In this guide
There are two completely different things called a soil test and confusing them costs people real money.
One is an agronomic test. You mail a bag of dirt to a lab, and a few weeks later you get back pH, phosphorus, potassium and some other numbers that tell you what to add before you plant. It costs between three and forty dollars depending on the state and it is genuinely useful once you own the place.
The other is a soil and site evaluation for an on-site wastewater system. Somebody licensed digs a pit or a set of borings on your parcel, reads the soil profile in place, and writes down whether and how a septic system can be built there. It costs hundreds of dollars, it has to be done on site, and in most of the country it is the single approval that decides whether you can ever legally live on the land.
Those are not the same test. They do not answer the same question, they are not performed by the same people, and a lab report full of nutrient numbers tells you exactly nothing about whether your county will issue a septic permit. This article covers the second one first, because that is the one with a yes or no attached to it.
The test that decides whether you can build
Every one of the ten states we sell in requires some form of soil and site evaluation before an on-site wastewater permit will issue. What differs is the method, and the method has been shifting for forty years.
The classic percolation test measures how fast water drops in a pre-soaked hole, in minutes per inch. It is simple and it is also, in EPA's own words, a test with proven shortcomings. Its central weakness is that it cannot see time. A hole dug in August on a parcel that sits under water in February will produce a perfectly respectable number.
A soil profile evaluation reads the dirt instead. A trained person opens a pit or a set of borings and describes what is there: texture, structure, depth to bedrock or to a clay layer, and the gray and orange mottling called redoximorphic features, which is the permanent record a seasonally high water table leaves behind in soil colour. That record is there in August. It is why the calendar matters less than it used to.
| State | What the rule runs on | Where it is written |
|---|---|---|
| Texas | Soil texture classes from two borings or two backhoe pits | 30 TAC Chapter 285 |
| North Carolina | Soil morphology, no perc test in the rule | 15A NCAC 18E |
| Florida | Soil profile plus wet-season water table estimate | Chapter 62-6 F.A.C. |
| Arizona | Soil characterization required on constrained sites, perc otherwise | A.A.C. R18-9-A310 |
| Minnesota | At least three soil observations, texture-based loading rate | Minn. R. 7080.1720 |
| Colorado | Visual and tactile profile in a test pit, perc paired with a pit | Regulation 43, 5 CCR 1002-43 |
| Arkansas | Soil morphology with seasonal water table interpretation | ADH Onsite Wastewater Rules |
| New Mexico | Either a perc rate or a visual soil profile | 20.7.3 NMAC |
| Nevada | Owner perc test in rule, soil evaluation in current guidance | NAC 444 and NDEP WTS-25 |
| Oregon | Test pits described by the agent, roughly 75 feet apart | OAR 340-071-0150 |
Two of those rows deserve a note because a lot of published guidance is out of date on them. Florida's onsite sewage program moved from the Department of Health to the Department of Environmental Protection on 1 July 2021, and the governing rule is now Chapter 62-6 of the Florida Administrative Code. County health departments still run the permit counter, which is why so many pages still cite the old chapter. And North Carolina replaced its old .1900 septic rules with 15A NCAC 18E, which runs on soil morphology and does not use a percolation test at all.
Nevada is its own case and worth knowing if you are buying there. The administrative code still contains a percolation test the property owner may perform, with an engineer verifying the data. Current state guidance substitutes a soil evaluation supervised by a design engineer, soil scientist or geologist instead. Nevada is the one state in the ten where a landowner can legally run the test themselves, and it is still worth hiring out.
Who is allowed to do it
Not you, in nine of ten states. This is a licensed activity and the license differs, which is useful to know before you go looking for somebody.
Texas accepts a licensed site evaluator or a professional engineer, and a PE may evaluate without a separate site evaluator license. North Carolina uses Licensed Soil Scientists for soil characteristics and Licensed Geologists for geologic conditions, and local health department agents also evaluate. Florida's rule lists engineers with soils training, department personnel, master septic tank contractors and certified professional soil scientists. Arizona recognises registered engineers, geologists and sanitarians plus holders of a department-recognised training certificate. Arkansas uses a Designated Representative, and where the seasonal water table drives the sizing it has to be a Soil Qualified Designated Representative. Colorado requires a degree in soil science, agronomy or geology with soil morphology coursework, or completion of the state's own OWTS soil evaluation training. Minnesota runs it through MPCA certification. In Oregon the county sanitarian or a qualified private contractor does it, and you dig the pits.
The practical version: call the county health department and ask who evaluates in that county. They keep lists, and they will tell you over the phone.
What a failing result means
A soil evaluation does not usually come back as a flat no. It comes back as a more expensive yes. The conventional answer is a septic tank and a gravity trench field, and when the soil will not support that, EPA's catalogue of alternatives is the menu your designer will work from.
A chamber system replaces gravel with connected plastic chambers and is used where groundwater is high. Drip distribution puts laterals into the top six to twelve inches of soil and works in shallow soil without building a mound, at the cost of a dose tank, a pump and electricity. An aerobic treatment unit injects oxygen into the tank and is used on small lots, high water tables and inadequate soil, and it carries a service contract in most states. A mound system builds a sand mound to hold the trench where depth to bedrock or water table is short, and the imported sand is where the cost lives. A recirculating sand filter does something similar in a box. An evapotranspiration bed evaporates the effluent instead of infiltrating it, which only works in a hot dry climate and is therefore an Arizona, New Mexico and Nevada option rather than a Florida one.
Here is where we stop short of a number. We looked for a government or extension source publishing current installed costs for conventional versus engineered systems and there is not one. Every figure available comes from contractors and cost-aggregator sites, so we are not going to dress one up as research. What is defensible is the ordering: every engineered alternative costs materially more to install, permit and operate than a conventional gravity trench, and aerobic units add an ongoing service obligation. Get quotes in the county you are actually buying in.
One real published figure does exist for the evaluation itself. Oregon charges $700 for a site evaluation on a single family dwelling and $1,038 for a standard construction-installation permit, rising to $1,566 for an alternative system. Those are permit fees rather than construction costs, but they are an honest anchor and they show the premium the alternative carries even at the regulatory layer.
The free federal data to pull before you pay anybody
USDA's Natural Resources Conservation Service publishes the national soil survey through Web Soil Survey, and it is free. You draw a box over a parcel and generate a custom soil resource report as a PDF. For a land buyer it is the cheapest hour of due diligence available anywhere.
The interpretations worth pulling are under Suitabilities and Limitations for Use. Under Sanitary Facilities there is Septic Tank Absorption Fields, rated not limited, somewhat limited or very limited. Under Building Site Development there is Dwellings With Basements, Dwellings Without Basements, and Local Roads and Streets on the same scale. Then under Soil Properties and Qualities, pull depth to a restrictive feature, depth to water table, drainage class, flooding and ponding frequency, and shrink-swell potential.
A parcel that comes back Very Limited for septic tank absorption fields is not necessarily unbuildable. It means the odds of needing an engineered system went up, and that is worth knowing before you make an offer rather than after.
Now the caveat, and it is the most important sentence in this article. NRCS prints it on every report: onsite investigation is needed to supplement this information in some cases, and the map may not be valid at the scale you have zoomed to. NC State Extension says it harder in a publication written for exactly this audience, warning that the soil survey does not provide enough detail to decide land suitability for septic systems and should not be substituted for an onsite evaluation. The same publication makes the point that suitable and unsuitable soils can occur side by side on the same lot.
While you are pulling free federal data, pull two more. FEMA's Flood Map Service Center gives you the effective flood map and zone for the parcel. The US Fish and Wildlife Service's National Wetlands Inventory mapper gives you a wetland overlay. Neither is a formal determination, and the wetland mapper in particular is not the same thing as an Army Corps jurisdictional call, but both are free and both have talked people out of bad parcels.
The agronomic test, kept short and kept correct
Once you own the place and want to grow something, the agronomic test is cheap and worth doing. Where to send it depends on your state, and here is a fact the generic articles miss: four of our ten states do not run a public land-grant soil lab at all.
Arkansas tests free for Arkansas taxpayers, dropped at the county extension office. Florida's UF/IFAS lab runs $3 for pH and lime requirement and $7 to add phosphorus, potassium, calcium and magnesium. Texas A&M's routine analysis is $12. Minnesota's regular lawn and garden test is $22. North Carolina is free outside the peak season and $5 per sample during it. Colorado State runs $40 for the basic panel and $47.50 for the complete one. Arizona, Nevada, New Mexico and Oregon have no public lab and their extension services publish directories of private ones instead.
Sample it properly or do not bother. Take cores from the surface down to about six inches, keep the depth consistent between years, and build each composite from fifteen to twenty subsamples across the area. Sample the garden and the pasture separately rather than mixing them. Stay out of old manure piles, fertilizer bands and fence lines. Retest every two to three years for annual crops and pastures.
Two things the national articles get wrong for half our footprint. First, a routine test will not give you a usable nitrogen number in a warm humid climate, because nitrogen keeps changing form. UF/IFAS states outright that a reliable nitrogen soil test does not exist for Florida conditions. In the arid West the opposite is true and nitrate-nitrogen is in the routine panel, because it persists in dry soil.
Second, and this one is costly if you act on bad advice: the standard Bray phosphorus test does not work on calcareous western soils. Those soils are alkaline and contain free lime, and the Bray extractant can read effectively zero on ground that has adequate available phosphorus. The correct extractant above roughly pH 7 is Olsen. New Mexico State Extension says plainly that New Mexico soils favour the formation of a calcium-phosphate mineral plants cannot use, and that Olsen is what correlates in high-pH soils. If you read a national ideal-phosphorus table that does not name an extraction method, it is not telling you about your dirt.
Which leads to the advice most likely to waste your money out west: do not add lime. Soil pH in New Mexico normally runs between 6.5 and 8.4 and most of it is alkaline. Free lime is already the problem, tying up phosphorus and iron. The salinity package that arid-west ground actually needs, with saturated paste conductivity and a sodium adsorption ratio, is the one test that is never in the base price: $57 extra at Colorado State and $35 extra at Texas A&M.
The claim we removed
The earlier version of this article said soil testing improves what your land is worth. We went looking for evidence and could not support it for the kind of ground we sell.
What the literature actually supports is narrower. Inherent soil productivity is capitalized into cropland prices, which is why Iowa farmland trades off a soil productivity index derived from the NRCS survey that anybody can look up for free. Commissioning a lab test does not change that index. There is one extension report of a fertility premium on Iowa cropland, and it is a 2004 newsletter item about row-crop ground where fertility is a direct input to income. It does not transfer to a five-acre recreational parcel in Apache County, and we are not going to pretend it does.
The thing that demonstrably affects rural land value is septic suitability. In North Carolina, an improvement permit backed by a recorded plat is valid without expiration and conveys with the parcel, which is a documented, durable, transferable right to build. An agronomic soil report is a shopping list for amendments. Both are useful. Only one of them is an asset.
The order to do this in
The order to do this in
Pull Web Soil Survey before you make an offer.
Free, takes about an hour, and tells you whether the parcel's soils rate limited for septic absorption fields and for dwellings.
Pull the FEMA flood map and the wetlands mapper at the same time.
Also free. A parcel in a flood zone or with mapped wetlands is a different conversation, and better to have it before the offer.
Call the county health department and ask who evaluates there.
Ask for the list of approved evaluators, the current fee, and whether there are known soil problems in that subdivision. They know.
Pay for the site evaluation before you commit to a house plan.
This is the approval everything else hangs on. Find out whether you are looking at a conventional trench or an engineered alternative while you still have choices.
If a seller says the parcel has a perc test, ask for the paper.
Ask who performed it, when, and whether a permit issued off it. What expires is the permit, and the rules differ by state.
Do the agronomic test after closing, not before.
It costs between nothing and $47.50 depending on your state, and it answers a question that only matters once the land is yours.
Where we fit
We hand every buyer the parcel number and the county, which is everything you need to pull the soil survey and make the health department call yourself. We would far rather you run that check during due diligence than discover a mound system after closing.
What we do not do is represent that a parcel will pass a site evaluation. We have not run one, and anybody in this business who tells you a raw parcel is build-ready without an evaluation in hand is guessing on your money. If you are working through the rest of the diligence, the companion pieces are the guide to living off the grid and what to know about water catchment systems.
If you are shopping for ground you intend to build on, our homestead land listings are the right place to start, and the soil survey is free before you spend a dollar.
The honest summary is that one of these tests tells you whether you can live there and the other tells you what to put on the garden. They cost about the same order of money as each other and they are not interchangeable.
Pull the free soil survey first, make the health department call second, and pay for the evaluation before you pay for anything else. The dirt has already decided. You are just finding out what it decided.
