Section 611.161  Case-by-Case Reduced Subpart Y Monitoring for Wholesale and Consecutive Systems

The Agency may issue a SEP reducing monitoring under Subpart Y as they apply to a wholesale system or a consecutive system, otherwise than as Section 611.500 provides, subject to limitations:

a)         The Agency must consider the certain system-specific factors in making its determination:

1)         The amount and percentage of finished water the PWS provides;

2)         Whether finished the PWS provides water seasonally, intermittently, or full-time;

3)         Improved DBP occurrence information based on IDSE results;

4)         Significant changes in the supplier's raw water quality, treatment, or distribution system after completing the IDSE; and

5)         Other considerations bearing on DBP occurrence in the supplier's distribution system and the ability of the reduced monitoring to detect DBP in that distribution system.

b)         Any reduced monitoring the Agency allows under this Section must require that the PWS maintain a minimum of one compliance monitoring location.

c)         The supplier must report any changes in its raw water quality, treatment, or distribution system or any other factors arising after the Agency issues the SEP under this Section that would bear on occurrence of DBP in the supplier's distribution system and the supplier's ability to detect DBP in its distribution system under the reduced monitoring.

BOARD NOTE:  This Section derives from 40 CFR 142.16(m) and the preamble discussion at 71 Fed. Reg. 388, 430-31 (Jan. 4, 2006).  USEPA stated that the State may authorize reduced monitoring under a State-devised procedure.  The Board borrowed from USEPA's special primacy requirements for its subpart V:  State 2 Disinfection Byproducts Requirements and the accompanying preamble discussion to derive the procedure in this Section.

(Source:  Amended at 47 Ill. Reg. 16486, effective November 2, 2023)