King County Area, Washington
The dominant drainage class is Moderately well drained and the dominant hydrologic group is B (moderate infiltration). This report summarizes the major soil map units across the survey area to help you understand what to expect when buying, building, or gardening in King County Area, Washington.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Alderwood gravelly sandy loam, 8 to 15 percent slopes | 126K | Moderately well drained | B | Very limited | Very limited |
| Alderwood gravelly sandy loam, 0 to 8 percent slopes | 29K | Moderately well drained | B | Very limited | Very limited |
| Everett very gravelly sandy loam, 8 to 15 percent slopes | 28K | Somewhat excessively drained | A | Somewhat limited | Very limited |
| Alderwood and Kitsap soils, very steep | 27K | Moderately well drained | B | Very limited | Very limited |
| Alderwood gravelly sandy loam, 15 to 30 percent slopes | 19K | Moderately well drained | B | Very limited | Very limited |
| Arents, Alderwood material, 6 to 15 percent slopes | 14K | Moderately well drained | B/D | Very limited | Very limited |
| Buckley gravelly silt loam, 0 to 3 percent slopes | 14K | Poorly drained | C/D | Very limited | Very limited |
| Everett very gravelly sandy loam, 0 to 8 percent slopes | 13K | Somewhat excessively drained | A | Not limited | Very limited |
| Urban land | 12K | Not rated | Not rated | ||
| Water | 11K | Not rated | Not rated | ||
| Everett-Alderwood gravelly sandy loams, 6 to 15 percent slopes | 10K | Somewhat excessively drained | A | Somewhat limited | Very limited |
| Kitsap silt loam, 2 to 8 percent slopes | 9K | Moderately well drained | C | Very limited | Very limited |
| Seattle muck | 8K | Very poorly drained | B/D | Very limited | Very limited |
| Beausite gravelly sandy loam, 15 to 30 percent slopes | 5K | Well drained | C | Very limited | Very limited |
| Beausite gravelly sandy loam, 6 to 15 percent slopes | 4K | Well drained | C | Very limited | Very limited |
| Everett very gravelly sandy loam, 15 to 30 percent slopes | 4K | Somewhat excessively drained | A | Very limited | Very limited |
| Indianola loamy sand, 5 to 15 percent slopes | 4K | Somewhat excessively drained | A | Not limited | Very limited |
| Norma sandy loam | 4K | Poorly drained | A/D | Very limited | Very limited |
| Puyallup fine sandy loam | 4K | Well drained | A | Very limited | Very limited |
| Kitsap silt loam, 15 to 30 percent slopes | 4K | Moderately well drained | C | Very limited | Very limited |
What This Means
Building & Foundations
About 77% of soils are rated "very limited" for dwellings with basements. Specific challenges include steep slopes, poor drainage in some areas, flood-prone areas. A geotechnical assessment is recommended before building.
Septic Systems
About 93% of soils are rated "very limited" for septic absorption fields. Despite good drainage overall, limitations may stem from shallow bedrock, steep slopes, or seasonal conditions. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.
Gardening & Agriculture
Well-drained soils on sloped terrain — good for most plants but watch for erosion. Terracing, contour planting, and mulching help retain moisture and topsoil. Drip irrigation is more effective than sprinklers on slopes.