Island of Oahu, Hawaii
The dominant drainage class is 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 Island of Oahu, Hawaii.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Rough mountainous land | 56K | Well drained | B | Very limited | Very limited |
| Rock land | 38K | Well drained | D | Very limited | Very limited |
| Helemano silty clay, 30 to 90 percent slopes | 25K | Well drained | A | Very limited | Very limited |
| Water > 40 acres | 14K | D | Not rated | Not rated | |
| Tropohumults-Dystrandepts association | 13K | Well drained | A | Very limited | Very limited |
| Fill land, mixed | 12K | Well drained | B | Very limited | Somewhat limited |
| Coral outcrop | 11K | Excessively drained | Very limited | Very limited | |
| Kapaa silty clay, 40 to 100 percent slopes | 11K | Well drained | B | Very limited | Very limited |
| Wahiawa silty clay, 3 to 8 percent slopes | 10K | Well drained | B | Not limited | Somewhat limited |
| Wahiawa silty clay, 0 to 3 percent slopes | 10K | Well drained | B | Not limited | Somewhat limited |
| Rock outcrop | 8K | C | Very limited | Very limited | |
| Stony steep land | 7K | Well drained | A | Very limited | Very limited |
| Mamala cobbly silty clay loam, 0 to 12 percent slopes, MLRA 163 | 7K | Well drained | D | Very limited | Very limited |
| Stony land | 6K | Well drained | B | Very limited | Very limited |
| Waikane silty clay, 40 to 70 percent slopes | 6K | Well drained | C | Very limited | Very limited |
| Lualualei extremely cobbly clay, 3 to 35 percent slopes, MLRA 166 | 6K | Well drained | C | Very limited | Very limited |
| Paumalu-Badland complex | 6K | Well drained | B | Very limited | Very limited |
| Jaucas sand, 0 to 15 percent slopes, MLRA 163 | 5K | Excessively drained | A | Very limited | Very limited |
| Molokai silty clay loam, 3 to 7 percent slopes, MLRA 158 | 4K | Well drained | C | Not limited | Very limited |
| Lahaina silty clay, moist, 3 to 7 percent slopes, MLRA 167 | 4K | Well drained | B | Not limited | Somewhat limited |
What This Means
Building & Foundations
About 83% of soils are rated "very limited" for dwellings with basements. Specific challenges include shallow bedrock, steep slopes, flood-prone areas. A geotechnical assessment is recommended before building.
Septic Systems
About 80% 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.