Septic suitability in Boulder County, CO
Very limited
USDA puts Boulder County, CO at "Very limited" for septic absorption fields, the dominant reading across 95.5% of the county's soil. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 95.5% of the county. The county spans 726.416 square miles, home to 330,262 people.
What this number does and doesn't tell you
Boulder 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.
Boulder County: conventional vs. engineered cost
95.5% of Boulder 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.
How Boulder County, CO compares
Among the 3,058 rated counties on this site, Boulder County, CO ranks 591 most-constrained nationally, and 3 of 63 within Colorado.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems