U.S. Geological Survey, Sacramento, CA, United States.
U.S. Geological Survey, Sacramento, CA, United States.
Sci Total Environ. 2021 Jun 1;771:145223. doi: 10.1016/j.scitotenv.2021.145223. Epub 2021 Jan 18.
In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the US maximum contaminant level of 10 μg/L. High concentrations of arsenic are often associated with high pH (greater than 7.8) or reduced geochemical conditions. Although most wells have low arsenic (<3 μg/L) and do not have changing arsenic concentrations, this study found that most wells with concentrations above 10 μg/L had arsenic trends. Overall, about 24% of wells had time-series trends since 2010 and 59% had paired-sample trends since 2000. Most wells had decreasing arsenic trends, even in wells with higher arsenic concentrations. These wells often had co-detections of increasing nitrate and sulfate trends that reflect oxic groundwater likely derived from agricultural recharge. Wells with increasing arsenic trends were deeper or located in the valley trough where aquifer materials are more fine-grained and where reducing conditions favor arsenic mobility. Wells with arsenic trends also tend to be clustered near areas of higher well density. Groundwater pumping in these areas has likely increased the contribution of younger, more oxic groundwater in wells with declining arsenic or, less frequently, increased the contribution of higher pH or reduced groundwater in wells with rising arsenic. Projections of arsenic trends indicate that 37 wells with high arsenic presently will be below 10 μg/L in ten years. Unfortunately, these improvements will be largely offset by 31 wells that are expected to increase above 10 μg/L in addition to expected rises in nitrate in wells where arsenic decreased. This study shows how human-altered flow systems can impact the natural geochemical character of water in both beneficial and deleterious ways.
在加利福尼亚州的圣华金河谷（SJV），自 2010 年以来，约有 10%的饮用水井中的砷浓度超过了美国 10μg/L 的最大污染物水平。高浓度的砷通常与高 pH 值（大于 7.8）或还原地球化学条件有关。尽管大多数水井中的砷含量较低（<3μg/L）且砷浓度没有变化，但本研究发现，大多数浓度超过 10μg/L 的水井都有砷浓度趋势。总体而言，自 2010 年以来，约有 24%的水井存在时间序列趋势，自 2000 年以来，59%的水井存在配对样本趋势。大多数水井的砷浓度呈下降趋势，即使在砷浓度较高的水井中也是如此。这些水井通常伴随着硝酸盐和硫酸盐浓度增加的趋势，反映出可能来自农业补给的氧化地下水。砷浓度呈上升趋势的水井往往更深，或位于河谷槽中，含水层物质更细，还原条件有利于砷的迁移。砷浓度呈上升趋势的水井也往往集中在井密度较高的地区附近。这些地区的地下水开采可能增加了砷浓度下降的水井中年轻、更氧化地下水的贡献，或者，在砷浓度上升的水井中，增加了高 pH 值或还原地下水的贡献。砷浓度趋势的预测表明，目前有 37 口高砷水井在十年内将降至 10μg/L 以下。不幸的是，这些改善将在很大程度上被预计将砷浓度增加超过 10μg/L 的 31 口井以及砷浓度下降的水井中硝酸盐浓度预计上升所抵消。本研究表明，人为改变的水流系统如何以有益和有害的方式影响水的自然地球化学特征。
