Washington County, Oregon
The dominant drainage class is Well drained and the dominant hydrologic group is C (slow infiltration, moderate runoff). 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 Washington County, Oregon.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Aloha silt loam | 28K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Woodburn silt loam, 0 to 3 percent slopes | 21K | Moderately well drained | C | Very limited | Very limited |
| Melby silt loam, 2 to 30 percent slopes | 20K | Well drained | C | Very limited | Very limited |
| Olyic silt loam, 30 to 60 percent slopes | 20K | Well drained | B | Very limited | Very limited |
| Melby silt loam, 30 to 60 percent slopes | 16K | Well drained | C | Very limited | Very limited |
| Tolke silt loam, 5 to 30 percent slopes | 15K | Well drained | B | Very limited | Very limited |
| Olyic silt loam, 5 to 30 percent slopes | 14K | Well drained | B | Very limited | Very limited |
| Wapato silty clay loam | 12K | Poorly drained | C/D | Very limited | Very limited |
| Laurelwood silt loam, 12 to 20 percent slopes | 12K | Well drained | B | Very limited | Very limited |
| Woodburn silt loam, 3 to 7 percent slopes | 11K | Moderately well drained | C | Very limited | Very limited |
| McBee silty clay loam | 10K | Moderately well drained | C | Very limited | Very limited |
| Cornelius and Kinton silt loams, 7 to 12 percent slopes | 9K | Moderately well drained | C | Somewhat limited | Very limited |
| Cornelius and Kinton silt loams, 12 to 20 percent slopes | 9K | Moderately well drained | C | Very limited | Very limited |
| Hembre silt loam, 30 to 60 percent slopes | 8K | Well drained | B | Very limited | Very limited |
| Laurelwood silt loam, 7 to 12 percent slopes | 8K | Well drained | B | Somewhat limited | Very limited |
| Murtip-Caterl-Laderly complex, 30 to 60 percent slopes | 8K | Well drained | B | Very limited | Very limited |
| Cornelius and Kinton silt loams, 2 to 7 percent slopes | 8K | Moderately well drained | C | Somewhat limited | Very limited |
| Helvetia silt loam, 2 to 7 percent slopes | 8K | Moderately well drained | C | Somewhat limited | Very limited |
| Quatama loam, 0 to 3 percent slopes | 7K | Moderately well drained | C | Very limited | Very limited |
| Verboort silty clay loam, 0 to 3 percent slopes | 7K | Poorly drained | D | 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 100% 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.