All public water systems that monitor quarterly under the Stage 2 Disinfection By-Product Rule are required to perform Operational Evaluation Levels each quarter once the system has monitored for three quarters. The purpose of the OEL is to show which sites have the possibility of being out of compliance with THMs or HAAs the next quarter. For those sites that predicted to exceed the Operational Evaluation Levels (basically the MCLs for THMs and HAAs), the water system is to complete the checklist on the second page of the form. The checklist guides the water system through a series of steps to determine why the site may exceed the MCLs so that actions can be taken to prevent the noncompliance. The completed checklist is to be submitted to the Division of Water (DOW) within 90 days of the end of the quarter.
Example: ABC Water System started monitoring for THMs and HAAs under the Stage 2 Rule in October of 2013. They take four samples a quarter, in October, January, April and July. The April 2014 monitoring will be ABC Water System’s third quarter of monitoring. They will calculate the OELs for each site using three quarters of data and the DOW OEL Form. If the OEL is exceeded, ABC Water System will complete the checklist and submit the form to the DOW. ABC Water System will calculate OELs every quarter from April 2014 forward.
The Kentucky DOW revised the OEL Form based on comments and suggestions from several water systems. That revised form can be found on the Drinking Water Forms page at http://water.ky.gov/DrinkingWater/Pages/Forms.aspx. The OEL Form is in the Compliance Forms section.