利用时域反射仪测定饱和砂土中非水相液体

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。

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

A study in laboratory was conducted applying by time domain reflectomatry to investigate the relationships between the non-aqueous phase liquids (NAPLs) content and soil dielectric properties, electrical conductivity. And the NAPLs content estimated by dielectric mixing model (CDM) and the measured were compared and then calibrated the CDM model by fitting a parameter a. In the experiments, the colza oil and motor oil were added respectively into the saturated sandy soil with water. The results showed that there was no significant difference for soil dielectric constant in the range of the volume oil content between from 0 to 0.05 m₃ m_-3 in the saturated sandy soil. And after, soil dielectric constant decreased with the NAPL content increased with a linear relationship. Soil bulk density and the NAPLs types did not influence soil dielectric constant for the same saturation. There was a linear negative correlation between the NAPLs content and soil electrical conductivity with R₂ = 0.96. Soil bulk density did not influence electrical conductivity for the same saturation. The dielectric mixed model (a=0.5) overestimated the NAPLs content in the saturated sandy soil, with the average root mean square error of 0.038 cm₃ cm_-3. After adjusting the parameter a to 0.52, the dielectric mixed model could improve the accuracy by 23.2%. This study results showed that time domain reflectometry can be applied to monitor the NAPLs contamination in soil.