Island of Oahu, Hawaii

Survey Area HI990• Hawaii

The dominant drainage class is Well drained and the dominant hydrologic group is B (moderate infiltration). The most common soil order is Mollisols — grassland soils with a thick, dark, fertile topsoil rich in organic matter. 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. Search your address to find the exact soil composition, drainage, and series details at your specific location.

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

Soil Orders in This Area

The USDA classifies every soil into one of 12 soil orders. Here are the dominant orders found in this survey area.

Mollisols

Fertile grassland soils with thick, dark topsoil. Among the best for agriculture, building, and gardening.

Ultisols

Strongly weathered clay soils of the Southeast. Acidic and naturally low in nutrients. Clay subsoil can slow drainage.

Oxisols

Deeply weathered tropical soils. Nutrient-poor despite appearing lush. Rare in the continental US.

Vertisols

High-clay soils that shrink and swell dramatically. Fertile but challenging for foundations and septic systems.

Andisols

Volcanic ash soils — light, porous, and fertile. Excellent drainage, but low density can complicate foundations.

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.