Allegany County, MD's soil, for a septic absorption field
Very limited
In Allegany County, MD, 91.3% of the surveyed land carries a "Very limited" rating for a standard septic drain field. That reading means a conventional system is a poor bet here - 91.3% of Allegany County lands in the strictest "very limited" bucket USDA uses. Allegany County, MD is 422.199 square miles with a population of 67,097.
What Allegany County's reading doesn't cover
Two lots a mile apart in Allegany County can carry different soil, even though they share one countywide rating. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Allegany County will actually do.
What a system would cost here
With 91.3% of Allegany 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, Allegany County, MD is the 1,131-most-constrained of 3,058 rated counties for septic soil. Within Maryland alone it ranks 3 of 23.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems