填埋场底土污染物浓度实测值和理论解的比较

为了研究现场条件下污染物在粘性土中的运移机理,对运行13年的苏州七子山填埋场进行了钻孔取样.通过对土样进行分层切片、加去离子水混合并结合室内小型离心机分离,得到了填埋场底土中Cl-,Na+及COD的孔隙水浓度.将室内试验测试值和一维扩散理论进行了比较,结果表明,实测浓度剖面与扩散曲线差别较大,可见水力梯度引起的对流和机械弥散作用比分子扩散作用来得重要.将实测值与一维对流弥散解析解的计算值亦进行了比较,结果表明试验数据较为发散,但可以采用一维对流弥散理论进行大致的拟合,从而可得到运移参数的取值范围.进一步的理论预测表明,当填埋场运行30年之后,Cl-的影响深度可达到10 m以上.为了防止和延缓渗滤液污染物的进一步运移,填埋场应采取有效措施阻止渗滤液的扩散.

Comparisons of measurements of contaminant concentration in landfill bottom soils with theoretical solutions

A field investigation at a 13 - year - old landfill site was carried out to study the mechanism of contaminant transport through landfill bottom soils. To assess the extent of vertical contaminant migration, continuous samples of the shallow till were obtained beneath the buried wastes and at selected locations not affected by the generated contaminants in the landfill. These samples were sectioned, and extruded pore waters were analyzed for chloride, sodium and chemical oxygen demand (COD). The field concentration profiles for chloride, sodium and COD were compared with the simulated profiles generated using a one - dimensional porous media diffusion model. The results from this comparison shows that there are large differences between the calculated curves and the filed data, indicating that advection and mechanical dispersion are clearly more important than molecular diffusion, and thus for shallow depths the soils cannot be considered as diffusion barriers. Despite the scatter of the data, the upper 4 m of the bottom soils can be approximately represented using a one - dimensional advection - dispersion approach. In calibrating the one - dimensional porous media transport model to the observed chloride profile, values for the Darcy velocity (1E-10-5E-9 m/s) , the effective diffusion coefficients and dispersive parameters for these regionally important clay deposits were obtained. The maximum migration depth of chloride was predicted to be about 10 m after 30 years of landfill operation on the basis of the obtained transport parameters. Finally, effective methods were suggested to control the successive migration of the contaminant.