Perc Test & Site Evaluation
The soil and percolation evaluation that determines how your septic system is sized and designed.
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Updated October 19, 2026
The foundation of a system that works
A percolation (perc) test measures how quickly water drains through your soil — the single most important factor in sizing your drainfield and choosing your system type. We run the test, document the results, and design your system around them, so it's approved by the county and built to perform for decades.
What we test
Soil texture and class, depth, and how quickly your ground absorbs water across the proposed drainfield area.
Why it matters
Your soil class sets the drainfield size and whether you need a conventional or aerobic system — it drives the whole design.
We design around it
We document the results and engineer a permitted system matched to your actual site conditions.
What Texas actually requires on your lot
Most people ask for a "perc test," but the requirement in the rule is broader. Section 285.30 says a complete site evaluation must be performed on every tract of land where an on-site system will be installed, and it must be done by a licensed site evaluator or a professional engineer. That evaluation includes drilling two soil borings in the proposed disposal area and logging what comes out of them. A timed percolation test is one accepted way to characterize the soil; a soil texture analysis from those borings is the other, and in this region it is the one that usually settles the design.
What we record, and why each item matters
The evaluation logs the soil texture and class at depth, the depth to any restrictive horizon, the depth to groundwater, drainage characteristics, slope, and the features around the proposed area. Each of those maps to a rule: the soil class sets the loading rate that sizes the dispersal field, the restrictive horizon and water table decide whether a conventional absorptive field can keep its required two feet of separation, and slope decides whether surface application is even on the table. Nothing in the report is filler — it is the evidence the county reviewer reads.
What the result changes for you
The result determines your system type, the size of the dispersal field, and therefore the largest single variable in your price. Good, well-draining soil with deep groundwater can support a conventional gravity system and the smallest field. Heavy clay or a shallow water table moves the design to an aerobic system with spray or drip. Because we run the evaluation and design the system, there is no gap between what was found and what gets built — and no second opinion to pay for.
Standalone evaluation or part of an install
If you are buying land and want to know before closing, we can run the evaluation on its own. If you are moving ahead with an installation, it is still quoted as its own line, separate from the installed system price. Either way, start with our free land pre-check: it reads the USDA soil survey, FEMA flood mapping, and the wetlands inventory for the address and tells you the likely answer in under a minute — useful for deciding whether a lot is worth an on-site visit at all.
Frequently asked questions
Is a perc test required in Texas?
A complete site evaluation is required on every tract where a system will be installed (§285.30). A timed percolation test is one accepted method within that evaluation; a soil texture analysis from the required borings is the other, and it is what is most often used here.
Who is allowed to perform it?
A licensed site evaluator or a professional engineer. It is not something a contractor, a realtor, or a homeowner can self-certify, and the county reviewer checks who signed it.
Can I use the perc test from the lot next door?
No. The rule calls for an evaluation on every tract where a system will be installed, and soils change over short distances — a neighbor's borings say nothing reliable about where your field would go.
What happens if the soil fails?
Very few lots fail outright. Poor results usually mean the design moves from a conventional drainfield to an aerobic system with spray or drip dispersal. The real disqualifiers are different — lot size limits in platted subdivisions, or no room to meet required setbacks.
How much does a perc test cost?
We quote the evaluation on its own, whether you're buying land or moving ahead with an install; it isn't part of the flat installed system price. Our perc test cost guide breaks down the market range and what drives it.
How long does it take?
The field work is normally a single visit. What takes longer is scheduling and the written report that goes into the permit packet, so start it before you need the permit rather than after.
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