AWWA ACE60074

In 2002, the City of Henderson, Nevada, completed construction of one of the first ultraviolet (UV) disinfection facilities in the United States for surface water treatment. Henderson's UV project was one of the first regulator-approved installations for Cryptosporidium inactivation in the U.S. In the past few years, the project has received lots of attention, and many of the challenges faced on the project have influenced engineering decisions on subsequent projects around the country. This last paper on the Henderson UV project will address the successful completion of the project and the resolution of the many challenges faced during design, construction, and start-up. The 15-mgd Henderson facility uses medium-pressure reactors for inactivation of Giardia and Cryptosporidium. Following the completion of construction, the final step in implementation consisted of on-site performance testing and validation testing based on protocols developed in cooperation with the Nevada State Health Division (NSHD). The purpose of testing was to verify performance guarantees provided by the UV manufacturer. In November 2002, the initial on-site validation testing showed poor disinfection performance, and the manufacturer was required to make reactor modifications that would improve disinfection performance to meet the project requirements. In May 2003, modified UV reactors were successfully validated on-site. Construction to accommodate the modified reactors will be completed by the end of 2003. This paper addresses several critical topics and real-world lessons for UV projects including: providing protection against risk through the development of specifications for UV equipment, including guarantees, bonds, penalties, and courses for remedial action if necessary; the importance of designing and constructing UV facilities to provide flexibility for the future to allow for subsequent test results, technology changes, and regulatory changes; results of headloss testing and implications for plant operations; results and implications of on-site validation testing for contract compliance; incorporating validation results in establishing a control strategy and operational setpoints; planned future follow-up validation testing to meet the requirements of the US Environmental Protection Agency's UVDGM, respond to a new target inactivation level for Cryptosporidium, and to optimize system operations under the UVDGM; and, comparison of initial O&M and performance guarantees to actual values upon start-up. At the end of 2003, the City of Henderson will complete one of the first UV projects for drinking water disinfection in the U.S. This paper represents the final chapter in the well-publicized Henderson case study. The results to be presented represent important information on the implementation of UV disinfection that will allow utilities with subsequent UV disinfection projects to face the same challenges successfully and to capitalize on the lessons learned.