Perc Test and Soil Test for a Wisconsin Septic System

By Wisconsin Well and Septic · Published 2026-11-10 · Updated 2026-11-11

Before a new septic system can go in, the site needs a perc test, which in Wisconsin means a soil evaluation done by a state certified soil tester [1][2]. State code says a soil evaluation for a septic system must be performed by a certified soil tester, often called a CST [1]. The county reviews that report before it will issue the sanitary permit the project needs [3]. This guide covers what the tester does, when you need one, and how to check a tester's credential before you hire.

What a Wisconsin soil test involves

Many people still say "perc test," but Wisconsin's rules size a system from the soil itself. Under SPS 385, the maximum rate at which wastewater can be applied to the soil is set from each layer's texture, structure and consistence [1]. That is why the tester digs and describes the soil rather than only timing how fast water drains.

What the code requires on site:

• At least three soil excavations. A minimum of 3 soil profile evaluation excavations is used to outline the area where the system will go [1].
• At least one soil pit. For a home sending 1,000 gallons a day or less, at least one excavation per site has to be a soil pit [1]. Shawano County describes this as a backhoe pit [3].
• Hand tools for borings. Borings are made with a soil bucket auger, probe or similar sampler at least 2 inches across, and a power auger may not be used [1].
• Workable conditions. Soil color has to be judged in good light, and frozen soil must be thawed before it is evaluated [1].

For each pit or boring, the tester records the layer thickness, Munsell color, mottles or redoximorphic features, soil texture, structure, consistence, roots, boundaries and any saturated soil, groundwater or bedrock [1]. Mottles are read as signs of seasonal saturation unless the tester documents an exception [1].

The tester then writes a report on the state's format. Each page, or the title sheet of a bound report, carries the tester's signature, ID number and date [1]. The report includes a scaled site plan, elevations, slope and the soil descriptions [1].

When you need a certified soil tester

A new septic system. A septic system cannot be installed unless the owner holds a valid sanitary permit and the plans are approved [4]. Counties want the soil report first. In Shawano County, a sanitary permit may not be issued until the soil test has been reviewed and approved [3]. Public Health Madison and Dane County lists a soil evaluation by a certified soil tester as the first step toward a sanitary permit [5].

A replacement system or a new drainfield. The same permit rule applies when you replace a treatment or dispersal component, such as the drainfield or mound [4]. Waukesha County tells owners with a failed absorption field to contact a certified soil tester to find out what type of replacement the site can take [6].

Projects near the system. Check with your county before you build an addition, shed, deck or pool. Waukesha County, for example, evaluates the septic system for those projects to confirm minimum distances are kept [6].

Who uses the soil report

The soil report is not the design. In Shawano County, the licensed plumber uses the soil test to design the system and submit the sanitary permit application [3]. In Dane County, the design comes from a master plumber, a master plumber restricted, or a certified designer, who then submits the permit application [5]. When the county has everything it needs, it must decide on the sanitary permit within 30 days [4].

The county must review soil and site reports within 6 months of receiving them [1]. It can accept the report, reject it, ask for more information, or require verification [1]. For verification, the county can ask for open soil pits, and the tester who wrote the report must be on site if the county asks [1].

A Central Sands note

The Wisconsin Department of Safety and Professional Services (DSPS) suspended the hydrograph procedure in April 2024 because of erratic groundwater levels [7]. That method is used to evaluate soil and groundwater conditions for a proposed system, and the suspension covers parts of Adams, Juneau, Portage, Waushara and Wood counties [7]. In August 2025, DSPS said the suspension would continue until controls are written into SPS 385 [7]. If your lot is in those counties, ask the tester how this affects your site.

How to check a certified soil tester's credential

Soil tester certification comes from DSPS [2]. To earn it, a person must be at least 18 and pass a state exam [2]. Renewal requires at least 12 hours of continuing education [2].

To check a tester:

1. Go to LicensE at license.wi.gov and choose "License Lookup" [8].
2. Search by credential number, individual name, organization name or license type [8].
3. When you search by number, put a space on each side of the dash, as in 1234 - 123 [8].

The tester's ID number also appears on each signed page of the soil report, or on the title sheet of a bound report [1], so you can compare the two. One more rule: a soil tester who works for a county's septic program may not do private soil tests in the area that office covers or the areas next to it [2].

Perc test cost

HomeGuide's perc test guide, written January 31, 2024, lists $200 to $1,500 for hand-dug test holes and a report, and $500 to $3,000 or more when holes are dug with an excavator [9]. These are national estimates, not Wisconsin prices or quotes. HomeGuide describes the timed drainage test used in other states, while Wisconsin requires the soil pit and profile work described above [1][9], so ask each tester for a written price. See our guide to well and septic costs in Wisconsin for more ranges.

Perc test FAQ

Does Wisconsin still use a perc test?

The common name stuck, but SPS 385 sets soil application rates from the soil's texture, structure and consistence, recorded in soil pits by a certified soil tester [1]. Ask for a "soil evaluation" or "soil test" when you call [1].

How many holes does a soil test need?

Usually at least three soil excavations, and for a typical home at least one of them must be a soil pit [1]. Your county can require more where the soil varies [1].

Can a soil test be done in winter?

The code does not ban winter work, but frozen soil must be thawed before color, texture, structure and consistence are evaluated [1]. Ask the tester how they handle frozen ground.

Who applies for the sanitary permit?

The owner must hold the permit before work starts [4]. In practice, county pages say the licensed plumber designs the system from the soil test and submits the application [3][6].

How do I know the soil tester is certified?

Search the tester's name or number in the DSPS LicensE lookup at license.wi.gov [8]. The tester's ID number should be on the signed soil report [1].

Get quotes for a soil test

If you are planning a new or replacement septic system, you can send one request through our free Get quotes form to reach soil testing companies in your area. We're a referral service, not a contractor. We pass your request to independent local contractors who may contact you.

Contractors who get your request may pay us a referral fee. We don't check licenses, and a listing here is not an endorsement.

Sources

1. Wis. Admin. Code ch. SPS 385, Soil and Site Evaluations (SPS 385.10, 385.20, 385.30, 385.40, 385.50), https://docs.legis.wisconsin.gov/document/administrativecode/ch.%20SPS%20385.pdf (fetched Nov 10, 2026). CST required; 3 excavations, one soil pit at 1,000 gpd or less; no power auger; frozen soil thawed; application rates from texture, structure, consistence; report signatures and contents; 6-month county review; verification.
2. Wis. Admin. Code ch. SPS 305 (SPS 305.33, Soil testers), https://docs.legis.wisconsin.gov/document/administrativecode/ch.%20SPS%20305.pdf (fetched Nov 10, 2026). Certification required; age 18 and exam; 12 hours continuing education; county-employee limit.
3. Shawano County, Soil and Site Evaluations (CST), https://www.co.shawano.wi.us/departments/planning-and-development/private-onsite-wastewater-treatment-systems/soil-and-site-evaluations-cst/ (fetched Nov 10, 2026). Permit not issued until soil test approved; 3 excavations with a backhoe pit; plumber designs and applies.
4. Wis. Admin. Code ch. SPS 383 (SPS 383.21, Sanitary permits), https://docs.legis.wisconsin.gov/document/administrativecode/ch.%20SPS%20383.pdf (fetched Nov 10, 2026). Valid sanitary permit and plan approval before installation or replacement of treatment or dispersal components; county decides on a complete application within 30 days (383.21(2)(c)).
5. Public Health Madison and Dane County, Private Wells and Septic Systems, https://publichealthmdc.com/home-environment/private-wells-septic-systems (fetched Nov 10, 2026). Soil test by a certified soil tester; designers allowed.
6. Waukesha County, Septic Systems, https://www.waukeshacounty.gov/parks-and-land-use/environmental-health/septic-systems/ (fetched Nov 10, 2026). Failed absorption field, contact a CST; plumber submits the sanitary permit; review for additions and outbuildings.
7. Wisconsin DSPS, Private Onsite Wastewater Treatment Systems (POWTS) program page, https://dsps.wi.gov/a-z-programs-list/powts/ (notices dated 7/30/2025 and 8/22/2025; fetched Nov 10, 2026). Hydrograph procedure suspension and counties affected.
8. Wisconsin DSPS, Credentialing and LicensE FAQ, https://dsps.wi.gov/credentialing-and-license-faq/ (fetched Nov 10, 2026). LicensE lookup steps and number format.
9. HomeGuide, "How Much Does a Perc Test Cost?" by Tamatha Hazen, January 31, 2024, https://homeguide.com/costs/perc-test-cost (fetched Nov 10, 2026). $200 to $1,500 hand-dug; $500 to $3,000+ excavator.