Section 611.925  Subpart Y Compliance Monitoring Location Recommendations

a)         A supplier's IDSE report must include its recommendations and justification for where and during what months it will conduct TTHM and HAA5 monitoring for Subpart Y.  The supplier must base its recommendations on the criteria set forth in subsections (b) through (e).

b)         The supplier must select the number of monitoring locations specified in the applicable of subsections (b)(1) through (b)(13), subject to the limitations of subsections (b)(14) and (b)(15).  The supplier will use these recommended locations as Subpart Y routine compliance monitoring locations, unless the Agency requires different or additional locations.  The supplier should distribute locations throughout the distribution system to the extent possible.

1)         A Subpart B system supplier that serves fewer than 500 persons must annually collect samples from two monitoring locations:  one sample from the highest TTHM location and one sample from the highest HAA5 location.

2)         A Subpart B system supplier that serves 500 to 3,300 persons must quarterly collect samples from two monitoring locations:  one sample from the highest TTHM location and one sample from the highest HAA5 location.

3)         A Subpart B system supplier that serves 3,301 to 9,999 persons must quarterly collect samples from two monitoring locations:  one sample from the highest TTHM location and one sample from the highest HAA5 location.

4)         A Subpart B system supplier that serves 10,000 to 49,999 persons must quarterly collect samples from four monitoring locations:  two samples from the highest TTHM locations, one sample from the highest HAA5 location, and one sample from an existing Subpart I compliance location.

5)         A Subpart B system supplier that serves 50,000 to 249,999 persons must quarterly collect samples from eight monitoring locations:  three samples from the highest TTHM location, three samples from the highest HAA5 locations, and two samples from existing Subpart I compliance locations.

6)         A Subpart B system supplier that serves 250,000 to 999,999 persons must quarterly collect samples from 12 monitoring locations:  five samples from the highest TTHM location, four samples from the highest HAA5 locations, and three samples from existing Subpart I compliance locations.

7)         A Subpart B system supplier that serves 1,000,000 to 4,999,999 persons must quarterly collect samples from 16 monitoring locations:  six samples from the highest TTHM location, six samples from the highest HAA5 locations, and four samples from existing Subpart I compliance locations.

8)         A Subpart B system supplier that serves more than 5,000,000 persons must quarterly collect samples from 20 monitoring locations:  eight samples from the highest TTHM location, seven samples from the highest HAA5 locations, and five samples from existing Subpart I compliance locations.

9)         A groundwater system supplier that serves fewer than 500 persons must annually collect samples from two monitoring locations:  one sample from the highest TTHM location and one sample from the highest HAA5 location.

10)         A groundwater system supplier that serves 500 to 9,999 persons must annually collect samples from two monitoring locations:  one sample from the highest TTHM location and one sample from the highest HAA5 location.

11)         A groundwater system supplier that serves 10,000 to 99,999 persons must quarterly collect samples from four monitoring locations:  two samples from the highest TTHM locations, one sample from the highest HAA5 location, and one sample from an existing Subpart I compliance location.

12)         A groundwater system supplier that serves 100,000 to 499,999 persons must quarterly collect samples from six monitoring locations:  three samples from the highest TTHM locations, two samples from the highest HAA5 locations, and one sample from an existing Subpart I compliance location.

13)         A groundwater system supplier that serves more than 500,000 persons must quarterly collect samples from eight monitoring locations:  three samples from the highest TTHM locations, three samples from the highest HAA5 locations, and two samples from existing Subpart I compliance locations.

14)         The supplier must monitor during the month of highest DBP concentrations.

15)         A supplier on quarterly monitoring must take dual sample sets every 90 days at each monitoring location, except for a Subpart B system supplier that serves 500 to 3,300 persons.  A groundwater system supplier that serves 500 to 9,999 persons which is on annual monitoring must take dual sample sets at each monitoring location.  Any other supplier that is on annual monitoring or which is a Subpart B system supplier that serves 500 to 3,300 persons is required to take individual TTHM and HAA5 samples (instead of a dual sample set) at the locations with the highest TTHM and HAA5 concentrations, respectively.  For a supplier that serves fewer than 500 people, only one location with a dual sample set per monitoring period is needed if the highest TTHM and HAA5 concentrations occur at the same location and month.

c)         The supplier must recommend Subpart Y compliance monitoring locations based on standard monitoring results, system-specific study results, and Subpart I compliance monitoring results.  The supplier must follow the protocol in subsections (c)(1) through (c)(8).  If required to monitor at more than eight locations, the supplier must repeat the protocol as necessary.  If the supplier does not have existing Subpart I compliance monitoring results or if the supplier does not have enough existing Subpart I compliance monitoring results, the supplier must repeat the protocol, skipping the provisions of subsections (c)(3) and (c)(7) as necessary, until the supplier has identified the required total number of monitoring locations.

1)         The location with the highest TTHM LRAA not previously selected as a Subpart Y monitoring location.

2)         The location with the highest HAA5 LRAA not previously selected as a Subpart Y monitoring location.

3)         The existing Subpart I average residence time compliance monitoring location (maximum residence time compliance monitoring location for a groundwater system) with the highest HAA5 LRAA not previously selected as a Subpart Y monitoring location.

4)         The location with the highest TTHM LRAA not previously selected as a Subpart Y monitoring location.

5)         The location with the highest TTHM LRAA not previously selected as a Subpart Y monitoring location.

6)         The location with the highest HAA5 LRAA not previously selected as a Subpart Y monitoring location.

7)         The existing Subpart I average residence time compliance monitoring location (maximum residence time compliance monitoring location for a groundwater system) with the highest TTHM LRAA not previously selected as a Subpart Y monitoring location.

8)         The location with the highest HAA5 LRAA not previously selected as a Subpart Y monitoring location.

d)         The supplier may recommend locations other than those specified in subsection (c) if the supplier includes a rationale for selecting other locations.  If the Agency approves the alternative locations, the supplier must monitor at these locations to determine compliance under Subpart Y.

e)         The supplier's recommended schedule must include Subpart Y monitoring during the peak historical month for TTHM and HAA5 concentration, unless the Agency approves another month.  Once the supplier has identified the peak historical month, and if the supplier is required to conduct routine monitoring at least quarterly, the supplier must schedule Subpart Y compliance monitoring at a regular frequency of every 90 or fewer days.

BOARD NOTE:  Derived from 40 CFR 141.605 (2016).

(Source:  Amended at 42 Ill. Reg. 1140, effective January 4, 2018)