What a site evaluation is and what the evaluator actually tests and documents.

A site evaluation is a mandatory, pre-design investigation performed on every tract where an OSSF will be installed, conducted by a licensed site evaluator or a professional engineer, and documented in a report submitted with the planning materials (30 TAC §285.30). The evaluator drills two soil borings or excavates two backhoe pits at opposite ends of the proposed disposal area, performs a soil texture analysis (and a sieve/gravel analysis in Class II or III soils), checks for a restrictive horizon, looks for groundwater indications within 24 inches of the bottom of the excavation, determines slope and poor-drainage/complex-slope areas, delineates the 100-year floodplain from FEMA maps, and locates every feature that triggers a separation distance under §285.91(10) — all plotted on the scale site drawing required by §285.5(a) (30 TAC §285.30). TCEQ states this pre-construction evaluation must occur before an OSSF is constructed, installed, altered, extended, or repaired, and that it includes a survey of the entire lot plus a soil analysis in the proposed disposal area (TCEQ, Getting a Permit for an OSSF); local authorities add mechanics, e.g., Williamson County requires the owner to open two profile holes 24 inches wide and 5 feet deep (or to solid rock) at opposite ends of the drainfield and keep them open for inspector verification (Williamson County OSSF Guide).

Reviewed August 2026. Links go to the sources this answer was checked against.