Public water systems (PWSs) implement ultraviolet (UV) disinfection for the inactivation of regulated pathogens in accordance with the requirements of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Ground Water Rule (GWR), and the guidance provided by the Ultraviolet Disinfection Guidance Manual (UVDGM). Since the UVDGM was published in 2006, there has been considerable advancement in the understanding and application of UV technologies, particularly in the area of UV dose monitoring and validation. This documentation presents new approaches and procedures for monitoring and validation that leverage these advances. The contents of this document meet the requirements of the LT2ESWTR and conform to the underlying principles of the UVDGM. These additional approaches and recommendations are presented for consideration when applying UV disinfection for the inactivation of Cryptosporidium, Giardia, and viruses. The beneficiaries for this document include UV system manufacturers, validators, consultants, utilities, and regulators. Detailed information is presented on designing test plans, conducting evaluations, and reporting of results associated with four new UV calculated dose monitoring approaches. These methods and procedures may provide utilities with more cost-effective and robust implementation of UV disinfection. In addition, checklists and validation report outlines are presented to aid Regulators in approving systems. This document also provides recommendations on general procedures and reference documentation that support approaches currently being used but not documented in the UVDGM for validating and operating a UV system.

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