Section 611.7903  Compliance Requirements

a)         Compliance with MCLs for regulated PFAS in Section 611.311(c) must be determined based on the analytical results obtained at each sampling point.

b)         For suppliers monitoring quarterly, compliance with the MCL is determined by the running annual average at each sampling point.

c)         If a supplier fails to collect the required number of samples specified in Section 611.7902, this is a monitoring violation as described in Section 611.7905(c), and compliance calculations must be based on the total number of samples collected.

d)         Suppliers monitoring triennially whose sample result equals or exceeds the trigger level of 2.0 ng/l for either PFOS or PFOA, 5 ng/l for HFPO-DA, PFHxS, or PFNA, or a Hazard Index of 0.5 for the Hazard Index PFAS, must begin quarterly sampling for all regulated PFAS in the next quarter at the sampling point.  Suppliers monitoring annually whose sample result equals or exceeds the MCL of 4.0 ng/l for either PFOS or PFOA, 10 ng/l for HFPO-DA, PFHxS, or PFNA, or a Hazard Index of 1 for the Hazard Index PFAS, must begin quarterly sampling for all regulated PFAS in the next quarter at the sampling point.

e)         Except as provided in this subsection (e), if a sample result exceeds an MCL, the supplier will not be considered in violation of the MCL until it has completed one year of quarterly sampling at the sampling point with the triggering sample used as the first quarter of monitoring for the running annual average calculation. However, whenever a sample result in any quarter (or quarterly average, if more than one compliance sample is available in a quarter because a confirmation sample was required by the Agency) causes the running annual average to exceed the MCL at a sampling point regardless of the subsequent quarterly monitoring results required to complete a full year of monitoring (e.g., the results from a single sample are more than 4 times the MCL), the supplier is out of compliance with the MCL immediately.

f)         Suppliers must calculate compliance using the following method to determine MCL compliance at each sampling point:

1)         For each PFAS regulated by an individual MCL:

A)        For suppliers monitoring quarterly, divide the sum of the measured quarterly concentrations for each analyte by the number of quarters samples were collected for that analyte during the consecutive quarters included in the calculation.  If more than one compliance sample for that analyte is available in a quarter because a confirmation sample was required by the Agency, suppliers must average all the results in a quarter then average the quarterly averages.  Rounding does not occur until the end of the calculation. If the running annual average exceeds the MCL, the supplier is not in compliance with the MCL requirements.

B)        For suppliers monitoring annually, if the concentration measured is equal to or exceeds an MCL for regulated PFAS, the supplier is required to initiate quarterly monitoring for all regulated PFAS beginning in the next quarter at the sampling point, with the triggering sample result used as the first quarter of monitoring for the running annual average calculation.

C)        For suppliers monitoring triennially, if the concentration measured is equal to or exceeds the trigger level, the supplier is required to initiate quarterly monitoring for all regulated PFAS beginning in the next quarter at the sampling point, with the triggering sample result used as the first quarter of monitoring for the running annual average calculation.

D)        For the purpose of calculating MCL compliance, if a sample result is less than the practical quantitation level (PQL) for a regulated PFAS, in compliance with the following table, zero is used for that analyte solely to calculate the running annual average.

Section 611.7903 (f)(1)(D) Practical Quantitation Levels (PQLS) For PFAS Contaminant

2)         For each PFAS regulated under the Hazard Index MCL:

A)        For suppliers monitoring quarterly, divide the observed sample analytical result for each analyte included in the Hazard Index by the corresponding HBWC listed in Section 611.311(c) to obtain a hazard quotient for each analyte for each sampling event at each sampling point.  Sum the resulting hazard quotients together to determine the Hazard Index for the quarter.  If the Agency requires a confirmation sample for an analyte in the quarter, suppliers must average these results for each analyte in that quarter and then determine the hazard quotient(s) from those average values, then sum the hazard quotients.  Once the Hazard Indices for the individual quarters are calculated, they are averaged to determine a running annual average. If the running annual average Hazard Index exceeds the MCL and two or more Hazard Index analytes had an observed sample analytical result at or above the PQL in any of the quarterly samples collected to determine the running annual average, the supplier is in violation of the Hazard Index MCL.  No rounding occurs until after the running annual average Hazard Index is calculated.

B)        If the Hazard Index calculated using the results of an annual sample equals or exceeds the Hazard Index MCL, the supplier must initiate quarterly sampling for all regulated PFAS beginning in the next quarter at the sampling point, with the triggering sample result used as the first quarter of monitoring.

C)        If the Hazard Index calculated using the results of a triennial sample equals or exceeds the Hazard Index trigger level, the supplier must initiate quarterly sampling for all regulated PFAS beginning in the next quarter at the sampling point, with the triggering sample result used as the first quarter of monitoring.

D)        If a sample result is less than the practical quantitation level for a regulated PFAS, in compliance with the table 1 to subsection (f)(1)(D), zero is used for that analyte solely to calculate the running annual average.

BOARD NOTE:  This Section derives from 40 CFR 141.903

(Source:  Added at 50 Ill. Reg. 2531, effective February 17, 2026)