Collaborative Research: Enhancing the sustainability of groundwater pumping from low-arsenic aquifers in southern Asia - a case-study in Vietnam south of Hanoi.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。过去二十年来，南亚地区数以百万计的浅管井开采的地下水中砷含量升高，人们对这一问题的重视往往掩盖了一个事实，即砷含量低的缺氧含水层也很普遍，而且在受影响的地区，经常可以进行钻探。该提案解决了评估低砷含水层脆弱性的两个关键问题：(1)溶解有机碳或颗粒有机碳（DOC或POC）是否驱动含水层对铁氧氢氧化物的微生物溶解；(2)砷的吸附和沉淀在多大程度上减弱了高砷地下水进入低砷含水层的影响。拟议的实地调查利用了以前记录的：(a)在河内以南15公里的一个村庄，与高砷地下水有关的灰砂和与低砷地下水有关的橙砂在同一深度近距离对比，以及(b)河内市大量抽取地下水，导致前者的水通过后者横向抽取。这种结构特别适合于阐明决定在整个受影响区域继续依靠低砷含水层提供饮用水的可持续性的关键过程。科学价值：前所未有的最先进的分析方法组合将应用于先前记录的从橙色砂到灰色砂的转变，分别对应于低砷到高砷的地下水：构成活细胞膜的磷脂脂肪酸（PLFAs）的14c分析，x射线吸收光谱法探测含水层砂中As和Fe的氧化还原状态和结合环境，地下水的3H-3He定年，以及石英颗粒的光激发发光（OSL）定年。这些测量将为检验下列关于南亚低砷含水层脆弱性的工作假设提供基础。无论相关的预测是否经得起更严格的审查，拟议的研究的影响将超出砷问题，因为它们解决了地下水中氧化还原控制的更普遍的问题。与砷释放到地下水有关的铁氧氢氧化物的还原溶解主要是由与含水层砂同时沉积的POC的微生物降解驱动的。地下水平流的H2 DOC不会导致铁氢氧化物的显著还原性溶解，因此不会引发橙砂向灰色的转化或As的释放。H3高硫酸盐（SO4）地下水与高砷地下水混合，导致含水层沉积物中POC氧化导致砷硫化物沉淀。主要从As硫化物沉淀去除As和As与磷酸（PO4）的竞争吸附两方面来预测As在橙砂中的H4突破。更广泛的影响-河内几个市政供水厂分发的饮用水含有100 ？Ýg/L，即超过世卫组织饮用水中砷含量指南（10 ?Ýg/L）的十倍。这是由于从橙色含水层抽取的地下水处理不足，但可能部分来自邻近的灰色含水层。作为我们的最后一个工作假设，拟议的研究将有助于确定河内市市政供水和南亚类似位置的地下水抽水站是否可以通过有利于河水的携带而在源头降低地下水的砷含量。H5通过减少含水层来抽取河水的市政供水系统，由于增加SO4和降低PO4的双重作用，将受益于在抽取之前减少As。Eawag是我们在这个项目中的瑞士合作伙伴，在与河内科技大学的长期合作过程中，与城市水资源管理者建立了广泛的联系网络。负责模拟地下水和砷运输的环境咨询公司QEA的工程师将与麻省理工学院的一位高级水文学家协商，帮助确保研究结果转化为实际建议。一名越南学生的研究生研究将在项目期间支付，并部分支付Lamont-Doherty的博士后工作。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Emphasis on the elevated level of arsenic in groundwater tapped by millions of shallow tubewells across southern Asia over the past two decades has tended to obscure that anoxic aquifers that are low in As are also widespread and often within reach of drilling in the affected regions. This proposal addresses two key issues for assessing the vulnerability of low-As aquifers: (1) whether dissolved or particulate organic carbon (DOC or POC) drives aquifers towards microbial dissolution of Fe oxyhydroxides and (2) to what extent adsorption and precipitation of As attenuate the impact of high-As groundwater drawn into low-As aquifers. The proposed field investigation takes advantage of the previously documented (a) juxt-apposition at the same depth of grey sands associated with high-As groundwater and orange sands with low-As groundwater in a village 15 km south of Hanoi and (b) large groundwater withdrawals by the city of Hanoi resulting in water from the former being drawn laterally through the latter. The configuration is particularly well-suited to shed light on the key processes that determine the sustainability of continued reliance on low-As aquifers for the provision of drinking water throughout the affected region. Scientific merit ¡V An unprecedented combination of state-of-the-art analytical methods will be applied to a previously documented transition from orange to grey sands corresponding to low- to high-As groundwater, respectively: 14C-analysis of phospholipid fatty acids (PLFAs) constituting the membranes of living cells, probing of the redox state and bonding environment of As and Fe in aquifer sands by X-ray absorption spectroscopy, 3H-3He dating of groundwater, and optically-stimulated luminescence (OSL) dating of quartz grains. These measurements will provide the basis for testing the following suite of working hypotheses pertaining to the vulnerability of low-As aquifers in southern Asia. Whether the associated predictions hold up to closer scrutiny or not, the implications of the proposed research will extend beyond the As problem as they address the more general question of redox control in groundwater. H1 Reductive dissolution of Fe oxyhydroxides associated with the release of As to groundwater is driven primarily by the microbial degradation of POC deposited at the same time as the aquifer sands. H2 DOC advected by groundwater flow does not result in significant reductive dissolution of Fe oxyhydroxides and therefore does not trigger conversion of orange sands to grey or the release of As. H3 Mixing of high-sulfate (SO4) groundwater with high-As groundwater results in precipitation of As-sulfides fueled by the oxidation of POC in the aquifer deposit.H4 Breakthrough of As through orange sands can be predicted by considering mainly As removal by precipitation of As-sulfides and competitive adsorption of As and phosphate (PO4).Broader Impact - Drinking water distributed by several of Hanoi¡¦s municipal water supply plants contains 100 ?Ýg/L As, i.e. over ten-fold the WHO guideline for As in drinking water of 10 ?Ýg/L. This is due to insufficient treatment of groundwater drawn from orange aquifers but presumably originating in part from adjacent grey aquifers. Expressed as the last of our working hypotheses, the proposed research will help determine whether the As content of groundwater tapped by the municipal water supply of the city of Hanoi, and similarly situated groundwater pumping stations throughout southern Asia, could be lowered at the source by favoring entrainment of river water, herewith reducing the need for treatment:H5 Municipal water supplies engineered to draw river water through a reducing aquifer would benefit from a reduction in As prior to abstraction due to the dual effect of increasing SO4 and lowering PO4. Eawag, our Swiss partner in this project, has built an extensive network of contacts with city water managers over the course of a long-term collaboration with the Hanoi University of Science. Engineers at QEA, the environmental consultancy charged with modeling groundwater and As transport, in consultation with a senior hydrologist at MIT, will help ensure that the outcome of the research is translated into practical recommendations. Graduate research by one student in Vietnam will be covered over the duration of the project and partially covered for post-doctoral work at Lamont-Doherty.