Snohomish 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 Snohomish County Area, Washington.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Tokul gravelly medial loam, 0 to 8 percent slopes | 61K | Moderately well drained | B | Very limited | Very limited |
| Tokul gravelly medial loam, 8 to 15 percent slopes | 44K | Moderately well drained | B | Very limited | Very limited |
| Alderwood gravelly sandy loam, 0 to 8 percent slopes | 42K | Moderately well drained | B | Very limited | Very limited |
| Elwell-Olomount-Rock outcrop complex, 30 to 60 percent slopes | 34K | Moderately well drained | C | Very limited | Very limited |
| Alderwood-Urban land complex, 2 to 8 percent slopes | 27K | Moderately well drained | B | Very limited | Very limited |
| Puget silty clay loam | 24K | Poorly drained | C | Very limited | Very limited |
| Tokul-Winston gravelly loams, 25 to 65 percent slopes | 20K | Moderately well drained | C | Very limited | Very limited |
| Tokul-Ogarty-Rock outcrop complex, 25 to 65 percent slopes | 19K | Moderately well drained | C | Very limited | Very limited |
| Everett very gravelly sandy loam, 0 to 8 percent slopes | 18K | Somewhat excessively drained | A | Not limited | Very limited |
| Tokul gravelly medial loam, 15 to 30 percent slopes | 15K | Moderately well drained | B | Very limited | Very limited |
| Ragnar fine sandy loam, 0 to 8 percent slopes | 15K | Well drained | A | Not limited | Very limited |
| Sultan silt loam | 14K | Moderately well drained | C | Somewhat limited | Very limited |
| Alderwood gravelly sandy loam, 8 to 15 percent slopes | 14K | Moderately well drained | B | Very limited | Very limited |
| Norma loam | 14K | Poorly drained | B/D | Very limited | Very limited |
| Water | 12K | Not rated | Not rated | ||
| Mukilteo muck | 12K | Very poorly drained | B/D | Very limited | Very limited |
| Pastik silt loam, 0 to 8 percent slopes | 12K | Moderately well drained | C | Very limited | Very limited |
| Elwell silt loam, 3 to 30 percent slopes | 12K | Moderately well drained | C | Very limited | Very limited |
| Skykomish gravelly loam, 0 to 30 percent slopes | 11K | Somewhat excessively drained | A | Very limited | Very limited |
| Getchell-Oso-Rock outcrop complex, 30 to 65 percent slopes | 10K | Moderately well drained | C | Very limited | Very limited |
What This Means
Building & Foundations
About 86% 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 97% 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.