Pima County, AZ's soil, for a septic absorption field
Very limited
In Pima County, AZ, 62.7% of the surveyed land carries a "Very limited" rating for a standard septic drain field. 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. Pima County, AZ is 9,188.692 square miles with a population of 1,080,149.
What Pima County's reading doesn't cover
Pima County's rating is an average across the whole county, not a promise about any one lot inside it. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Pima County will actually do.
What a system would cost here
With 62.7% of Pima 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.
Pima County's rank among Arizona counties
Nationally, Pima County, AZ is the 2,670-most-constrained of 3,058 rated counties for septic soil. Within Arizona alone it ranks 13 of 15.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems