Yongfeng Jia

Contrasting distributions of groundwater arsenic and uranium in the western Hetao basin, Inner Mongolia: Implication for origins and fate controls.

Although As concentrations have been investigated in shallow groundwater from the Hetao basin, China, less is known about U and As distributions in deep groundwater, which would help to better understand their origins and fate controls. Two hundred and ninety-nine groundwater samples, 122 sediment samples, and 14 rock samples were taken from the northwest portion of the Hetao basin, and analyzed for geochemical parameters. Results showed contrasting distributions of groundwater U and As, with high U and low As concentrations in the alluvial fans along the basin margins, and low U and high As concentrations downgradient in the flat plain. The probable sources of both As and U in groundwater were ultimately traced to the bedrocks in the local mountains (the Langshan Mountains). Chemical weathering of U-bearing rocks (schist, phyllite, and carbonate veins) released and mobilized U as UO2(CO3)2(2-) and UO2(CO3)3(4-) species in the alluvial fans under oxic conditions and suboxic conditions where reductions of Mn and NO3(-) were favorable (OSO), resulting in high groundwater U concentrations. Conversely, the recent weathering of As-bearing rocks (schist, phyllite, and sulfides) led to the formation of As-bearing Fe(III) (hydr)oxides in sediments, resulting in low groundwater As concentrations. Arsenic mobilization and U immobilization occurred in suboxic conditions where reduction of Fe(III) oxides was favorable and reducing conditions (SOR). Reduction of As-bearing Fe(III) (hydr)oxides, which were formed during palaeo-weathering and transported and deposited as Quaternary aquifer sediments, was believed to release As into groundwater. Reduction of U(VI) to U(IV) would lead to the formation of uraninite, and therefore remove U from groundwater. We conclude that the contrasting distributions of groundwater As and U present a challenge to ensuring safe drinking water in analogous areas, especially with high background values of U and As.

Sources of groundwater salinity and potential impact on arsenic mobility in the western Hetao Basin, Inner Mongolia

The quality of groundwater used for human consumption and irrigation in the Hetao Basin of Inner Mongolia, China is affected by elevated salinity as well as high arsenic (As) concentrations. However, the origin of high salinity and its potential impact on As mobility in the Basin remain unclear. This study explores both issues using stable isotopic compositions and Cl/Br ratios of groundwater as well as the major ions of both groundwater and leachable salts in aquifer sediments. Limited variations in δ18O and δ2H (-11.13 to -8.10, -82.23 to -65.67) with the wide range of Total Dissolved Solid (TDS, 351-6734mg/L) suggest less contribution of direct evaporation to major salinity in groundwater. Deuterium excess shows that non-direct evaporation (capillary evaporation, transpiration) and mineral/evaporite dissolution contribute to >60% salinity in groundwater with TDS>1000mg/L. Non-direct evaporation, like capillary evaporation and transpiration, is proposed as important processes contributing to groundwater salinity based on Cl/Br ratio and halite dissolution line. The chemical weathering of Ca, Mg minerals and evaporites (Na2SO4 and CaSO4) input salts into groundwater as well. This is evidenced by the fact that lacustrine environment and the arid climate prevails in Pleistocene period. Dissolution of sulfate salts not only promotes groundwater salinity but affects As mobilization. Due to the dissolution of sulfate salts and non-direct evaporation, groundwater SO42- prevails and its reduction may enhance As enrichment. The higher As concentrations (300-553μg/L) are found at the stronger SO42- reduction stage, indicating that reduction of Fe oxide minerals possibly results from HS- produced by SO42- reduction. This would have a profound impact on As mobilization since sulfate is abundant in groundwater and sediments. The evolution of groundwater As and salinity in the future should be further studied in order to ensure sustainable utilization of water resource in this water scarce area.

Influences of groundwater extraction on flow dynamics and arsenic levels in the western Hetao Basin, Inner Mongolia, China

Data on spatiotemporal variations in groundwater levels are crucial for understanding arsenic (As) behavior and dynamics in groundwater systems. Little is known about the influences of groundwater extraction on the transport and mobilization of As in the Hetao Basin, Inner Mongolia (China), so groundwater levels were recorded in five monitoring wells from 2011 to 2016 and in 57 irrigation wells and two multilevel wells in 2016. Results showed that groundwater level in the groundwater irrigation area had two troughs each year, induced by extensive groundwater extraction, while groundwater levels in the river-diverted (Yellow River) water irrigation area had two peaks each year, resulting from surface-water irrigation. From 2011 to 2016, groundwater levels in the groundwater irrigation area presented a decreasing trend due to the overextraction. Groundwater samples were taken for geochemical analysis each year in July from 2011 to 2016. Increasing trends were observed in groundwater total dissolved solids (TDS) and As. Owing to the reverse groundwater flow direction, the Shahai Lake acts as a new groundwater recharge source. Lake water had flushed the near-surface sediments, which contain abundant soluble components, and increased groundwater salinity. In addition, groundwater extraction induced strong downward hydraulic gradients, which led to leakage recharge from shallow high-TDS groundwater to the deep semiconfined aquifer. The most plausible explanation for similar variations among As, Fe(II) and total organic carbon (TOC) concentrations is the expected dissimilatory reduction of Fe(III) oxyhydroxides.RésuméLes données spatio-temporelles des variations des niveaux piézométriques sont cruciales pour la compréhension du comportement de l’arsenic (As) et la dynamique des systèmes aquifères. On dispose de peu de connaissance sur l’influence de l’exploitation des eaux souterraines sur le transport et la mobilisation de l’As dans le bassin de l’Hetao, Mongolie intérieure (Chine). Ainsi les niveaux d’eau souterraines ont été enregistrés sur 5 piézomètres de 2011 à 2017 et sur 57 puits d’irrigation et deux forages multiniveaux en 2016. Les résultats montrent que les niveaux piézométriques dans la zone irriguée à partir des eaux souterraines présentent deux baisses chaque année du fait de prélèvements très importants d’eau souterraine alors que les niveaux piézométriques du secteur irrigué par dérivation de la rivière (Fleuve Jaune) présentent deux pics chaque année résultant de l’irrigation par les eaux de surface. De 2011 à 2016, les niveaux piézométriques du secteur irrigué par les eaux souterraines présentent une tendance à la baisse du fait d’une surexploitation. Des échantillons d’eau souterraine ont permis une analyse géochimique chaque année de juillet 2011 à 2016. Une augmentation des tendances d’évolution des concentrations en éléments totaux dissous et As dans les eaux souterraines a été observée. Du fait d’une inversion de la direction des écoulements des eaux souterraines, le lac Shakai devient une nouvelle source de recharge des aquifères. Les eaux du lac renferment des sédiments en surface du fonds du lac, caractérisés par une forte composante d’éléments solubles qui entraine une augmentation de la salinité des eaux souterraines. De plus, l’exploitation des eaux souterraines induit un fort gradient hydraulique à la baisse, ce qui amène un drainage des eaux souterraines superficielles de forte teneur en éléments dissous (TDS) vers les parties profondes de l’aquifère semi-captif. L’explication la plus plausible à des variations similaires des concentrations en As, Fe(II) et organique total dissous (TOC) est. la réduction dissimilatrice attendue des oxyhydroxydes de Fe(III).ResumenLos datos sobre las variaciones espaciotemporales en los niveles de agua subterránea son cruciales para comprender el comportamiento y la dinámica del arsénico (As) en los sistemas de agua subterránea. Poco se sabe sobre las influencias de la extracción de agua subterránea en el transporte y la movilización de As en la cuenca de Hetao, Mongolia Interior (China), por lo que se registraron niveles de agua subterránea en cinco pozos de monitoreo desde 2011 a 2016 y en 57 pozos de riego y dos pozos multinivel en 2016. Los resultados mostraron que el nivel freático en el área de riego de agua subterránea tenía dos depresiones cada año, inducido por la extracción de agua subterránea, mientras que los niveles de agua subterránea en el área de riego de agua derivada del río tenían dos picos cada año, como resultado del riego de agua superficial. De 2011 a 2016, los niveles de agua subterránea en el área de riego con aguas subterráneas presentaron una tendencia decreciente debido a la extracción excesiva. Las muestras de agua subterránea se tomaron para análisis geoquímicos cada año en julio desde 2011 a 2016. Se observaron tendencias crecientes en sólidos totales disueltos (TDS) y As. Debido a la dirección inversa del flujo del agua subterránea, el lago Shahai actúa como una nueva fuente de recarga de agua subterránea. El agua del lago había inundado los sedimentos cercanos a la superficie, que contienen abundantes componentes solubles y una mayor salinidad del agua subterránea. Además, la extracción de agua subterránea indujo a fuertes gradientes hidráulicos descendentes, que llevaron a la reposición de filtraciones desde aguas subterráneas poco profundas de alta TDS hasta el acuífero semi confinado profundo. La explicación más plausible para variaciones similares entre las concentraciones de As, Fe (II) y carbono orgánico total (TOC) es la reducción disimilatoria esperada de los oxihidróxidos de Fe (III).摘要地下水时空变化的数据对于了解地下水系统中砷特性和动力特征至关重要。有关(中国)内蒙古河套盆地地下水开采对砷的运移和活动化的影响知之甚少,因此,从2011年到2016年在5个观测井以及2016年在57个灌溉井记录了地下水位。结果显示,在地下水灌溉区地下水位每年有两个低槽;这两个低槽由地下水开采引起,而在引河(黄河)水灌溉区,地下水位每年有两个高峰,这是由于地表水灌溉造成的。2011年到2016年,由于地下水超采,地下水灌溉区的地下水水位呈现下降趋势。2011年到2016年每年7月为进行地球化学分析而采取地下水采样。观测到地下水中总溶解固体含量和砷都有增长的趋势。由于地下水流方向反转,沙海湖成为新的地下水补给源。湖水冲刷含有大量溶解成分的近地表沉积物,增加了地下水的盐度。另外,地下水开采引起了强烈向下的水力梯度,导致浅层总固体含量高的地下水向深部半承压含水层越流补给。针对砷、铁和总有机碳含量类似的变化,似乎最可信的解释就是预料中的铁氢氧化合物异化还原反应。ResumoDados de variações espaçotemporais nos níveis das águas subterrâneas são cruciais para a compreensão do comportamento e dinâmica do arsênio (As) em sistemas de águas subterrâneas. Pouco se sabe a respeito das influências da extração de águas subterrâneas sobre o transporte e mobilização de As na Bacia de Hetao, Mongólia Interior (China), assim, níveis de águas subterrâneas foram registrados em cinco poços de monitoramento de 2011 a 2016 e em 57 poços de irrigação e dois poços multiníveis em 2016. Os resultados mostraram que o nível das águas subterrâneas na área irrigada com águas subterrâneas teve duas recessões a cada ano, induzidas pela extração extensiva de águas subterrâneas, enquanto os níveis das águas subterrâneas na área irrigada com água desviada do rio (Rio Amarelo) tinham dois picos por ano, resultantes da irrigação com águas superficiais. De 2011 a 2016, os níveis de águas subterrâneas na área de irrigação com águas subterrâneas apresentaram tendência decrescente devido à superextração. Realizou-se amostragens de águas subterrâneas para análise geoquímica anualmente, em julho, de 2011 a 2016. Foram observadas tendências crescentes sólidos solúveis totais (SST) e As. Devido à direção inversa do fluxo de águas subterrâneas, o Lago Shahai atua como uma nova fonte de recarga de águas subterrâneas. A água do lago carreou sedimentos próximos da superfície, com abundantes componentes solúveis, e aumentou a salinidade das águas subterrâneas. Além disso, a extração de águas subterrâneas induziu fortes gradientes hidráulicos descendentes, encaminhando a recarga de vazamento de águas subterrâneas rasas de alto SST para o aquífero semiconfinado profundo. A explicação mais plausível para variações semelhantes entre as concentrações de As, Fe (II) e carbono orgânico total (COT) é a redução dissimilatória esperada de oxihidróxidos de Fe (III).

Identification of groundwater redox process induced by landfill leachate based on sensitive factor method

Landfill site is a significant source of groundwater pollution. To ensure that the groundwater contamination of landfills can be controlled and repaired scientifically, the identification of groundwater pollution process is needed. On the basis of biogeochemical process of leachate pollutants in the groundwater environment, a sensitive factor method for the identification of groundwater redox process from landfills was established in this research. The method encompasses four phases, including sensitive factors selection, redox zone characterization, weight calculation, and redox zone identification. In the sensitive factor index system employed here, five indicators involving dissolved oxygen (DO), nitrite, Fe2+, sulfide, and CO2 were selected. The boundary of each redox zones was determined by the quantitative method, and the weight of each indicator was calculated by combined weight method. This method was applied to a landfill site in the northeast of China. The result showed that there were five redox zones that appeared in pollution plume, including methanogenic zone (MGZ), sulfate reduction zone (SRZ), iron reduction zone (IRZ), nitrate reduction zone (NRZ), and oxygen reduction zone (ORZ). The results were consistent with the actual situation of the site. The sensitive factor method was scientific and effective to identify the groundwater redox process in landfill and can provide reference data related to investigation and remediation of groundwater pollution in landfill sites.

Distribution, formation and human-induced evolution of geogenic contaminated groundwater in China: A review

The sustainability of groundwater usage faces quality problem caused by anthropogenic activity as well as geogenic contamination. With varied climate zones, geomorphology and geological background, China faces a variety of geogenic contaminated groundwater (GCG) reported known as high TDS, Fe, Mn, As, F, I, NH4+, U, Cr and low I, Se, etc., may still exist some others not fully known yet. The problem of GCG is more significant in northern China due to extensive groundwater usage, arid climate and widespread Holocene strata. High salinity groundwater is mainly distributed in semi-arid/arid northwestern inland basins and coastal areas. Elevated Fe and Mn are frequently concomitant and controlled by redox potential, prevailing in the Sanjiang Plain, Yellow River Basin, and middle and lower reaches of the Yangtze River Basin. High As groundwater occurs in reducing aquifer is mainly distributed in the Yellow River, Yangtze River and Huai River Basins as well as the Songnen Plain and Xinjiang. Fluoride is characterized by its areal distribution in northern China in comparison with scatter occurrence in the south. The dissolution of F-bearing minerals as well as evaporation effect both contribute to elevated F. High iodine groundwater mainly distributed in the Yellow-Huai-Hai River Basin and low iodine prevailing in piedmont areas both pose health issues. Iodine is related to decomposition of organic matter (OC) as well as marine origin. Contributed by OC mineralization naturally-occurring NH4+ was found in reducing aquifers. The GCG triggers endemic disease in addition to reduce groundwater resource. The co-occurrence like high TDS and F, As and F are frequently observed posing major challenges for mitigation. Anthropogenic influence like abstraction and pollutant infiltration would alter groundwater flow and the redox condition causing the further evolution of GCG. Identification of GCG should be made in rural areas where private wells prevail to ensure residents health.