St. Mary's County, MD: the USDA septic-suitability picture

Very limited

St. Mary's County, MD: USDA's soil survey calls 85.7% of the county "Very limited" for a septic leach field. That reading means a conventional system is a poor bet here - 85.7% of St. Mary's County lands in the strictest "very limited" bucket USDA uses. For scale: 358.589 square miles and 116,469 people call St. Mary's County home.

Before you rely on this for one lot

Two lots a mile apart in St. Mary's County can carry different soil, even though they share one countywide rating. 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 St. Mary's County, MD

St. Mary's 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.

How St. Mary's County, MD compares

Among the 3,058 rated counties on this site, St. Mary's County, MD ranks 1,640 most-constrained nationally, and 8 of 23 within Maryland.

Further reading

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