The Sand Island Wastewater Treatment Plant (SIWWTP) is the largest wastewater treatment facility in the State of Hawaii. It provides primary treatment of municipal wastewater from metropolitan Honolulu, with disposal through a deep ocean outfall. The SIWWTP operates under a NPDES permit which includes a 301(h) waiver that allows for less than secondary treatment levels. Under the 1998 renewal of the NPDES permit EPA added a bacterial limit that would require disinfection. The City and County of Honolulu evaluated various disinfection methods and selected UV disinfection, primarily due to less risk and greatest reliability meeting the disinfection goals compared to other disinfection methods. This resulted in the construction of the largest primary effluent/low quality water UV disinfection facility in the world. The facility has been in operation for over a year and has been reliably providing disinfection of the effluent to meet bacterial permit limits.