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。强调过去二十年来南亚数百万浅管井开采的地下水中砷含量升高，往往掩盖了砷含量低的缺氧含水层也很普遍，而且往往在受影响地区的钻探范围内。这一建议解决了两个关键问题，评估低砷含水层的脆弱性：（1）是否溶解或颗粒有机碳（DOC或POC）驱动含水层对微生物溶解的铁羟基氧化物和（2）在何种程度上的吸附和沉淀的As削弱高砷地下水的影响低砷含水层。拟议的实地调查利用了先前记录的（a）在河内以南15 km的一个村庄中，与高As地下水相关的灰色砂和与低As地下水相关的橙子砂在相同深度处的平行沉积，以及（B）河内市抽取大量地下水，导致前者的水通过后者横向抽取。该组合特别适合于阐明决定整个受影响地区持续依赖低砷含水层提供饮用水的可持续性的关键过程。科学价值……五.将对先前记录的从橙子到灰色砂的过渡（分别对应于低砷到高砷地下水）应用前所未有的最先进分析方法组合：14 C-分析构成活细胞膜的磷脂脂肪酸（PLFAs），通过X射线吸收光谱探测含水层砂中As和Fe的氧化还原状态和结合环境，地下水的~ 3 H-~ 3 He测年和石英颗粒的光释光测年。这些测量结果将为检验以下关于南亚低砷含水层脆弱性的一套工作假设提供基础。无论相关的预测是否经得起更仔细的审查，所提出的研究的影响将超出As问题，因为它们解决了地下水中更普遍的氧化还原控制问题。 H1还原溶解铁氢氧化物与释放的As地下水驱动的POC沉积在同一时间作为含水层砂的微生物降解。 H2 DOC平流的地下水流不会导致显着的还原溶解的铁氢氧化物，因此不会触发转换的橙子砂灰色或释放的As。 H3高硫酸盐（SO 4）地下水与高砷地下水混合，导致含水层沉积物中POC的氧化导致砷硫化物沉淀。H4通过橙子砂的砷突破可以通过主要考虑砷硫化物沉淀和砷和磷酸盐（PO 4）的竞争吸附来预测。更广泛的影响-河内几个城市分布的饮用水城市供水厂有100？10 μ g/L As，即超过世界卫生组织饮用水中砷含量指南10？100g/L。这是由于对从橙子含水层抽取的地下水处理不足，但据推测部分地下水来自邻近的灰色含水层。作为我们工作假设的最后一项，拟议的研究将有助于确定河内市市政供水以及整个南亚类似位置的地下水泵站所抽取的地下水的As含量是否可以通过有利于河水夹带而在源头降低，从而减少处理的需要：H5通过减少含水层抽取河水的市政供水将受益于抽取前As的减少，这是由于增加SO 4和降低As的双重影响。PO4 Eawag是我们在该项目中的瑞士合作伙伴，在与河内科学大学的长期合作中，与城市水管理人员建立了广泛的联系网络。负责模拟地下水和As运输的环境咨询公司QEA的工程师与麻省理工学院的一位高级水文学家协商，将有助于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进行，部分用于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.