During the start of the construction of 200 new flats on a former dry cleaner facility in central Stockholm, a large contamination of chlorinated solvents 6-10 m bgl was identified. The building process was threatened to be stopped causing significant delay and extra costs. An immediate solution to remove risk of intrusion of vapors into the coming buildings, and to stop contaminant migration from the site, was needed. This was the challenge HSB Bostad AB presented to Ejlskov.

The solution

Trap & Treat® CAT 100™ was installed on site to provide efficient source treatment and immediate risk removal, preventing potential residual off-site migration towards the neighboring property. Full scale remediation work was performed while construction activities were maintained operational across the site. Furthermore, the task was completed at a price close to 50% of the cost for traditional clean up solutions as e.g. excavation.

Services provided by Ejlskov

Full-scale application of Trap & Treat® CAT 100™ in-situ remediation, including:

• Review of existing soil- and groundwater data to estimate contaminant mass distribution and extent
• Unique remedial design targeting the varying contaminant levels inside the impacted area
• Fast and dynamic installation allowing the building process to continue unaffected
  
  

Remediation process and results

Injection works were carried out while several other contractors were simultaneously on site. The implementation of the injection works was carried out according to plan, and client expectations were met with regard to minimal disturbance of the ongoing construction work and remedial goal according to the authority requirements (a minimum of an order of magnitude reduction in groundwater concentrations within 3 to 5 months post remediation works).

The remedial strategy was to target the source zone and to create a permeable reactive barrier to treat migrating dissolved contamination. In the source zone (triangular grid layout), a total of 9,050 kg of CAT 100™ were injected across 182 points. In the barrier, 5,900 kg of CAT 100™ were injected into 69 injection points distributed along 70 meters of the down gradient property boundary.

Based on the rapid decrease in concentrations indicated by samples collected during and after injection works, the client received approval from the local environmental authorities to proceed with the construction works (layout of concrete foundations). This allowed the property developer to keep the construction project on schedule.

Groundwater monitoring data gathering 12 months post injection works, show PCE concentrations in both source and barrier zone reduced from levels up to 90,000 μg/l in the source zone and 50,000 μg/l along the site boundary to non-detect levels or one order of magnitude less than pre-injection. Temporary generation of 1,2 DCE and vinyl chloride has been observed as long as mother products had been present. Monitoring data from specific dissolved gases show proof that biological activity is occurring in the treatment zone as part of the enhanced reductive dichlorination process.