Formatted Title

Striking the Balance: Integrating ISTR and Bioremediation Amidst Underground Utilities, Active Infrastructure, and Delicate Thermal Demands

Background/Objectives

Clay National Guard Center (CNGC) in Marietta, Georgia, was used for aircraft maintenance and storage. Historical contamination was discovered in 2009 and the project is associated with the treatment for impacts to both the soil and groundwater. In the in situ thermal remediation (ISTR) design process, it is important to design the heating treatment system compatible with the site layout and contaminants distribution. Pollutants are simultaneously present under a building, beneath a road, and have migrated across the property line into the neighboring Lockheed Martin area. The source zone area of elevated VOC concentrations in the soil and groundwater is well defined and surrounding the source zone is an area of lower VOC concentrations in the groundwater.  The combined use of thermal remediation and heat enhanced anaerobic bioremediation strategies are designed to meet these challenges. Faced with the intricate challenge, there lies a contradiction where we require heating up to ~100°C for efficient chemical removal, yet, adjacent areas demand a lower temperate to ensure protection of critical structures and utilities.

Approach/Activities

Heating and extraction wells, strategically positioned at varying angles, are installed around the building, along the roadside, and near the property line to address the remediation of contaminants present below the building and roadway and crossing the property line.  The primary objective of this implementation is to guarantee the uninterrupted functionality of the building throughout the operational phase. Simultaneously, it ensures no interference of the traffic in the treatment area, mitigating the need for closures because of system operation. This approach enhances operational efficiency and minimizes disruption to activities with the national guard center.
In addition, the design has implemented a series of measures aimed at minimizing the effects of thermal remediation on subsurface utility infrastructure. The precise location of utilities is ensured using a combination of hand digging and Hydrovac excavation during well drilling to prevent any damage. Furthermore, the layout of heating and extraction wells has been optimized to avoid overheating issues for these vital utilities. Temperature-sensitive fiber optic communication lines and electric lines have been exposed to ambient air through excavation, guaranteeing their resilience to excessive heat. Additionally, a natural gas line has been relocated and water lines were converted from PVC to steel to ensure their uninterrupted operations during the remediation.  These comprehensive measures are implemented to preserve the integrity of utility networks and meet operational requirements throughout the execution of thermal remediation procedures.

As a polishing step, heat-enhanced anaerobic bioremediation and recirculation (HEABR) system is set to be operated during and after the completion of the thermal remediation process across the area of lower impacts in the groundwater. The recirculation system consists of 40 biorecirculation (BR) wells spaced across the treatment area, with 16 wells within the ISTR TTZ and the remaining 24 wells in the surrounding area with lower COC concentrations in the groundwater. The BR wells will play a pivotal role in the extraction and recirculation of heat- and substrate-amended groundwater within the treatment area, with the ultimate objective of achieving groundwater concentrations of less than 5 μg/L for TCE, 70 μg/L for cis-1,2-DCE, and 5 μg/L for carbon

Results/Lessons Learned

This project is currently in the construction and utility protection process. The heating process will be conducted once the system and well installation are finished. The unique challenges posed by the site—ensuring protection to underground utilities, maintaining active infrastructure operations, and managing delicate thermal demands—promise to offer unprecedented insights into future environmental remediation endeavors under similar complex conditions.