What Tompkins County, NY's soil rates for a septic system
Very limited
In Tompkins County, NY, 90% of the surveyed land carries a "Very limited" rating for a standard septic drain field. Practically, that rules out a simple gravity system for most of the county - 90% of it sits in USDA's most-constrained bucket. Tompkins County, NY is 474.65 square miles with a population of 105,602.
What Tompkins County's reading doesn't cover
Nothing about Tompkins County, NY's SSURGO figure applies to a specific address - it's a county-wide average. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Tompkins County will actually do.
What a system would cost here
With 90% of Tompkins 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.
Tompkins County's rank among New York counties
Nationally, Tompkins County, NY is the 1,266-most-constrained of 3,058 rated counties for septic soil. Within New York alone it ranks 32 of 61.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems