Toole County, Montana
The soil mapped across Toole County is predominantly classified well drained. Below is what that classification means for a basement, what it does not mean, and what the three repairs it points to cost here.
27% of the county’s mapped soil area falls in classes the USDA describes as wet enough to need artificial drainage for ordinary use. Saturated soil against a foundation wall is what creates hydrostatic pressure.
Linear extensibility 11.1% in the top metre — very high. One of the most expansive substrates there is. Foundation damage occurs here in houses with faultless waterproofing.
Shallowest annual water table maps at about 195 cm (6.4 ft) below the surface — water table deep, at or beyond the limit the survey reports. A typical US basement floor sits just under 200 cm, which is also the deepest the soil survey reports.
Source: BasementSoil physiographic region model — region “Missouri Plateau (unglaciated Great Plains)”. Not a soil survey of this county. Why.
What the ground here is made of
Missouri Plateau (unglaciated Great Plains). Weathered clay shales and sandstones, Pierre Shale and equivalents
The water table is deep, so basements rarely flood — but Pierre Shale is one of the most expansive substrates in North America. The risk here is mechanical, not hydraulic.
How the county’s soil area splits between drainage classes
| USDA drainage class | Share of mapped area | |
|---|---|---|
| excessively drained | 1% | |
| somewhat excessively drained | 4% | |
| well drained | 43% | |
| moderately well drained | 25% | |
| somewhat poorly drained | 15% | |
| poorly drained | 10% | |
| very poorly drained | 3% |
Drainage class definitions: USDA NRCS SSURGO. Highlighted row is the dominant condition (drclassdcd). Wettest class present in the county: poorly drained.
Key soil values for Toole County
| Dominant drainage class | well drained — water leaves readily; the profile is saturated only briefly after rain |
|---|---|
| Wettest class present | poorly drained |
| Area needing artificial drainage | 27% |
| Linear extensibility (shrink-swell) | 11.1% — very high modelled |
| Shallowest annual water table | 195 cm (6.4 ft) |
| Hydrologic soil group | C/D |
| Physiographic region | Missouri Plateau (unglaciated Great Plains) |
| Expected radon zone | Zone 1 (highest) — predicted indoor average above 4 pCi/L, the level at which EPA recommends fixing expected, not the official designation |
| Basements in this state | a large share of homes have one |
What the three likely repairs cost in Montana
| Reference job | Modelled range in MT |
|---|---|
| Interior drain along two walls + sump pump | $5,150–$11,050 |
| Exterior excavation of one 40 ft wall | $3,900–$11,000 |
| Underpinning on 10 piers | $15,300–$32,650 |
Reference basement 30 × 40 ft. Price book 2026.08, updated 2026-08-11, regional factor for MT: ×1.02. Run your own dimensions.
Given this soil, the order of operations here
- Do not start with waterproofing. The dominant signal here is soil that changes volume, not soil that stays wet. Get a structural engineer’s letter first ($400–$1,150) — it costs a fraction of the repair and it is the only document that tells you whether piers are actually needed.
- Keep soil moisture constant. With expansive clay the enemy is the wet–dry cycle, not water itself. Consistent watering near the foundation and extended downspouts do more than any coating.
- Get the second and third quote before you sign anything. Same scope, in writing, from firms that are not owned by the same parent. How to do it without paying twice.
Questions about Toole County soil
Does “well drained” soil mean my basement will flood?
No. The class describes how long the soil profile stays saturated in an average year across mapped areas of the county. It raises or lowers the statistical odds of hydrostatic pressure against a wall. It says nothing about your grading, your footing drain or your downspouts — which is usually what decides whether water actually gets in.
Which number should I care about most?
Whichever is highest, because they point at different contractors. High moisture and water table risk is a drainage and pump problem. High crack risk with low moisture risk — common on the Colorado Front Range and in the Flint Hills — is a structural problem, and a waterproofing salesman is the wrong person to call about it.
A contractor told me my county has “the worst soil in the state”. Is that true?
Check it here and on the USDA source we link. It is a specific, checkable claim, and in our experience of the sales scripts it is used loosely. Toole County scores 51 out of 100 overall on our combined index, which is elevated for the counties we cover.
Will my homeowners insurance pay for this?
Almost certainly not, if the cause is groundwater seeping in gradually. That is excluded from standard US homeowners policies, and the exclusion is usually the reason people find this site. What is and is not covered.
Does “well drained” soil mean my basement will flood?
No. The class describes how long the soil profile stays saturated in an average year across mapped areas of the county. It raises or lowers the statistical odds of hydrostatic pressure against a wall. It says nothing about your grading, your footing drain or your downspouts — which is usually what decides whether water actually gets in.
Which number should I care about most?
Whichever is highest, because they point at different contractors. High moisture and water table risk is a drainage and pump problem. High crack risk with low moisture risk — common on the Colorado Front Range and in the Flint Hills — is a structural problem, and a waterproofing salesman is the wrong person to call about it.
A contractor told me my county has “the worst soil in the state”. Is that true?
Check it here and on the USDA source we link. It is a specific, checkable claim, and in our experience of the sales scripts it is used loosely. Toole County scores 51 out of 100 overall on our combined index, which is elevated for the counties we cover.
Will my homeowners insurance pay for this?
Almost certainly not, if the cause is groundwater seeping in gradually. That is excluded from standard US homeowners policies, and the exclusion is usually the reason people find this site. What is and is not covered.
Nearby counties
Neighbours in the same physiographic region behave similarly. Different region on the other side of the county line means genuinely different ground.
All 56 counties in Montana · More about “well drained” soil
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