Perc Test: Cost, Rules and What to Do Before Buying Land

A perc test (percolation test) measures how fast water drains into a lot's soil, in minutes per inch. County or state health agencies use it, or a soil evaluation that has replaced it, to decide whether land without sewer service can have a septic system. For a land buyer, that approval often decides whether the lot can be built on.

The EPA says it "does not regulate single family home septic systems." States, tribes and local governments do, so the rule that matters is the one for the county where the land sits. EPA's 2002 onsite wastewater manual (page 5-9) says "Many states no longer accept the percolation test as the primary suitability criterion." People still say "perc test" for whatever soil evaluation the local office uses, and so does this guide.

Pillar, a land research platform, wrote this guide. Rules, fees and prices come from the agency pages and cost guides linked below, checked November 10, 2026. Confirm them with the permitting office. Nothing here is legal or engineering advice.

How does a perc test work?

The classic method is the falling head test in Table 3-8 of EPA's 1980 onsite wastewater design manual:

1. Dig. Commonly at least three holes, 6 inches wide, spaced across the planned drainfield at the planned system depth.
2. Prepare. Scratch the sides and add 2 inches of gravel.
3. Soak. Keep at least 12 inches of clear water in each hole for at least 4 hours, preferably overnight in clay.
4. Measure. Except in sandy soil, start 15 to 30 hours after soaking began. Set the water 6 inches above the gravel, read the drop every 30 minutes and refill to the 6-inch level after each reading. Take at least three readings, and keep going until two drops in a row differ by no more than 1/16 inch. In sandy soil, or where the first 6 inches drains in under 30 minutes, EPA has readings every 10 minutes for one hour.
5. Calculate. Divide the time by the last drop. EPA's example: a 5/8 inch drop in 30 minutes is 48 minutes per inch.

That is EPA's 1980 procedure. An official test follows the permitting authority's method, and states that still use the test set their own hole count and pass range. Pennsylvania requires "six or more tests" and lists 6 to 90 minutes per inch for conventional absorption areas. Maryland generally requires a rate of at least 1 inch per 30 minutes after prewetting, with an exception for systems approved under COMAR 26.04.02.05V, and west of the fall line a rate faster than 2 minutes per inch "may not be approved." Soil can fail by draining too slowly or too fast.

Many states now use a soil evaluation instead, in which an evaluator digs pits or borings and describes the soil. EPA's 2002 manual (page 4-12) says the soil's structure, texture and consistence "are better predictors of the soil's hydraulic capacity than percolation tests." South Carolina hasn't used perc tests "since the late 1970's because they are not very accurate," and notes that a site can pass in dry weather and fail in a wet period.

Who does the perc test in your state?

Eight states, each read from its own rule or agency page. The county office has the final say on your lot.

• North Carolina: soil evaluation by the local health department, or by a professional engineer, licensed soil scientist or licensed geologist under the state's private permit options (G.S. 130A-336).
• Virginia: soil evaluation first. The rule says "When the estimated percolation rates are in question, percolation tests may be performed," with a minimum of three holes.
• Georgia: soil evaluation. The state manual (Section C, updated March 2026) assigns it to a certified soil classifier, registered engineer or registered geologist when a Level 3 soil survey is required, or to a qualified environmental health specialist with County Board of Health approval.
• Texas: soil evaluation. EPA's 2002 manual (page 2-23) records that "In 1996 Texas eliminated percolation test requirements for onsite systems." TCEQ tells applicants to arrange a site evaluation by a licensed site evaluator or professional engineer and says it "is not often the OSSF permitting authority," so start with the local one.
• Florida: site evaluation that "assesses soil, topography and other conditions," per Florida DEP's permitting FAQ (modified September 24, 2026). DEP permits in 17 counties and county health departments in the other 50.
• Pennsylvania: timed perc test after a soil profile pit. The local sewage enforcement officer issues the permit and must conduct, observe or confirm the tests. A limiting zone within 20 inches of the surface means no perc test and a denied permit, with one exception in the rule.
• Maryland: timed perc test with a site evaluation, "conducted under the supervision of the Approving Authority." In Calvert County, a health department specialist runs the test while a licensed septic installer digs.
• South Carolina: soil evaluation by an SCDES inspector. Above the Fall Line, the applicant arranges backhoe pits.

For other states, search the health or environmental agency's site for "onsite wastewater" or "onsite sewage," then call the county office.

How much does a perc test cost?

National figures come from contractor marketplaces and cost sites, so treat them as estimates and not as a local quote:

• Angi (updated September 15, 2026) puts the national average "around $1,300," with most homeowners paying between $750 and $1,900.
• HomeGuide says most test holes cost $100 to $500 each, and lists $400 to $3,000 for a 1-acre lot with 4 to 7 holes.

What the agency charges is a separate number, and it may not include the digging:

• South Carolina's SCDES lists "Application Fee: $150" for a single-home septic permit, with the site and soil evaluation done by its inspector.
• Virginia's Three Rivers Health District charges $320 for a certification letter filed with a private evaluator's documentation and $350 without, for systems up to 1,000 gallons per day. Its fee table doesn't include what the private evaluator charges.
• Calvert County, Maryland says the septic installer who digs the test holes charges their own excavation fee.

Before you budget, ask the county office for its fee, who supplies the excavator and what a retest costs.

How long is a perc test good for?

It depends on the state and on which document you hold. Cost sites often give one range; HomeGuide says "2 to 5 years, depending on the local regulations." The agency sources we checked run from 18 months to no expiration:

• North Carolina: an improvement permit issued with a plat is valid without expiration; one issued with a site plan is valid for five years (G.S. 130A-336). A change of ownership doesn't affect it if the site and the facility it serves are unchanged and stay under the facility owner's control.
• Virginia: a septic permit is valid for 18 months, and state law allows another 18 months if a building permit has been obtained or building has started. If construction hasn't begun after 18 months, the health department revalidates the permit when it was issued under the state rules and the site conditions haven't changed. Certification letters "do not expire and shall convey with the land," but they don't have to name the system type. The Three Rivers Health District says its construction permits "do not transfer with a change of property ownership," so ask the local health department how a seller's documents apply to you.
• South Carolina: "Permits to Construct are good for five years."
• Pennsylvania: a permit expires if construction hasn't begun within 3 years. It can transfer to a new owner with the local agency's written approval.
• Calvert County, Maryland: "Percolation testing is valid for 2-years and can be renewed every 2-years," and renewals "may be denied."

If a seller says the lot "already perced," ask for the document. Check its date, whether it transfers to you, and the system type and bedroom count it covers.

What happens if land fails a perc test?

A failed perc test means the measured drainage didn't meet the local criteria. It doesn't by itself decide whether the whole lot is buildable. Another spot or an alternative system may work, but the permitting authority has to evaluate and approve it:

• Test another spot. NC State Extension notes that "unsuitable soils and suitable soils can occur side by side on the same lot."
• Use an alternative system. EPA's guide to septic system types calls a mound system "an option in areas of shallow soil depth, high groundwater, or shallow bedrock." State rules decide what you can use. Pennsylvania's rate table lists elevated sand mounds from 3 to 180 minutes per inch, and North Carolina's rule .0509 lets an unsuitable site be reclassified with site modifications, an interceptor drain or advanced pretreatment.
• Connect to sewer. If a public sewer can serve the lot, the septic question gives way to capacity and connection questions. Get the answer in writing; our will-serve letter guide covers what to ask.
• Reprice or walk away. Some sites stay unsuitable. North Carolina's rule says an improvement permit "shall not be issued for a site which is classified unsuitable," and Maryland doesn't allow systems in flood plain soils or on slopes over 25 percent.

Don't count on a retest in dry weather. Some guides suggest testing in summer, when the water table is lower. USDA's soil survey says the opposite: perc tests "should be performed during the season when the water table is highest and the soil is at minimum absorptive capacity." Maryland's rule sets testing "at the time of the year when the highest water table is present" in areas with seasonally high water tables.

Do you need a perc test before buying land?

If the lot has no sewer service and you plan to build, yes. Get the septic approval before closing, or keep the right to cancel if it doesn't come. South Carolina's regulator says that without its septic permit "you cannot obtain a county building permit."

The usual tool is a contingency in the purchase contract. These points are general, and a local real estate attorney should write the actual terms:

• Tie it to an approval. NC State Extension suggests making the purchase "conditional upon the issuance of a permit for a specific type of septic system." A test result alone is weaker: Calvert County warns that "a passing percolation test alone does not mean that the property is buildable."
• Name the house. State the bedroom count you need. The same extension guide says to "ask whether the approval affects the number of bedrooms that can be built in the home."
• Match the deadline to the testing calendar. Calvert County usually tests new construction lots during its wet season, which "typically runs anywhere from March to May." Prince George's County, Maryland posted on April 15, 2026 that wet season testing would close on April 17 because of drought conditions and observation well readings. Where testing follows the wet season, a due diligence period signed in summer can end before the county will test. Ask the office how long the field evaluation takes and when it expects to issue a decision, and set the deadline after both.
• Say who pays and who gets access. Either side can pay. List the application fee, the excavator, any private evaluator and a retest, and give the evaluator the right to enter and dig before closing.
• Decide what a failure does. Write down whether you can cancel and recover the deposit, or reopen the price if only a costlier system is approved.

How can you check a lot's soil for free before a perc test?

USDA's Web Soil Survey publishes a free rating called "Septic Tank Absorption Fields." Use it to decide which lots deserve a paid evaluation first. The steps follow NRCS's help page and Soil Data Explorer guide:

1. On the Area of Interest tab, draw a box around the lot.
2. Open the Soil Data Explorer tab, then "Suitabilities and Limitations for Use."
3. Open "Sanitary Facilities" and choose "Septic Tank Absorption Fields."
4. Display the rating as a map and a table, and read the reasons listed for each soil.
5. Use the Shopping Cart tab to save a report.

NRCS's description of the rating says it considers only the soil between 24 and 60 inches deep and weighs water movement, depth to a water table, ponding, depth to bedrock or a cemented pan, and flooding. "Somewhat limited" soils have limitations that "can be overcome or minimized by special planning, design, or installation." "Very limited" soils have limitations that "generally cannot be overcome without major soil reclamation, special design, or expensive installation procedures."

A real record: on November 10, 2026 we pulled the rating from USDA Soil Data Access for two Wake County, North Carolina map units, CrB and CrD, the same units used in our soil survey guide. All four component records came back "Very limited," each listing "Depth to saturated zone" and "Slow water movement" at 1.00, the highest score. The steeper CrD added "Slope" at 0.633. The 14-row CSV and retrieval notes preserve the values. A buyer of a lot mapped in these units has a reason to ask about a seasonal water table and slow-draining soil before paying for field work.

Know its limits:

• It's a screen. NRCS says "onsite evaluation is required before the final site is selected." Soil survey maps were made at scales of 1:12,000 to 1:63,360, and "Other components with different ratings may be present in each map unit."
• It rates a conventional field. It doesn't say whether a mound could work or what the health department will approve. NC State Extension says a soil survey "does not provide enough detail to make a decision on land suitability for septic systems." Keep the contingency whatever the map says.

What changes when you buy several lots?

• Results are lot by lot. NC State Extension's advice: "If you are comparing a number of lots, apply for a permit for each lot."
• Septic rules set lot sizes. Texas's rule, 30 TAC 285.4, covers subdivisions of single family homes platted or created after the rule took effect that use individual septic systems. Their lots must be at least 1/2 acre with a public water supply and at least one acre without. TCEQ's 2017 rules compilation gives the same figures. The rule treats older, smaller lots separately, so confirm the current rule and any local requirements with the permitting authority. In Maryland, a lot recorded and approved on or after November 18, 1985 needs a sewage disposal area that fits "an initial and two replacement on-site sewage disposal systems" and is at least 10,000 square feet per dwelling.
• Soil work comes before subdivision approval. Georgia's manual recommends a preliminary soil study "prior to developmental improvements" and requires a soil map from a high intensity soil study before the county health authority approves a subdivision.

Drainfields, replacement areas and setbacks take land out of every lot, so carry the septic assumption into the yield and budget in your feasibility study.

Where Pillar fits

The Pillar team wrote this guide, and Pillar is land research software. Before paying for field work on a list of lots, you can use Pillar's map layers to view floodplain, wetlands, topography and zoning over parcel boundaries, and upload a GIS file, such as a shapefile or GeoJSON of mapped soils, to view beside them. Coverage and plan access vary by dataset. That supports the first pass in our desktop site screening checklist. Mapped soil, flood and wetland data is not a site evaluation, and only the permitting authority can approve a septic system.

Quick answers

Can you do your own perc test? You can dig a hole and time the water for your own information. For a permit, the official process applies: Pennsylvania's sewage enforcement officer must conduct, observe or confirm the tests, and Maryland's run under the approving authority's supervision.

Who pays for a perc test, the buyer or the seller? Whoever the contract says. Agree on it in writing, including excavation and any retest.