Formatted Title
Facing Subsidence Challenges during Thermal Remediation at an Active Industrial Site
Background/Objectives
An active industrial site was constructed over an area with a high organic matter clay. The source zone, containing PCE, was delineated using conventional and MIP investigation methods. After the investigation was concluded, a viability study was conducted to define which remediation technology should be used on the site. Due to the site geology and the client requirements to clean up the site as fast as possible, thermal remediation was determined to be the most viable remediation technique for the site
Approach/Activities
The treatment area consisted of 900 m2 in which 53 electrodes were installed to cover the treatment area. The estimated treatment time required was between 90-120 days of operations. When the thermal system started the heating rate was very good, suggesting that the heating model was correct. One month after the system started, a small area of the site began showing signs of subsidence. After a few days of continued heating the subsidence became more expressive and operations had to be stopped until a structural survey could be conducted to guarantee operational safety for all workers at the site. During the structural investigation it was discovered that there was an unknown excavation in parts of the site that were not properly recompacted. The structural support of the building was determined to be structurally safe, however reinforcements were installed on the walls and measuring equipment was used to monitor for any additional movement. After 45 days it was decided that the thermal system could be restarted. The thermal system ran for aproximatly another 60 days when it reached the remediation goals.
Results/Lessons Learned
Besides all of the structural challenges that were faced on this project, the remediation goals were achieved in all groundwater and soil samples. The remediation finished using less energy than estimated even with the downtime associated with the structural work. A lot of work had to be done after the remediation to rebuild the site floor and some walls. The savings during installation and operations helped to keep this project inside the initial budget.