Perc tests and soil evaluations

What a perc test is

Tennessee's rule defines it as a way to judge whether land can take sewage by timing how fast undisturbed soil in standard test holes absorbs water.

The result is a percolation rate, reported in minutes per inch: how many minutes it takes the water level in the hole to drop one inch.

Sources: Tennessee Rule 0400-48-01, Regulations to Govern Subsurface Sewage Disposal Systems (April 2014, revised; current file on the TN Secretary of State site); Missouri 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal Systems (Code of State Regulations, 9/30/20)

Perc test versus soil evaluation

A perc test measures one thing: how fast water drains. A soil evaluation (called a soil profile description in Oklahoma and a soil morphology evaluation in Missouri) looks at the soil itself, including its texture, depth to rock and signs of a seasonal high water table.

Missouri's rule says soil permeability and soil percolation are different soil features with no direct correlation.

The Arkansas Department of Health says a perc test is only a rough estimate, and it uses soil pits to find the depth to rock, impervious layers and the wet-season groundwater level.

Oklahoma State University Extension explains that both very fine (clay) and very coarse (sandy or rocky) soils are poor at treating septic wastewater, which is why soil texture matters as much as drain speed.

In Oklahoma, a perc test may only be used to site a conventional subsurface absorption field. Other system types must be designed from a soil profile description.

Sources: Missouri 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal Systems (Code of State Regulations, 9/30/20); Arkansas Department of Health, Onsite Wastewater FAQs (no date shown); Oklahoma State University Extension, PSS-2271 Soil-based Septic System Decisions in Oklahoma (Abit, print code 0913); Oklahoma DEQ, OAC 252:641 Individual and Small Public On-site Sewage Treatment Systems (amendments effective 9-15-24)

How a perc test is done

The tester digs several holes across the proposed drain field, down to the depth the trenches will be. The sides and bottom of each hole are scratched to remove smeared soil, and loose soil is taken out.

The holes are soaked first so the soil swells the way it would in a wet season. In Arkansas, Missouri and Tennessee the holes are kept filled with at least 12 inches of water for at least 4 hours, and Arkansas and Tennessee prefer overnight.

After the soak, the water is set to a fixed depth and the drop is timed. The rate is the time divided by the inches the water fell.

Each state spells out the hole count and timing, summarized in the table below.

Sources: Arkansas State Board of Health, Rules Pertaining to Onsite Wastewater Systems (effective Sep 5, 2024); Oklahoma DEQ, OAC 252:641 Individual and Small Public On-site Sewage Treatment Systems (amendments effective 9-15-24); Missouri 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal Systems (Code of State Regulations, 9/30/20); Tennessee Rule 0400-48-01, Regulations to Govern Subsurface Sewage Disposal Systems (April 2014, revised; current file on the TN Secretary of State site)

Who may do a perc test in each state

Arkansas: a Designated Representative certified by the Arkansas Department of Health (registered engineers, land surveyors, licensed master plumbers, registered sanitarians or similarly qualified people). Only a Soil Qualified Designated Representative may design a standard system from seasonal water table data.

Oklahoma: soil tests may only be done by Oklahoma-registered Professional Engineers, Professional Land Surveyors, Professional Sanitarians or Professional Environmental Specialists, soil scientists, or DEQ staff. Anyone doing soil profiles must also be DEQ certified.

Missouri: an engineer, sanitarian, registered geologist, soil scientist, or a person trained and certified by the Department of Health and Senior Services. A soil morphology evaluation is done by a soil scientist unless an engineer, geologist or sanitarian has special training.

Tennessee: an engineer or surveyor licensed in Tennessee. An approved soil consultant or a registered professional environmentalist may also do perc tests if not employed by a state, regional, district, county or municipal environment department. A perc test may only follow a soil evaluation by an approved soil consultant.

Sources: Arkansas State Board of Health, Rules Pertaining to Onsite Wastewater Systems (effective Sep 5, 2024); Oklahoma DEQ, OAC 252:641 Individual and Small Public On-site Sewage Treatment Systems (amendments effective 9-15-24); Missouri 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal Systems (Code of State Regulations, 9/30/20); Tennessee Rule 0400-48-01, Regulations to Govern Subsurface Sewage Disposal Systems (April 2014, revised; current file on the TN Secretary of State site)

What a failed perc test means

Failing means the soil drains too slowly (or, in some cases, too fast) for a standard gravity drain field. It does not always mean the lot cannot have a septic system.

Arkansas: soil slower than 75 minutes per inch is unsuitable for a standard system.

Oklahoma: any hole slower than 75 minutes per inch cannot be used for a conventional absorption field. Appendix A of the rule still lists a lagoon as allowed at any perc rate, and a spray irrigation field after an aerobic unit as allowed if sized with Group 5 soil criteria.

Missouri: slower than 60 minutes per inch, the design must be drawn up and signed by a registered engineer unless a soil evaluation sizes the system. Slower than 120 minutes per inch, systems are not permitted except lagoons or systems designed under the rule's advanced-system sections.

Tennessee: absorption rates slower than 75 minutes per inch are unsuitable for a conventional system, and the rule says perc results alone are not conclusive about a site.

Common alternatives, per the EPA, include aerobic treatment units for small lots or poor soils, mound systems for shallow soil, high groundwater or shallow bedrock, and sand filters for high water tables.

Sources: Arkansas State Board of Health, Rules Pertaining to Onsite Wastewater Systems (effective Sep 5, 2024); Oklahoma DEQ, OAC 252:641 Individual and Small Public On-site Sewage Treatment Systems (amendments effective 9-15-24); Missouri 19 CSR 20-3.060 Minimum Construction Standards for On-Site Sewage Disposal Systems (Code of State Regulations, 9/30/20); Tennessee Rule 0400-48-01, Regulations to Govern Subsurface Sewage Disposal Systems (April 2014, revised; current file on the TN Secretary of State site); US EPA, Types of Septic Systems (last updated May 4, 2026)

What a perc test costs [EST]

[EST] HomeAdvisor (page updated Jun 19, 2026) puts a professional perc test at $750 to $1,900, with an average of $1,300. A basic single-hole test can be as little as $300, and larger or complex tests can reach $3,000 or more.

[EST] HomeAdvisor adds $370 to $770 for a land survey if the property lines need mapping first.

[EST] This Old House (page modified 03/12/2026) gives $700 to $2,000 for a perc test. It notes its cost data comes from Angi estimates, and Angi owns HomeAdvisor, so these two figures are not independent.

These are national figures. Prices in Arkansas, Oklahoma, Missouri and Tennessee can differ.

Sources: HomeAdvisor, How Much Does a Perc Test Cost? (updated Jun 19, 2026); This Old House, How Much Does a Septic Tank Installation Cost? (modified 03/12/2026)