GroMoPo Metadata for Yinchuan Multilayer aquifer MODFLOW model

Pumping-induced leakage across aquitards may induce a deterioration of water quality in multi-layer aquifer systems. It is critical to understand long-term trends of water quality parameters when assessing the sustainability of groundwater abstraction. Daily drinking water needs of 2.2 million people in Yinchuan region of northwest China are solely met by groundwater resources, but long-term groundwater withdrawal has created an extensive cone of depression (294 km(2) in area) in confined aquifer causing increased vertical recharge. In this study, a model was established and calibrated with head data, then was incorporated with field tracer tests to provide key information on the hydro-dispersive characteristics of the contaminant for assessing both the current and future state of the aquifer system. The results confirmed a close association between water quality deterioration and high downward fluxes of high chloride groundwater, most notably near the center of the cone of depression. On a temporal scale, water quality degradation remains slow, largely due to the high, pre-existing storage of good quality water. Modeling suggests that the water quality in the upper confined aquifer will lose its potability over a 25 km(2) and 50 km(2) area within 200 years under the current and intensified pumping conditions, respectively. Elevated chloride values were also detected toward the east of the cone, highlighting the impact of hydrological settings on the vertical groundwater flow. Modeling of potential aquifer remediation shows an even slower response with a further 250 years or more required for potability to be restored in affected areas. The findings can provide valuable guidance to for decision makers and support the sustainable management of aquifer exploitation. (c) 2020 Elsevier Ltd. All rights reserved.

抽水引发的弱透水层（aquitards）越流可能导致多层含水层系统的水质恶化。在评估地下水开采可持续性时，掌握水质参数的长期变化趋势至关重要。中国西北银川地区220万人口的日常饮用水需求完全依靠地下水资源满足，但长期的地下水开采已在承压含水层（confined aquifer）中形成了面积达294 km²的大范围降落漏斗（cone of depression），导致垂向补给量增加。本研究建立了模型并利用水头数据进行校准，随后结合野外示踪试验，获取了污染物水动力弥散（hydro-dispersive）特征的关键信息，以此评估含水层系统的当前与未来状态。研究结果证实，水质恶化与高氯化物地下水的强向下通量存在密切关联，尤以降落漏斗中心附近最为显著。从时间维度来看，水质退化进程仍较为缓慢，这在很大程度上源于原有优质地下水的高储量。模型模拟结果显示，在当前开采与强化开采工况下，上层承压含水层的水质将分别在200年内于25 km²与50 km²的范围内丧失可饮用性（potability）。研究还在降落漏斗东侧检测到氯化物浓度升高的现象，凸显了水文地质条件对地下水流垂向运动的影响。对含水层修复方案的模拟表明，受影响区域的水质恢复进程更为缓慢，需250年及以上才能恢复可饮用性。本研究结果可为决策者提供重要参考，助力含水层开采的可持续管理。©2020 爱思唯尔有限公司（Elsevier Ltd.）保留所有权利。