WAC 246-290-451   Disinfection of drinking water.  (1) No portion of a public water system containing potable water shall be put into service, nor shall service be resumed until the facility has been effectively disinfected.

     (a) In cases of new construction, drinking water shall not be furnished to the consumer until satisfactory bacteriological samples have been analyzed by a laboratory certified by the state; and

     (b) In cases of existing water mains, when the integrity of the main is lost resulting in a significant loss of pressure that places the main at risk to cross-connection contamination, the purveyor shall use standard industry practices such as flushing, disinfection, and/or bacteriological sampling to ensure adequate and safe water quality prior to the return of the line to service;

     (c) If a cross-connection is confirmed, the purveyor shall satisfy the reporting requirements as described under WAC 246-290-490(8).

     (2) The procedure used for disinfection shall conform to standards published by the American Water Works Association, or other industry standards acceptable to the department.

     (3) The purveyor of a system using surface water or GWI shall meet disinfection requirements specified in Part 6 of this chapter.

     (4) The purveyor of a system using groundwater shall meet the requirements under subsection (6) of this section if required by the department to disinfect for any of the following reasons:

     (a) Determination that the groundwater source is in hydraulic connection to surface water under WAC 246-290-640(4);

     (b) A history of unsatisfactory source coliform sampling; or

     (c) A microbiological contaminant threat within the sanitary control area as defined in WAC 246-290-135.

     (5) The purveyor of a groundwater system that is required to disinfect as a result of becoming a SSNC due to repeated total coliform MCL or major repeat violations shall meet the requirements under subsection (7) of this section.

     (6) If disinfection is required under subsection (4) of this section, the following requirements must be met:

     (a) Provide a minimum contact time at or before the first customer of:

     (i) Thirty minutes if 0.2 mg/L free chlorine residual is maintained;

     (ii) Ten minutes if 0.6 mg/L free chlorine residual is maintained; or

     (iii) Any combination of free chlorine residual concentration (C), measured in mg/L and contact time (T), measured in minutes, that result in a CT product (C x T) of greater than or equal to six; and

     (b) Maintain a detectable residual disinfectant concentration in all active parts of the distribution system, measured as total chlorine, free chlorine, combined chlorine, or chlorine dioxide.

     (c) The department may require the purveyor to provide longer contact times, higher chlorine residuals, or additional treatment to protect the health of consumers served by the water system.

     (d) To demonstrate the required level of treatment is maintained, the purveyor shall:

     (i) Monitor the residual disinfectant concentration at the point of entry to the distribution system, or at a department-approved location, at least once every Monday through Friday (except holidays) that water is supplied;

     (ii) Calculate the daily CT value at or before the first customer; and

     (iii) Submit monthly groundwater treatment reports to the department using a department-approved form by the tenth day of the following month.

     (e) All analyses required in this subsection shall be conducted in accordance with EPA standard methods.

     (f) The purveyor may be required to monitor the residual disinfectant concentration each calendar day water is supplied to the distribution system if the department considers treatment operation is unreliable.

     (g) The department may require the use of continuous residual analyzers and recorders to assure adequate monitoring of residual concentrations.

     (7) If disinfection is required under subsection (5) of this section, or a chemical disinfectant is added to a groundwater source for any other reason, the following requirements must be met:

     (a) Monitor residual disinfectant concentration at representative points throughout the distribution system once each day, excluding weekends and holidays, and at the same time and location of routine and repeat coliform sample collection. Frequency of disinfection residual monitoring may be reduced upon written request to the department if it can be shown that disinfection residuals can be maintained on a reliable basis without the provision of daily monitoring.

     (b) Maintain a detectable residual disinfectant concentration in all active parts of the distribution system, measured as total chlorine, free chlorine, combined chlorine, or chlorine dioxide. Water in the distribution system with an HPC level less than or equal to 500 organisms/mL is considered to have a detectable residual disinfectant concentration.

     (c) The department may require the purveyor to provide higher chlorine residuals, or additional treatment to protect the health of consumers served by the water system.

     (d) All analyses required in this subsection shall be conducted in accordance with EPA standard methods.

     (e) The department may require the use of continuous residual analyzers and recorders to assure adequate monitoring of residual concentrations.



[Statutory Authority: RCW 43.20.050 and 70.119A.080. 10-20-068, § 246-290-451, filed 9/29/10, effective 11/1/10. Statutory Authority: RCW 43.20.050 (2) and (3) and70.119A.080 . 03-08-037, § 246-290-451, filed 3/27/03, effective 4/27/03. Statutory Authority: RCW 43.02.050 [43.20.050]. 99-07-021, § 246-290-451, filed 3/9/99, effective 4/9/99.]