Step 4: Determine Operational Evaluation Level
The Stage 2 DBPR states that a system exceeds the Operational Evaluation Level (OEL) if one of the following occurs at any compliance monitoring location (40 CFR 141.626(a)):
- TTHM compliance monitoring results for the two previous quarters plus two times the TTHM result for the current quarter, divided by 4, exceeds 0.080 milligrams per liter (mg/L); or
- HAA5 compliance monitoring results for the two previous quarters plus two times the HAA5 result for the current quarter, divided by 4, exceeds 0.060 mg/L.
You can use the formula below to determine if you have an OEL exceedance. Example 1.1 shows how this formula can be used with distribution system TTHM and HAA5 data.
- Formula for Determining if You Have an OEL Exceedance.
For both TTHM and HAA5 and for each compliance monitoring location, calculate the following:
A = B = C = D =
(A + B + (2 * C)) / 4 = D
TTHM or HAA5 result for the quarter before the previous quarter (mg/L) TTHM or HAA5 result for the previous quarter (mg/L)
TTHM or HAA5 result for the current quarter (mg/L)
your Operational Evaluation Value (mg/L) If D for TTHM is > 0.080 mg/L, you have an OEL Exceedance If D for HAA5 is > 0.060 mg/L, you have an OEL Exceedance. If the OEL is exceeded, you must take the following actions:
- Conduct an operational evaluation to determine the cause of the exceedance(s).
- Submit a written report of the evaluation to the State no later than 90 days after being notified of the analytical result that caused the exceedance(s).
- Keep a copy of the operational evaluation report and make it available to the public upon request.
Download Stage 2 Operational Evaluation.