Operational Evaluation Level for Disinfectants/Disinfection Byproducts Rule

As Stage 2 of the Disinfectants and Disinfection Byproducts Rule is further implemented, public water systems are now required to meet Operational Evaluation Levels (OELs). A system exceeds the OEL when the sum of the two previous quarters’ results for Trihalomethanes (TTHM) and Haloactic Acids (HAA5), plus twice the current quarter’s result, divided by 4 to determine an average, exceeds a maximum contaminant level. See formula below:

1Q + 2Q + (2 X 3Q)       >     0.08 (TTHM) or

             4                      >     0.06 (HAA5)

An OELs exceedance is not a violation. Instead, the Ohio EPA states that the new requirement is “designed to warn water systems of potential future MCL exceedances.” However, water systems with an OELs exceedance are required to submit Ohio EPA Form 5031 within 90 days of notification, and those that do not submit the form will receive a reporting violation. For more information on completing the OELs report, visit the Ohio EPA website.