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

Editor’s Note: The following material is incorporated into this rule by reference: 1) Guidance Manual for Surface Water System Treatment Requirements (Jefferson City: Missouri Department of Natural Resources, 1992). In accordance with section 536.013(4), RSMo, the full text of material incorporated by reference will be made available to any interested person at the Office of the Secretary of State and the headquarters of the adopting state agency.

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 conventional filtration treatment as a required treatment technique within eighteen (18) months of the determination.
   2. (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.
   3. (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.
   4. (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.
   5. (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(5) but must maintain the information on file at the system treatment plant or office.

2. (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

3. (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. 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.

4. (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) Failure to maintain the minimum residual disinfectant concentration as required in this rule is a violation of a treatment technique which requires public notification as 10 CSR 60-4

specified in 10 CSR 60-8.010(1) and (7) (B)2.

1. (E) 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.
2. (F) The frequency of sampling shall be as set forth in 10 CSR 60-4.080(3).

1. (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(1) and(7)(B)2.
   5. (E) The residual disinfectant concentration must be measured at least at the same points in the distribution system and at the same time as total coliforms are sampled as specified in 10 CSR 60-4.020. Failure to comply with this subsection is a monitoring violation which requires public notification as specified in 10 CSR 60-8.010(2).

AUTHORITY: section 640.100, RSMo (1994).* Original rule filed July 12, 1991, effective Feb. 6, 1992. Amended: Filed Feb. 1, 1996, effective Oct. 30, 1996. *Original authority 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995.