Expansive Soil in Alaska: County Ratings
None of the 22 rated counties in Alaska have a dominant shrink-swell rating of High or Very High. Each rating below is the NRCS shrink-swell class covering the largest share of the county's mapped soil acres, computed from USDA SSURGO data. Open a county for the full class breakdown and what it means for a slab foundation.
| County | Dominant class | High + Very High share | Survey coverage |
|---|---|---|---|
| Aleutians West Census Area | Low | 0% | 89% |
| Anchorage Borough | Low | 0% | 54% * |
| Bethel Census Area | Low | 0% | 98% |
| Denali Borough | Low | 20% | 95% |
| Dillingham Census Area | Low | 0% | 95% |
| Fairbanks North Star Borough | Low | 0% | 94% |
| Haines Borough | Low | 0% | 65% * |
| Hoonah-Angoon Census Area | Low | 0% | 49% * |
| Juneau Borough | Low | 0% | 48% * |
| Kenai Peninsula Borough | Low | 0% | 54% * |
| Kusilvak Census Area | Low | 0% | 100% |
| Lake and Peninsula Borough | Low | 0% | 100% |
| Nome Census Area | Low | 0% | 100% |
| North Slope Borough | Low | 0% | 86% |
| Northwest Arctic Borough | Moderate | 0% | 100% |
| Petersburg Borough | Low | 0% | 54% * |
| Sitka Borough | Low | 0% | 63% * |
| Skagway Borough | Low | 0% | 32% * |
| Southeast Fairbanks Census Area | Low | 0% | 88% |
| Valdez-Cordova Census Area | Low | 0% | 17% * |
| Yakutat City and Borough | Low | 0% | 43% * |
| Yukon-Koyukuk Census Area | Low | 0% | 97% |
* Less than 80% of this county's map acres have completed soil survey data; treat its rating as provisional.
How these ratings are computed
Ratings come from USDA NRCS SSURGO soil survey data: for each soil component we take the maximum linear extensibility percent (lep_r) in the top 100 cm, apply the NRCS Handbook Part 618 class limits (Low under 3 percent, Moderate 3 to 6, High 6 to 9, Very High 9 and above), assign map units by plurality of component percent, and roll acres up to the county. Full details on the methodology section of the lookup page. A county rating is not a parcel-level geotechnical assessment.