美国环境保护局（USEPA）的长期2 强化地表水处理规则（LT2）要求所有水系统 在避免过滤状态下操作，向其表面添加第二种消毒剂 处理系统或添加过滤。如LT2规则所述，最经济的 满足LT2要求的未过滤系统的解决方案通常是紫外线 （紫外线）消毒。 每个未经过滤的水设施必须了解并解决可能影响环境的所有问题 选择治疗方法前最好的消毒方法。紫外线消毒 可能不是所有情况下的最佳选择。具有周期性高浊度事件的系统， 味道和气味问题、消毒副产品（DBP）合规性问题、铁和 锰问题或其水源供应可能发生重大变化 需要考虑其他消毒剂以确定最佳的第二消毒剂。 特殊的水系统。 其他替代方案可能允许这些系统处理它们的问题 并同时使其系统符合LT2的要求 并保持未经过滤的水系统。在这种背景下，本研究讨论了阿拉斯加未过滤水系统的三个方面（Ketchikan公用事业公司、科迪亚克市和锡特卡市及自治区） 有水质挑战，需要仔细审查可用的 消毒剂选择完成前的消毒替代品。包括数字。

The U.S. Environmental Protection Agency's (USEPA's) Long Term 2 Enhanced Surface Water Treatment Rule (LT2) requires all water systems operating under filtration avoidance status to add a second disinfectant to their treatment system or to add filtration. As stated in the LT2 rule, the most economical solution for unfiltered systems to meet the requirements of LT2 is typically ultraviolet (UV) disinfection. Each unfiltered water utility must understand and address all issues that could affect the best method of disinfection before selecting their treatment approach. UV disinfection may not be the best choice in all cases. Systems that have periodic high turbidity events, taste and odor issues, disinfection byproduct (DBP) compliance issues, iron and manganese concerns or the potential for significant changes to their source water supply need to consider other disinfectants to determine the best second disinfectant for their particular water system. Other alternatives may allow these systems to deal with their specific challenges and bring their system into compliance with LT2 at the same time and remain an unfiltered water system. In this context, this study discusses three (Ketchikan Public Utilities, the City of Kodiak, and the City and Borough of Sitka) of Alaska's unfiltered water systems that have water quality challenges that necessitated careful review of the available disinfection alternatives before disinfectant selection was completed. Includes figures.