Updated September 16, 2026
Short answer
In Texas the 'perc test' is the TCEQ site evaluation required for every septic permit: a licensed site evaluator or engineer digs two soil borings on the proposed drainfield area and classifies the soil. Bought on its own, it is commonly quoted at roughly $250–$600 depending on the county, how remote the lot is, and whether the evaluator also prepares the system design. From Quick Flow Septic it costs nothing extra — the evaluation is included in the flat installed price ($9,000–$15,500), because its result is what decides which system you need.
Texas doesn't require a timed perc test — it requires a site evaluation
A classic percolation test times how fast water drains out of a hole. Texas replaced that with the site evaluation in 30 TAC §285.30: a licensed site evaluator or professional engineer classifies the soil texture from two borings or backhoe pits at opposite ends of the proposed disposal area, dug to two feet below the planned excavation or to a restrictive layer. Some evaluators still run a percolation test as a supplement, but the soil classification is what the county permit requires. When a Texan says 'perc test', this evaluation is what they mean.
What a standalone evaluation costs, and what drives it
Bought by itself — for example before you close on a piece of land — a site evaluation is commonly quoted in the $250–$600 range across Texas. The price moves with travel distance to a rural lot, whether the evaluator hand-augers or brings a backhoe for pits, whether the county requires extra paperwork, and whether the evaluator also prepares the system design (an engineer-sealed design for an aerobic system costs more than the evaluation alone). Those are market-typical figures, not a Quick Flow price.
When it's included for free
If the evaluation is part of a new installation, you should not be paying for it as a separate line. Quick Flow Septic includes the site evaluation, the system design, and the county permit filing in its 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. The only time an evaluation costs money on its own is when you want the answer without an install, and for that first look there is a free online option.
What the evaluator actually does on your lot
The visit takes a couple of hours. The evaluator locates the proposed disposal area with the required setbacks from wells, property lines, foundations, and any water body, makes the two borings, records the texture class of each soil layer (Classes Ia through IV), notes any restrictive horizon, and looks for the mottling that reveals a seasonal water table. The result goes into a report and a site sketch the county needs with the permit application.
What happens if the soil 'fails'
In Texas soil doesn't pass or fail — it decides the system. Classes Ib through III with two feet of suitable soil below the excavation allow a conventional gravity drainfield. Class IV clay, a shallow water table, or rock close to the surface rule the conventional field out and point to an aerobic treatment unit with spray or drip dispersal. That is the single biggest swing in a septic budget: $9,000 versus $13,500 or $15,500 installed — and it is exactly the question the evaluation answers.
Before you buy land: check for free first
You do not need to pay for an evaluation to get a strong first read. Our free land pre-check pulls the USDA soil survey rating for septic absorption fields, the FEMA flood zone, and mapped wetlands for any Texas address and tells you which system type you are likely looking at, in about ten seconds. Use it before you make an offer; the licensed evaluation then confirms it on the ground once you are ready to build.
Free tool
Will your lot need an aerobic system? Check the address.
USDA soil rating, FEMA flood zone, and mapped wetlands for any Texas address — plus the system type and flat price you're likely looking at. About ten seconds, no account.
Classic perc test vs. the Texas site evaluation
| Timed percolation test | Texas site evaluation (§285.30) | |
|---|---|---|
| What it measures | Minutes per inch for water to drain from a test hole | Soil texture class in two borings, restrictive layers, groundwater indicators |
| Who performs it | Varies by state | Licensed site evaluator or professional engineer |
| Required for a Texas permit | No | Yes — on every tract that will get a system |
| Typical standalone cost | — | About $250–$600 (market-typical) |
| With a Quick Flow installation | — | Included in the flat installed price |
What the evaluation result means for the system and the price
| Evaluation finding | System the rule allows | Flat installed price |
|---|---|---|
| Class Ib–III soil with 2 ft of suitable soil below the excavation | Conventional gravity drainfield | $9,000 |
| Class IV clay, shallow water table, or rock near the surface | Aerobic unit with spray dispersal | $13,500 |
| Same, on a small lot, wooded lot, or where spray isn't allowed | Aerobic unit with drip dispersal | $15,500 |
Frequently asked questions
How much does a perc test cost in Texas?
Bought on its own, a Texas site evaluation — what most people call the perc test — is commonly quoted at roughly $250–$600, depending on the county, the lot's distance, and whether a system design is included. From Quick Flow Septic it costs nothing extra: the evaluation is included in the flat installed price.
Is a perc test required in Texas?
A timed percolation test is not; a site evaluation is. Under 30 TAC §285.30 every tract that will get a septic system needs an evaluation by a licensed site evaluator or professional engineer before the county will issue a permit.
Who can do a perc test in Texas?
A TCEQ-licensed site evaluator or a licensed professional engineer. Many installers hold the evaluator license as well, which is how the evaluation, the design, and the installation can come from one company.
Can I do my own perc test?
You can dig and look, but the county will not accept it. The evaluation that goes with the permit must be signed by a licensed site evaluator or a professional engineer.
How long does a site evaluation take?
A couple of hours on site for the two borings and the sketch, then a few days for the written report. The county's review of the full permit package is separate and varies by county.
How long is a perc test good for?
Counties differ on how old an evaluation can be, and an evaluation done years ago for a different house or disposal area usually has to be redone because the design flow and the disposal area have changed. If you are buying a lot that was 'perced' years ago, treat it as useful information rather than a permit-ready document.
Does Quick Flow Septic charge for the soil evaluation?
No. The site evaluation, the design, and the county permit filing are included in the flat installed price of every system we install.
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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