Septic suitability in Nantucket County, MA
Very limited
Nantucket County, MA's SSURGO dominant class comes back "Very limited", covering 77.6% of the county. Practically, that rules out a simple gravity system for most of the county - 77.6% of it sits in USDA's most-constrained bucket. The county spans 46.192 square miles, home to 14,670 people.
What this number does and doesn't tell you
Nantucket County'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.
Nantucket County: conventional vs. engineered cost
77.6% of Nantucket County 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, Nantucket County, MA ranks 2,155 most-constrained nationally, and 9 of 14 within Massachusetts.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems