Rivett Michael O, Tremblay-Levesque Laurent-Charles, Carter Ruth, Thetard Rudi C H, Tengatenga Morris, Phoya Ann, Mbalame Emma, Mchilikizo Edwin, Kumwenda Steven, Mleta Prince, Addison Marc J, Kalin Robert M
Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow G1 1XJ, UK.
CARE International in Malawi, P/Bag A89, Lilongwe, Malawi.
Sci Total Environ. 2022 Feb 1;806(Pt 2):150598. doi: 10.1016/j.scitotenv.2021.150598. Epub 2021 Sep 28.
This longitudinal flood-relief study assessed the impact of the March 2019 Cyclone Idai flood event on E. coli contamination of hand-pumped boreholes in Mulanje District, Malawi. It established the microbiological water-quality safety of 279 community supplies over three phases, each comprising water-quality survey, rehabilitation and treatment verification monitoring. Phase 1 contamination three months after Idai was moderate, but likely underestimated. Increased contamination in Phase 2 at 9 months and even greater in Phase 3, a year after Idai was surprising and concerning, with 40% of supplies then registering E. coli contamination and 20% of supplies deemed 'unsafe'. Without donor support for follow-up interventions, this would have been missed by a typical single-phase flood-relief activity. Contamination rebound at boreholes successfully treated months earlier signifies a systemic problem from persistent sources intensified by groundwater levels likely at a decade high. Problem extent in normal, or drier years is unknown due to absence of routine monitoring of water point E. coli in Malawi. Statistical analysis was not conclusive, but was indicative of damaged borehole infrastructure and increased near-borehole pit-latrine numbers being influential. Spatial analysis including groundwater flow-field definition (an overlooked sector opportunity) revealed 'hit-and-miss' contamination of safe and unsafe boreholes in proximity. Hydrogeological control was shown by increased contamination near flood-affected area and in more recent recharge groundwater otherwise of good quality. Pit latrines are presented as credible e-coli sources in a conceptual model accounting for heterogeneous borehole contamination, wet season influence and rebound behavior. Critical to establish are groundwater level - flow direction, hand-pump plume draw, multiple footprint latrine sources - 'skinny' plumes, borehole short-circuiting and fast natural pathway (e.g. fracture flow) and other source influences. Concerted WASH (Water, Sanitation and Hygiene) sector investment in research and policy driving national water point based E. coli monitoring programs are advocated.
这项纵向洪水救济研究评估了2019年3月伊代气旋洪水事件对马拉维姆兰杰区手动抽水钻孔中大肠杆菌污染的影响。该研究分三个阶段确定了279个社区供水点的微生物水质安全性，每个阶段包括水质调查、修复和处理验证监测。伊代气旋过后三个月的第一阶段污染程度为中等，但可能被低估了。在9个月后的第二阶段污染加剧，在伊代气旋过后一年的第三阶段污染甚至更严重，这令人惊讶且令人担忧，当时40%的供水点检测到大肠杆菌污染，20%的供水点被认为“不安全”。如果没有捐助者对后续干预措施的支持，典型的单相洪水救济活动就会忽略这一点。几个月前成功处理过的钻孔出现污染反弹，这表明存在系统性问题，持续的污染源因地下水位可能处于十年高位而加剧。由于马拉维缺乏对供水点大肠杆菌的常规监测，正常年份或干旱年份的问题程度尚不清楚。统计分析没有得出确凿结论，但表明受损的钻孔基础设施和钻孔附近化粪池数量增加有影响。包括地下水流场定义（一个被忽视的领域机会）在内的空间分析揭示了安全和不安全钻孔在附近区域的“偶然”污染。受洪水影响地区附近以及原本水质良好的近期补给地下水中污染增加，这表明了水文地质控制的作用。在一个解释钻孔异质污染、雨季影响和反弹行为的概念模型中，化粪池被认为是可信的大肠杆菌来源。关键是要确定地下水位-水流方向、手动泵羽流抽取、多个足迹化粪池源-“细”羽流、钻孔短路和快速自然路径（如裂隙流）以及其他源影响。提倡水、环境卫生和个人卫生（WASH）部门协调投资于研究和政策，推动国家基于供水点的大肠杆菌监测计划。
