Septic soil in Union County, NC, by the numbers
Very limited
Soil across 71.5% of Union County, NC rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 71.5% of it sits in USDA's most-constrained bucket. Union County, NC is 632.739 square miles with a population of 263,386.
What Union County's reading doesn't cover
This is a countywide, area-weighted figure across every soil survey map unit in Union County, NC - never a reading for one specific parcel. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Union County will actually do.
What a system would cost here
With 71.5% of Union 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.
How Union County, NC compares
Nationally, Union County, NC is the 2,422-most-constrained of 3,058 rated counties for septic soil. Within North Carolina alone it ranks 52 of 97.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems