Research On Spatial Layout Optimization Method Of Soil Remediation Monitoring Points In Contaminated Sites

With the rapid development of cities and the acceleration of the adjustment of industrial structure,the relocation and suspension of industries and enterprises have left behind a large number of complex polluted sites,which pose a serious threat to the safety of urban human settlement environment and hinder the development of urban society and economy.In this context,soil remediation monitoring of contaminated sites is particularly important.However,at present,the layout process of soil remediation monitoring points in contaminated sites generally cannot take into account the representatieness of the feature space or the uniformity of the geographical space of the monitoring points.Therefore,this study took Shougang site in Beijing as an example and proposed an optimization method for the spatial layout of soil remediation monitoring points in contaminated sites:Combined with the key pollution risk sources,functional zones and media types,the site pollution risk factors were established.Based on this,the spatial stratification method of the contaminated site was constructed,and the geographical layout optimization method of the monitoring points was proposed.The other monitoring point layout optimization methods and the proposed monitoring point layout optimization method（layered uniformity method）are compared and analyzed.The main conclusions are as follows:（1）The simulated values of atmospheric deposition pollution risk are correlated with Hg,PAHs2₃,PAHs4₆ and PAHs16,but not with other pollutants;The simulation values of potential runoff pollution risk only have significant difference on whether the soil samples at the depth of 3.5-5 m exceed the standard or not,and have no significant difference on whether the soil samples at the depth of 0～1m and 1～3.5m exceed the standard or not.The land use function of the site can be divided into 23 functional types,and the medium types can be divided into two types:permeable surface and impervious surface.（2）The pollution risk factors were graded and spatially superimposed,and the spatial stratification rules were established.A total of 23 basic units of spatial stratification were obtained.Further establish the spatial stratification rules of sampling layer depth and laboratory layer depth to realize the spatial stratification of soil sampling layer depth and laboratory layer depth.Among them,the depth of soil sampling layer includes three categories:0～1m,0～3.5m and 0～5m,and the depth of soil testing layer includes six categories:0～1m,1～3.5m and 3.5～5m and their combinations.（3）Based on the spatial stratification results of basic units and the classification of monitoring points,feature space optimization was realized,and the sample size was divided into the minimum sample size and the recommended sample size.The optimization objective function and the spatial simulated annealing algorithm were constructed based on the minimization criterion of average minimum distance to optimize the geospatial layout.（4）Comparison experiments of different spatial layout optimization methods were set up,and overall representativeness index and deviation index were put forward to evaluate the optimization effect of monitoring points in feature space and geographical space respectively.The overall representativeness and deviation index of the spatial layout optimization method based on the minimum sample size are 1 and 0.6237,respectively.The overall representativeness and deviation index of the spatial layout optimization method based on the recommended sample size are 1 and 0.4451,respectively,which are better than the simple random method,the spatial uniform method and the hierarchical random method.