Time-lapse electrical resistivity tomography (ERT) measurements provide indirectobservations of hydrological processes in the Earth's shallow subsurface at high spatial and temporal resolution. ERT has been used in the past decades to detect leaks and monitor the evolution of associated contaminant plumes. Specifically, inverted resistivity images allow visualization of the dynamic changes in the structure of the plume. However, existing methods do not allow the direct estimation of leak parameters (e.g. leak rate, location, etc.) and their uncertainties. We propose an ensemble-based data assimilation framework that evaluates proposed hydrological models against observed time-lapse ERT measurements without directly inverting for the resistivities. Each proposed hydrological model is run through the parallel coupled hydro-geophysical simulation code PFLOTRAN-E4D to obtain simulated ERT measurements. The ensemble of model proposals is then updated using an iterative ensemble smoother. We demonstrate the proposed framework on synthetic and field ERT data from controlled tracer injection experiments. Our results show that the approach allows joint identification of contaminant source location, initial release time, and solute loading from the cross-borehole time-lapse ERT data, alongside with an assessment of uncertainties in these estimates. We demonstrate a reduction in site-wide uncertainty by comparing the prior and posterior plume mass discharges at a selected image plane. This framework is particularly attractive to sites that have previously undergone extensive geological investigation (e.g., nuclear sites). It is well suited to complement ERT imaging and we discuss practical issues in its application to field problems.

延时电阻层析成像（ERT）测量以高空间和时间分辨率提供了对地球浅层地下水文过程的间接观测。ERT在过去的几十年中一直用于检测泄漏并监视相关污染物羽流的演变。具体而言，反向电阻率图像允许可视化羽状结构的动态变化。但是，现有方法不允许直接估计泄漏参数（例如泄漏率，位置等）及其不确定性。我们提出了一个基于整体的数据同化框架，该框架根据观测到的延时ERT测量值对拟议的水文模型进行评估，而无需直接反演电阻率。通过并行耦合的水文地球物理模拟代码PFLOTRAN-E4D运行每个提出的水文模型，以获得模拟的ERT测量值。然后，使用迭代整体平滑器更新模型建议的整体。我们展示了从受控示踪剂注入实验合成和现场ERT数据的拟议框架。我们的结果表明，该方法可以根据跨孔时延ERT数据联合识别污染物源位置，初始释放时间和溶质负荷，并评估这些估计中的不确定性。我们通过比较在选定图像平面上的前后羽流排放，证明了站点范围内不确定性的降低。该框架对于以前已经进行了广泛地质调查的地点（例如核地点）特别有吸引力。它非常适合作为ERT成像的补充，我们讨论了将其应用于现场问题的实际问题。