Larimer County spells out the modern soil evaluation in detail: minimum two test pits in the proposed treatment area, typically 40–50 feet apart, dug to 8 feet (or to groundwater/bedrock) with a benched 45-degree entry. Pits stay open for inspection by the county and the soils engineer, and evaluations are done by a professional engineer or under one's supervision.

Pit spec	Minimum two test pits in the proposed soil treatment area, typically 40–50 feet apart, 8 feet deep (or to groundwater/bedrock if shallower), with a flat bench at 4 feet and a 45-degree slope back to the surface for entry.
Who performs	A professional engineer, or work done under an engineer's supervision. Full engineered design is required when percolation rates fall outside 5–60 minutes per inch, soil types are R/3A/4/4A/5, bedrock or groundwater is within 4 feet, pressure distribution is used, or slopes exceed 30%.
County inspection	The county inspects open test pits during the permit application at no extra charge; if pits are filled in before you apply, a separate site evaluation (with an extra fee) is required. Site evaluations have been mandatory for new OWTS applications since June 4, 2018.
Timing	Allow at least 5 business days to schedule a site evaluation; keep pits barricaded and open until the county and designer have both looked.

Details to confirm with the county

We couldn't confirm the following from Larimer County's official pages. Check these with the county before you rely on them:

• Current site-evaluation fee amounts (county fee schedule).
• Winter practice when pits can't be dug — ask Environmental Health.

Verified July 2026 · Source: Larimer County — Septic Systems (OWTS) site evaluation requirements