N.Y. Comp. Codes R. & Regs. tit. 10, § 5-1.64 – Operational evaluation levels.

(a) If a system exceeds the operational evaluation level at any monitoring location when the sum of the two previous quarters’ TTHM results plus twice the current quarter’s TTHM result, divided by 4 to determine the average, exceeds 0.080 mg/L, or when the sum of the two previous quarters’ HAA5 results plus twice the current quarter’s HAA5 result, divided by 4 to determine the average, exceeds 0.060 mg/L.
(b) If a system exceeds the operational evaluation level, it shall conduct an operational evaluation and 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 of the operational evaluation level. The written report shall be made available to the public upon request.
(c) The operational evaluation shall include an examination of the operational practices for system treatment(s) and the distribution system, 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 future exceedances.
1. (1) A system may request, and the State may allow, limiting the scope of the evaluation if the system is able to identify the cause of the operational evaluation level exceedance.
2. (2) The request to limit the scope of the evaluation does not extend the schedule in subdivision (b) of this section for submitting the written report. The State shall approve this limited scope of evaluation in writing, and the system shall keep that approval with the completed report.