Section 611.604  Nitrate Monitoring

Each supplier must monitor to determine compliance with the MCL for nitrate in Section 611.301.

a)         Suppliers must monitor at the following frequencies:

1)         CWSs and NTNCWSs

A)        GWSs:  annually;

B)        SWSs and mixed systems:  quarterly.

BOARD NOTE:  Derived from 40 CFR 141.23(d)(1).

2)         Transient non-CWSs:  annually.

BOARD NOTE:  Derived from 40 CFR 141.23(d)(4).

b)         Quarterly Monitoring for GWSs

1)         A CWS or NTNCWS supplier that is a GWS must initiate quarterly monitoring in the quarter following any one sample that has a nitrate concentration equal to or greater than 50 percent of the MCL.

2)         The Agency must grant a SEP that reduces the monitoring frequency to annual after the supplier has completed quarterly sampling for at least four quarters if it determines that the sampling point is reliably and consistently below the MCL.

A)        The request must include the following minimal information:  the results from four consecutive quarterly samples.

B)        In issuing the SEP, the Agency must specify the level of the contaminant upon which the "reliably and consistently" determination was based.  All SEPs that allow less frequent monitoring based on an Agency "reliably and consistently" determination must include a condition requiring the supplier to resume quarterly monitoring under subsection (b)(1) if it violates the MCL specified by Section 611.301 for nitrate.

BOARD NOTE:  Derived from 40 CFR 141.23(d)(2).

c)         Reduction of Monitoring Frequency for SWSs and Mixed Systems

1)         The Agency must grant a SEP that allows a CWS or NTNCWS supplier that is a SWS or mixed system to reduce its monitoring frequency to annually if it determines that all analytical results from four consecutive quarters are less than 50 percent of the MCL.

2)         As a condition of the SEP, the Agency must require the supplier to initiate quarterly monitoring, beginning the next quarter, if any one sample is greater than or equal to 50 percent of the MCL.

BOARD NOTE:  Derived from 40 CFR 141.23(d)(3).

d)         This subsection corresponds with 40 CFR 141.23(d)(4), which the Board has codified at subsection (a)(2).  This statement maintains structural consistency with USEPA rules.

e)         After completion of four consecutive quarters of monitoring, each CWS or NTNCWS supplier monitoring annually must take samples during the quarters that resulted in the highest analytical result.

BOARD NOTE:  Derived from 40 CFR 141.23(d)(5).

(Source:  Amended at 44 Ill. Reg. 6996, effective April 17, 2020)