Expansive Soil in Maryland: County Ratings
None of the 24 rated counties in Maryland 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 |
|---|---|---|---|
| Allegany County | Low | 5% | 96% |
| Anne Arundel County | Low | 0% | 95% |
| Baltimore County | Low | 1% | 88% |
| Baltimore City | Low | 10% | 75% * |
| Calvert County | Low | 0% | 86% |
| Caroline County | Low | 0% | 98% |
| Carroll County | Low | 0% | 99% |
| Cecil County | Low | 2% | 82% |
| Charles County | Low | 0% | 92% |
| Dorchester County | Low | 0% | 71% * |
| Frederick County | Low | 6% | 98% |
| Garrett County | Low | 0% | 99% |
| Harford County | Low | 5% | 94% |
| Howard County | Low | 0% | 97% |
| Kent County | Low | 0% | 91% |
| Montgomery County | Low | 1% | 96% |
| Prince George's County | Low | 0% | 94% |
| Queen Anne's County | Low | 0% | 91% |
| Somerset County | Low | 0% | 44% * |
| St. Mary's County | Low | 0% | 89% |
| Talbot County | Low | 0% | 78% * |
| Washington County | Low | 9% | 97% |
| Wicomico County | Low | 0% | 94% |
| Worcester County | Low | 0% | 76% * |
* 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.