What Is a Perc Test? How Septic Soil Testing Actually Works

The literal procedures defined by Arkansas, Delaware, and Missouri measure how quickly water moves into saturated soil where a septic system's absorption area may be placed. They express the result in minutes per inch: the elapsed time for the water level in a prepared hole to fall one inch. The result is one part of a state-specific septic design or suitability decision.

There is no single national perc test. Across the 13 states researched for this site, the same search phrase can refer to a timed water test, a soil-profile examination, or a broader site evaluation.

How the 13 states treat the perc test

State	Current method	Evaluator or decision-maker
Arkansas	A literal percolation test remains available alongside a seasonal-water-table route.	A Designated Representative performs percolation testing. Only a Soil Qualified Designated Representative may design from seasonal-water-table data, and the Authorized Agent has final approval.
Missouri	Either a percolation test or soil morphology may be used.	A registered Percolation Tester or On-Site Soil Evaluator performs the applicable work. The administrative authority decides which method applies.
Tennessee	A literal percolation-test route remains available, and a soil evaluation may determine whether an area is eligible for it.	The test must be run by one of the professionals listed in the rule and statute. A TDEC Environmental Scientist may evaluate a typical individual lot, while an Approved Soil Consultant is required when a soil map is required.
Delaware	The Class D soil scientist may assign a rate from the state's soil framework or require hydraulic-conductivity or literal percolation testing.	The Class D Soil Scientist/Site Evaluator prepares the full evaluation. A Class A Percolation Tester has the narrower testing-only credential, and DNREC reviews the submission.
Alabama	Alabama recognizes four site-evaluation methods: percolation testing, detailed soil mapping, soil morphology, and the unified method. Procedure subsection numbers were recently recodified, so confirm current citations with ADPH.	Credentials depend on the method and include specified engineers, surveyors, geologists, Professional Soil Classifiers, and the current Public Health Environmental Site Specialist role. The county health department administers the permit.
Virginia	Soil morphology is primary. A district or local health department may require a percolation test to verify a questioned estimated rate.	Nearly all applicants use a private licensed onsite soil evaluator or professional engineer. The health department controls the verification decision.
Georgia	The rule defines a percolation test, while the dossier's current-practice evidence says septic submissions center on a Level III soil report rather than a standalone timed test.	A Department-certified Soil Classifier prepares the soil evaluation submitted to the county board of health.
Indiana	No current timed percolation procedure appears in the residential rule.	An Indiana-registered professional soil scientist conducts and signs the evaluation. The local health department administers the permit.
Vermont	No current timed percolation procedure appears in the rule. The method uses excavated test pits and soil morphology.	A Class A, B, BW, or Class 1 designer works within the applicable scope. DEC or a delegated municipality handles the permit.
Rhode Island	No current timed percolation procedure appears in the rule. The process is a soil evaluation.	A Class IV Soil Evaluator performs the soil-evaluation work, with RIDEM as the statewide permitting authority.
Maine	No current timed percolation procedure appears in the rule. The process uses observation holes and soil-profile descriptions.	A Maine Licensed Site Evaluator handles a typical non-engineered system, and the Local Plumbing Inspector handles the municipal permit path.
North Carolina	No current timed percolation procedure appears in the current soil-and-site-evaluation rules.	The evaluator may be county environmental health staff, a Licensed Soil Scientist, or an Authorized On-Site Wastewater Evaluator, depending on the permit route.
South Carolina	No current timed percolation procedure appears in Regulation 61-56. The state uses a site evaluation.	Certified SCDES staff or a qualifying licensed private professional performs the evaluation, subject to SCDES review.

What happens during a literal perc test

The Arkansas, Delaware, and Missouri procedures are three illustrative examples, not the full list of states that retain a timed test. Each prepares test holes, wets the soil, establishes a water level, and times the drop, but their exact instructions are not interchangeable.

Arkansas's 2024 rule requires at least three holes across the primary absorption area and one in the secondary area. Its standard holes are 18 inches deep and 12 inches across, with 2 inches of coarse sand or fine gravel protecting the bottom. Maintain clear water 12 inches above the gravel, preferably overnight but for no less than four hours. After saturation, set the water at 6 inches above the gravel and measure the fall over 30 minutes. For the fast-soil procedure, after at least 24 hours of saturation, if the first six inches drain in under 30 minutes, take readings at 10-minute intervals for one hour and use the final 10-minute drop.

Missouri requires at least four holes, each 6 to 8 inches across and dug to the proposed bottom of the absorption system. Its rule calls for at least four hours of presoaking and ordinarily a 24-hour swelling period before repeated readings. Sandy soil has a specific exception when one filling drains in under 10 minutes.

Delaware requires at least three 6-inch holes when a Class D soil scientist calls for a measured test. After a minimum four-hour presoak, the procedure includes stabilization cycles and timed readings that continue until successive drops meet the rule's consistency requirement. Delaware then averages the holes.

Because these procedures differ, a hole count, soak period, or reading method from one state should not be carried into another state's permit application.

What does the result measure, and why does a septic design need it?

Virginia defines its retained procedure as measuring clean-water movement under saturated conditions. Arkansas separately requires testing at the proposed absorption-system depth. The conclusion that this is different from surface infiltration is an editorial inference from those separate rules: the measured result is not a general rating of how quickly rain disappears from the ground surface.

The number matters differently in each rule. In Arkansas, percolation data can size the absorption area, but the area cannot be smaller than seasonal-water-table data would require for the same site. Arkansas also says a rate slower than 75 minutes per inch is unsuitable for a standard system. Delaware treats a rate slower than 120 minutes per inch as unacceptable for the affected part of the site and does not allow a design rate faster than 20 minutes per inch without Department approval. Missouri permits a percolation-only evaluation for standard systems only in appropriate areas, with acceptable rates from 10 through 60 minutes per inch. Missouri also says the permitting authority chooses which evaluation method applies.

The Arkansas, Delaware, and Missouri rules show why “pass” and “fail” can be misleading. The same measured rate can sit inside one state's stated range and outside another's. In those states, a result may also lead to a different system design rather than a simple yes or no.

States that do not use timed percolation tests

Indiana's current residential rule does not contain the word “percolation.” Before a permit is issued, an Indiana-registered professional soil scientist performs an on-site evaluation and describes the soil profile, ordinarily to five feet or until an impenetrable layer is reached. The report covers soil horizons, seasonal high groundwater, bedrock, slope, and other site characteristics.

Vermont's current rule also contains no percolation procedure. A licensed designer evaluates excavated test pits using USDA soil-description methods. The rule requires at least two excavations for certain smaller in-ground and at-grade leachfields, and at least three for a mound or bottomless sand filter.

Rhode Island calls its process a soil evaluation. Its rule requires at least two test holes within 25 feet of the proposed leachfield and at least 25 feet apart, with one on the up-gradient side and one on the down-gradient side. The holes are used to examine the soil profile, restrictive layers, bedrock, and seasonal high groundwater. Maine uses a site evaluation by a Licensed Site Evaluator, with test pits called observation holes. Maine's rule records soil texture, color, consistency, limiting conditions, and slope, but prescribes no timed infiltration procedure.

Delaware sits between the two models. Its Class D soil scientist may assign a rate from the state's soil-texture framework or require a hydraulic conductivity or literal percolation test. Arkansas and Missouri expressly retain two routes: a timed percolation test or a soil-based seasonal-water-table or morphology evaluation, with credential and approval limits attached to the choice.

North Carolina and South Carolina also use soil or site evaluations rather than a timed water-drop procedure. Georgia's rule still defines a percolation test, but the Georgia dossier found that current septic submissions center on the Level III soil report prepared by a certified Soil Classifier. Virginia uses soil morphology as its primary evaluation and keeps a literal test as a secondary tool a health department may require when it questions the estimated rate.

What should you ask for in your state?

Start with the permitting authority, not the test name. Ask what evaluation and report are required for the parcel, who may sign them, whether the authority must witness or approve fieldwork, and whether a designer needs to be involved before testing begins.

Required credentials differ by state and by method. Use the state-specific roles in the table above, then confirm the required credential and permit path with the reviewing authority before hiring an evaluator.

What happens after the field evaluation?

The four examples below show how an evaluation feeds a state-specific design and permit chain. In Delaware, the Class D scientist submits the site evaluation to DNREC, then a Class B or C designer handles design and permitting for the applicable system. In Maine, the Licensed Site Evaluator puts the soil findings and design on the HHE-200 application. For a typical system in an organized municipality, that application goes to the municipal Local Plumbing Inspector. In Indiana, the local health department administers the permit. In Arkansas, the Designated Representative's testing, design, and inspection remain subject to the Department's Authorized Agent, followed by construction approval, final inspection, and a permit for operation. In each of these four examples, a favorable field result is not the same document as permission to install.

FAQ

How long does a perc test take?

There is no supported national duration in the 13 dossiers. Missouri ordinarily adds a 24-hour swelling period after at least four hours of presoaking. Arkansas's standard procedure allows a minimum four-hour saturation period and prefers overnight saturation, while its fast-soil procedure requires at least 24 hours of saturation before the under-30-minute trigger is assessed. Delaware's measured-test procedure includes at least four hours of presoaking and ordinarily at least four hours of readings, or as little as one hour in fast-draining soil. Indiana, Vermont, Rhode Island, and Maine use different soil-evaluation field and review steps instead.

Can a property fail a perc test?

Arkansas and Delaware show how a rule can reject a tested area or a standard-system design. Arkansas calls soil slower than 75 minutes per inch unsuitable for a standard system. Delaware rejects the affected area when the rate is slower than 120 minutes per inch. Those are state-specific thresholds, not national cutoffs.

Can I perform the test myself?

The covered rules assign the work to named professionals or agency staff. Arkansas requires a Designated Representative, Missouri a registered tester or evaluator, Delaware licensed Class A or Class D professionals depending on scope, and Indiana an Indiana-registered professional soil scientist. Confirm the required credential with the authority that will review the application before hiring anyone or digging holes.

Does a good perc rate guarantee a septic permit?

No such guarantee appears in the cited state processes. Tennessee's rule says percolation results are not conclusive evidence of suitability. Arkansas keeps final approval with the Authorized Agent. Delaware separately reviews the site evaluation and the later design and permit application.

Is there a reliable national average price?

The 13 dossiers do not support one. Available cost evidence differs by state and may cover different services. Use the state guide and request an itemized local quote.

Where do I find the process for my property?

Use the state guide for Virginia, North Carolina, Georgia, Missouri, Maine, Tennessee, Alabama, South Carolina, Delaware, Indiana, Rhode Island, Vermont, or Arkansas. Each guide follows that state's terminology, credentials, and permit path.