Last updated and sources checked: September 19, 2026.
A soil-profile evaluation describes the soil layers and conditions that influence treatment and dispersal. A perc test measures how quickly water enters prepared, wetted soil under test conditions. They answer related questions, but they are not interchangeable. Ask the authority responsible for your parcel which evidence and evaluator qualifications it accepts before ordering either service.
This guide helps you read the resulting information. The complete Kansas City septic guide explains how it fits into the broader project.
What does each investigation establish?
| Evidence | Useful question it helps answer | What it does not establish alone |
|---|---|---|
| Online soil survey | Which mapped limitations deserve investigation? | The conditions at the exact proposed field |
| Soil-profile evaluation | What layers, structure and limiting conditions occur where examined? | Final acceptance of every possible layout |
| Perc test | How did water infiltrate under the specified test conditions? | All limiting conditions deeper in the soil profile |
| Approved design and permit | What installation has been accepted under a particular submission? | That a later house or field relocation is covered |
KDHE explains that soil properties can change over short distances, so survey maps cannot replace site-specific assessment. Its guidance also identifies two perc-test limitations: the test does not reveal all profile restrictions, and dry cracks in certain clay soils can distort results. This is why a “fast perc” should prompt interpretation rather than automatic celebration. KDHE WMS 18-04-1, soil surveys and measuring absorption.
What should you look for in a soil report?
Look first for locations, observations and conclusions. A report that cannot be connected to your parcel plan is difficult to use when the layout changes. Ask the evaluator to explain the relationship between each observed limitation and the options referred for design or authority review.
The vocabulary matters. Texture describes the proportions of sand, silt and clay; structure concerns how particles group together. Two descriptions containing the word “clay” can therefore have different implications. Depth to a restrictive layer or water condition is a separate issue from texture. Missouri DHSS explains these distinctions in its soil-component guidance. DHSS soil characteristics.
Use this original report-review checklist:
- Location: Can the evaluation points be located on the same plan used by the designer?
- Coverage: Were both the proposed field and any required replacement area considered?
- Observations: Are layer descriptions, limiting conditions and relevant site characteristics recorded?
- Interpretation: Does the report distinguish measured or observed conditions from recommendations?
- Project basis: Does it identify the proposed use or design information supplied to the evaluator?
- Next decision: Who determines the acceptable system options, and what further work is required?
- Changes: What would require further evaluation if the proposed layout moves?
The NRCS field book is a professional reference for consistent site and soil descriptions. It can help explain report terminology; it is not a homeowner installation manual. NRCS field-description reference, version 4.0.
An example: reading findings without jumping to a design
Consider an imaginary report-reading exercise, not a real property or an approved soil evaluation. The purpose is to separate an observation, an interpretation and the decision that still belongs to the evaluator, designer or authority. No depths, loading rates or system dimensions are supplied because those would need actual field evidence and the governing criteria.
| Example wording in the project file | What you can reasonably take from it | What to ask next |
|---|---|---|
| “Evaluation locations are shown on the attached sketch.” | The findings relate to identifiable places. | Does the proposed dispersal area stay within the area evaluated, or has the layout moved? |
| “A limiting condition was observed.” | The report identifies a condition that may constrain the design. | What was observed, where was it recorded, and which accepted criterion does the designer apply to it? |
| “Additional evaluation is recommended.” | The evidence file is incomplete for the stated next step. | Who performs the additional work, what question will it resolve, and who accepts the result? |
| “A system option is proposed for review.” | Someone has developed a proposal. | Has the responsible office accepted it, or are review comments still outstanding? |
Notice what the exercise does not establish: a passing parcel, a failed parcel, a required technology or a construction price. Those conclusions require more than recognizing a phrase. Keep the report, its location drawing and the proposed site plan together, so a change in the house or field location does not silently separate the design from its evidence.
A useful handoff note might read: “The evaluator documented the west area; the current house plan moves the proposed field east; please confirm whether the existing evaluation covers that revision.” That question is much more actionable than “Do we have good soil?” It identifies the decision and the specific gap without pretending to interpret a professional’s field measurements.
How does the local process affect what you order?
In Johnson County, Kansas, the published residential process calls for a county soil-profile analysis before design and construction, and the applicant receives a letter identifying options for the lot. Use that program’s current instructions if it governs your property. Do not substitute a privately ordered test without confirming acceptance. Johnson County residential systems.
Missouri’s state construction-application instructions identify both perc-test and soil-morphology routes, with qualification and report requirements. Local applicability still matters. A statewide form does not prove that every local program will accept the same submission for every system. Missouri instructions, soil information.
The county requirements hub is the starting point for that call. Describe your parcel and project, then ask what to order, from whom, and how the findings enter permit review.
How can you use Web Soil Survey responsibly?
Save a map of the area of interest, its date and the relevant interpretation with your planning records. Use mapped differences to ask whether alternative field locations deserve investigation. NRCS describes Web Soil Survey as a source for planning data and notes that some engineering applications require onsite investigation. USDA Web Soil Survey.
A useful map note reads, “Mapped limitation to ask the evaluator about.” An unsupported note reads, “Approved for septic.” Keep the first distinction intact when sharing records with a builder, seller or lender.
What should you do if the first location is unsuitable?
Ask what specific limitation was found, whether another location merits evaluation and which complete system arrangements the authority will consider. Do not assume that a larger tank, more expensive treatment unit or imported soil automatically cures the limitation. The next decision is a scoped feasibility review, not buying equipment.
For a new house, use new-home septic planning before freezing the layout. For a purchase, use the land-purchase checklist to separate an initial investigation from a documented feasibility decision. Keep your questions and report references together in the project planner.