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首页> 外文期刊>Canadian Water Resources Journal >Numerical modelling in support of a conceptual model for groundwater flow and geochemical evolution in the southern Outaouais Region, Quebec, Canada
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Numerical modelling in support of a conceptual model for groundwater flow and geochemical evolution in the southern Outaouais Region, Quebec, Canada

机译：数值模型支持加拿大魁北克省奥陶阿伊斯南部地区地下水流动和地球化学演化的概念模型

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摘要

A two-dimensional vertical-section numerical model for groundwater flow and transport using age, tritium and chloride was used to help validate a conceptual model of geochemical evolution within a representative regional-scale hydrogeological system in the Outaouais Region, Quebec, Canada. The flow system includes up to 30 m of Quaternary sediments and marine clays overlying fractured silicate rock of the Canadian Shield. Calibration of the regional flow model using observed piezometric levels and tritium concentrations showed that shallow groundwater flow is dominated by local flow systems limited to 30-40 m depth, 1-5 km long, and with groundwater residence times of 10-50 years. Intermediate systems, on the order of 5-15 km long, are less extensive than initially thought and are characterised by maximum depths of about 100 m and residence times of 200-6000 years. A model-calibrated hydraulic conductivity of 8x10(-5) m.s(-1) was required in the upper 50 m of the fractured bedrock. The active flow zone was inferred to extend to depths of about 100-150 m, with any deeper regional flow essentially negligible. Differences between tritium-based ages and simulated mean residence times were attributed to mixing of groundwater in open boreholes. Concentrations of He-4 could be explained by diffusive transport from deeper and older groundwater, exacerbated by sampling. With new insight from the numerical modelling, the conceptual flow model has been updated to now include only a weak component of regional flow combined with significant local- and intermediate-scale flow systems connected to the upper fractured bedrock. The simulated flow system is also consistent with the geochemical evolution of the region, which is dominated by young Ca-HCO3-type waters in the unconfined aquifer and by older Cl- signatures from the remnant Champlain Sea seawater.
机译：利用年龄，tri和氯化物建立的二维垂直剖面数值模型，用于地下水的流动和运输，以帮助验证加拿大魁北克奥陶瓦伊斯地区具有代表性的区域规模水文地质系统中地球化学演化的概念模型。流动系统包括长达30 m的第四纪沉积物和覆盖在加拿大盾构裂化硅酸盐岩上的海相粘土。使用测得的测压高度和tri浓度对区域流量模型进行的校准表明，浅层地下水流主要由局限在30-40 m深度，1-5 km长且地下水停留时间为10-50年的局部水流系统控制。中间系统的长度约为5-15公里，不如最初想像的那样广泛，其最大深度约为100 m，停留时间为200-6000年。在裂缝基岩的上部50 m中需要模型校准的8×10（-5）m.s（-1）的水力传导率。据推测，活动流带的深度约为100-150 m，任何较深的区域流基本上可以忽略不计。基于tri的年龄和模拟的平均停留时间之间的差异是由于裸眼中的地下水混合所致。 He-4的浓度可以用较深和较老的地下水的扩散传输来解释，采样会加剧这种情况。借助数值建模的新见识，概念性流模型已更新为现在仅包括区域流的薄弱部分，以及与上部裂缝性基岩相连的大量局部和中尺度流系统。模拟的水流系统也与该区域的地球化学演化相一致，该区域的主要化学成分是无限制含水层中年轻的Ca-HCO3型水域和尚普兰海水中残留的较旧Cl-特征。

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