Waterworks that demonstrate at least 4-log (99.99%) inactivation of viruses by a chlorine treatment process and conduct compliance monitoring of their disinfectant residual are exempt from the triggered source water monitoring provisions of the GWR.
Compliance monitoring consists of determining and maintaining the disinfectant residual every day that the groundwater source sends water to the distribution system. The residual must continuously remain above a minimum concentration specified by the Office of Drinking Water (ODW) at a sample location prior to the water entering the distribution system.
If you believe that your treatment system will provide 4-log inactivation of viruses, please contact your local ODW field office. If the ODW agrees with your assessment, you will receive a written acknowledgement exempting your waterworks from the triggered source water monitoring provisions of the GWR, provided that the compliance monitoring requirements of the GWR for your treatment system(s) are maintained.
If you do NOT receive written concurrence from the ODW that your waterworks achieves 4-log treatment prior to December 1, 2009, you will be required to comply with the triggered source water monitoring provisions of the GWR.
Note that ODW has not yet approved any Ultraviolet Light (UV) or Membrane units for 4-log inactivation removal of viruses.
Waterworks may wish to upgrade their existing treatment systems to provide 4-log treatment. Plans and specifications for modifications or upgrades to treatment systems must be approved and issued a construction permit by the ODW, prior to installation, in accordance with the Waterworks Regulations.