Stochastic simulation of groundwater pollution considering uncertainty of parameters and boundary conditions
XU Ya-ning1,2, LU Wen-xi1,2, WANG Zi-bo1,2, JIA Shun-qing1,2, WANG Han1,2, PAN Zi-dong1,2
1. Key Laboratory of Groundwater Resources and Environmental, Ministry of Education, Jilin University, Changchun 130012, China; 2. College of New Energy and Environment, Jilin University, Changchun 130012, China
Abstract:In order to investigate the influences of random changes in model parameters and boundary conditions on the output uncertainty of groundwater solute transport model, combined application of Monte Carlo simulation and risk assessment were applied to illustrate the uncertainty analysis results of a hypothetical example. Firstly, a numerical simulation model of groundwater solute transport was established, then the parameters with greater impacts on the model output screened by local and global sensitivity analysis, together with the boundary conditions of the model (the first type of boundary conditions—head value) were set as random variables.Then the Gaussian Process Regression (GPR) method of optimizing hyperparameters was employed to establish an alternative model of the simulation model to complete the Monte Carlo stochastic simulation. Finally, statistical analysis and interval estimate of the results of random simulation were carried out, and the probability distribution function of pollutant concentration was used to estimate the risk of different degrees of pollution of observation wells 1, 2, and 3. The results show that when the confidence level was greater than 80%, the confidence intervals of the pollutant concentration values in observation wells 1, 2, and 3 were 34.77~35.03, 57.74~58.04, and 100.07~100.69mg/L, respectively. In addition, in observation wells 1, 2, and 3, the risk of slight pollution was 6%, 100% and 100%, respectively; the risk of moderate pollution was 0%, 0% and 99.6%, respectively; the risk of heavy pollution was 0%, 0%, and 0.5%, respectively. The present study can provide a reliable reference for pollution remediation and rational utilization of groundwater.
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