Oklahoma / Ottawa County
Score 38 · moderate · #13 of 77 in OK
Crawl space moisture in Ottawa County, OK
51% of Ottawa 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 — 50% of acres — it averages 1.3 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.3 ft
- 2Wet soils 51%
- 3Moisture score 38
- 4EPA radon zone 3
Reading the Ottawa County soil survey
The score of 38 combines four parts, each from the USDA survey: wet drainage classes contribute 37.3 points of 100 on their own scale, group D soils 49.3, a shallow water table 40.2, and flooding 7.7; the weights are on the methodology page. The dominant hydrologic group is D (37% of acres): very slow infiltration, high runoff (clays, high water table).
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 on the soils that report a water table — about 50% of Ottawa County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Ottawa County against the rest of Oklahoma
Ottawa County ranks 13 of 77 Oklahoma counties, 21 points above the state median of 17. That puts it in the wettest quarter of the state. Statewide, 11% of mapped soil is in the wet drainage classes; here it is 51%, half again the state figure or more. After somewhat poorly drained, the next most common class is somewhat excessively drained at 27%.
Flooding. 2.1% of acres with a flooding class are rated frequent; 9.5% 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 3.8% of acres.
What it means for a crawl space here
In a moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those first.
Radon. EPA radon zone 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Ottawa County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area OK115; drainage covers 95% of 309,600 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.