Abstract
Shallow groundwater is the main source for drinking water in Kabul, Afghanistan. It comes from a multitude of shallow hand-pumped wells spread over the whole city area. The groundwater is characterised by slightly oxic redox conditions. Interactions with aquifer carbonates lead to near-neutral pH and high degrees of hardness. The mostly negative water budget of the Kabul Basin is the result of strong evaporation which leads to an increase in salt and also of some undesirable constituents, e.g. borate. Several years of drought have aggravated this problem. The shallow groundwater in the city has received tremendous amounts of pollution due to a lack of proper waste disposal and sewage treatment. Common indicators are elevated concentrations of nutrients such as nitrate and faecal bacteria. The high infant mortality can at least partially be attributed to the insufficient water hygiene. Acid generated during the mineralisation of the wastewater is hidden due to the strong pH buffering capacity of the groundwater system. Redox and pH conditions preclude significant mobilisation of trace metals and metalloids.
Résumé
Une nappe peu profonde est la principale source d’alimentation en eau à Kaboul, Afghanistan. Elle provient d’une multitude de puits peu profonds équipés de pompes à main répartis sur l’ensemble de l’agglomération. La nappe se caractérise par des conditions redox légèrement oxiques. Les interactions avec les carbonates de l’aquifère résultent en un pH presque neutre et des degrés de dureté élevés. Le bilan d’eau la plupart du temps négatif du Bassin de Kaboul est le résultat d’une forte évaporation qui conduit à une augmentation du sel et aussi de quelques composants indésirables, e.g. les borates. Plusieurs années de sécheresse ont aggravé ce problème. L’aquifère peu profond dans la ville a absorbé d’énormes quantités de pollution du fait de l’absence d’enlèvement des ordures et de traitement des eaux d’égout. Des indicateurs courants sont les concentrations élevées en éléments nutritifs tels que les nitrates et les bactéries fécales. L’importante mortalité infantile peut être attribuée au moins partiellement à la propreté insuffisante de l’eau. L’acide produit pendant la minéralisation des eaux usées est masqué du fait du fort effet tampon du pH de la nappe. Les conditions de redox et de pH empêchent une mobilisation significative des métaux traces et des métalloïdes.
Resumen
El agua subterránea somera es la principal fuente de abastecimiento de agua potable en Kabul, Afghanistan. Ella proviene de una gran cantidad de pozos poco profundos con bombas de mano que se encuentran distribuidos en la toda el área de la ciudad. El agua subterránea está caracterizada por condiciones levemente oxido reductoras. Las interacciones con acuíferos carbonáticos conducen a valores de pH cercanos a los neutros y altos grados de dureza. El balance hídrico mayormente negativo de la cuenca de Kabul es el resultado de una fuerte evaporación que conduce a un incremento en sales y también de algún constituyente no deseado, por ejemplo boratos. Varios años de sequías han agravado este problema, El agua subterránea somera en la ciudad ha recibido elevadas cantidades de contaminantes debido a la falta de una adecuada disposición de residuos y tratamiento de aguas residuales. Indicadores comunes son las elevadas concentraciones de nutrientes tales como nitrato y bacterias fecales. La elevada mortalidad infantil puede ser, al menos parcialmente, atribuida a la insuficiente higiene del agua. Los ácidos generados durante la mineralización del agua residual son ocultados debido a la fuerte capacidad amortiguadora del pH del sistema de aguas subterráneas. Las condiciones redox y de pH son un importante obstáculo para la movilización de metales trazas y metaloides.
摘要
浅层地下水是阿富汗喀布尔饮用水的主要来源。这些水来自遍布整个城区的大量的压水井。地下水具有轻微氧化性的氧化还原条件。与含水层碳酸盐之间的相互作用导致地下水的高硬度和近于中性的pH值。喀布尔盆地大部分水量负均衡是强蒸发的结果, 这也导致了盐分的增加和一些不良组分 (如硼酸盐) 的出现。数年的干旱加重了这种状况。由于缺乏适当的垃圾处置和污水处理, 城市浅层地下水接纳了大量的污染物。通常的标志为养分 (如硝酸盐和粪便细菌) 浓度的升高。高婴儿死亡率至少部分与水卫生条件差有关。由于地下水系统对pH的强缓冲能力, 污水矿化过程中产生的酸被掩盖了。氧化还原与pH条件阻碍了痕量金属和类金属发生显著的运移。
Resumo
A principal origem de água para beber em Kabul (Afeganistão) é água subterrânea sub-superficial. Essa água provém de um grande número de poços pouco profundos, equipados com bombas manuais, que se encontram espalhados por toda a área da cidade. A água subterrânea caracteriza-se por apresentar condições redox ligeiramente óxicas. A interacção com os carbonatos presentes no aquífero levam a que o pH seja aproximadamente neutro e a água tenha um elevado grau de dureza. O balanço predominatemente negativo da Bacia de Kabul resulta da forte evaporação que leva a um aumento da concentração de sais e de alguns constituintes indesejáveis, por exemplo, o borato. Vários anos de seca agravaram este problema. As águas subterrâneas pouco profundas da cidade também receberam quantidades tremendas de poluição devido à falta duma apropriada gestão dos resíduos e de tratamento dos esgotos. Elevadas concentrações de nutrientes, tais como nitrato e bactérias fecais, são indicadores frequentes de contaminação. A elevada mortalidade infantil pode, pelo menos em parte, ser atribuída à insuficiente higiene da água. O ácido gerado durante os processos de mineralização das águas residuais é ocultado devido à elevada capacidade tampão de pH da água subterrânea. As condições redox e de pH impedem uma mobilização significativa de metais e metalóides.
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Acknowledgements
This report is a result of close cooperation with Afghan authorities and universities. For their continuous help without which this report would not have been possible we would like to thank the following institutions: Ministry of Mines and Industries (MMI); Ministry of Irrigation, Water Resources and Environment (MIWRE); Kabul University, Faculty of Geosciences (KU); Kabul Polytechnic University (KPU). Financial support for this study was provided by the Foreign Office of the Federal Republic of Germany through the project “Improving groundwater protection for the preventative avoidance of drought problems in the Kabul Basin, Afghanistan” (AA Gz: GF07 385.28/3 16/03).
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Houben, G., Tünnermeier, T., Eqrar, N. et al. Hydrogeology of the Kabul Basin (Afghanistan), part II: groundwater geochemistry. Hydrogeol J 17, 935–948 (2009). https://doi.org/10.1007/s10040-008-0375-1
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DOI: https://doi.org/10.1007/s10040-008-0375-1