What Blaine County, MT's soil rates for a septic system

Very limited

Soil across 80.3% of Blaine County, MT rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 80.3% of it sits in USDA's most-constrained bucket. Blaine County covers 4,227.517 square miles and counts 6,903 residents.

This is a county figure, not a parcel figure

This is a countywide, area-weighted figure across every soil survey map unit in Blaine County, MT - never a reading for one specific parcel. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Blaine County.

System cost, conventional vs. engineered

Given Blaine County's rating, plan for the engineered-system range rather than the conventional one. The engineered-system range, $10,000-$40,000 (mound or aerobic treatment), is the more realistic number to plan around, against $3,000-$8,000 for a conventional system on the rare lot that passes.

Blaine County's rank among Montana counties

Nationally, Blaine County, MT is the 2,028-most-constrained of 3,058 rated counties for septic soil. Within Montana alone it ranks 30 of 54.

Further reading

How this rating is built, and its real limits · Conventional vs. engineered septic systems