Septic suitability in Chatham County, NC
Very limited
Chatham County, NC's SSURGO dominant class comes back "Very limited", covering 60.7% of the county. Practically, that rules out a simple gravity system for most of the county - 60.7% of it sits in USDA's most-constrained bucket. The county spans 681.474 square miles, home to 83,874 people.
What this number does and doesn't tell you
Chatham 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.
Chatham County: conventional vs. engineered cost
60.7% of Chatham 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, Chatham County, NC ranks 2,716 most-constrained nationally, and 70 of 97 within North Carolina.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems