Obtaining Credit for UV Systems for Drinking Water - A Case Study


  • David S. Briley, PE - Hazen and Sawyer

Some water systems are turning to UV disinfection for compliance with the new USEPA rules; Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 Disinfectant/Disinfection ByProducts Rule (DBPR). This presentation will outline the process that a water treatment plant (WTP) in North Carolina went through to obtain inactivation credit for Crypto. and Giardia for their UV disinfection system. This WTP has been in operation since 2009. The WTP is classified as a Bin 1 facility but inactivation credit for the UV system in order to reduce free chlorine contact time in the WTP and reduce DBP formation.

The challenges and considerations for obtaining inactivation credit for primary disinfection with UV disinfection for this facility will be discussed. The presentation will focus on the issues critical to regulatory agencies that water systems need to address. In particular, the following topics will be covered:

• What credit is being requested and how UV fits in a multiple barrier approach
• Relating Validation Test to Full-Scale Installation
• Differences between State requirements and the USEPA UV Disinfection Guidance Manual
• UV System Control Philosophy and Fail-Safes to ensure continued disinfection
• Calibration of UV sensors
• Maintenance Requirements
• Recordkeeping and reporting requirements
• Lamp Breakage Response Plans
• Contingency Planning

An update will also be provided on current trends in regulatory approval of UV disinfection systems for Crypto. and Giardia inactivation credit throughout the U.S. as well as the approval process for water systems in Virginia.

For more information, please contact the author at dbriley@hazenandsawyer.com.

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