Study On The Optimized Sampling Method Of Industrial Soil Heavy Metal Survey

With the rapid economic development and urban expansion after China’s reform and opening up,a large number of industrial relocation sites with varying degrees of soil contamination have been left behind,some of which have not even been properly disposed of,harmed to urban environmental safety and public health seriously.So that soil site surveys have become particularly important as the primary process of soil management.However,the lack of soil contamination information or relevant laws or technical regulations in China often leads to the inappropriate selection of monitoring sites,which makes the inaccuracy of soil contamination simulation or increased costs for actual soil surveys.Therefore,this study established a set of optimized sampling methods based on the probability of contamination for industrial sites,and applied it to the study of actual sites,in order to improve the simulation efficiency and reduce the cost of work and provide assistance for subsequent soil remediation and treatment.The study area is an industrial moved site in Nanjing,the research objects are Cu,Ni,Pb,Cd,As,Hg,75 points were laid out in the initial survey,and 104 additional points were added to form the total sample points.Firstly,the total sample data were transformed and fitted with semi-variance functions,and then kriging was applied to simulate the heavy metal contamination characteristics of the site soil.Based on the results of the contamination characteristics,Cu and As,which are highly representative of the contamination,were selected to optimized sample.After setting the contamination criteria,the initial sample data were simulated with the probability distribution of contamination using the indicated kriging method,and the suspected contamination range is divided according to the set threshold value,and range of suspected high contamination was used as an optimized area.Considering the site production layout,suspected pollution sources and natural information,optimized points were placed in this area.The optimized results were compared with the simulation results of the unoptimized,uniformly optimized and total sample survey,and the accuracy analysis was carried out in terms of the polluted area prediction accuracy and the optimized sampling points number,and the applicability of the method was concluded.And Geo-accumulation Index Method,Single Factor Index Method and Nemerow Composite Index Method were used to conduct soil contamination assessment.The main results were as follows:(1)Different pollution characteristics led to different method’s effect.For Cu with discrete distribution,the accuracy of the pollution area predicted by the optimized method is not significantly improved compared with the no-optimized situation,and is also not as good as the uniform optimized method;while for As with concentrated pollution,the optimized method was better than the uniform optimized method and could bring significant accuracy improvement.(2)The results of varying the optimized points number showed that the improvement of prediction accuracy increased with the increase of site’s number.Therefore,it is necessary to ensure a certain number of sample points in the site survey.(3)The principle of interpolation method,historical production background,pollution sources and pollutant characteristics are one of the reasons for difference in the use of the method.This optimized method is more suitable for sites with high localized point-like pollution under the influence of human.In this situation,the optimized method is better than traditional method.Finally,this research conducted a summary of method based and made relevant recommendations for industrial soil surveys of the future.