利用时域反射仪测定饱和砂土中非水相液体

Determining Non-Aqueous Phase Liquids in Saturated Sandy Soil Using Time Domain Reflectometry

利用时域反射技术,以饱和砂土和菜籽油、机油为研究对象,室内模拟研究了非水相液体(NAPLs,nonaqueous phase liquids)污染土壤的介电常数和电导率的变化规律,确定了饱和砂土中NAPLs含量的预测模型。研究表明:1饱和砂土中体积含油量在0~0.05 cm^3/cm^3时,土壤介电常数并无显著变化;随着NAPLs体积含量的进一步增加,介电常数呈线性减小趋势;土壤体积质量和NAPLs类型对相同饱和度的土壤介电常数未产生影响。2饱和土壤的电导率与NAPLs含量存在良好的线性负相关关系(R2=0.96);土壤体积质量对相同饱和度的土壤电导率未产生影响。3混合介电模型(a=0.5)高估了饱和砂土中NAPLs含量,平均RMSE为0.038 cm^3/cm^3;参数a调整为0.52后,混合介电模型提高了预测精度,比原混合介电模型(a=0.5)预测精度可以提高23.2%。本研究结果表明可利用时域反射技术监测污染土壤的介电常数与电导率并测定饱和土壤中NAPLs的含量。

The polluted sandy soils by rapeseed oil and motor oil were prepared artificially and then the correlation of the contents of the non-aqueous phase liquids （NAPLs） with soil dielectric properties and electrical conductivity was investigated with time domain reflectometry （TDR）. The dielectric mixing model was used to predict NAPLs content and then calibrated by fitting a parameter of α. The results showed that soil dielectric constant did not change with oil content （v/v） below 0.05 cm^3/cm^3 in the saturated sandy soil. However, soil dielectric constant decreased with the increasing NAPLs content linearly above the oil content of 0.05 cm^3/cm^3. Soil bulk density and the types of NAPLs did not affect soil dielectric constant for the same saturation of the soil. There was a linear negative correlation between the NAPLs content and soil electrical conductivity with R2=0.96. Soil bulk density did not affect electrical conductivity for the same saturation of the soil. The dielectric mixed model with α=0.5 overestimated the NAPLs content in the saturated sandy soil, with the average root mean square error of 0.038 cm^3/cm^3. After adjusting the parameter？ α ？to 0.52, the predicting accuracy of the dielectric mixed model was increased by 23.2%. Therefore, TDR can be applied to determine the contents of NAPLs in contaminated soils.