Stochastic analysis of the efficiency of coupled hydraulic-physical barriers to contain solute plumes in highly heterogeneous aquifers

JOURNAL OF HYDROLOGY

卷:553

Article

Pedretti, Daniele¹  Masetti, Marco²  Beretta, Giovanni Pietro² 

[1] Geol Survey Finland GTK, Espoo, Finland

[2] Univ Milan, Dipartimento Sci Terra A Desio, Milan, Italy

关键词: Cutoff walls;    Aquifer heterogeneity;    Solute transport;    Risk;    Uncertainty;    Pump-and-treat;   

DOI  :  10.1016/j.jhydrol.2017.08.051

来源: Elsevier

【 摘 要 】

The expected long-term efficiency of vertical cutoff walls coupled to pump-and-treat technologies to contain solute plumes in highly heterogeneous aquifers was analyzed. A well-characterized case study in Italy, with a hydrogeological database of 471 results from hydraulic tests performed on the aquifer and the surrounding 2-km-long cement-bentonite (CB) walls, was used to build a conceptual model and assess a representative remediation site adopting coupled technologies. In the studied area, the aquifer hydraulic conductivity K-a [mid] is log-normally distributed with mean E(Y-a) = 0.32, variance sigma(2)(Ye) = 6.36 (Y-a = In K-a) and spatial correlation well described' by an exponential isotropic variogram with integral scale less than 1/12 the domain size. The hardened CB wall's hydraulic conductivity, K-w [m/d], displayed strong scaling effects and a lognormal distribution with mean E(Y-w) = -3.43 and sigma(2)(Yw) = 0.53 (Y-w = log(10)K(w)). No spatial correlation of K-w was detected. Using this information, conservative transport was simulated' across a CB wall in spatially correlated 1-D random Y-a fields within a numerical Monte Carlo framework. Multiple scenarios representing different K-w values were tested. A continuous solute source with known concentration and deterministic drains' discharge rates were assumed. The efficiency of the confining system was measured by the probability of exceedance of concentration over a threshold (C*) at a control section 10 years after the initial solute release. It was found that the stronger the aquifer heterogeneity, the higher the expected efficiency of the confinement system and the lower the likelihood of aquifer pollution. This behavior can be explained because, for the analyzed aquifer conditions, a lower K-a generates more pronounced drawdown in the water table in the proximity of the drain and consequently a higher advective flux towards the confined area, which counteracts diffusive fluxes across the walls. Thus, a higher sigma(2)(Ye) results in a larger amount of low K-a values in the proximity of the drain, and a higher probability of not exceeding C*. (C) 2017 Elsevier B.V. All rights reserved.

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