Maine / Penobscot County
Score 51 · elevated · #3 of 10 in ME
Crawl space moisture in Penobscot County, ME
73% of Penobscot County's soil falls in hydrologic group D or a dual D group: clays and high water tables that shed water slowly. Where a seasonal water table is reported — 71% of acres — it averages 1 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1 ft
- 2Wet soils 46%
- 3Moisture score 51
- 4EPA radon zone 1
Reading the Penobscot County soil survey
The score of 51 combines four parts, each from the USDA survey: wet drainage classes contribute 48.2 points of 100 on their own scale, group D soils 65, a shallow water table 59.9, and flooding 2.8; the weights are on the methodology page. The dominant hydrologic group is D (42% 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 across much of Penobscot County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Penobscot County against the rest of Maine
Penobscot County ranks 3 of 10 Maine counties, 5 points above the state median of 46. Only 2 other counties in the state score higher. Statewide, 37% of mapped soil is in the wet drainage classes; here it is 46%. After poorly drained, the next most common class is well drained at 19%.
Flooding. 2.5% of acres with a flooding class are rated frequent; 0.6% 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 7.4% 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. Penobscot 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 Penobscot County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey areas ME612, ME614; drainage covers 94% of 2,275,290 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.