Colbert County, AL's soil, for a septic absorption field
Very limited
Soil across 67.8% of Colbert County, AL rates "Very limited" in USDA's septic-absorption-field interpretation. That reading means a conventional system is a poor bet here - 67.8% of Colbert County lands in the strictest "very limited" bucket USDA uses. Colbert County, AL is 592.953 square miles with a population of 58,785.
What Colbert County's reading doesn't cover
USDA's survey covers the whole of Colbert County, AL at once, not any single address. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Colbert County will actually do.
What a system would cost here
With 67.8% of Colbert County rating "Very limited", a standard gravity system is not a safe assumption here. 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, Colbert County, AL is the 2,534-most-constrained of 3,058 rated counties for septic soil. Within Alabama alone it ranks 49 of 67.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems