Minnesota / Watonwan County
Score 59 · elevated · #19 of 87 in MN
Crawl space moisture in Watonwan County, MN
69% of Watonwan County's mapped soil is somewhat poorly to very poorly drained, which means ground that stays wet near the surface for significant periods. Where a seasonal water table is reported — 93% of acres — it averages 1.1 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.1 ft
- 2Wet soils 69%
- 3Moisture score 59
- 4EPA radon zone 1
Reading the Watonwan County soil survey
The score of 59 combines four parts, each from the USDA survey: wet drainage classes contribute 70 points of 100 on their own scale, group D soils 45.6, a shallow water table 77.5, and flooding 5.1; the weights are on the methodology page. The dominant hydrologic group is C/D (55% of acres): D when undrained, C when drained.
A water table under two feet is the single most important number here. A crawl-space floor is usually 18 to 36 inches below the joists and often below outside grade, so in a wet season groundwater can stand at or above the crawl-space floor across much of Watonwan County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Watonwan County against the rest of Minnesota
Watonwan County ranks 19 of 87 Minnesota counties, 12 points above the state median of 47. That puts it in the wettest quarter of the state. Statewide, 55% of mapped soil is in the wet drainage classes; here it is 69%. After poorly drained, the next most common class is moderately well drained at 17%.
Flooding. 2.2% of acres with a flooding class are rated frequent; 4.8% of acres with a flooding class are rated occasional. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods. Ponding — water standing at the surface with nowhere to go — affects 1.4% of acres.
What it means for a crawl space here
In an elevated county the soil supplies more moisture than average, but a vented crawl space can work if the ground is covered: the code lets vent area drop from 1 sq ft per 150 to 1 per 1500 with a Class I vapor retarder on the ground, which is an admission of how much moisture comes from below. Grading, gutters and a ground cover usually decide whether a crawl space here stays dry before any decision about sealing it.
Radon. Watonwan County is in EPA radon zone 1, the highest predicted potential. A sealed crawl space and a radon system share most of their parts — the liner, the sealed seams, a fan — so if you are encapsulating, test for radon first and design both together. EPA itself says the zone map is not a reason to skip testing in zones 2 and 3.
Near Watonwan County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MN165; drainage covers 99% of 281,300 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.