St. Louis city's SSURGO septic rating
Very limited
St. Louis city, MO: USDA's soil survey calls 56.9% of the county "Very limited" for a septic leach field. That reading means a conventional system is a poor bet here - 56.9% of St. Louis city lands in the strictest "very limited" bucket USDA uses. The county spans 61.717 square miles, home to 279,695 people.
What this number does and doesn't tell you
St. Louis city's rating is an average across the whole county, not a promise about any one lot inside it. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
St. Louis city: conventional vs. engineered cost
56.9% of St. Louis city carrying a "Very limited" reading changes the realistic budget here. 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, St. Louis city, MO ranks 2,783 most-constrained nationally, and 113 of 114 within Missouri.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems