G360 Institute for Groundwater Research, University of Guelph, Canada.
G360 Institute for Groundwater Research, University of Guelph, Canada.
J Contam Hydrol. 2021 Aug;241:103838. doi: 10.1016/j.jconhyd.2021.103838. Epub 2021 May 27.
This study applies innovative methods to characterize and quantify the magnitude of groundwater flow in a fractured and variably cemented sandstone aquifer to inform an in-situ remediation strategy for trichloroethene (TCE) contamination. A modified active-distributed temperature sensing (A-DTS) approach in which fiber optic cables were permanently grouted in the borehole was used to quantify groundwater flow rates. Two additional tracer tests were conducted: 1) fluorescein tracer injection followed by rock coring and sampling for visual mapping and porewater analysis, and 2) deployment of passive flux meters in conventional monitoring wells to evaluate groundwater velocity and mass flux distributions. Forced gradient injection of fluorescein tracer suggests a dual porosity flow system wherein higher rates of groundwater flow occur within discrete features including highly permeable bedding planes and fractures, with slower flow occurring within the rock matrix. Tracer was observed and detected in the unfractured matrix porewater >1.5 m away from the injection well. Beyond this distance, >6 m radially away from the injection hole, tracer was primarily detected within and adjacent to high transmissivity fractures serving as preferential flow paths. The Darcy flux calculated using active distributed temperature sensing (A-DTS) shows depth-discrete values ranging from 7 to 60 cm/day, with average and median values of 23 and 17 cm/day, respectively. Passive Flux Meters (PFMs) deployed in three conventional monitoring wells with slotted screens and sand filter packs showed groundwater flux values ranging from 2 to 11 cm/day, with an overall average of 4 cm/day and are likely biased low due to spreading in the sand pack. The study results were used to inform an in-situ remediation system design including the proposed injection well spacing and the amendment delivery approach. In addition, the results were used to build confidence in the viability of delivering an oxidant to the rock matrix via advective processes. This is important because 1) the matrix is where the majority of the TCE mass occurs, and 2) it provides insights on processes that directly affect remedial performance expectations given advective delivery to preferential pathways and the matrix overcomes diffusion only conditions.
本研究应用创新方法对裂隙和胶结程度变化的砂岩含水层中的地下水流动进行了特征描述和量化，为三氯乙烯（TCE）污染的原位修复策略提供了信息。采用了一种改良的主动分布式温度传感（A-DTS）方法，即将光纤电缆永久地灌入钻孔中，以量化地下水流动速率。还进行了另外两个示踪剂测试：1）荧光素示踪剂注入后进行岩芯采样和取样，以进行可视化映射和孔隙水分析，2）在常规监测井中部署被动通量计，以评估地下水速度和质量通量分布。荧光素示踪剂的强制梯度注入表明存在双孔隙流系统，其中较高的地下水流动速率发生在离散特征中，包括高渗透性的层面和裂缝，而在岩石基质中则流动较慢。示踪剂在离注入井 1.5 米以上的未破裂基质孔隙水中被观察到并检测到。在这个距离之外，离注入孔 6 米远的地方，示踪剂主要在高透水性裂缝中被检测到，这些裂缝是优先流动路径。使用主动分布式温度传感（A-DTS）计算的达西通量显示出从 7 到 60cm/天的深度离散值，平均值和中位数分别为 23cm/天和 17cm/天。在三个带有开槽筛网和砂滤包的常规监测井中部署的被动通量计（PFMs）显示地下水通量值在 2 到 11cm/天之间，平均通量为 4cm/天，由于在砂包中扩散，通量值可能偏低。研究结果用于为原位修复系统设计提供信息，包括建议的注入井间距和注入方式。此外，研究结果还增强了对通过对流过程将氧化剂输送到岩石基质的可行性的信心。这很重要，因为 1）基质是 TCE 质量的主要存在位置，2）它提供了有关直接影响修复性能预期的过程的信息，因为对流输送到优先路径和基质克服了仅扩散条件。
