Direct current (DC) resistivity has been widely investigated for non-invasive mapping of dense non-aqueous phase liquids (DNAPLs); however, due to its difficulty in distinguishing DNAPLs from adjacent soils, the DC method is limited for static detection of DNAPLs and more often employed for monitoring DNAPL changes over time. Time-domain induced polarization (IP) can provide complementary information to better discriminate between DNAPL, water and surrounding soils. Since highly resistive DNAPLs tend to laterally spread and pool on polarizable (chargeable) clay lenses, combined DC and IP (DCIP) has the potential to enhance static detection, and also monitoring of DNAPL source zones (SZs). The objective of this study is to assess DCIP for characterizing and monitoring DNAPL SZs at the field-scale. A new DNAPL-DCIP numerical model was first developed that couples a 3D multiphase flow model, which simulates DNAPL release and remediation scenarios, with a 3D DCIP model, which calculates the corresponding resistivity and chargeability response. The sensitivity of the DCIP response to key DNAPL and soil properties was then analyzed at a single subsurface location, closely matching previous theoretical and experimental observations. Finally, a field-scale simulation of DNAPL release and remediation was conducted, with simultaneous mapping by DCIP surveys. Results demonstrate that chargeability can provide enhanced understanding of the lithological distribution that controls the variability in the DNAPL SZ, with time-lapse resistivity being used to monitor DNAPL mass changes during SZ remediation. This numerical study suggests that combined DCIP can be valuable for site characterization and time-lapse monitoring performance at DNAPL-impacted sites.

中文翻译：

---

结合直流电阻率和感应极化的 DNAPL 源区的测绘和监测：场尺度数值研究

直流 (DC) 电阻率已被广泛研究用于密集非水相液体 (DNAPL) 的非侵入式绘图；然而，由于难以区分 DNAPLs 和相邻土壤，DC 方法仅限于静态检测 DNAPLs，更常用于监测 DNAPL 随时间的变化。时域诱导极化 (IP) 可以提供补充信息，以更好地区分 DNAPL、水和周围土壤。由于高电阻 DNAPL 倾向于横向扩散并聚集在可极化（可充电）粘土透镜上，因此组合 DC 和 IP (DCIP) 具有增强静态检测以及 DNAPL 源区 (SZ) 监测的潜力。本研究的目的是评估 DCIP 以表征和监测现场规模的 DNAPL SZ。首次开发了一种新的 DNAPL-DCIP 数值模型，该模型将模拟 DNAPL 释放和修复场景的 3D 多相流模型与计算相应电阻率和充电率响应的 3D DCIP 模型相结合。然后在单个地下位置分析 DCIP 响应对关键 DNAPL 和土壤特性的敏感性，与之前的理论和实验观察结果密切匹配。最后，进行了 DNAPL 释放和修复的现场规模模拟，同时通过 DCIP 调查进行映射。结果表明，可充电性可以增强对控制 DNAPL SZ 变异性的岩性分布的理解，延时电阻率用于监测 SZ 修复过程中的 DNAPL 质量变化。