A Researchon Optimizing Well Spacing Methods Of Groundwater Monitoring Network

Groundwater monitoring network optimization is economically and scientifically reliable techniques of groundwater management. Application of numerical simulation in multi-objective groundwater monitoring network optimization model can maximize the reliability of the monitoring system, to obtain the minimum number of monitoring wells and the location of monitoring wells, and minimize monitoring cost of groundwater monitoring system. In this paper, the groundwater polluted by ammonia in a hoggery site in Beijing was taken as a research object. A MODFLOWand a MT3 DMS model coupling Monte Carlo method based on hydrogeologicalparameters was established for groundwatermonitoring well design under uncertainty. Then the probability density function of the radius of influence was built with the results of Monte Carlo analysis, to establish a multi-objective simulation optimization model of groundwater monitoring network;NSGA-II was used to optimize two objective functions of the optimization model, one was to maximize the monitoring reliability, and the other was to minimize the monitoring wells. Finally, the results of simulation and optimization model wascalibrated. The conliusion of this paper draws following:1?The plume boundary of ammonia obtained by the simulation optimization model is much positively correlated with hydrogeological parameters. The higher the recharge rate and hydraulic conductivity, the more infiltration of ammonia to the groundwater from pond, which makes the expansion of the boundary of ammonia, vice versa.The plume boundary of ammonia is alsoaffected by different environmental standards of ammonia.Actually, plume boundary is one of the decisive factors of the number of monitoring wells.2?Monitoring system established by multi-objective simulation optimization model of groundwater based on numerical simulation can be more truly reflect the complex information of groundwater environment, increase the relationship of simulation optimization model and the actual hydrogeological information.NSGA-II was used to solve the multi-objective simulation optimization model of groundwater.NSGA-II can guarantee the global convergence of multiple objective functions, to prevent local convergence of multiple parameter under uncertainty. Two objective functions of this paper were converged to 10 generations and 20 generations.3?The results of the NSGA-II algorithm show that, to maximize the reliability of the monitoring network, the number of monitoring wells was 3,which locate on the 19 th, 23 th and 39 th position. Best location of monitoring wells were located on the lower reaches of plume of ammonia which are triangular. The maximum reliability of simulation optimization model was 76.8%.The boundary of plume will spread to the border area of agricultural land with the reducing of environmental standard of ammonia. Then 4 monitoring wells should be established on 19 th, 20 th, 23 th and 39 th position.