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

Very limited

Soil across 68.8% of Carbon County, MT rates "Very limited" in USDA's septic-absorption-field interpretation. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 68.8% of Carbon County's land. Carbon County covers 2,047.889 square miles and counts 11,498 residents.

This is a county figure, not a parcel figure

USDA's survey covers the whole of Carbon County, MT at once, not any single address. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Carbon County.

System cost, conventional vs. engineered

Given Carbon 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.

Where this sits nationally

Nationally, Carbon County, MT is the 2,506-most-constrained of 3,058 rated counties for septic soil. Within Montana alone it ranks 47 of 54.

Further reading

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