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Spatial and temporal variation of dissolved arsenic concentrations in the intermediate aquifer of the Lahontan Valley, Nevada.

机译：内华达州拉洪坦河谷中层含水层中溶解砷浓度的时空变化。

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摘要

A study was conducted in the intermediate-depth alluvial aquifer (50-500 ft) of Lahontan Valley, Nevada, to determine if there is temporal and spatial stability of dissolved arsenic concentrations, and if chemical mechanisms commonly associated with arsenic mobility are responsible for any trends observed. This aquifer is an alkaline and reducing environment that is chemically distinct from hydrologic units above and below it. Five wells previously observed to have substantial concentrations of both As(V) and As(III) were chosen to represent a groundwater flow-path and were sampled monthly from February 2004 -- August 2005 . Arsenic concentrations were observed to be statistically unchanged for the sampling period at each well, as were the majority of other chemical constituents and physical characteristics. Spatially, total arsenic activities [AsT] increased nearly seven-fold along the flow-path, and the ratio of the concentration of arsenic as arsenite to total arsenic ([As(III)]/[AsT]) decreased. The concentration of total arsenic correlated with dissolved organic carbon (DOC), [HCO 3-], and distance along flow-path (p = 0.04, 0.01, 0.02, respectively).;NETPATH 2.0 and Visual MINTEQ 2.3 geochemical models were employed to model geochemical reactions controlling potential arsenic release to the aquifer using both field -measured and modeled electric potential (Eh) values. Models show minor desorption of AsO43- from hydrous ferric oxides (HFO) along the flow-path (∼0.5%), and to a lesser degree with increased pH. H3AsO3 desorbed to a greater degree along the flow-path according to models, with little pH dependence. Arsenic out-competed phosphate for sorption sites according to the models. Competition from other ligands was also likely. Model analysis indicated that reductive dissolution of HFO did not occur at field-measured Eh and average pH for each well. However, under MINTEQ-computed Eh values that were considerably lower, HFO reductive dissolution was shown to occur, potentially releasing arsenic to groundwater. Further research into the strong correlation of AsT with DOC and HCO3- is suggested.
机译：在内华达州Lahontan谷的中深冲积含水层（50-500英尺）中进行了一项研究，以确定溶解的砷浓度是否存在时空稳定性，以及通常与砷迁移相关的化学机制是否是造成这种情况的原因。观察到的趋势。该含水层是碱性和还原性环境，在化学上不同于其上方和下方的水文单元。从2004年2月至2005年8月，每月取样5口以前被观测为同时具有较高浓度的As（V）和As（III）的井来代表地下水的流动路径。在每个孔的采样期间，砷的浓度在统计上没有变化，其他大多数化学成分和物理特征也是如此。在空间上，总砷活度[AsT]沿流径增加了近7倍，砷中砷的浓度与总砷的比率（[As（III）] / [AsT]）降低了。总砷浓度与溶解有机碳（DOC），[HCO 3-]和沿流径的距离有关（分别为p = 0.04、0.01、0.02）。采用NETPATH 2.0和Visual MINTEQ 2.3地球化学模型使用现场测量和模型化的电势（Eh）值对地球化学反应进行模型控制，以控制潜在的砷释放到含水层中。模型显示，AsO43-从含水三氧化二铁（HFO）沿流动路径解吸的程度较小（〜0.5％），并且随着pH的升高解吸程度较小。根据模型，H3AsO3在流动路径上的解吸程度更高，对pH的依赖性很小。根据模型，砷比磷酸盐更具竞争优势。来自其他配体的竞争也是可能的。模型分析表明，在现场测得的Eh和每个孔的平均pH值下均未发生HFO的还原溶解。但是，在MINTEQ计算的Eh值低得多的情况下，HFO还原溶解被证明会发生，可能将砷释放到地下水中。建议进一步研究AsT与DOC和HCO3-的强相关性。

著录项

  • 作者

    Meinert, Michael S.;

  • 作者单位

    University of Nevada, Reno.;

  • 授予单位 University of Nevada, Reno.;
  • 学科 Hydrology.;Geochemistry.;Chemistry Inorganic.
  • 学位 M.S.
  • 年度 2009
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 水文科学（水界物理学）;无机化学;地质学;
  • 关键词

  • 入库时间 2022-08-17 11:38:27

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