PURPOSE: This rule establishes minimum disinfectant levels and treatment requirements to assure the inactivation and removal of pathogenic organisms.

PUBLISHER’S NOTE: The secretary of state has determined that the publication of the entire text of the material which is incorporated by reference as a portion of this rule would be unduly cumbersome or expensive. Monthly verification that 100% of flow was filtered through both stages and that first stage was preceded by coagulation step

Monthly verification that both a slow sand filter and a preceding separate stage of filtration treated 100% of flow from surface water and ground water under the direct influence of surface water sources Summary of CT values for each day as described in section (18) of this rule

Summary of CT values for each day as described in section (18) of this rule

Validation test results demonstrating operating conditions that achieve required UV dose Monthly report summarizing the percentage of water entering the distribution system that was not treated by UV reactors operating within validated conditions for the required dose specified in subsection (18)(D) of this rule

This material as incorporated by reference in this rule shall be maintained by the agency at its headquarters and shall be made available to the public for inspection and copying at no more than the actual cost of reproduction. This note applies only to the reference material. The entire text of the rule is printed here.

1. (1) The requirements of this rule apply to primary community and noncommunity public water systems that the department has required to disinfect and to secondary systems with a source of water from a primary water system that the department has required to disinfect, even if the water is obtained through another secondary system.

   1. (A) Water systems using water obtained in whole or in part from a source determined by the department to be surface or ground water under the direct influence of surface water must install or construct facilities to provide 10 CSR 60-4

Within 10 days following the month in which monitoring was conducted, beginning on the applicable treatment compliance date in section (12) of this rule Within 10 days following the month in which monitoring was conducted, beginning on the applicable treatment compliance date in section (12) of this rule

Within 10 days following the month in which monitoring was conducted, beginning on the applicable treatment compliance date in section (12) of this rule Within 10 days following the month in which monitoring was conducted, beginning on the applicable treatment compliance date in section (12) of this rule No later than the applicable treatment compliance date in section (12) of this rule

Within 10 days following the month in which monitoring was conducted, beginning on the applicable treatment compliance date in section (12) of this rule

conventional filtration treatment as a required treatment technique within eighteen (18) months of the determination.

1. (B) Any water system that the department determines to be a groundwater system under the direct influence of surface water may appeal the decision by notifying the department in writing. The appeal must be accompanied by a report prepared by an engineer that confirms that the water system’s groundwater source is not directly influenced by surface water. The report must be supported by analytical data prepared by a laboratory that is acceptable to the department. Source sampling must be accomplished during the period the source is most susceptible to surface water influence. The department’s approval of the report will result in the water system’s source being redefined as groundwater not under the direct influence of surface water.
2. (C) If at any time in the department’s opinion, the quality of a water source appears to

have changed to be under the direct influence of surface water, the water system must submit, at the department’s written request, an engineer-prepared report that describes the current condition of the water source. If a report is not submitted, the source will be reclassified as groundwater supply under the direct influence of surface water.

1. (D) The department reserves the authority to make the final determination of whether or not a source is defined as groundwater under the direct influence of surface water.
2. (E) Primary systems which use water obtained from groundwater not under the direct influence of surface water and which the department requires to disinfect and secondary public water systems do not have to meet the requirements of section (2) of this rule but may be required to provide disinfection detention as deemed necessary by the department. These systems also do not have to submit reports to the department as required by 10 CSR 60-7.010(4) but must maintain the information on file at the system treatment plant or office.

1. (2) Contact Time and Removal Credit.

   1. (A) Any water system providing required treatment, and existing water systems practicing conventional filtration treatment on February 6, 1992, will be credited with 99.68 percent (2.5 log) Giardia lamblia cyst removal and 99.0 percent (2.0 log) virus removal, excluding the disinfection process, provided that they meet the turbidity maximum contaminant levels in 10 CSR 60-4.050. A system may request additional credit for treatment process removal or inactivation of Giardia lamblia cysts and viruses by submitting a report prepared by an engineer to the department including studies of Giardia cyst and virus removal or inactivation. The department reserves the authority to make the final determination of removal credit.
   2. (B) The residual disinfectant concentration

2. (C) disinfectant contact time (T) values in the Missouri Guidance Manual for Surface Water System Treatment Requirements, 1992, must be used for determining the percentage of Giardia lamblia cyst and virus removal or inactivation by disinfection.

   1. (C) The percentage of removal and inactivation of Giardia lamblia cysts and viruses will be determined as the sum of the percent removals and inactivations of the individual treatment and disinfection processes. The percent removal and inactivation of Giardia lamblia cysts must be at least 99.9 percent (3.0 log) and of viruses must be 99.99 percent (4.0 log).
   2. (D) Disinfectant contact time must be determined for each system by evaluations performed as specified in the Missouri Guidance Manual for Surface Water System Treatment Requirements, 1992, which is incorporated by reference. Results of the evaluations, including the determined disinfectant contact times, must be submitted to the department for review. The evaluation must be submitted within one (1) year of the date that the system is covered by the requirements of this rule, except that new water treatment facilities will not be issued a Final Approval of Construction under 10 CSR 60-3.010 until disinfection contact times are determined and submitted to the department.

3. (3) For any water system adding a disinfectant, only free available chlorine or chloramines will be accepted as the disinfectant entering the distribution system. The residual disinfectant concentration in the water entering the distribution system cannot be less than 0.5 milligrams per liter (mg/L) free available chlorine or 1.0 mg/L chloramines for more than four (4) hours.

   1. (A) Systems using chloramines as the disinfectant residual entering the distribution system must add and mix the chlorine prior to the addition of ammonia.
   2. (B) At the department’s discretion, any system may be required to provide breakpoint chlorination or to provide operational test data and other information that the department may require to demonstrate that the system daily meets all of the requirements of section (2) of this rule and all of the other requirements of this section.
   3. (C) At least one (1) application point for chlorine or chloramines must be prior to filtration with a residual maintained through the filters.
   4. (D) If at any time the disinfectant residual entering the distribution system falls below the levels established in this section, the system must notify the department as soon as possible but no later than by the end of the next business day. The system must notify the department by the end of the next business day whether or not the disinfectant residual was restored to the levels established in this section within four (4) hours. The department may require public notice for continuing or persistent violations of this requirement.
   5. (E) A residual disinfectant concentration in the water entering the distribution system of less than 0.2 mg/L for at least four (4) hours is a treatment technique violation which requires public notice pursuant to 10 CSR 60- 8.010.
   6. (F) The frequency of sampling shall be as set forth in 10 CSR 60-4.080(3).

4. (4) The residual disinfectant concentration in the distribution system measured as total chlorine or combined chlorine cannot be less than 0.2 mg/L in more than five percent (5%) of the samples each month for any two (2) consecutive months that the system supplies water to the public.

   1. (A) Heterotrophic plate count may be used in lieu of or as a supplement to residual disinfectant concentration analysis.
   2. (B) Water in the distribution system with a heterotrophic bacteria concentration less than or equal to five hundred (500) colonies per milliliter is deemed to have 0.2 mg/L residual disinfectant concentration for the purpose of determining compliance with this rule.
   3. (C) Water in the distribution system with a heterotrophic bacteria concentration of greater than five hundred (>500) colonies per milliliter is deemed to have less than 0.2 mg/L residual disinfectant concentration for the purpose of compliance with this rule.
   4. (D) Failure to maintain the minimum residual disinfectant concentration required in this rule is a violation of a treatment technique which requires public notification as specified in 10 CSR 60-8.010.
   5. (E) Public water systems that use chlorine or chloramines must measure the residual disinfectant level in the distribution system at the same point in the distribution system and at the same time as total coliforms are sampled, as specified in 10 CSR 60-4.022(4)-(8). Failure to comply with this subsection is a monitoring violation which requires public notification as specified in 10 CSR 60-8.010.

5. (5) Maximum Residual Disinfectant Levels.

   1. (A) Maximum residual disinfectant levels (MRDL) applicable to all community and nontransient noncommunity water systems using chlorine, chloramines or chlorine dioxide and to all transient noncommunity water systems using chlorine dioxide are—

Disinfectant Residual MRDL (mg/L) Chlorine 4.0 (as Cl2) Chloramines 4.0 (as Cl2) Chlorine dioxide 0.8 (as ClO2)

1. (B) Control of Disinfectant Residuals. For chlorine and chloramines, a public water system is in compliance with the MRDL when the running annual average of monthly averages of samples taken in the distribution system, computed quarterly, is less than or equal to the MRDL. For chlorine dioxide, a public water system (PWS) is in compliance with the MRDL when daily samples are taken at the entrance to the distribution system and no two

1. (2) consecutive daily samples exceed the MRDL. MRDLs are enforceable in the same manner as maximum contaminant levels. Notwithstanding the MRDLs, systems may increase residual disinfectant levels in the distribution system of chlorine or chloramines (but not chlorine dioxide) to a level and for a time necessary to protect public health, to address specific microbiological contamination problems caused by circumstances such as, but not limited to, distribution line breaks, storm run-off events, source water contamination events, or cross-connection events.

2. (6) Enhanced Disinfection Requirements.

   1. (A) In addition to the requirements in sections (1)–(4) of this rule, surface water and groundwater under the direct influence of surface water systems must comply with the requirements in this section.

   2. (B) General Requirements.

      1. 1. This section (6) establishes or extends

treatment technique requirements in lieu of maximum contaminant levels for the following contaminants: Giardia lamblia, viruses, heterotrophic plate count bacteria, Legionella, Cryptosporidium, and turbidity. Each surface water and groundwater under the direct influence of surface water system must provide treatment of its source water that complies with these treatment technique requirements and are in addition to those identified in sections (1)–(4) of this rule. The treatment technique requirements consist of installing and properly operating water treatment processes which reliably achieve:

1. A. At least ninety-nine percent (99%)

(2-log) removal of Cryptosporidium between a point where the raw water is not subject to recontamination by surface water runoff and a point downstream before or at the first customer; and

1. B. Compliance with the profiling and

benchmark requirements under the provisions of subsection (6)(C) of this rule.

1. 2. A public water system subject to the

requirements of this section (6) is in compliance with the requirements of paragraph (6)(B)1. of this rule if it meets the applicable filtration requirements in 10 CSR 60-4.050 and the disinfection requirements in sections (2)–(4) and subsection (6)(C) of this rule.

1. (C) Disinfection Profiling and Benchmarking.

   1. 1. Disinfection profile. A disinfection

profile is a summary of Giardia lamblia inactivation through the treatment plant measured through the course of a year. A public water system subject to the requirements of this section (6) must determine its total trihalomethanes (TTHM) annual average and its HAA5 annual average. The annual average is the arithmetic average of the quarterly averages of four (4) consecutive quarters of monitoring. If the annual average exceeds the levels in subparagraph (6)(C)1.D. then the requirements in paragraph (6)(C)2. apply.

1. A. The TTHM annual average must

be the annual average during the same period as is used for the HAA5 annual average.

1. B. The HAA5 annual average must be

the annual average during the same period as is used for the TTHM annual average.

1. (I) Those systems that have collect-

ed four (4) quarters of HAA5 occurrence data that meets the routine monitoring sample number and location requirements for TTHM in 10 CSR 60-4.094 may use those data to determine whether the requirements of this section apply.

1. (II) Those systems that did not col-

lect four (4) quarters of HAA5 occurrence data that meets the provisions of part (6)(C)1.B.(I) of this rule by March 31, 2000 must either:

1. (a) Conduct monitoring for

HAA5 that meets the routine monitoring sample number and location requirements for TTHM in 10 CSR 60-4.094 to determine the HAA5 annual average and whether the requirements of paragraph (6)(C)2. of this rule apply; or

1. (b) Comply with all other provi-

sions of this section as if the HAA5 monitoring had been conducted and the results required compliance with paragraph (6)(C)2. of this rule.

1. C. The system must submit data to the

department on the schedule required by the department.

1. D. Any system having either a TTHM

annual average greater than or equal to 0.064 mg/L or an HAA5 annual average greater than or equal to 0.048 mg/L during the period identified in subparagraphs (6)(C)1.A. and B. of this rule must comply with paragraph (6)(C)2. of this rule.

1. 2. Disinfection profiling requirements

and compliance dates vary depending on system size. Surface water and groundwater under the direct influence of surface water systems serving a population of more than ten thousand (10,000) must monitor profiling data according to subparagraph (6)(C)2.B. through (6)(C)2.C. Surface water and groundwater under the direct influence of surface water systems serving a population of less than ten thousand (10,000) must monitor profiling data according to subparagraph (6)(C)2.D.

1. A. Any system that meets the criteria

in subparagraph (6)(C)1.D. of this rule must develop a disinfection profile of its disinfection practice for a period of up to three (3) years.

1. B. The system must monitor daily for

a period of twelve (12) consecutive calendar months to determine the total logs of inacti- 10 CSR 60-4

vation for each day of operation, based on the CT99.9 values in Tables 1 through 8 of the Missouri Guidance Manual for Surface Water System Treatment Requirements, 1992, as appropriate, through the entire treatment plant. This system must begin this monitoring when requested by the department. As a minimum, the system with a single point of disinfectant application prior to entrance to the distribution system must conduct the monitoring set forth in this subparagraph (6)(C)2.B. A system with more than one (1) point of disinfectant application must conduct this monitoring for each disinfection segment. The system must monitor the parameters necessary to determine the total inactivation ratio, using analytical methods in 10 CSR 60-5.010, as follows:

1. (I) The temperature of the disin-

fected water must be measured once per day at each residual disinfectant concentration sampling point during peak hourly flow;

1. (II) If the system uses chlorine, the

pH of the disinfected water must be measured once per day at each chlorine residual disinfectant concentration sampling point during peak hourly flow;

1. (III) The disinfectant contact

time(s) must be determined for each day during peak hourly flow; and

1. (IV) The residual disinfectant con-

centration(s) of the water before or at the first customer and prior to each additional point of disinfection must be measured each day during peak hourly flow.

1. C. In lieu of the monitoring conduct-

ed under the provisions of subparagraph (6)(C)2.B. of this rule to develop the disinfection profile the system may elect to meet the requirements of part (6)(C)2.C.(I) of this rule. In addition to the monitoring conducted under the provisions of subparagraph (6)(C)2.B. of this rule to develop the disinfection profile, the system may elect to meet the requirements of part (6)(C)2.C.(II) of this rule.

1. (I) A PWS that has three (3) years of

existing operational data may submit those data, a profile generated using those data, and a request that the department approve use of those data in lieu of monitoring under the provisions of paragraph (6)(C)2. of this rule. The department must determine whether these operational data are substantially equivalent to data collected under the provisions of subparagraph (6)(C)2.B. of this rule. These data must also be representative of Giardia lamblia inactivation through the entire treatment plant and not just of certain treatment segments. Until the department approves this request, the system is required to conduct monitoring under the provisions of subparagraph (6)(C)2.B. of this rule.

1. (II) In addition to the disinfection

profile generated under subparagraph (6)(C)2.B. of this rule, a PWS that has existing operational data may use those data to develop a disinfection profile for additional years. Such systems may use these additional yearly disinfection profiles to develop a benchmark under the provisions of paragraph (6)(C)3. of this rule. The department will determine whether these operational data are substantially equivalent to data collected under the provisions of subparagraph (6)(C)2.B. of this rule. These data must also be representative of inactivation through the entire treatment plant and not just of certain treatment segments.

1. D. The system must monitor once per

week on the same calendar day, for a period of twelve (12) consecutive calendar months, to determine the total logs of inactivation for each week of operation, based on the CT99.9 values in Tables 1 through 8 of the Missouri Guidance Manual for Surface Water System Treatment Requirements, 1992, as appropriate, through the entire treatment plant. As a minimum, the system with a single point of disinfectant application prior to entrance to the distribution system must conduct the monitoring set forth in this subparagraph. A system with more than one (1) point of disinfectant application must conduct this monitoring for each disinfection segment. The system must monitor the parameters necessary to determine the total inactivation ratio, using analytical methods in 10 CSR 60-5.010, as follows:

1. (I) The temperature of the disin-

fected water must be measured at each residual disinfectant concentration sampling point during peak hourly flow;

1. (II) If the system uses chlorine, the

pH of the disinfected water must be measured at each chlorine residual disinfectant concentration sampling point during peak hourly flow;

1. (III) The disinfectant contact time(s)

must be determined during peak hourly flow; and

1. (IV) The residual disinfectant con-

centration(s) of the water before or at the first customer and prior to each additional point of disinfection must be measured during peak hourly flow.

1. E. The system must calculate the total

inactivation ratio as follows:

1. (I) The system may determine the

total inactivation ratio for the disinfection segment based on either of the following methods:

1. (a) Determine one (1) inactiva-

tion ratio (CTcalc/CT99.9) before or at the first customer during peak hourly flow; or

1. (b) Determine successive

(CTcalc/CT99.9) values, representing sequential inactivation ratios, between the point of disinfectant application and a point before or at the first customer during peak hourly flow. Under this alternative, the system must calculate the total inactivation ratio by determining (CTcalc/CT99.9) for each sequence and then adding the (CTcalc/CT99.9) values together to determine ((CTcalc/CT99.9)); and

1. (II) The system must determine the

total logs of inactivation by multiplying the value calculated in part (6)(C)2.D.(I) of this rule by three (3.0).

1. F. A system that uses either chlo-

ramines or ozone for primary disinfection must also calculate the logs of inactivation for viruses using a method identified in the United States Environmental Protection Agency’s Office of Water document, Alternative Disinfectants and Oxidants Guidance Manual, Volume 99 Issue 14 of EPA 815-R, published April 1999. This document is incorporated by reference without any later amendments or modifications. To obtain a copy, contact the U.S. Government Printing Office at 732 North Capitol Street NW, Washington, D.C. 20401, toll free (866)512-1800 or by visiting https://bookstore.gpo.gov.

1. G. The system must retain disinfec-

tion profile data in graphic form, as a spreadsheet, or in some other format acceptable to the department for review as part of sanitary surveys conducted by the department.

1. 3. Disinfection benchmarking.

   1. A. Any system required to develop a

disinfection profile under the provisions of paragraphs (6)(C)1. and 2. of this rule and that decides to make a significant change to its disinfection practice must consult with the department in writing prior to making such change. Significant changes to disinfection practice are:

1. (I) Changes to the point of disin-

fection;

1. (II) Changes to the disinfectant(s)

used in the treatment plant;

1. (III) Changes to the disinfection

process; and

1. (IV) Any other modification identi-

fied by the department.

1. B. Any system that is modifying its

disinfection practice must calculate its disinfection benchmark using one (1) of the following procedures:

1. (I) For each year of profiling data

collected and calculated under paragraph (6)(C)2. of this rule, the system must determine the lowest average monthly Giardia lamblia inactivation in each year of profiling data. The system must determine the average Giardia lamblia inactivation for each calendar month for each year of profiling data by dividing the sum of Giardia lamblia inactivation by the number of values calculated for that month; or

1. (II) The disinfection benchmark is

the lowest monthly average value (for systems with one (1) year of profiling data) or average of lowest monthly average values (for systems with more than one (1) year of profiling data) of the monthly logs of Giardia lamblia inactivation in each year of profiling data.

1. C. A system that uses either chlo-

ramines or ozone for primary disinfection must also calculate the disinfection benchmark for viruses using a method approved by the department.

1. D. The system must submit the fol-

lowing information to the department as part of its consultation process:

1. (I) A description of the proposed

change;

1. (II) The disinfection profile for

Giardia lamblia (and, if necessary, viruses) under paragraph (6)(C)2. of this rule and benchmark as required by subparagraph (6)(C)3.B. of this rule; and

1. (III) An analysis of how the pro-

posed change will affect the current levels of disinfection.

1. (D) Filtration Sampling Requirements. A public water system subject to the requirements of this section (6) that provides conventional filtration treatment must conduct continuous monitoring of turbidity for each individual filter as indicated in 10 CSR 60- 4.050(2)(D)1.

AUTHORITY: section 640.100, RSMo 2016.* Original rule filed July 12, 1991, effective Feb. 6, 1992. Amended: Filed Feb. 1, 1996, effective Oct. 30, 1996. Amended: Filed Dec. 15, 1999, effective Sept. 1, 2000. Amended: Filed March 17, 2003, effective Nov. 30, 2003. Amended: Filed Aug. 12, 2015, effective March 30, 2016. Amended: Filed June 13, 2018, effective Feb. 28, 2019. *Original authority: 640.100, RSMo 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995, 1996, 1998, 1999, 2002, 2006, 2012, 2014.