San Luis Obispo County's SSURGO septic rating
Very limited
San Luis Obispo County, CA: USDA's soil survey calls 96.6% of the county "Very limited" for a septic leach field. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 96.6% of San Luis Obispo County's land. For scale: 3,300.842 square miles and 281,843 people call San Luis Obispo County home.
Before you rely on this for one lot
Two lots a mile apart in San Luis Obispo County can carry different soil, even though they share one countywide rating. 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 San Luis Obispo County, CA
San Luis Obispo 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, San Luis Obispo County, CA ranks 426 most-constrained nationally, and 5 of 57 within California.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems