EPA Issues Guidance Memo on Dichlor and Trichlor

This week, EPA issued a guidance memo (link below) to help states implement the microbial inactivation/disinfection requirements when Dichlor (Dichloroisocyanuric acid) or Trichlor (Trichloroisocyanuric acid) are used as a disinfectant.  EPA does not approve disinfectants under the SDWA but there are standards for inactivation/disinfection that must be met.  The presence of cyanuric acid from these disinfectants interferes with commonly used analytical methods for measuring free chlorine residual.  The memo provides a link to a calculator that will help determine the free chlorine concentrations when Dichlor and Trichlor are used.  EPA recommends that states review the water systems using, or planning to use, Dichlor and Trichlor to assure that there is adequate microbial inactivation.  EPA will continue to work with others in the water industry to develop additional information on this topic.

Dichlor Trichlor Memo 2018-04-18