Formatted Title
Remediation of CVOCs under Six Occupied Residential Buildings by ERH
Background/Objectives
Due to the concentrations of CVOCs in groundwater, the installation and operation of a thermal remediation system were carried out beneath six residential buildings, each one with 36 floors. The objective is to present the challenges encountered during the implementation and operation of the system along with the results obtained from the operation of the remediation system.
Approach/Activities
The area under evaluation had a long history of environmental management efforts, which began in 2007. Over the years, various remediation techniques were employed to address the presence of CVOC contamination. These techniques included the injection of substances like sodium permanganate, ozone, and enhanced reductive dechlorination (EHC). Additionally, since 2011, a vapor extraction system had been in operation, and it was expanded in 2017 to mitigate potential risks to affected parties.
Based on the past results and recognizing the limitations of the remediation techniques used thus far, further studies were conducted. These studies encompassed toxicological risk assessments for human health, environmental investigations, and intervention plans. Their goal was to gain a better understanding of the contamination within the aquifer and to provide more detailed information about the hydrogeological characteristics of the area.
The most recent evaluation led to the implementation of a thermal remediation. This approach was chosen because the thermal process offers more uniform heating in both vertical and horizontal direction when compared to fluid injection processes for decontamination, treating the entire soil volume evenly.
Installation and operation proved challenging due to the site's location in a residential condominium garage. For the installation of 130 electrodes, which were co-located with vapor recovery wells, two drilling methods were employed. The choice depended on factors like the depth of the point, the garage ceiling height, ease of access, and the presence of aerial installations above the site. Some wells were installed using a 10-inch manual auger in 11.00 m deep boreholes, while others were drilled with a small hydraulic hollow stem drill auger, equipped with a 10-inch hollow auger for 18.00 m boreholes.
The installation of remediation lines involved digging trenches in the floor, connecting groups of electrodes to main lines. These main lines were placed in tray-type hollow cable trays, leading to the primary system. Careful planning ensured that these lines did not interfere with residents.
Several measures were taken to prevent vapor intrusion into the environment and the escape of vapors into underground utilities on-site. A structural report of the area was prepared to identify the connections of columns and walls, ensuring they were sealed during system implementation. Once heating stages commenced, daily monitoring of volatile organic compounds (VOCs) took place in the mapped underground utilities and Vacuum measurements were taken to confirm depressurization throughout the heating area.
Monthly ambient air sampling was conducted throughout the remediation area to confirm that there were no vapor inhalation risks in the garage area.
Results/Lessons Learned
In terms of remediation efficiency and effectiveness, this was evaluated through the collection of samples from groundwater, soil vapors, and in situ monitoring of volatiles. In groundwater, there was an initial increase in the concentration of specific contaminant quantities (SQIs), which is expected due to the warming process, increasing the solubility of compounds in the water. However, after the peak of contaminant mass removal, concentrations started to decrease, and after the operation of the two phases, no concentrations above the established remediation targets were found.
Soil vapor monitoring campaigns were conducted to track remediation progress. Data from the post-heating campaign indicated that no point had concentrations exceeding intervention values. Overall, the results from these various analyses illustrate the effectiveness of the remediation techniques used in removing contaminants from the aquifer. Presently, no point exhibits concentrations that suggest ongoing risks.