Formatted Title
High-Resolution Investigation and Application of a Thermal Remediation System Combined with Bioremediation and Multiphase Extraction Techniques
Background/Objectives
Soil gas, soil, and groundwater impacts were identified in an industrial area located in the metropolitan region of São Paulo, Brazil from a leaking underground storage tank (UST). Site investigation and characterization were completed to define the nature and extent and prepare a conceptual site model (CSM) and a human health risk assessment. The updated CSM was used to complete a remediation alternatives study, bench-scale tests, and the application of a treatment train to reduce the mass of trichloroethylene (TCE), dichloroethylene, vinyl choride, and light non-aqueous phase liquids (LNAPL) contaminants retained in the source area. TCE was used for degreasing at the Site until the late 1980s and was replaced with kerosene that was stored in a UST until 2005. The UST conveyed the degreaser via underground piping to the production lines inside an industrial warehouse. LNAPL plumes have been identified both around the underground lines and in the former production warehouse area where a concrete box received effluents containing chlorinated solvents. TCE and daughter products, polycyclic aromatic compounds, and total petroleum hydrocarbons were released impacting the groundwater above the respective criteria.
Approach/Activities
The CSM was updated with the high-resolution site characterization tools: membrane interface probe and optical image profiler. Based on the high-resolution characterization, whole core soil sampling and installation of multilevel monitoring well locations were selected and installed where evidence of impacts were noted. To limit offsite migration of TCE and daughter products, the interim remedy of two permeable reactive barriers (PRBs) in the downgradient portion of the plume were installed perpendicular to groundwater flow. The PRBs were constructed by injecting 7,750 kilograms of an in situ chemical reduction (ISCR) amendment by direct push methodology. The performance monitoring of the PRB was completed quarterly to evaluate volatile organic compounds and ISCR performance parameters (sulfate, nitrate, total organic carbon, volatile fatty acids, and microbial population). In addition to the PRB, a thermal remediation system (electrical resistance gheating [ERH]) was implemented with a combined multiphase extraction (MPE) system to treat the TCE and daughter products in the center of mass and recovery of LNAPL accumulated in this region.
Results/Lessons Learned
The performance monitoring results have shown ISCR has produced favorable conditions for abiotic and biotic reduction of TCE and daughter products after the implementation of the PRBs. Additionally, the thermal remediation system and multiphase extraction systems were installed in the source area have operated for 1.5 months and is scheduled to reach its operating temperature by December 2023. Implementation methods and performance monitoring results from the PRB and thermal system will be presented.