Study On Three-dimensional Visual Modeling In Heavy Metal Contaminated Sites

To confirm the distribution character of target pollutants and pollution boundary in contaminated site and calculate the amount of earthwork exceeding the standard are the key problems for governance of contaminated site and remediation of polluted soil. The soil type is divided into three layers, with obvious heterogeneity. The traditional method analyzes contaminated site by generalizing three-dimensional into two-dimensional, which ignores the distribution characteristics of the vertical direction and increases the calculation error of amount of polluted earthwork. Three-dimensional simulation can make full use of sample data of different depth in the site, reduce the forecasting error, and predict more accurate distribution of pollutants in the three-dimensional space.In the paper,77sample points were set, and each point’s lithological data was recorded, while samples of different depth were collected and209detection samples were analyzed. The research in this paper analyzed distribution characteristics and the prediction results of Pb in contaminated sites.(1) According to the distribution characteristics of Pb in soil, the theory of regionalized variables is applied this paper. The sample data were lognormally transformed.And the method of variogram fitting is used, distribution characteristics of ground Pb in the horizontal and vertical direction is analyzed.The results of horizontal variation fitting function show:the random variation of Pb in soil accounted for10.90%of the total variability, less than25%, which shows that the distribution of Pb content in soil has stable structure and randomness. The source of variation is mainly took by structural variation, and the distribution of Pb within57m has strong spatial correlation. The results of vertical variation fitting function show the sample variation of different layers is3.1times than of same layer, so the variability of soil types is the dominant factor of vertical variation of Pb.(2) To achieve accurate pollution boundary and prediction of quantity of earthwork exceeding the standard, three-dimensional geological modeling technology is used to construct geological model of the site, based which three-dimensional prediction model is set up, and then the model parameters are optimized.Determination of key parameters of the geological model:according to the minimum distance between sample points, the grid number is set as40×40; to compare the visual effect of different interpolation methods, the nearest neighbor method is most suitable for describing the landform of the site. Determination of key parameters prediction model: cross-validation analysis is used to select the optimum interpolation method and the interpolation parameters, the results showed that the Kriging interpolation method has the highest precision.By the optimal model, it is determined that the boundary of the area exceeding the standard of each layer which value at risk is over331mg/kg, and the amount of polluted earthwork. The amount of polluted earthwork is263300m3, among which the construction waste is mainly exist carrier Pb pollution, the amount of earthwork is142700m3, followed by the miscellaneous fill layer87700m3, the original soil pollution33100m3..