AWWA WQTC63971

The Washington State Department of Health (DOH) has been actively involved in the development of ultraviolet (UV) disinfection for regulatory credit since 2001. The City of Seattle's efforts to obtain Limited Alternative to Filtration (LAF) designation for the Cedar River supply and efforts to use UV technology as a primary disinfectant prompted early involvement by DOH in reviewing validation protocols, developing UV treatment technique violation (TTV) parameters, determining UV monitoring and operating parameters, and developing monitoring and reporting forms. To date the DOH has granted regulatory disinfection credit to two surface water supplies in the State. DOH staff evaluated disinfection credit requirements for UV technology under three separate rule applications: the Surface Water Treatment Rule (SWTR) for Giardia lamblia inactivation; the Limited Alternative to Filtration (LAF) for Giardia lamblia and Cryptosporidium inactivation; and, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) for Cryptosporidium inactivation. Three separate regulatory approaches were developed since the regulatory basis for pathogen inactivation varies for each of these rule applications. For compliance with the SWTR, UV light can provide the primary Giardia lamblia inactivation barrier. Water systems must calculate their minimum inactivation ratio (ratio of disinfection provided to disinfection required) on a daily basis. A water system incurs a TTV in any month when the inactivation ratio is less than one on more than any day in that month. This inactivation requirement served as the basis for evaluation of UV disinfection in accordance with the SWTR. Chemical disinfection is still required to inactivate viruses and provide a residual disinfectant as required by the SWTR. The UV disinfection requirements for a source that qualifies for a Limited Alternative to Filtration were developed based upon the criteria in the 1996 Safe Drinking Water Act Amendments. The underlying inactivation requirement is that treatment provides greater public health protection than would be provided by the combination of filtration and chlorination. Includes figures, extended abstract only.