Abstract：
Legionella occurrence monitoring is not required by United States Environmental Protection Agency (USEPA) drinking water regulations, and few occurrence studies exist for Legionella in source water or distribution systems. Legionella occurrence was monitored in Las Vegas Valley (Las Vegas, Nevada, USA) drinking water sources, including non-treated surface water, seasonal groundwater (61 wells, before and after chlorination), finished water (after treatment at water treatment facilities), and chlorinated distribution system water (at 9 reservoirs and 75 sample locations throughout the network). Legionella pneumophila was detected at least once at each of the wells sampled before chlorination, with an overall positivity rate of 38% (343/908). During well start-up (time<2 hours; turbidity>3 NTU), L. pneumophila concentrations averaged 2,792±353 MPN/100 mL, with a median of 105 MPN/100 mL, and range of <1 to 90,490 MPN/100 mL across 61 seasonally operated (typically April-October) groundwater wells. After initial flushing (turbidity<3 NTU), the average concentration decreased by more than two orders of magnitude to 24±3 MPN/100 mL but ranged from <1 to >2,273 MPN/100 mL. This trend indicates that stagnation (up to 391 days) contributed to greater initial concentrations, and flushing alone was incapable of complete L. pneumophila elimination. L. pneumophila concentration was significantly, positively correlated with total aqueous adenosine triphosphate (ATP) (p<0.00001, r=0.41-0.71), turbidity (p<0.00001, r=0.27-0.51), orthophosphate (p=0.35-0.076, r=0.51-0.59), and pump depth (p=0.032, r=0.40). During a full-scale assessment of chlorination (Ct=0.7 to 10.5 mg-min/L; T=26.6-28.1°C), substantial reduction of Legionella spp. (up to 2.5 logs) was observed; although, detectable concentrations were still measured. Extrapolating from a Chick-Watson model (log inactivation=0.28*(Ct); R2=0.87) constructed from the full-scale chlorination results, 3- and 4-log inactivation in Las Vegas Valley groundwater would require 10.8 and 14.3 mg-min/L, respectively; at least 3-log inactivation was required to bring Legionella spp. to below detection at the studied well. Chlorine exposure (Ct=0.1 to 10.9 mg-min/L) at most wells discharging directly to the distribution system was insufficient to fully inactivate Legionella spp. After discussing these findings with the state regulatory agency, direct-to-distribution wells (38 of 61 wells) remained out of operation; the distribution system, wells, and reservoirs were monitored for Legionella and chlorine residual, and additional treatment scenarios were identified for further evaluation. Legionella was either not detected or was well controlled in surface water, finished effluent from the drinking water treatment plant, chlorinated reservoirs, and the chlorinated distribution system. This study emphasizes the importance of utility-driven, non-regulatory research in order to protect public health and also identifies the need for greater occurrence monitoring and guidance for Legionella in groundwater supplies.
摘要：
军团菌的发生监测不是美国环境保护局（USEPA）饮用水法规所要求的，关于军团菌在水源水或分配系统中的发生研究很少。在拉斯维加斯山谷（拉斯维加斯，内华达,美国)饮用水源，包括未经处理的地表水，季节性地下水(61口井，氯化之前和之后)，成品水（在水处理设施处理后），和氯化分配系统水（在整个网络中的9个水库和75个样本位置）。在氯化前取样的每个孔中至少检测到一次嗜肺军团菌，总体阳性率为38%(343/908)。开井期间（时间<2小时；浊度>3NTU），肺炎支原体浓度平均为2,792±353MPN/100mL，中位数为105MPN/100mL，在61个季节性作业(通常为4-10月)的地下水井中，<1至90,490MPN/100mL的范围。初始冲洗后（浊度<3NTU），平均浓度下降了两个数量级以上，为24±3MPN/100mL，但范围为<1至>2,273MPN/100mL。这种趋势表明，停滞（长达391天）有助于提高初始浓度，仅靠潮红不能完全消除嗜肺乳杆菌。嗜肺L.浓度显著，与水总三磷酸腺苷（ATP）呈正相关（p<0.00001，r=0.41-0.71），浊度（p<0.00001，r=0.27-0.51），正磷酸盐（p=0.35-0.076，r=0.51-0.59），和泵深（p=0.032，r=0.40）。在全面评估氯化过程中（Ct=0.7至10.5mg-min/L；T=26.6-28.1°C），军团菌的大幅减少。(高达2.5日志);虽然,可检测的浓度仍然被测量。从Chick-Watson模型推断（对数失活=0.28*（Ct）；R2=0.87），从全尺寸氯化结果构建，拉斯维加斯山谷地下水的3-和4-对数失活需要10.8和14.3mg-min/L，分别；至少需要3个对数的灭活才能带来军团菌。低于所研究井的检测。在大多数直接排放到分配系统的井中，氯暴露（Ct=0.1至10.9mg-min/L）不足以完全灭活军团菌。在与国家监管机构讨论了这些发现之后，直接分配井(61口井中的38口)仍未运行；分配系统，Wells,监测水库的军团菌和余氯，并确定了其他治疗方案进行进一步评估.在地表水中未检测到军团菌或得到很好的控制，饮用水处理厂的成品废水，氯化水库，和氯化分配系统。这项研究强调了公用事业驱动的重要性，非监管研究，以保护公众健康，并确定需要对地下水供应中的军团菌进行更多的监测和指导。
