Buchanan County, VA: the USDA septic-suitability picture
Very limited
Buchanan County, VA's SSURGO dominant class comes back "Very limited", covering 92.4% of the county. A standard gravity system routinely fails on ground like this; the same share of the county falls in USDA's worst absorption-field bucket outright. For scale: 502.855 square miles and 18,632 people call Buchanan County home.
Before you rely on this for one lot
Buchanan County's rating is an average across the whole county, not a promise about any one lot inside it. 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 Buchanan County, VA
Buchanan 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.
Where this sits nationally
Among the 3,058 rated counties on this site, Buchanan County, VA ranks 988 most-constrained nationally, and 9 of 110 within Virginia.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems