Soil Test vs Perc Test
“It passed a perc test” is the phrase everyone uses. Arkansas does not decide on it — and the state says so in its own words.
Arkansas rules and guidance. Verified August 10, 2026.
Ask around about buying rural land and someone will tell you to make sure it percs. Listings say “perc tested.” Buyers write it into offers. It is the single most widely repeated idea in rural property, and in Arkansas it is not the thing that decides.
This is not a technicality or a matter of opinion. It comes from the regulator. The Arkansas Department of Health states that the percolation test provides only a rough estimate of the soil's ability to move water. What governs is the Designated Representative and the county Environmental Health Specialist using soil pits to determine depth to rock, impervious layers and anticipated wet-season groundwater — and the department is explicit that this additional information is what produces a design capable of overcoming the soil's limitations.
Read the second half of that sentence again, because it is the part that changes how a homeowner should think. The purpose of the evaluation is not to issue a pass or a fail. It is to produce enough information to design around whatever is there. That is a fundamentally different activity from timing water in a hole.
What each one actually is
The percolation test
A hole is bored, pre-soaked, filled with water, and the rate at which the level drops is timed. The output is a number — minutes per inch — describing how fast water left that hole, on that day, at that depth.
It is a genuine measurement of a genuine property. Its limits are that it measures one point at one depth on one day, it is sensitive to how it was performed and to recent weather, and it says nothing about why the soil behaves that way — or what lies below the bottom of the hole.
The soil evaluation
An excavation is opened deep enough to expose the profile in section, and the soil is read layer by layer. It is closer to reading a core than running a stopwatch.
What that exposes:
- The sequence and thickness of horizons — which layers are present and how deep each runs.
- Depth to rock or to an impervious layer, and whether either is continuous or interrupted.
- Redoximorphic colour patterns — the mottling and grey tones that record where water has stood seasonally. This is how a wet-season water table is identified in August, months from the season that produced it.
- Structure and texture by layer, which is what actually governs how water moves.
The last point is the one worth holding on to. A pit dug in dry weather can reveal that a site is saturated in March. A perc test run the same day cannot.
Why the rule needs a profile, not a rate
There is a specific reason Arkansas cannot run on percolation rates, and it sits in the definition of depth to bedrock.
Where rock and soil horizons are interlayered, the rules define depth to bedrock as the cumulative thickness of soil layers at least four inches thick within seventy-two inches of the surface. It is a running total of qualifying layers across the top six feet.
A percolation test cannot produce that number. It has no way to count layers, no way to measure their thickness, and no way to see what is below the hole. Only an open profile can. The rule is written in the language of a soil pit because a soil pit is the instrument it assumes.
Which ground a parcel sits on is what makes that definition bite hard in some places and barely at all in others — that is a separate question, and it has its own page. What matters here is that the evidence standard is the same everywhere in Arkansas, and it is a profile.
Two failure modes a rate alone will miss
A restrictive layer below the hole. Water can leave a test hole at a perfectly acceptable rate and then meet something dense a foot below it. The rate looked fine; the site will still perch water on top of the field.
A seasonal water table. Ground that is dry and permeable in September can be saturated in March. A rate measured in September records the September condition. Colour patterns in a profile record the March one, because the soil keeps the evidence.
Who is licensed to do this
The evaluation is not a task for a general contractor or an excavator, however experienced. It is done by a Designated Representative, a state licence with a defined qualifying route.
Act 402 of 1977 qualifies professional engineers, registered professional land surveyors, registered professional sanitarians and licensed master plumbers, along with similarly qualified individuals considered case by case. The Designated Representative both evaluates and designs — and it is the same person who completes the permit application and whose authorisation is required for any later change to the design.
Two reliable ways to find one:
- The Arkansas Department of Health publishes a searchable licensee database, filterable by licence type, which is the authoritative way to confirm someone holds the credential they claim.
- The county health unit will supply the list of licensed local individuals who do soil tests and design systems. Worth noting: the county refers callers to licensees, not to contractors — which is a useful distinction when a name arrives from somewhere else.
Ask for the role by title when calling. County contacts for every town in this area are on the permit process page.
What a homeowner should do with the result
The evaluation is a document, and it is the most useful piece of paper a rural property will generate. Three things follow from having it.
It comes before the quote, not after
The evaluation determines the system type; the system type determines the price. A figure produced before the soil has been read is priced on an assumption, and on ground where the profile changes across a single parcel the difference is not marginal. The cost page sets out what is actually fixed and what is not — but the sequence is the point: evaluate, then design, then price.
An unfavourable result is information, not a verdict
Arkansas rules provide for engineered approaches to difficult soil, including seasonal water table adjustments and capping fills, with the adjustment credits capped. The evaluation is what tells a designer which of those a site will support.
What it is not is a score to be improved by re-testing. Somebody who suggests trying again in a different spot until a better number appears is describing a perc test, and describing the wrong instrument.
Keep it
Along with the permit file, the soil evaluation is what a future buyer, lender, inspector or insurer will want to see. It is also what makes a later repair cheaper, because the next professional does not start from nothing.
Questions For Whoever Evaluates
All six are ordinary parts of an Arkansas evaluation. Asking is not a challenge to anyone's competence — it is what turns a verbal answer into a record.
Common questions
The percolation test is not the governing evidence. The Arkansas Department of Health states that a perc test provides only a rough estimate of the soil's ability to move water. The Designated Representative and the county Environmental Health Specialist use soil pits to determine depth to rock, impervious layers and anticipated wet-season groundwater, and that information is what produces a workable design.
A soil pit is an excavation deep enough to expose the soil profile in section, so it can be read layer by layer. It shows the sequence and thickness of horizons, the depth at which rock or an impervious layer appears, and colour patterns that record where water has sat seasonally. A percolation hole shows how fast water leaves one hole on one day.
A Designated Representative. Act 402 of 1977 qualifies professional engineers, registered professional land surveyors, registered professional sanitarians and licensed master plumbers, along with similarly qualified individuals considered case by case. The Arkansas Department of Health publishes a searchable database of licensed Designated Representatives, and the county health unit will supply a list of local licensees on request.
Often, though not always, and not by re-testing until a better number appears. Arkansas rules provide for engineered approaches to unfavourable soil, including seasonal water table adjustments and capping fills with the adjustment credits capped. The evaluation is what tells a designer which of those approaches the site will support.
Before. The evaluation determines the system type, and the system type determines the price. A quote issued before the soil has been read is priced on an assumption, and the number can move substantially once the profile is known.
Need a soil evaluation on a parcel?
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Sources
- Arkansas Department of Health, onsite wastewater guidance — the statement that a percolation test provides only a rough estimate, and that soil pits are used to determine depth to rock, impervious layers and anticipated wet-season groundwater. Verified August 10, 2026.
- Arkansas Department of Health, Rules Pertaining to Onsite Wastewater Systems — the interlayered depth-to-bedrock definition, seasonal water table adjustments and capping fills, the primary and secondary absorption area requirement, and the role and authority of the Designated Representative. Verified August 10, 2026.
- Act 402 of 1977 as amended — qualifying professions for the Designated Representative licence.
- Arkansas Department of Health searchable onsite wastewater licensee database.
This page describes the kind of evidence Arkansas relies on and who is licensed to produce it. It does not evaluate any particular parcel, and no description of method substitutes for an evaluation carried out on the ground.