This learning lab is intended to educate, generate exposure, and solicit feedback from environmental professionals regarding the use of electrical imaging to characterize and monitor subsurface bioactivity over time (time-lapse imaging), which enables more efficient and effective bioremediation for the site and project stakeholders. Site managers (engineers, geologists, hydrogeologists, others), responsible parties, regulators, and bioremediation professionals will benefit from this Learning Lab which will have hands on examples of equipment used as well as examples of 3D data visualization.
Successful bioremediation starts with characterizing the spatial distribution of bioactivity in the subsurface. Understanding the extent of bioactive zones and their redox state are also important as this determines available options and related costs for bioremediation.
Traditional site characterization methods using monitoring wells offer only a limited view of critical biostructures with an extremely limited sample size relative to the size of the site as a whole. They also introduce oxygen into the subsurface which potentially alter bioactivity related conditions proximal to the well, and which can result in an incomplete or skewed understanding of actual subsurface conditions. Incorrect conceptual site models (CSMs) can impact the effectiveness and cost of bioremediation efforts.
Laboratory and field studies have demonstrated the effectiveness of electrical imaging in mapping subsurface bioactivity. These modern tools provide a detailed view of bioactivity structure and interactions, both laterally and vertically.
This learning lab will explore how environmental professionals can leverage electrical imaging to characterize and monitor bioactivity over time (static and time-lapse imaging), which enables more efficient and effective bioremediation for the site and project stakeholders.
Subsurface microbial ecology studies have historically taken place either in laboratories or discrete wells at scales of less than a meter. In recent years, field collected electrical imaging datasets have successfully visualized microbial biosignatures in the subsurface at much larger scales of one meter to hundreds of meters. Biogeophysical investigations at the laboratory scale and field scale confirm the electrical structures detected are due to bioactivity and assist in understanding community and composition of the biome. Interpretation and understanding of these biostructures is needed to improve the ability to utilize microbial communities for remediation.
Hundreds of NAPL impacted sites have been characterized by collecting electrical datasets ranging from 0.5-meter to 10-meter resolution. These datasets can be collected as both static electrical resistivity imaging (ERI) datasets and temporal datasets (TERI) to assess changes in subsurface bioactivity over time. Targeted drilling and chemical and biochemical samples are subsequently collected to calibrate the electrical imaging data to varying levels of bioactivity and structure in the subsurface. The resulting data sets are then integrated in 2D and 3D to develop robust conceptual site model (CSM) findings which have been used successfully to support monitored natural attenuation remedies at NAPL sites.
This presentation shows subsurface electrical structures (pictures) associated with bioactivity across a wide range of geologic settings and state of weathering at complex environmental sites. The depicted structures generated by bioactivity can be electrically conductive and/or electrically resistive depending on the activity of the setting. A basic model resulting from this body of evidence is that free product NAPL starts as a subsurface resistive zone that gradually develops conductance around it as a bioactive colony grows around the chemically different location. The electrical conductivity of these bioactive zones is higher than how normal geological or fluid signals present. Additionally, well developed bioactive colonies generate biogases during the degradation processes which can result in highly electrically resistive bubbles of trapped gas in the subsurface.
The patterns are dependent on a range of a subsurface parameters and are difficult to predict a priori. Therefore, the use of ultra-high resolution electrical imaging data (biogeophysics) can be key to understanding complex structure of the biome and optimizing resulting bioremediation strategies.
