Operational Evaluation Level – Stage 2 DBP Rule Process

The Stage 2 Disinfection By-Products (DBP) Rule requires monitoring for disinfection by-products, including Total Trihalomethane (TTHM) and Haloacetic Acid (HAA5) at specific sites within the distribution system. The Operational Evaluation Level (OEL) is a Stage 2 DBP Rule process for “predicting” the next quarter’s compliance for THMs and HAAs.

For those systems required to comply with the OEL rule, you will calculate your first OEL, by each location, when you have completed three quarters of monitoring and then every quarter afterwards.  If the OEL process “predicts” that a location will be out of compliance, two things should happen:

  1. The OEL form must be completed for each location that is predicted to be out of compliance for THMs and/or HAAs. The form must be sent to the Kentucky Division of Water (DOW) drinking water program within 90 days of receiving your current THM and HAA results.  The OEL form includes a close examination of your system’s treatment and distribution operational practices, including storage tank operations, excess storage capacity, distribution system flushing, changes in sources or source water quality and treatment changes or problems that may contribute to TTHM and HAA5 formation and what steps could be considered to minimize these exceedences.
  2. Use the OEL form to proactively implement treatment and distribution changes to avoid the predicted noncompliance.

The OEL form is now out on the Division of Water website for water systems to begin using.

It is important to note that only water systems on quarterly monitoring are required to do the OEL. Those on annual monitoring do not have to comply with this part of the Stage 2 Rule. Schedule 1 systems will need to comply with the OEL requirement after their third quarter of monitoring (which will be the fourth quarter of 2012). Reports are due no later than the tenth of the month following the quarter (first OEL report is due by April 10, 2013).

More information on the OEL rule may be found at 40 CFR141.626(a), by emailing envhelp@ky.gov or by contacting the Division of Water at 502-564-3410.

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