# 35 Ill. Adm. Code 6110.611.603: Section 611.603 Inorganic Monitoring Frequency > Illinois · Regulations · In force URL: https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_603 ## Section - **Citation:** 35 Ill. Adm. Code 6110.611.603 - **Heading:** Section 611.603 Inorganic Monitoring Frequency - **Jurisdiction:** Illinois - **Kind:** Regulations - **Status:** In force - **Text as of:** August 14, 2026 - **Source:** Compiled text - **Location:** Illinois Administrative Code / Title 35 / / Part 6110 / Section 611.603 Inorganic Monitoring Frequency ## Text Section 611 TITLE 35: ENVIRONMENTAL PROTECTION SUBTITLE F: PUBLIC WATER SUPPLIES CHAPTER I: POLLUTION CONTROL BOARD PART 611 PRIMARY DRINKING WATER STANDARDS SECTION 611.603 INORGANIC MONITORING FREQUENCY Section 611.603  Inorganic Monitoring Frequency The frequency of monitoring conducted to determine compliance with the revised MCLs in Section 611.301 for antimony, arsenic, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium, and thallium is as follows: a)         Suppliers must take samples at each sampling point, beginning in the initial compliance period, as follows: 1)         For a GWS supplier:  at least one sample during each compliance period; 2)         For an SWS or a mixed system supplier:  at least one sample each year. BOARD NOTE: Derived from 40 CFR 141.23(c)(1). b)         SEP Application 1)         The supplier may apply to the Agency for a SEP that allows reduction from the monitoring frequencies specified in subsection (a) under subsections (d) through (f) and 35 Ill. Adm. Code 602.600. 2)         The supplier may apply to the Agency for a SEP that relieves it of the requirement for monitoring cyanide under subsections (d) through (f) and 35 Ill. Adm. Code 602.600 if it can demonstrate that its system is not vulnerable due to a lack of any industrial source of cyanide. BOARD NOTE:  Derived from 40 CFR 141.23(c)(2) and (c)(6). c)         SEP Procedures.  The Agency must review the request under the SEP procedures of 35 Ill. Adm. Code 602.600 based on consideration of the factors in subsection (e). BOARD NOTE:  Derived from 40 CFR 141.23(c)(6). d)         Standard for SEP Reduction in Monitoring.  The Agency must grant a SEP that allows a reduction in the monitoring frequency if the supplier demonstrates that all previous analytical results were less than the MCL if the supplier meets the following minimum data requirements: 1)         For GWS suppliers:  a minimum of three rounds of monitoring OTE:  Derived from 40 CFR 141.23(c)(6). d)         Standard for SEP Reduction in Monitoring.  The Agency must grant a SEP that allows a reduction in the monitoring frequency if the supplier demonstrates that all previous analytical results were less than the MCL if the supplier meets the following minimum data requirements: 1)         For GWS suppliers:  a minimum of three rounds of monitoring. 2)         For an SWS or mixed system supplier:  annual monitoring for at least three years. 3)         A supplier that uses a new water source is not eligible for a SEP until it completes three rounds of monitoring from the new source. BOARD NOTE:  Derived from 40 CFR 141.23(c)(4). e)         Standard for SEP Monitoring Conditions.  As a condition of any SEP, the Agency must require that the supplier take a minimum of one sample during the term of the SEP.  In determining the appropriate reduced monitoring frequency, the Agency must consider the following: 1)         Reported concentrations from all previous monitoring; 2)         The degree of variation in reported concentrations; and 3)         Other factors that may affect contaminant concentrations, such as changes in groundwater pumping rates, changes in the CWS's configuration, the CWS's operating procedures, or changes in stream flows or characteristics. BOARD NOTE:  Derived from 40 CFR 141.23(c)(3) and (c)(5). f)         SEP Conditions and Revision 1)         A SEP will expire at the end of the compliance cycle for which it was issued. BOARD NOTE:  Derived from 40 CFR 141.23(c)(3). 2)         In issuing a SEP, the Agency must specify the level of the contaminant upon which the "reliably and consistently" determination was based.  A SEP must provide that the Agency will review and, if appropriate, revise its determination of the appropriate monitoring frequency when the supplier submits new monitoring data or when other data relevant to the supplier's appropriate monitoring frequency become available he Agency must specify the level of the contaminant upon which the "reliably and consistently" determination was based.  A SEP must provide that the Agency will review and, if appropriate, revise its determination of the appropriate monitoring frequency when the supplier submits new monitoring data or when other data relevant to the supplier's appropriate monitoring frequency become available. BOARD NOTE:  Derived from 40 CFR 141.23(c)(6). g)         A supplier that exceeds the MCL as determined in Section 611.609, must monitor quarterly for that contaminant, beginning in the next quarter after the violation occurred. BOARD NOTE: Derived from 40 CFR 141.23(c)(7). h)         Reduction of Quarterly Monitoring 1)         The Agency must grant a SEP that reduces the monitoring frequency to that specified by subsection (a) if it determines that the sampling point is reliably and consistently below the MCL. 2)         A request for a SEP must include the following minimal information: A)        For a GWS:  two quarterly samples. B)        For an SWS or mixed system supplier:  four quarterly samples. 3)         In issuing the SEP, the Agency must specify the level of the contaminant upon which the "reliably and consistently" determination was based.  Any SEP that allows less frequent monitoring based on an Agency "reliably and consistently" determination must include a condition requiring the supplier to resume quarterly monitoring for any contaminant under subsection (g) if it violates the MCL specified by Section 611.609 for that contaminant. BOARD NOTE: Derived from 40 CFR 141.23(c)(8). i)          A new system supplier or a supplier whose system uses a new source of water must demonstrate compliance with the MCL within a period of time specified by a permit issued the Agency.  The supplier must also comply with the initial sampling frequencies specified by the Agency to ensure a system can demonstrate compliance with the MCL t. BOARD NOTE: Derived from 40 CFR 141.23(c)(8). i)          A new system supplier or a supplier whose system uses a new source of water must demonstrate compliance with the MCL within a period of time specified by a permit issued the Agency.  The supplier must also comply with the initial sampling frequencies specified by the Agency to ensure a system can demonstrate compliance with the MCL.  Routine and increased monitoring frequencies must be conducted in compliance with this Section. BOARD NOTE: Derived from 40 CFR 141.23(c)(9). ## Nearby sections - [35 Ill. Adm. Code 6110.611.601 Section 611.601 Monitoring Frequency](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_601.md) - [35 Ill. Adm. Code 6110.611.602 Section 611.602 Asbestos Monitoring Frequency](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_602.md) - [35 Ill. Adm. 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Code 6110.611.612 Section 611.612 Monitoring Requirements for Old Inorganic MCLs](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_612.md) - [35 Ill. Adm. Code 6110.611.631 Section 611.631 Special Monitoring for Inorganic Chemicals (Repealed)](https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_631.md) --- Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/STATE_IL_IAC_T35_P6110_S611_603. Check the current official text before relying on it. Not legal advice.