Section 611.641  State-Only MCLs

a)         An analysis of substances for the purpose of determining compliance with the State-only MCLs of Section 611.310 must be made as follows:

1)         The Agency must issue a SEP requiring CWS suppliers utilizing surface water sources to collect samples during the period of the year when contamination by pesticides is most likely to occur.  The Agency must require the supplier to repeat these analyses at least annually.

2)         The Agency must issue a SEP requiring CWS suppliers utilizing only groundwater sources to collect samples at least once every three years.

b)         If the result of an analysis made under subsection (a) indicates that the level of any contaminant exceeds its State-only MCL, the CWS supplier must report to the Agency within seven days and initiate three additional analyses within one month.

c)         When the average of four analyses made under subsection (a), rounded to the same number of significant figures as the MCL for the substance in question, exceeds the State-only MCL, the CWS supplier must report to the Agency and give notice to the public under Subpart T of this Part.  Monitoring after public notification must be at a frequency designated by the Agency and must continue until the MCL has not been exceeded in two successive samples or until a monitoring schedule as a condition to a variance, adjusted standard, or enforcement action becomes effective.

d)         Analysis made to determine compliance with the State-only MCLs of Section 611.310 must be made in accordance with the appropriate methods specified in Section 611.645.

BOARD NOTE:  This provision now applies only to State-only MCLs.  This Section originally derived from 40 CFR 141.24(a) through (e), which USEPA removed and reserved.

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