Johnson Timothy C, Versteeg Roelof J, Day-Lewis Frederick D, Major William, Lane John W
Subsurface Insights, LLC, Hanover, NH 03755.
U.S. Geological Survey Office of Groundwater, Branch of Geophysics, 11 Sherman Place, Unit 5015, Storrs, CT 06269.
Ground Water. 2015 Nov-Dec;53(6):920-32. doi: 10.1111/gwat.12291. Epub 2014 Dec 2.
Biostimulation is increasingly used to accelerate microbial remediation of recalcitrant groundwater contaminants. Effective application of biostimulation requires successful emplacement of amendment in the contaminant target zone. Verification of remediation performance requires postemplacement assessment and contaminant monitoring. Sampling-based approaches are expensive and provide low-density spatial and temporal information. Time-lapse electrical resistivity tomography (ERT) is an effective geophysical method for determining temporal changes in subsurface electrical conductivity. Because remedial amendments and biostimulation-related biogeochemical processes often change subsurface electrical conductivity, ERT can complement and enhance sampling-based approaches for assessing emplacement and monitoring biostimulation-based remediation. Field studies demonstrating the ability of time-lapse ERT to monitor amendment emplacement and behavior were performed during a biostimulation remediation effort conducted at the Department of Defense Reutilization and Marketing Office (DRMO) Yard, in Brandywine, Maryland, United States. Geochemical fluid sampling was used to calibrate a petrophysical relation in order to predict groundwater indicators of amendment distribution. The petrophysical relations were field validated by comparing predictions to sequestered fluid sample results, thus demonstrating the potential of electrical geophysics for quantitative assessment of amendment-related geochemical properties. Crosshole radar zero-offset profile and borehole geophysical logging were also performed to augment the data set and validate interpretation. In addition to delineating amendment transport in the first 10 months after emplacement, the time-lapse ERT results show later changes in bulk electrical properties interpreted as mineral precipitation. Results support the use of more cost-effective surface-based ERT in conjunction with limited field sampling to improve spatial and temporal monitoring of amendment emplacement and remediation performance.
生物刺激越来越多地用于加速对顽固性地下水污染物的微生物修复。生物刺激的有效应用需要在污染物目标区域成功布设改良剂。修复性能的验证需要在布设后进行评估和污染物监测。基于采样的方法成本高昂，且提供的时空信息密度较低。时间推移式电阻层析成像（ERT）是一种用于确定地下电导率随时间变化的有效地球物理方法。由于修复改良剂和与生物刺激相关的生物地球化学过程通常会改变地下电导率，ERT可以补充并增强基于采样的方法，用于评估改良剂的布设情况和监测基于生物刺激的修复过程。在美国马里兰州布兰迪万的国防部再利用与营销办公室（DRMO）场地进行的一次生物刺激修复工作中，开展了现场研究，以证明时间推移式ERT监测改良剂布设和行为的能力。利用地球化学流体采样来校准岩石物理关系，以便预测改良剂分布的地下水指标。通过将预测结果与封存流体样本结果进行比较，对岩石物理关系进行了现场验证，从而证明了电地球物理学在定量评估与改良剂相关的地球化学性质方面的潜力。还进行了跨孔雷达零偏移距剖面测量和钻孔地球物理测井，以扩充数据集并验证解释结果。除了描绘改良剂在布设后头10个月内的运移情况外，时间推移式ERT结果还显示了后期整体电学性质的变化，解释为矿物沉淀。结果支持结合有限的现场采样使用成本效益更高的地面ERT，以改善对改良剂布设和修复性能的时空监测。
