Septic suitability in Cascade County, MT
Very limited
Cascade County, MT's SSURGO dominant class comes back "Very limited", covering 88.5% of the county. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 88.5% of the county. The county spans 2,698.211 square miles, home to 84,523 people.
What this number does and doesn't tell you
Nothing about Cascade County, MT's SSURGO figure applies to a specific address - it's a county-wide average. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Cascade County: conventional vs. engineered cost
88.5% of Cascade County carrying a "Very limited" reading changes the realistic budget here. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
Where this sits nationally
Among the 3,058 rated counties on this site, Cascade County, MT ranks 1,417 most-constrained nationally, and 6 of 54 within Montana.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems