Free septic soil test: will your land perc?

How to use the septic soil check, step by step

Enter a place, read the headline rating, then read why. The whole check takes under a minute. Here is what to do and what each part of the result means.

1. Enter your land. Type a street address ("1200 FM 1488, Magnolia, TX"), a town ("Magnolia, TX"), or coordinates ("30.21, -95.75"). Buying raw land with no address? Zoom the map to the parcel and click the spot where the house and drain field would go. In Google Maps, right-click the parcel to copy its coordinates.
2. Read the headline rating. The colored label is USDA's rating for a conventional septic drain field at that exact point: green Not limited, amber Somewhat limited, red Very limited.
3. Read the "Why" line. These are USDA's limiting factors, in order of how much they matter — for example "the water table rises close to the surface for part of the year." The reason tells you which system you will need far better than the color does.
4. Check the likely system. We turn those reasons into the septic system you will most likely be required to build, then hand it to the cost estimator. Click Price this system to see a line-by-line estimate.
5. Scan the other land-work cards. The same soil gets rated for a slab house, a basement, trenches, a driveway and a pond. Red on "basement" or "driveway" is a cost warning you want before you buy, not after.
6. Read the soil facts table. Water table and bedrock depth are shown in feet and inches. Under about 2–3 feet for either is the usual reason a conventional system will not fit.
7. Compare with your county. The bar shows what share of the whole county's soil is rated each way. If your spot is green in a mostly red county, you may have found one of the good lots — confirm it fast.
8. Take the next step. Book a perc test or soil evaluation with the licensed evaluator your state requires, and make any land purchase contingent on a passing result.

A worked example: Magnolia, Texas

Typing "Magnolia, TX" returns Very limited because water soaks in slowly through dense subsoil. The likely system is an aerobic unit with spray or drip, or a mound, and the estimator opens with that system already chosen. The county bar shows Montgomery County is almost entirely rated very limited — so this is the normal case there, not bad luck. The right move is to budget for an aerobic system before making an offer, then confirm it with a site evaluator.

What each soil term means

What does this soil check actually look up?

It reads the official US soil survey — the same data county sanitarians and site evaluators start from. USDA's Natural Resources Conservation Service maps soil for almost every county in the country and publishes it as the Soil Survey Geographic Database, SSURGO.

For each patch of mapped soil, NRCS rates how well it suits common uses. The tool pulls six of them for your exact point: a septic drain field, a house on a slab, a house with a basement, shallow excavations, a driveway or local road, and a pond. It also returns the soil series, drainage class, depth to the seasonal water table and depth to bedrock.

Those ratings come in three grades. Not limited means the soil suits the use. Somewhat limited means a problem that good design or planning can handle. Very limited means a problem that takes special design, real extra cost or ongoing maintenance to overcome.

Why check the soil before you buy land?

Because the soil decides which septic system you can build, and the system can swing the bill by five figures. A conventional gravity system is the cheapest option there is. A mound or an aerobic unit on the same house costs far more, and an aerobic unit adds a maintenance contract for as long as you own it.

Our septic system cost guide breaks those numbers down, and the mound system cost guide covers the most common upgrade. Roughly one in five US homes relies on a septic system, according to the EPA, and plenty of those lots were bought by people who never asked this question first.

The soil check costs nothing and takes ten seconds. A failed deal over a lot that will not perc costs the earnest money, the survey and the perc test — if you are lucky enough to find out before closing. It belongs near the top of any raw land buying checklist.

How do you read your result?

The septic rating and its reasons

The reasons matter more than the grade. "Very limited — slow water movement" and "very limited — depth to saturated zone" lead to different systems. Slow soil usually means a bigger field or a treatment unit. A high water table usually means raising the field above grade, which is what a mound does.

Water table and bedrock depth

These two numbers are why most rural lots fail a conventional design. Every state requires a minimum depth of unsaturated soil under the drain field so effluent is treated before it reaches groundwater. If the seasonal water table or bedrock sits inside that zone, the field has to go up, or the effluent has to be treated harder first. Shallow rock also makes any digging slower and pricier — see the excavation cost guide.

Drainage class and hydrologic group

These tell you how wet the ground stays. Drainage class runs from "excessively drained" to "very poorly drained." Hydrologic group runs from A (sandy, soaks up rain) to D (tight, sheds rain). Poorly drained, group C or D soil is where you plan for french drains and grading before anything else gets built.

The other land-work ratings

The same survey answers the questions that come after septic. A "very limited" basement rating is a warning about water and cost on a basement dig. The road rating speaks to the base under a gravel driveway. The pond rating tells you whether a new pond is likely to hold water or will need a clay liner.

What septic system will your soil need?

Your rating points to a system type; a site evaluation confirms it. The tool suggests the likely system from USDA's limiting factors and passes it straight to our septic cost estimator, where you can change it.

The EPA describes each of these system types in plain terms, and our guide to septic system types walks through what each one costs to build and run.

How common is "very limited" septic soil?

Far more common than most land buyers expect. We ran the county-wide numbers for five fast-growing counties in the states this site covers. The share below is the portion of each county's rated soil acreage that USDA grades very limited for a conventional drain field.

Basis: USDA NRCS SSURGO via Soil Data Access, dominant soil component per map unit, weighted by map-unit acreage; "not rated" acreage (water, urban land) excluded. Rounded to whole percent.

That is why aerobic units are routine around Conroe and Magnolia, and why so many Florida systems are mounds. It does not mean you cannot build in those counties. It means the cheap system is the exception, and your budget should assume so.

Septic soil by state: all 50 states

The septic soil check works for every state, and the numbers below show why every state needs it. For each state we picked a fast-growing county where most new rural homes are on septic, and pulled the share of its rated soil USDA grades for a conventional drain field. Click a town to run the check there.

Basis: USDA NRCS SSURGO via Soil Data Access, dominant soil component per map unit, weighted by map-unit acreage, "not rated" land excluded. A survey area is usually one county; a few cover part of a county or a region, and are named as USDA names them. These are the hard, wet and shallow soils that ratings flag most often — a high share is normal, which is exactly why a lot-by-lot check matters.

What the pattern says: in most of the country, conventional-friendly soil is the exception. Wyoming's Laramie County, New Mexico's Sandoval County and Alabama's Baldwin County have the largest shares rated not limited in this sample, while coastal and glacial counties — Lee in Florida, Barnstable in Massachusetts, Sussex in Delaware — are rated very limited almost everywhere, mainly because of sand over a shallow water table.

Who issues septic permits in other states?

Almost always your county or local health department, under rules your state sets. A few states run the program directly. The EPA keeps a list of every state's septic program contact — start there, then ask the county office who may perform the soil evaluation and what it costs.

EPA: State Septic System Program Contacts →

Septic soil rules in Texas, Florida, North Carolina, Tennessee and Georgia

All five states issue permits on an on-site evaluation, not on the USDA map. The map tells you what to expect; the evaluation decides. Here is who does it in each state.

Septic soil evaluation in Texas

The local permitting authority — usually the county, acting as TCEQ's authorized agent — issues the permit. A licensed site evaluator digs the soil profile holes.

Texas grades soil by texture class under 30 TAC §285.30 rather than relying on a classic timed perc test, and a high water table or restrictive layer within the design depth is what pushes most rural lots to an aerobic unit with spray.

Septic soil evaluation in Florida

The county health department takes the application and does the site evaluation; the program has sat under Florida DEP since July 2021.

Florida sizes the drain field from soil texture and the estimated seasonal high water table under Chapter 62-6, F.A.C. Where the water table sits close to the surface, the field gets raised — which is why so many Florida systems are mounds.

Septic soil evaluation in North Carolina

The county health department evaluates the site and issues an Improvement Permit, then a Construction Authorization. You may also hire a licensed soil scientist for the evaluation.

North Carolina's rules, 15A NCAC 18E, judge suitability from a soil profile — texture, structure, depth to a restrictive horizon and to seasonal wetness — not from a single perc number.

Septic soil evaluation in Tennessee

TDEC's Division of Water Resources runs the program; in most counties you apply through the local environmental field office or county health department.

Tennessee permits on a soil evaluation under rule chapter 0400-48-01, and new subdivisions are commonly mapped with a high-intensity soil map drawn by a soil scientist before lots are approved for septic.

Septic soil evaluation in Georgia

Your county environmental health office (under the Georgia Department of Public Health) issues the permit, and a DPH-certified contractor must install the system.

Georgia sets statewide standards in DPH Rules Chapter 511-3-1, while county boards of health set lot sizes and siting. A soil evaluation of the lot decides absorption-field size.

Our septic installation hub covers permits and licensing in more depth, state by state.

Will my land perc? How to tell before the perc test

You can predict a perc test result surprisingly well from the USDA soil map. The septic rating above is built from the same properties a site evaluator looks at in the pit: texture, permeability, depth to the seasonal water table and depth to rock.

Land that USDA rates "not limited" for septic absorption fields usually perks. "Somewhat limited" land usually perks with a larger field. "Very limited" land often fails a conventional design — not because it is unbuildable, but because it needs a mound, aerobic unit or drip system. Our perc test guide covers test day and what to do if land fails a perc test.

What is the best soil for a septic system?

Deep, well-drained loam or loamy sand with the water table far below the surface. It soaks up effluent at a steady rate and gives the soil time to treat it. That combination earns a "not limited" rating.

Septic system with a high water table: what are the options?

Raise the field, treat the effluent harder, or both. A seasonal high water table is the most common reason USDA rates rural soil very limited for septic, and it drives the high shares for Lee County and Montgomery County in the table above.

A mound system builds the drain field above grade in imported sand. An aerobic treatment unit cleans effluent before it reaches the soil. Where water stands near the surface, a curtain drain is sometimes used to lower it first, where local rules allow.

How to use Web Soil Survey for septic — and the faster way

Web Soil Survey is USDA's official soil map; this tool reads the same data without the setup. On Web Soil Survey you draw an area of interest, open "Suitabilities and Limitations," then "Sanitary Facilities," then "Septic Tank Absorption Fields." It is excellent, and slow if you only want one answer.

The soil check above goes straight to that rating for the exact point you enter, adds the limiting reasons in plain English and links the result to costs. For a whole parcel with several soil types, Web Soil Survey is still the better view, and the result box links there so you can check our work.

Soil map, perc test or site evaluation: what is the difference?

Is a USDA soil map as good as a perc test?

No — and it is not meant to be. Soil surveys are drawn for planning. A single map unit can contain small inclusions of different soil, and the boundary lines are interpretations drawn from field samples and aerial imagery.

A perc test or soil profile evaluation looks at the actual hole on your actual lot. Use the soil check to decide whether a property is worth that next step, and what to ask the evaluator. Our guide to perc tests explains what happens on the day, and the perc test cost guide covers what you will pay.

What should you do with the result?

• Not limited: price a conventional system in the estimator, then book the perc test or evaluation to confirm it.
• Somewhat limited: ask the evaluator specifically about the limiting reason, and budget for a larger field.
• Very limited: price the likely alternative system before you make an offer, and make the purchase contingent on a passing evaluation.
• Repairing an old system? Soil is the usual reason fields fail — see drain field replacement cost and our drain field guide.
• Building from scratch? Soil comes first in our guide to preparing land for a house.