Marengo County, AL's soil, for a septic absorption field

Very limited

Soil across 93.6% of Marengo County, AL rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 93.6% of it sits in USDA's most-constrained bucket. Marengo County, AL is 976.898 square miles with a population of 18,512.

What Marengo County's reading doesn't cover

USDA's survey covers the whole of Marengo 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 Marengo County will actually do.

What a system would cost here

With 93.6% of Marengo 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.

Marengo County's rank among Alabama counties

Nationally, Marengo County, AL is the 854-most-constrained of 3,058 rated counties for septic soil. Within Alabama alone it ranks 8 of 67.

Further reading

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