Ada County, Idaho
The most common soil here is Chilcott, on about 8% of the land: a silt loam, smooth, like flour. Purdam and Power come next.
About 91% of the land drains well, and 3% stays wet for long stretches.
USDA rates 86% of the land very limited for a standard septic drain field, and 46% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 1% of the land floods occasionally or more, and bedrock lies within 40 inches under 42% of it.
Soils change over short distances, so look up an address below for the soil at that exact spot and the reasons behind each rating.
The soils you're most likely standing on
The biggest named soils in Ada County, Idaho, each drawn five feet deep from its official USDA description, in its recorded colors.
Dots mark gravel; white flecks mark lime. Shares are by acres across the survey area, and each mapped patch usually mixes several of these soils.
The biggest mapped areas
The dominant drainage class is Well drained and the dominant hydrologic group is D (very slow infiltration, high runoff). The most common soil order is Aridisols — dry-climate soils with limited organic matter and often calcium carbonate accumulation. 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 Ada County, Idaho. 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 |
|---|---|---|---|---|---|
| Chilcott-Catchell-Chardoton complex, 0 to 4 percent slopes | 33K | Well drained | D | Somewhat limited | Very limited |
| Purdam silt loam, 0 to 2 percent slopes | 26K | Well drained | C | Somewhat limited | Very limited |
| Tadpole-Corder complex, 0 to 2 percent slopes | 26K | Well drained | B | Not limited | Somewhat limited |
| Catchell-Chilcott-Banbury complex, 1 to 12 percent slopes | 17K | Well drained | D | Very limited | Very limited |
| Elfkin-Dolman-Minveno complex, 1 to 8 percent slopes | 14K | Well drained | C | Very limited | Very limited |
| Chilcott-Sebree complex, 2 to 4 percent slopes | 14K | Well drained | D | Somewhat limited | Very limited |
| Chilcott-Sebree complex, 0 to 2 percent slopes | 12K | Well drained | D | Somewhat limited | Very limited |
| Tadpole-Purdam-Trevino complex, 0 to 5 percent slopes | 11K | Well drained | B | Not limited | Somewhat limited |
| Power silt loam, 0 to 2 percent slopes | 10K | Well drained | C | Not limited | Very limited |
| Scism silt loam, bedrock substratum, 2 to 4 percent slopes | 10K | Well drained | C | Somewhat limited | Very limited |
| Chilcott-Sebree complex, bedrock substratum, 2 to 4 percent slopes | 9K | Well drained | D | Very limited | Very limited |
| Colthorp silt loam, 0 to 2 percent slopes | 9K | Well drained | D | Very limited | Very limited |
| Corder-Tadpole complex, 2 to 8 percent slopes | 8K | Well drained | D | Very limited | Very limited |
| Elfkin-Chilcott-Power complex, 0 to 4 percent slopes | 8K | Well drained | C | Very limited | Very limited |
| Paulmyers silt loam, 0 to 3 percent slopes | 8K | Somewhat poorly drained | C | Very limited | Very limited |
| Quailridge-Hullsgulch-Cranegulch complex, 15 to 50 percent slopes | 8K | Well drained | A | Very limited | Very limited |
| Power-McCain silt loams, 2 to 4 percent slopes | 8K | Well drained | C | Not limited | Very limited |
| Truesdale fine sandy loam, 0 to 2 percent slopes | 7K | Well drained | B | Somewhat limited | Very limited |
| Elijah silt loam, 0 to 2 percent slopes | 7K | Well drained | C | Somewhat limited | Very limited |
| Kunaton-Rubble land complex, 2 to 8 percent slopes | 7K | Well drained | D | Very limited | Very 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.
What This Means
Building & Foundations
About 46% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 86% 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
Drainage is generally favorable for gardening. Adding compost and mulch will improve fertility and water retention. Test your soil's pH before planting — most vegetables prefer 6.0-7.0.