Tracing groundwater flow in the Borden aquifer using krypton-85
Tracing groundwater flow in the Borden aquifer using krypton-85
复制标题
使用 krypton-85 追踪 Borden 含水层中的地下水流
DOI：
10.1016/0022-1694(92)90114-b
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发表时间：
1992
影响因子：
6.4
通讯作者：
Guy G. Mathieu
中科院分区：
文献类型：
--
作者：
W. Smethie;D. Solomon;Sherry L. Schiff;Guy G. Mathieu
1989年10月，在安大略的博登含水层，测量了空气、土壤气体和地下水中的氪-85。在空气和土壤气体中测得的比活度分别为52.0 ± 2.0和53.6 ± 1.8衰变/分钟（dpm）cm− 3氪。这些测量结果与全球大气趋势非常一致，并表明氪-85进入博登现场的地下水位，而不会滞后于土壤气藏。五个地下水样品中的氪-85比活度范围为44.9 - 9.5 dpm cm− 3，对应于地下水年龄为2-17年，比活度单调下降（年龄的增加）沿着地下水流的路径。从地下水流的二维稳态模型计算的旅行时间与氪-在含水层的主要补给区，主要是垂直流动，但年龄比主要补给区下游的氪-85年龄大30-40%，主要是水平流动。分散对氪-85的分布的影响，通过模拟氪-85在博登含水层的运输与二维随时间变化的平流分散模型，使用稳态流场。在主要补给区的样品中，模型比活度与观测比活度之间的一致性非常好，但模型比活度比水平流区观测比活度低30-50%。旅行时间和氪-85年龄和模型氪-85和观察到的氪-85具体活动的差异被认为是小的考虑到存在于水力传导性和含水层的几何形状，因此在地下水流场的不均匀性。该模型模拟氪-85分布是不敏感的纵向色散的变化，只有弱敏感的横向色散的变化。地球化学惰性、定义明确的源函数以及对氪-85分散的不敏感性使得可以以简单的方式估计地下水年龄，并且氪-85的测量可以显着增强许多浅层地下系统中地下水流的特征。
Krypton-85 was measured in air, soil gas, and ground water at the Borden aquifer in Ontario in October 1989. The measured specific activities in air and soil gas were 52.0 ± 2.0 and 53.6 ± 1.8 disintegrations per min (dpm) cm−3krypton. These measurements are in excellent agreement with the global atmospheric trend and demonstrate that krypton-85 enters the water table at the Borden site without a lag in the soil gas reservoir. The krypton-85 specific activity in five groundwater samples ranged from 44.9 to 9.5 dpm cm−3corresponding to groundwater ages of 2–17 years with a monotonic decrease in specific activity (increase in age) along the groundwater flow path. Travel times calculated from a two-dimensional steady-state model of groundwater flow agree well with the krypton-85 ages in the main recharge region of the aquifer where flow is predominantly vertical, but were 30–40% older than the krypton-85 age downstream of the main recharge area where the flow is mainly horizontal. The effect of dispersion on the distribution of krypton-85 was determined by modelling the transport of krypton-85 in the Borden aquifer with a two-dimensional time-dependent advection dispersion model using the steady-state flow field. Agreement between model specific activity and observed specific activity was excellent for samples in the main recharge region, but the model specific activities were 30–50% lower than observed specific activities in the region of horizontal flow. The differences in travel times and krypton-85 ages and in model krypton-85 and observed krypton-85 specific activities are considered to be small given the heterogeneities that exist in the hydraulic conductivity and aquifer geometry and hence in the groundwater flow field. The model simulated krypton-85 distribution was not sensitive to changes in longitudinal dispersivity and was only weakly sensitive to changes in transverse dispersivity. The geochemical inertness, well-defined source function, and insensitivity to dispersion of krypton-85 allow estimates of groundwater age to be made in a straightforward manner and measurement of krypton-85 can significantly enhance the characterization of groundwater flow in many shallow subsurface systems.