Abstract: Groundwater can be contaminated by mining activities, landfill operations and chemical production processes. Both the tracing of pollution sources and the monitoring of pollutant transport trends demand the establishment of appropriate monitoring networks. The long-term operation of poorly designed groundwater pollution monitoring networks is inevitably accompanied by high monitoring costs. Thus, it is indispensable to undertake research on the optimal design of groundwater pollution monitoring networks, with the aim of acquiring data regarding changes in pollutant concentrations with utmost precision and at minimal monitoring costs. The primary optimizations of the groundwater pollution monitoring network encompass the optimization of the spatial monitoring positions of the monitoring wells and that of the monitoring frequency over time. At present, a variety of qualitative (such as hydrogeological analysis method) and quantitative (such as simulation-optimisation model method and kriging method) optimisation approaches have been put forward to address the optimal design issue of the groundwater pollution monitoring network, and numerous outcomes have been attained. Nevertheless, each method possesses its specific applicable scenarios, along with its respective advantages and disadvantages. The paper initially compiles the research findings on the optimal design of groundwater pollution monitoring networks over the past four decades. Subsequently, seven methods for the optimal design of groundwater pollution monitoring networks, which are currently employed in numerous domestic and international applications, are presented, evaluated, and contrasted. Finally, the paper concludes with a perspective on the primary research directions for the optimal design of groundwater pollution monitoring networks in the future. 

Key words: groundwater pollution, monitoring network, optimal design, monitoring location, monitoring frequency, pollution
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