Meng Fansong, Wang Jinguo, Zhao Yongsheng
School of Earth Science and Engineering, Hohai University, Nanjing 210098, China.
School of Earth Science and Engineering, Hohai University, Nanjing 210098, China.
J Hazard Mater. 2024 Oct 5;478:135618. doi: 10.1016/j.jhazmat.2024.135618. Epub 2024 Aug 22.
Effective characterization of dense non-aqueous phase liquid (DNAPL) source zones is crucial for remediating polluted sites. DNAPL often reside as residuals or pools within high-permeability lenses and above impermeable layers due to soil heterogeneity, gravity, and capillary barriers. Given the high cost of drilling, electrical resistivity tomography (ERT) techniques-including surface ERT and cross-borehole ERT, are commonly used for DNAPL source zone mapping and monitoring. However, the low spatial resolution of ERT increases uncertainty in source zone investigations. This study proposes a method for improving DNAPL mapping and monitoring by fusing surface and cross-borehole ERT data. Sandbox experiments were conducted to simulate a heterogeneous DNAPL source zone, employing both ERT methods for static mapping and dynamic monitoring. Reflective light imaging (RLM) was used to visualize DNAPL migration and provide saturation data, allowing for the quantification of ERT's effectiveness in characterizing DNAPL distribution. The results indicate that individual ERT methods face significant challenges in DNAPL source zone mapping due to background interference. Surface ERT alone tends to underestimate the extent of deeper DNAPL source zones. However, fusing surface and cross-borehole ERT results in a complementary enhancement of vertical spatial resolution, thereby improving the characterization of DNAPL source zones. The fusion of static and time-lapse ERT data substantially enhances DNAPL source zone mapping and monitoring capabilities. By calculating the ratio of the ERT-monitored area to the actual area using resistivity change contours (5 %, 10 %, 15 %), it was found that fusing surface and cross-borehole ERT data improved monitoring resolution by 50.48 % compared to surface ERT alone and by 22.95 % compared to cross-borehole ERT. Principal component analysis (PCA) was effective in fusing time-lapse data, while the weighted average method (WAM) outperformed PCA for static resistivity data fusion.
有效表征致密非水相液体（DNAPL）源区对于污染场地的修复至关重要。由于土壤非均质性、重力和毛细屏障作用，DNAPL通常以残余物或聚集体形式存在于高渗透性透镜体内部以及不透水层之上。鉴于钻探成本高昂，电阻层析成像（ERT）技术——包括表面ERT和跨孔ERT，常用于DNAPL源区测绘与监测。然而，ERT的低空间分辨率增加了源区调查的不确定性。本研究提出一种通过融合表面和跨孔ERT数据来改进DNAPL测绘与监测的方法。开展了砂箱实验以模拟非均质DNAPL源区，同时使用两种ERT方法进行静态测绘和动态监测。利用反射光成像（RLM）可视化DNAPL迁移并提供饱和度数据，从而能够量化ERT在表征DNAPL分布方面的有效性。结果表明，由于背景干扰，单一的ERT方法在DNAPL源区测绘中面临重大挑战。仅表面ERT往往会低估较深DNAPL源区的范围。然而，融合表面和跨孔ERT可实现垂直空间分辨率的互补增强，从而改进DNAPL源区的表征。静态和时移ERT数据的融合显著增强了DNAPL源区的测绘和监测能力。通过使用电阻率变化等值线（5%、10%、15%）计算ERT监测面积与实际面积的比值，发现融合表面和跨孔ERT数据相比单独使用表面ERT监测分辨率提高了50.48%，相比单独使用跨孔ERT提高了22.95%。主成分分析（PCA）在融合时移数据方面效果良好，而加权平均法（WAM）在静态电阻率数据融合方面优于PCA。
