Colorado / Alamosa County
Score 31 · moderate · #1 of 45 in CO
Crawl space moisture in Alamosa County, CO
Alamosa County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 67% of acres — it averages 3.2 ft below grade.
- 1Water table 3.2 ft
- 2Wet soils 36%
- 3Moisture score 31
- 4EPA radon zone 2
Reading the Alamosa County soil survey
The score of 31 combines four parts, each from the USDA survey: wet drainage classes contribute 32.6 points of 100 on their own scale, group D soils 35.9, a shallow water table 34, and flooding 9.5; the weights are on the methodology page. The dominant hydrologic group is A (42% of acres): high infiltration, low runoff (sands, gravels).
At 3.2 ft the seasonal water table is usually below a crawl-space floor, but the 67% of acres that report one are by definition the wettest parts of the county; on those lots, a wet spring can bring water close to the footings.
Alamosa County against the rest of Colorado
Alamosa County ranks 1 of 45 Colorado counties, 21 points above the state median of 10. Only no other county in the state scores higher. Statewide, 3% of mapped soil is in the wet drainage classes; here it is 36%, half again the state figure or more. After well drained, the next most common class is somewhat poorly drained at 24%.
Flooding. 5.1% of acres with a flooding class are rated frequent; 6.4% of acres with a flooding class are rated occasional; 2.5% 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.
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 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Alamosa County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area CO632; drainage covers 98% of 436,700 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.