Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02h. Optimizing Remedial Systems

Formatted Title:

Sustainable Application of Combined Remediation Technologies: Integration of DPE and DGR for Chlorinated Contaminants in a Short-Term Project

Background/Objectives:

The client is a household appliances manufacturing company, with an industrial unit in São Paulo, Brazil. In operation since 1969, the site has a history of contamination by organochlorines, with emphasis on chloroform, carbon tetrachloride, 1,1,2-trichloroethane and 1,2-dichloroethane. The contamination extends approximately 18 meters vertically, covering an area of 6,786 m². This contamination also presents health risks to the local receptors associated with vapor intrusion. The site had been managed by another environmental consultancy for 20 years and had already undergone remediation using DPE and ISCO techniques for a period of 8 years, without success in achieving the goals.

Approach/Activities:

To characterize the distribution of contaminants on the site, several field investigations were carried out with high resolution, pilot testing and development of a conceptual model focused on mass flow. Results of hydraulic profiling tool (HPT) indicated that the region with the highest concentrations of the plume in the dissolved phase presented pressure values predominantly below 500 kPa. It was also possible to identify the existence of preferential plume transport paths in the shallow portion of the phreatic aquifer. Furthermore, the areas with concentrations above the SSTLs were situated in the main paths with the greatest aquifer permeability. Based on this knowledge, the selection of the combined DPE and DGR remediation techniques was based on the definition of layers classified as transport and slow transport zones. Another criterion used was the choice of more sustainable techniques compared to thermal technology, initially suggested for this site remediation. Carbon emissions were estimated in the different technology installation scenarios (thermal vs. DPE/DGR), and the DPE/DGR combination resulted in savings of 1,911 tons of CO₂ emissions. Due to the horizontal and vertical extent of contamination on the site, 56 remediation wells were installed to ensure the technical feasibility of the system and the success of the operation in removing contaminants. All wells were sized and installed to extract vapors from the vadose zone of the soil, pump groundwater and reinject treated water, and could act combined or separately.

Results/Lessons Learned:

The system's performance resulted in the hydraulic lowering of the aquifer by up to 5 meters, exposing the layer of interest. The pressure data obtained in the main observation wells indicated a vacuum influence of less than -1 inH₂O, reaching -20 inH₂O, demonstrating the effectiveness of the system with the vacuum distribution in the area. Approximately 172 kg mass of chlorinated contaminants were extracted from the areas of interest. The remediation system operated for 24 months, and the remediation targets established for the site were achieved after 21 months, with the removal of 99% of the mass in the dissolved phase in the aquifer and 90% of the vapors accumulated in the subsurface. It is considered that the remediation was satisfactory as it was possible to shorten the project life cycle by meeting the established goals. The design, installation and operation of remediation with a results-oriented mindset allowed gains in sustainability, such as the reduction in greenhouse gas (GHG) emissions, and recirculation of water extracted from the same aquifer to maximize remediation gains and avoid the generation of liquid effluents into the collection network. Finally, the DPE/DGR remediation cost five times less than the thermal technology estimated costs proposed by the former environmental consultancy.

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Flavio Gutierres