Stage 2 Disinfection Byproducts Rule | Drinking Water Compliance Assistance

Stage 2 Disinfectants and Disinfection Byproducts Rules (DBPRs) protects public health by requiring compliance monitoring for trihalomethanes (TTHM) and haloacetic acids (HAA5). The rule targets public water systems with the greatest risk.

What to Do If There's an Exceedance

TTHM or HAA5 Maximum Contaminant Level (MCL)
If the public water system is on annual or less frequent monitoring and has exceeded an MCL for TTHMs or HAA5s, the system will need to:

  • Begin increased monitoring (quarterly monitoring) at all sampling locations
  • Submit an increased monitoring plan (DWAR30)
  • Begin Operational Evaluation Level (OEL) calculations (DWAR 33) to determine if there is an exceedance and if a Full Operation Evaluation Level Report (DWAR 36) is required

If the public water system is on quarterly monitoring and the local running annual average has exceeded an MCL for TTHMs or HAA5s, the system will need to:

  • Issue a Tier 2 public notice within 30 days of being notified by the lab of the exceedance
  • Complete a Full Operation Evaluation Level Report (DWAR 36), if there is an OEL exceedance