place a home, the questions Chapter 285 will ask are knowable in advance: what the soil is, how deep the water table sits, and whether the lot is in a floodplain. Our free land pre-check pulls the USDA soil survey, the FEMA flood map, and the wetlands inventory for any Texas address and tells you which system type you are likely looking at. The licensed site evaluation then confirms it on the ground — and it is included in our price.
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Table III design flow by home size (gallons per day)
| Bedrooms | With water-saving fixtures | Standard fixtures |
|---|---|---|
| 1–2 | 180 GPD | 225 GPD |
| 3 | 240 GPD | 300 GPD |
| 4 | 300 GPD | 375 GPD |
| 5 | 360 GPD | 450 GPD |
| 6 | 420 GPD | 525 GPD |
Soil classes under Chapter 285 and what they allow
| Soil class | Typical texture | Loading rate (gal/ft²/day) | Conventional drainfield allowed? |
|---|---|---|---|
| Ia | Gravel, coarse sand | — | No — drains too fast to treat effluent |
| Ib | Sandy loam, loamy sand | 0.38 | Yes, with 2 ft of suitable soil below the excavation |
| II | Loam, sandy clay loam | 0.25 | Yes, with 2 ft of suitable soil below the excavation |
| III | Clay loam, silty clay loam | 0.20 | Yes, with 2 ft of suitable soil below the excavation |
| IV | Clay, silty clay, sandy clay | 0.10 | No — aerobic with spray or drip dispersal |
Frequently asked questions
What is 30 TAC Chapter 285?
It is the chapter of the Texas Administrative Code that holds the TCEQ's rules for on-site sewage facilities — septic systems. It covers permitting, the required site evaluation, soil suitability, system sizing and design, dispersal methods, licensing, and maintenance. Counties enforce it as the TCEQ's authorized agents.
Do I need a permit for a septic system in Texas?
Yes. Under §285.3 a new on-site sewage facility must be permitted by the county's authorized agent before construction begins, and the county inspects the finished system before authorizing it to operate. Narrow acreage-based exceptions exist but rarely apply to residential lots in the counties we serve.
What is the site evaluation, and is it the same as a perc test?
The site evaluation (§285.30) is what Texans call the perc test. A licensed site evaluator or professional engineer makes two soil borings or backhoe pits on the proposed disposal area, classifies the soil texture, and checks for restrictive layers and groundwater indicators. Texas does not require a timed percolation test; the soil classification does that job.
Can I install a conventional septic system on clay soil in Texas?
Not on Class IV clay. Chapter 285 allows a conventional absorptive drainfield only in Classes Ib through III with two feet of suitable soil below the excavation. On clay the rule points to an aerobic treatment unit with spray or drip dispersal, which is what most Houston-area lots end up with.
Does the number of bedrooms really change the system size?
Yes. Table III sets the design flow from bedrooms and living area — 180, 240, 300, 360, and 420 gallons per day for 1–2 through 6 bedrooms with water-saving fixtures — and that flow sets the minimum tank size, the aerobic unit rating, and the dispersal area.
Is a maintenance contract required for an aerobic system?
Yes. Aerobic systems must be kept under a maintenance contract with a licensed maintenance provider. A two-year contract is typically included with a new installation, followed by an ongoing contract, and many counties require the provider to report the system's status.
Does Chapter 285 apply to a manufactured or mobile home?
Yes. Any dwelling without a public sewer connection needs a permitted on-site sewage facility, and the same site evaluation, sizing, and dispersal rules apply whether the home is site-built or manufactured.
Quick Flow Septic installs new septic systems across Harris County · Montgomery County · Fort Bend County · Waller County · Liberty County · Washington County · Grimes County · San Jacinto County · Walker County · Colorado County · Austin County · Wharton County.
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