Conventional systems typically don't require it. Aerobic systems serving sensitive watersheds (close to streams or wells) may require quarterly NH3, BOD, and TSS testing under Ohio EPA permits.
More detail
Effluent testing is a regulatory requirement for some ATU installations and a diagnostic tool for troubleshooting drain-field issues. The three standard parameters: BOD (biochemical oxygen demand, measures organic load), TSS (total suspended solids, measures particulate load), and NH3 (ammonia, indicator of bacterial digestion completeness). Standard Ohio ATU permits set effluent limits like BOD ≤ 25 mg/L, TSS ≤ 30 mg/L, NH3 ≤ 5 mg/L for surface-discharge systems. Conventional systems do not typically require testing because soil treatment in the drain field handles the residual load. For a homeowner with persistent drain-field issues despite routine pumping, a one-time effluent test ($150-$300) can diagnose whether the problem is upstream (bacterial digestion failure in the tank) or downstream (drain-field saturation). County health departments maintain lists of certified labs. Cincinnati effluent-testing scenarios: most local install teams encounter effluent testing as either an Ohio EPA permit requirement for ATU surface-discharge systems (quarterly schedule typical), or a one-off diagnostic to troubleshoot drain-field issues that persist despite normal pumping. Cost for a one-off diagnostic test is $150-$300 from a certified lab. The result helps separate upstream (tank-bacteria) from downstream (drain-field) failures.