2000年11月，华盛顿水渠，也就是水处理厂 哥伦比亚特区的供应商将其消毒剂从氯改为 氯胺，以减少消毒副产物（DBP）。然而，伴随这一变化的是第90名的增加 百分位铅水平从十亿分之十二（ppb）到70 ppb。哥伦比亚特区水与下水道管理局（DCWASA）进行的铅分析显示，铅的平均峰值浓度高达 在有铅服务线的家庭中为150 ppb。（Giani&Edwards 2004）。审查 剖面图显示，大部分铅溶解并来自铅 服务热线。 在春天，华盛顿水渠每年进行一次氯燃烧 连续五周。在这五周内，添加氯作为消毒剂 分布中的游离氯残留保持在约3.5 mg/L 系统2004年，氯气燃烧于4月开始。在此期间，潜在客户资料 在客户家中进行的测试显示，峰值铅水平大幅下降，<15 ppb 在几周的时间范围内（Schock&Giani？2004）。“烧伤”过后 完成后，氯胺被恢复。在接下来的几个月里，匹克领先 剖面浓度再次开始增加，远高于行动水平。 在同一时间段内，铅服务线从地面移除 并运到美国环境保护署的研究实验室 俄亥俄州辛辛那提。X射线衍射显示，大部分刻度由 氧化铅（Pb-IV），（Schock&Giani-2004）。肖克还透露，Pb IV 可能是由于使用导致的高氧化还原电位（ORP）而形成的 2000年之前的氯浓度超过3.5 mg/L（游离氯） DCWASA系统。当引入氯胺时，ORP因此降低 导致氧化铅溶解。从2003年3月开始，DCWASA进行了一系列pipeloop研究，以 确定最有效的最佳腐蚀控制处理。在这些研究中 确定添加正磷酸盐是最理想的治疗方法。信息技术 还讨论了潜在的改用氯气可能有助于加速铅的释放 还原过程。 DCWASA的里诺堡水质中心正在使用多个管道回路 协助优化腐蚀处理的设施。其中两个管道回路（管道回路#3 和#6）致力于研究氯胺和磷酸盐、氯和 磷酸盐和消毒剂的来回切换及其对铅的影响 从主要服务线中释放。研究氯的影响也是一个值得关注的问题 一旦磷酸盐有适当的机会，烧伤可能会导致铅释放 使铅钝化。 本文讨论了pipeloops#3和#6关于铅的发现 上述情况下的浸出浓度。包括3个参考文献、图表。

In November 2000 the Washington Aqueduct, which is the water treatment provider to the District of Columbia, switched its disinfectant from chlorine to chloramines in order to reduce disinfection byproducts (DBP). However, accompanying this change was an increase in 90th percentile lead levels from 12 parts per billion (ppb) to 70 ppb. Lead profiles conducted by District of Columbia Water & Sewer Authority (DCWASA) showed average peak concentrations up to 150 ppb in homes with lead service lines. (Giani & Edwards 2004). Review of the profiles indicated that the majority of the lead was dissolved and coming from the lead service lines. During the spring, the Washington Aqueduct conducts an annual chlorine burn for five consecutive weeks. During these five weeks, chlorine is added as the disinfectant with free chlorine residuals maintained at approximately 3.5 mg/L in the distribution system. In 2004, the chlorine burn initiated in April. During this time, lead profiles conducted at customer homes showed a dramatic decrease in peak lead levels, < 15 ppb in a few weeks time frame, (Schock & Giani?2004). After the "burn" was completed, chloramine was reinstated. Throughout the next few months, peak lead profile concentrations began to increase well above the action level again. During this same time frame, lead service lines were removed from the ground and shipped to the US Environmental Protection Agency's research laboratory in Cincinnati, Ohio. X-Ray diffractions revealed that the majority of the scale consisted of lead oxide (Pb -IV), (Schock & Giani - 2004). Schock also revealed that the Pb-IV could have formed due to high oxidation-reduction potential (ORP) caused by using chlorine concentrations prior to 2000 in excess of 3.5 mg/L (free chlorine) in the DCWASA system. When chloramines were introduced, the ORP decreased thus causing the lead oxide to dissolve. Beginning in March 2003, DCWASA engaged in a series of pipeloop studies to determine the most effective optimal corrosion control treatment. During these studies, it was determined that the addition of orthophosphate was the most optimal treatment. It was also discussed that potential switch back to chlorine might help speed up the lead reduction process. Several pipeloops were being utilized at DCWASA's Fort Reno Water Quality facility to assist in optimizing corrosion treatment. Two of these pipeloops (Pipeloops #3 and #6) were dedicated to study the effects of chloramines and phosphate, chlorine and phosphate and the switching back and forth of the disinfectants and their effects on lead release from the lead service lines. It was also a concern to study the effects a chlorine burn might have with regards to lead release once the phosphate has had a proper chance to passivate the lead. This paper discusses the findings of pipeloops #3 and #6 with regards to lead leaching concentrations under the scenarios previously mentioned. Includes 3 references, figures.