Formatted Title
Large-Scale, In Situ Thermal Remediation inside an Active Industrial Facility in Belgium: Challenges and Lessons Learned
Background/Objectives
As a result of historical industrial activities, chlorinated solvents are present in soil and groundwater beneath an active manufacturing building. A pump and treat system was installed and operated for nearly two decades, but contaminant recovery had declined and the presence of significant mass was confirmed in the subsurface. Therefore, ERM refined the remediation approach and deployed in situ thermal treatment (ISTT) using site supplied steam as the heating source.
Approach/Activities
Numerous challenges were encountered throughout the remediation programme related primarily to the entire treatment zone being inside a factory building with >100 workers and overlapping with site production activities, including:
- Health and Safety: The site continued manufacturing while remedial activities took place and the significant overlap between remediation infrastructure and work zones meant continuous monitoring for vapor intrusion and steam specific hazards. A robust programme of building stability monitoring was also implemented.
- Logistical: The factory layout limited access for drilling rigs and pipework had to be routed away from work zones, often at height. There was insufficient space for process equipment to be installed adjacent to the well field, and instead this had to be placed greater than 100 m away and conveyance pipework was installed in confined space tunnels. Additionally, the project staff in the field and office spanned multiple countries, with equipment shipping and delivery delays adding further complexity.
- Technical: The well array of both steam delivery and multi-phase extraction points could not be installed on a uniform grid, as placement was limited by drilling rig access. The need to pump groundwater during steam injection was also inhibited by ingress of silt and drawdown restrictions put in place to reduce potential stability issues. During the design process, regulators also required PFAS monitoring and treatment.
- Stakeholder Management: The presence of multiple vendors, installation schedules avoiding disruption of factory operations, consideration of surrounding residential properties, and daily client interactions all had to be carefully managed during the remediation works.
Results/Lessons Learned
To address the restricted well placement, additional shallow vapor wells were installed with smaller drilling equipment. These wells added an important contingency to the design as the radius of capture overlapped critical zones including factory worker offices, laboratories and other manufacturing areas. The extraction system was continually optimized to confirm hydraulic control and to maintain flow rates that would limit silt removal/process system blockages and reduce stability risks. Steam injection rates were modelled and optimized based on temperature response to enable the entire treatment zone to reach target temperature.
A typical ISTT well array would be isolated from the public to limit incidental thermal and chemical exposures. Due to the active nature of this project, this was not possible and several wells were located directly in high traffic areas; these wells were protected by metal structures to reduce impact or heat risks, and pipework was similarly isolated. An intensive manual and automatic monitoring programme was implemented via an innovative continuous real time vapor monitoring system and a stability monitoring plan. Emergency response protocols were developed in the event that issues such as vapor release occurred at night time or during weekends. Close and regular co-ordination and co-operation between all stakeholders was identified as a critical component for facilitating success on this project.
Despite the numerous challenges of this unique project, the system is currently working safely and has recovered significant contaminant mass to date. The lessons learnt during these works demonstrate that, if carefully designed and managed, ISTT can be effectively deployed in environments that historically would not have been considered as possible.