Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 611 - PRIMARY DRINKING WATER STANDARDS
Subpart Y - STAGE 2 DISINFECTION BYPRODUCTS REQUIREMENTS
Section 611.975 - Conditions Requiring Increased Monitoring

a) If a supplier is required to monitor at a particular location annually or less frequently than annually pursuant to Section 611.971 or Section 611.973, it must increase monitoring to dual sample sets once per quarter (taken every 90 days) at all locations if a TTHM sample exceeds 0.080 mg/l or an HAA5 sample exceeds 0.060 mg/l at any location.

b) A supplier is in violation of the MCL when the LRAA exceeds the Subpart Y MCLs in Section 611.312(b)(2), calculated based on four consecutive quarters of monitoring (or the LRAA calculated based on fewer than four quarters of data if the MCL would be exceeded regardless of the monitoring results of subsequent quarters). The supplier is in violation of the monitoring requirements for each quarter that a monitoring result would be used in calculating an LRAA if it fails to monitor.

c) A supplier may return to routine monitoring once it has conducted increased monitoring for at least four consecutive quarters, and the LRAA for every monitoring location does not exceed 0.060 mg/l for TTHM and 0.045 mg/l for HAA5.