PURPOSE: This rule establishes monitoring and other requirements for achieving compliance with maximum contaminant levels based on locational running annual averages for certain disinfection by-products and for achieving compliance with maximum residual disinfectant levels for chlorine and chloramine for certain consecutive systems. This rule incorporates the requirements of subpart V of 40 CFR part 141, Stage 2 Disinfectants/Disinfection By-Products, published in the January 4, 2006, Federal Register.

1. (1) Stage 2 Disinfectants/Disinfection By- Products (D/DBP) Rule General Requirements.

   1. (A) The requirements of this rule constitute national primary drinking water regulations. This rule establishes monitoring and other requirements for achieving compliance with maximum contaminant levels based on locational running annual averages (LRAA) for total trihalomethanes (TTHM) and haloacetic acids five (HAA5), and for achieving compliance with maximum residual disinfectant residuals for chlorine and chloramine for certain consecutive systems.
   2. (B) Applicability. This rule applies to community water systems and nontransient noncommunity water systems that use a primary or residual disinfectant other than ultraviolet light or deliver water that has been treated with a primary or residual disinfectant other than ultraviolet light.

   3. (C) Compliance Schedules.

      1. 1. Systems must comply with the

requirements in this rule on the following schedule. The department may grant up to an additional twenty-four (24) months beyond the deadlines specified below for compliance with maximum contaminant levels (MCL) and operational evaluation levels if capital improvements are required to comply with an MCL.

1. A. Systems that are not part of a com-

bined distribution system and systems that serve the largest population in the combined distribution system.

1. (I) Systems serving ≥ 100,000

population must comply with this rule by April 1, 2012.

1. (II) Systems serving 50,000–

99,999 population must comply with this rule by October 1, 2012.

1. (III) Systems serving 10,000–

49,999 population must comply with this rule by October 1, 2013.

1. (IV) Systems serving <10,000

population must comply with this rule by October 1, 2013, if no Cryptosporidium monitoring is required under 10 CSR 60- 4.052(2)(A)4. or October 1, 2014, if Cryptosporidium monitoring is required under 10 CSR 60-4.052(2)(A)4.

1. B. Other systems that are part of a

combined distribution system. Consecutive system or wholesale system must comply with this rule at the same time as the system with the earliest compliance date in the combined distribution system.

1. 2. Monitoring frequency is specified in

paragraph (2)(A)2. of this rule.

1. A. If you are required to conduct

quarterly monitoring, you must begin monitoring in the first full calendar quarter that includes the applicable compliance date in paragraph (1)(C)1. of this rule.

1. B. If you are required to conduct

monitoring at a frequency that is less than quarterly, you must begin monitoring in the calendar month recommended in the Initial Distribution System Evaluation (IDSE) report prepared under Standard Monitoring or the System Specific studies in 40 CFR part 141 subpart U, incorporated by reference in 10 CSR 60-4.092, or the calendar month identified in the monitoring plan developed under section (3) of this rule no later than twelve (12) months after the compliance date in this table.

1. 3. If you are required to conduct quar-

terly monitoring, you must make compliance calculations at the end of the fourth calendar quarter that follows the compliance date and at the end of each subsequent quarter (or earlier if the LRAA calculated based on fewer than four (4) quarters of data would cause the MCL to be exceeded regardless of the monitoring results of subsequent quarters). If you are required to conduct monitoring at a frequency that is less than quarterly, you must make compliance calculations beginning with the first compliance sample taken after the compliance date.

1. 4. For the purpose of the schedule in

paragraph (1)(C)1. of this rule, the department may determine that the combined distribution system does not include certain consecutive systems based on factors such as receiving water from a wholesale system only on an emergency basis or receiving only a small percentage and small volume of water from a wholesale system. The department may also determine that the combined distribution system does not include certain wholesale systems based on factors such as delivering water to a consecutive system only on an emergency basis or delivering only a small percentage and small volume of water to a consecutive system.

1. (D) Monitoring and Compliance.

   1. 1. Systems required to monitor quarter-

ly. To comply with MCLs in section 10 CSR 60-4.090(1)(D) you must calculate LRAAs for TTHM and HAA5 using monitoring results collected under this rule and determine that each LRAA does not exceed the MCL. If you fail to complete four (4) consecutive quarters of monitoring, you must calculate compliance with the MCL based on the average of the available data from the most recent four (4) quarters. If you take more than one (1) sample per quarter at a monitoring location, you must average all samples taken in the quarter at that location to determine a quarterly average to be used in the LRAA calculation.

1. 2. Systems required to monitor yearly or

less frequently. To determine compliance with the Stage 2 D/DBP MCLs in subsection 10 CSR 60-4.090(1)(D), you must determine that each sample taken is less than the MCL. If any sample exceeds the MCL, you must comply with the requirements of section (6) of this rule. If no sample exceeds the MCL, the sample result for each monitoring location is considered the LRAA for that monitoring location.

1. (E) Violation. You are in violation of the monitoring requirements for each quarter that a monitoring result would be used in calculating an LRAA if you fail to monitor.

1. (2) Routine Monitoring.

   1. (A) Monitoring.

      1. 1. If you submitted an IDSE report, you

must begin monitoring at the locations and months you have recommended in your IDSE report submitted under the monitoring location recommendations and chart in 40 CFR part 141 subpart U, which is incorporated by reference in 10 CSR 60-4.092, following the schedule in subsection (1)(C) of this rule, unless the department requires other locations or additional locations after its review. If you submitted a 40/30 certification or qualified for a very small system waiver under 40 CFR part 141 subpart U, which is incorporated by reference in 10 CSR 60-4.092, or you are a nontransient noncommunity water system serving less than ten thousand (10,000) population, you must monitor at the location(s) and dates identified in your monitoring plan under 10 CSR 60-4.090(3)(A)3., updated as required by section (3) of this rule.

1. 2. You must monitor at no fewer than

the number of locations identified in the following table. Source water type

Surface water system or ground water under the direct influence of surface water:

Ground water:

1 All systems must monitor during month of highest DBP concentrations. 2 Systems on quarterly monitoring must take dual sample sets every 90 days at each monitoring location, except for surface water systems or ground water under the direct influence of surface water serving 500–3,300. Systems on annual monitoring and surface water systems or ground water under the direct influence of surface water serving 500–3,300 are required to take individual TTHM and HAA5 samples (instead of a dual sample set) at the location with the highest TTHM and HAA5 concentrations, respectively. Only one (1) 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, if monitored annually).

1. 3. If you are an undisinfected system

that begins using a disinfectant other than ultraviolet (UV) light after the dates in 40 CFR part 141 subpart U for complying with the Initial Distribution System Evaluation requirements, you must consult with the department to identify compliance monitoring locations for this rule. You must then develop a monitoring plan under section (3) of this rule that includes those monitoring locations.

1. (B) Analytical methods. You must use an approved method listed in 10 CSR 60-5.010 for TTHM and HAA5 analyses. Analyses must be conducted by laboratories that have received certification by Environmental Protection Agency (EPA) or the department as specified in 10 CSR 60-5.010.

1. (3) Stage 2 D/DBP Rule Monitoring Plan.

   1. (A) Developing and implementing a monitoring plan.

      1. 1. You must develop and implement a

monitoring plan to be kept on file for depart- Stage 2 D/DBP Routine Monitoring

Population size category

<500 500–3,300 3,301–9,999 10,000–49,999 50,000–249,999 250,000–999,999 1,000,000–4,999,999 (cid:149) 5,000,000

<500 500–9,999 10,000–99,999 100,000–499,999 (cid:149)500,000

ment and public review. The monitoring plan must contain the following elements and be complete no later than the date you conduct your initial monitoring under this rule:

1. A. Monitoring locations;
2. B. Monitoring dates;
3. C. Compliance calculation proce-

dures; and

1. D. Monitoring plans for any other

systems in the combined distribution system if the department has reduced monitoring requirements.

1. 2. If you were not required to submit an

IDSE report under either Standard Monitoring or System Specific Studies in 40 CFR part 141 subpart U, and you do not have sufficient Stage 1 D/DBP rule monitoring locations to identify the required number of Stage 2 D/DBP rule compliance monitoring locations indicated in the Monitoring Location Recommendations table in 40 CFR part 141 subpart U, you must identify additional locations by alternating selection of locations representing high TTHM levels and Monitoring Frequency1

Per year Per quarter Per quarter Per quarter Per quarter Per quarter Per quarter Per quarter

Per year Per year Per quarter Per quarter Per quarter

high HAA5 levels until the required number of compliance monitoring locations have been identified. You must also provide the rationale for identifying the locations as having high levels of TTHM or HAA5. If you have more Stage 1 D/DBP rule monitoring locations than required for Stage 2 D/DBP rule compliance monitoring, detailed in the Monitoring Location Recommendations table in 40 CFR part 141 subpart U, you must identify which locations you will use for Stage 2 D/DBP rule compliance monitoring by alternating selection of locations representing high TTHM levels and high HAA5 levels until the required number of Stage 2 D/DBP rule compliance monitoring locations have been identified.

1. (B) If you are a surface water system or ground water under the direct influence of surface water system serving greater than three thousand three hundred (>3,300) people, you must submit a copy of your monitoring plan to the department prior to the date you conduct your initial monitoring under

10 CSR 60-4

Distribution system monitoring location total per monitoring period 2 this rule, unless your IDSE report submitted under 40 CFR part 141 subpart U contains all the information required by section (3) of this rule.

1. (C) You may revise your monitoring plan to reflect changes in treatment, distribution system operations and layout (including new service areas), or other factors that may affect TTHM or HAA5 formation, or for department-approved reasons, after consultation with the department regarding the need for changes and the appropriateness of changes. If you change monitoring locations, you must replace existing compliance monitoring locations with the lowest LRAA with new locations that reflect the current distribution system locations with expected high TTHM or HAA5 levels. The department may also require modifications in your monitoring plan. If you are a surface water system or ground water under the direct influence of surface water system serving greater than three thousand three hundred (>3,300) people, you must submit a copy of your modified monitoring plan to the department prior to the date you are required to comply with the revised monitoring plan.

1. (4) Reduced Monitoring.

   1. (A) You may reduce monitoring to the level specified in this subsection (4)(A) any time the LRAA is ≤0.040 mg/L for TTHM and ≤0.030 mg/L for HAA5 at all monitoring locations. You may only use data collected under the provisions of this rule or the Stage 1 D/DBP rule to qualify for reduced monitoring. In addition, the source water annual average total organic carbon (TOC) level, before any treatment, must be ≤4.0 mg/L at each treatment plant treating surface water or ground water under the direct influence of surface water, based on monitoring conducted under either 10 CSR 60-4.090(3)(B)1.C. or 10 CSR 60-4.090(3)(D). Source water type

Surface water system or ground water under the direct influence of surface water:

Ground water:

1 Systems on quarterly monitoring must take dual sample sets every 90 days. Stage 2 D/DBP Reduced Monitoring

Population size category

<500

500–3,300

3,301–9,999

10,000–49,999

50,000–249,999

250,000–999,999

1,000,000–4,999,999

(cid:149)5,000,000

<500

500-9,999

10,000-99,999

100,000-499,999

(cid:149)500,000 Monitoring Frequency1

…………

Per year

Per year

Per quarter

Per quarter

Per quarter

Per quarter

Per quarter

Every third year

Per year

Per year

Per quarter

Per quarter 10 CSR 60-4

Distribution system monitoring location per monitoring period

Monitoring may not be reduced.

1 TTHM and 1 HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement; one at the location and during the quarter with the highest HAA5 single measurement; and 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

2 dual sample sets: one at the location and during the quarter with the highest TTHM single measurement; and one at the location and during the quarter with the highest HAA5 single measurement.

2 dual sample sets at the locations with the highest TTHM and highest HAA5 LRAAs.

4 dual sample sets—at the locations with the two highest TTHM and two highest HAA5 LRAAs.

6 dual sample sets—at the locations with the three highest TTHM and three highest HAA5 LRAAs.

8 dual sample sets—at the locations with the four highest TTHM and four highest HAA5 LRAAs.

10 dual sample sets—at the locations with the five highest TTHM and five highest HAA5 LRAAs.

1 TTHM and 1 HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement; one at the location and during the quarter with the highest HAA5 single measurement; and 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

1 TTHM and 1 HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement; one at the location and during the quarter with the highest HAA5 single measurement; and 1 dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

2 dual sample sets: one at the location and during the quarter with the highest TTHM single measurement; and one at the location and during the quarter with the highest HAA5 single measurement.

2 dual sample sets; at the locations with the highest TTHM and highest HAA5 LRAAs.

4 dual sample sets at the locations with the two highest TTHM and two highest HAA5 LRAAs.

1. (B) You may remain on reduced monitoring as long as the TTHM LRAA ≤0.040 mg/L and the HAA5 LRAA ≤0.030 mg/L at each monitoring location (for systems with quarterly reduced monitoring) or each TTHM sample ≤0.060 mg/L and each HAA5 sample ≤0.045 mg/L (for systems with annual or less frequent monitoring). In addition, the source water annual average TOC level, before any treatment, must be ≤4.0 mg/L at each treatment plant treating surface water or ground water under the direct influence of surface water, based on monitoring conducted under either 10 CSR 60-4.090(3)(B)1.C. or 10 CSR 60- 4.090(3)(D).
2. (C) If the LRAA based on quarterly monitoring at any monitoring location exceeds either 0.040 mg/L for TTHM or 0.030 mg/L for HAA5 or if the annual (or less frequent) sample at any location exceeds either 0.060 mg/L for TTHM or 0.045 mg/L for HAA5, or if the source water annual average TOC level, before any treatment, >4.0 mg/L at any treatment plant treating surface water or ground water under the direct influence of surface water, you must resume routine monitoring under section 10 CSR 60-4.094(2) or begin increased monitoring if section 10 CSR 60-4.094(6) applies.
3. (D) The department may return your system to routine monitoring at the department’s discretion.

1. (5) Additional Requirements for Consecutive Systems. If you are a consecutive system that does not add a disinfectant but delivers water that has been treated with a primary or residual disinfectant other than ultraviolet light, you must comply with analytical and monitoring requirements for chlorine and chloramines in 10 CSR 60-5.010 and 10 CSR 60- 4.055(4)(E) and the compliance requirements in 10 CSR 60-4.090(4)(C)1. beginning April 1, 2009, unless required earlier by the department, and report monitoring results under 10 CSR 60-7.010(6)(C).

2. (6) Conditions Requiring Increased Monitoring.

   1. (A) If you are required to monitor at a particular location annually or less frequently than annually under section (2) or (4) of this rule, you must increase monitoring to dual sample sets once per quarter (taken every ninety (90) days) at all locations if a TTHM sample is >0.080 mg/L or an HAA5 sample is >0.060 mg/L at any location.
   2. (B) You are in violation of the MCL when the LRAA exceeds the Stage 2 D/DBP rule MCLs in subsection 10 CSR 60-4.090(1)(D), calculated based on four (4) consecutive quarters of monitoring (or the LRAA calculated based on fewer than four (4) quarters of data if the MCL would be exceeded regardless of the monitoring results of subsequent quarters). You are in violation of the monitoring requirements for each quarter that a monitoring result would be used in calculating an LRAA if you fail to monitor.
   3. (C) You may return to routine monitoring once you have conducted increased monitoring for at least four (4) consecutive quarters and the LRAA for every monitoring location is ≤0.060 mg/L for TTHM and ≤0.045 mg/L for HAA5.

3. (7) Operational Evaluation Levels.

   1. (A) You have exceeded the operational evaluation level at any monitoring location where the sum of the two (2) previous quarters of TTHM results plus twice the current quarter’s TTHM result, divided by four (4) to determine an average, exceeds 0.080 mg/L, or where the sum of the two (2) previous quarters of HAA5 results plus twice the current quarter’s HAA5 result, divided by four

4. (4) to determine an average, exceeds 0.060 mg/L.

   1. (B) If Operational Evaluation Levels are Exceeded.

      1. 1. If you exceed the operational evalua-

tion level, you must conduct an operational evaluation and submit a written report of the evaluation to the department no later than ninety (90) days after being notified of the analytical result that causes you to exceed the operational evaluation level. The written report must be made available to the public upon request.

1. 2. Your operational evaluation must

include an examination of system treatment and distribution operational practices, including storage tank operations, excess storage capacity, distribution system flushing, changes in sources or source water quality, and treatment changes or problems that may contribute to TTHM and HAA5 formation and what steps could be considered to minimize future exceedences.

1. A. You may request and the depart-

ment may allow you to limit the scope of your evaluation if you are able to identify the cause of the operational evaluation level exceedance.

1. B. Your request to limit the scope of

the evaluation does not extend the schedule in paragraph (7)(B)1. of this rule for submitting the written report. The department must approve this limited scope of evaluation in writing, and you must keep that approval with the completed report. (8) Requirements for Remaining on Reduced TTHM and HAA5 Monitoring Based on Stage 1 D/DBP Rule Results. You may remain on reduced monitoring after the dates identified in subsection (1)(C) of this rule for compliance with this rule only if you qualify for a 40/30 certification under 40 CFR part 141 subpart U or have received a very small system waiver under 40 CFR part 141 subpart U, plus you meet the reduced monitoring criteria in subsection (4)(A) of this rule, and you do not change or add monitoring locations from those used for compliance monitoring under the Stage 1 D/DBP rule. If your monitoring locations under this rule differ from your monitoring locations under the Stage 1 D/DBP rule, you may not remain on reduced monitoring after the dates identified in subsection (1)(C) for compliance with this rule.

1. (9) Requirements for Remaining on Increased TTHM and HAA5 Monitoring Based on Stage 1 D/DBP Rule Results. If you were on increased monitoring under 10 CSR 60- 4.090(3)(B)1., you must remain on increased monitoring until you qualify for a return to routine monitoring under subsection (6)(C) of this rule. You must conduct increased monitoring under section (6) of this rule at the monitoring locations in the monitoring plan developed under section (3) of this rule beginning at the date identified in subsection (1)(C) of this rule for compliance with this rule and remain on increased monitoring until you qualify for a return to routine monitoring under subsection (6)(C) of this rule.

2. (10) Stage 2 D/DBP Reporting and Record- Keeping Requirements.

   1. (A) Reporting requirements are found in 10 CSR 60-7.010, Reporting Requirements.
   2. (B) Record-keeping requirements are found in 10 CSR 60-9.010, Requirements for Maintaining Public Water System Records.

AUTHORITY: section 640.100, RSMo Supp. 2008.* Original rule filed Feb. 27, 2009, effective Oct. 30, 2009.

*Original authority: 640.100, RSMo 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995, 1996, 1998, 1999, 2002, 2006.