Here I is the distance along the path of the groundwater stream. In the practical condition, Dt is very large, so the second item of the formuia could be ignored This formula can be used to calculate the density curves of the section plane C 1 erfc( t Determine the pollutants arrival time At any position in the polluted area, use the solution of the e- quation(1), we can get the density-time curve. It is a erfc func- (C/C)0.5 Lime t Figure 2 density-time curve We may think the pollutants come to this position at t.We can determine the t, by the solution At ts time, C/C0=0.5 Because erfc(0)=1, so we can get 0 u could be calculated by the Darcy Principle, it shows that dh (8) where k is the hydraulic conductivity In this small area, we think the streamline should be approxi- 235 PDF文件使用" pdffactory"试用版本创建w, fineprint,com,cnPDF 文件使用 "pdfFactory" 试用版本创建 www.fineprint.com.cn