Walker County, AL: the USDA septic-suitability picture
Very limited
Walker County, AL: USDA's soil survey calls 92% of the county "Very limited" for a septic leach field. A standard gravity system routinely fails on ground like this; the same share of the county falls in USDA's worst absorption-field bucket outright. For scale: 791.061 square miles and 65,260 people call Walker County home.
Before you rely on this for one lot
This is a countywide, area-weighted figure across every soil survey map unit in Walker County, AL - never a reading for one specific parcel. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).
Budgeting for a system in Walker County, AL
Walker County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. 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, Walker County, AL ranks 1,039 most-constrained nationally, and 11 of 67 within Alabama.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems