Formatted Title
Adaptive Site Management via Innovative Monitoring of ISCO Remediation
Background/Objectives
The availability of cloud-connected and modestly priced sensors is transforming our ability to manage contaminated sites and their remediation. Significant research in our industry is focused on using field screening parameters (e.g., temperature, oxidation reduction potential [ORP], pH) in place of or in addition to traditional sampling/monitoring of chemicals of concern. Remote sensors provide insights at a resolution not previously possible, which opens up possibilities for managing contaminated sites in new and exciting ways. This summarizes the use of sensor-based monitoring of in situ ORP to remotely monitor and dynamically manage an in situ chemical oxidation (ISCO) remediation project in southern France.
Approach/Activities
Active remediation of a chlorinated solvent plume at a former industrial site in France involved daily (24/7) operation and continuous monitoring of a recirculatory ISCO system between January 2021 and September 2022. Subsurface infrastructure included paired injection/extraction well rows, traditional monitoring wells, and a high-density network of cloud-connected in situ sensors deployed within and around the target treatment area. Sodium permanganate, a strong oxidant, was delivered through injection wells until theoretical (injection mass and volume) and empirical goals, were met. Injection goals were based on total oxidant demand and pore-volume exchange metrics. Monitoring goals included multiple lines of evidence of sodium permanganate delivery and contaminant concentration reductions in soil and groundwater. Regulatory goals included achieving groundwater chlorinated solvent concentrations below 50 µg/L and soil chlorinated solvent concentrations below 150 µg/kg.
The preferred monitoring method, remote, in situ ORP monitoring, was achieved by installing sensor strings in borings around the treatment area. Each sensor array is a solar powered, cloud-connected with 12 to 14 vertically positioned sensors to measure ORP at discrete depths. Forty-four ORP sensor arrays (over 500 individual sensors) provided real-time hourly measurements of ORP throughout the ISCO treatment area. Sensor data were accessed remotely via application programming interface (API) for incorporation into project dashboards and interpretations. Remote ORP measurements confirmed and often predicted permanganate arrival, as evidenced via more traditional monitoring approaches described above. Additionally, discrete sensor installations captured the heterogeneity in subsurface delivery to enhance operations. This is achieved at a lower cost, requiring less ongoing work, and without the need for continuous on-site intervention. The multiple lines of evidence approach used during early monitoring of the system allowed for regulatory acceptance of the remote sensors as a viable monitoring option.
Results/Lessons Learned
A complementary monitoring approach using ORP sensor arrays from S3NSE Technologies, Inc. was piloted and then fully implemented at the site. The sensors refined the understanding of hydraulic conditions and allowed real-time adaptation and optimization of the injection and re-circulation approach resulting in improved remediation effectiveness and reduced likelihood of rebound. The quantity of sensor-based data (>10 million data points) dwarfed what was possible with conventional monitoring approaches, which reduced conventional groundwater monitoring needs, resulting in significant cost savings for the project.