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Operational Evaluation Requirements

Public water systems on quarterly monitoring schedules for disinfection byproducts must comply with operational evaluation requirements.

All community and non-transient, non-community water systems conducting DBP quarterly monitoring must also comply with the operational evaluation requirements. This evaluation assesses source water, treatment, and distribution system processes, and helps identify actions to decrease any high DBP levels and avoid maximum contaminant level violations. The Operational Evaluation must be completed when your system has an exceedance of the Operational Evaluation Level.

Calculating the Operational Evaluation Level

The operational evaluation level (OEL) must be calculated every quarter by using the three most recent quarters of results at one sample location.

Example formula: Q2 + Q3 + Q4 + Q4 / 4 = OEL

  • If the OEL for TTHM is more than 0.080 mg/L (80 µg/L) then you have an exceedance.
  • If the OEL for HAA5 is more than 0.060 mg/L (60 µg/L) then you have an exceedance.

Example data set for TTHM:

Calculations (mg/L) 4Q2016

OEL: 0.073+0.067+0.103+0.103/4=

0.0865 mg/L
LRAA: 0.056+0.073+0.067+0.103/4= 0.07475 mg/L

In this example the system has a TTHM OEL exceedance and would have to complete an Operational Evaluation. The system did not exceed the TTHM MCL. 

Operational Evaluation Report

In the event of an OEL exceedance, water systems must conduct an operational evaluation. The TCEQ provides the Operational Evaluation Report (TCEQ form 20797) to assist water systems with the evaluation. The operational evaluation prompts water systems to identify changes or problems within the water system that could be responsible for the exceedance and to assess possible solutions.

An OEL exceedance is not a violation and does not require a public notification. Failure to complete and return the Operational Evaluation Report  within 90 days of the exceedance will result in a monitoring and reporting violation and require that you provide public notification.

A maximum contaminant level violation can occur in the same quarter as an OEL exceedance.

Complete the Operational Evaluation Report and return to TCEQ within 90 days of notification of the exceedance to:                                                                             or                                                                            
TCEQ, Drinking Water Standards
MC-155 Attn OEL
P.O. Box 13087
Austin TX 78711-3087

  • If you need assistance completing the evaluation, or for help navigating the website contact the TCEQ DBP compliance coordinator at (512) 239-4691 or at the DBP email above.
  • To request free assistance for your DBP issues contact the Financial, Managerial, and Technical Assistance program at (512) 239-4691 or
  • To view your system's DBP results, visit Drinking Water Watch.