Nebraska / Jefferson County
Score 20 · moderate · #17 of 93 in NE
Crawl space moisture in Jefferson County, NE
Jefferson County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 14% of acres — it averages 1.9 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.9 ft
- 2Wet soils 1%
- 3Moisture score 20
- 4EPA radon zone 1
Reading the Jefferson County soil survey
The score of 20 combines four parts, each from the USDA survey: wet drainage classes contribute 18.5 points of 100 on their own scale, group D soils 37.7, a shallow water table 9.8, and flooding 5.9; the weights are on the methodology page. The dominant hydrologic group is C (72% of acres): slow infiltration (clay layers).
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 14% of Jefferson County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Jefferson County against the rest of Nebraska
Jefferson County ranks 17 of 93 Nebraska counties, 10 points above the state median of 10. That puts it in the wettest quarter of the state. Statewide, 9% of mapped soil is in the wet drainage classes; here it is 1%, below the state figure — the score here comes from flooding and ponding rather than drainage class alone. After moderately well drained, the next most common class is well drained at 43%.
Flooding. 0.1% of acres with a flooding class are rated frequent; 8% of acres with a flooding class are rated occasional; 5.2% of acres with a flooding class are rated rare. 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 17% 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. Jefferson 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 Jefferson County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area NE095; drainage covers 99% of 368,448 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.