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Chemical Production Site in South Wales

  • 27-06-2012

HBR have recently completed the first phase of a remediation project at an active chemical production site at Barry, South Wales. The works comprised an in-situ chemical oxidation (ISCO) approach to remediate soils and groundwater impacted with elevated concentrations of phenol, formaldehyde and BTEX compounds.

 

The remediation strategy was developed by the Client’s Engineer Atkins and HBR were awarded the contract through a competitive tendering process.

 

HBR’s remedial design was confirmed by conducting off-site bench-scale studies to determine oxidant choice and delivery concentrations. On-site pilot tests were also carried out to confirm oxidant volume requirements, by studying variances in hydrogeology, aquifer properties and contaminant distribution.

 

Laboratory studies assessed the natural oxidant demand of the aquifer material and a range of persulphate batch experiments run with and without the presence of activators (Fe and H2O2) on phenol impacted slurries recovered from site. Results showed a combined activator approach to provide the highest oxidative potential in combination with sodium persulphate.

 

remediation project Barry

Oxidant decay highlighted the rapid increase in oxidation potential (measured as persulphate equivalents) as the hydrogen peroxide reacted with sodium persulphate to form increasing numbers of hydroxyl radicals. This was shown to produce an equally rapid, complete, destruction of the principal contaminant, phenol. The rate of equivalent decay then slowed with continued consumption attributed to the oxidation of phenol, as it continued to desorb from the aquifer matrix into solution.

 

On-site trials determined oxidant persistence and showed a radius of influence of up to 30 metres, where fracture flow was the dominant mechanism. Site monitoring of geochemical parameters supported expected oxidation reaction observations. 

  

Successive injections were administered to the perched water using direct push rigs, whilst the deeper groundwater body was treated via a series of wells to a depth of 15mbgl. Phenol concentrations in the plume core were reduced from 10,100mg/l to <1,000mg/l within 10 weeks. The ISCO hardware was fitted with a pressure limiting fail-safe device and allowed the operations team to adjust and monitor the volume and rate of delivery at up to 6 injection points on a continuous basis. This enabled treatment efficiencies to be maximised across the site in response to the varied ground conditions encountered. Treatment of residual areas continued in response to periodic monitoring data.

 

This first phase of active treatment works will now be followed by a 12 month period of validation monitoring across the site by HBR, to demonstrate that contaminant concentrations remain at acceptable levels and that natural attenuation of residual phenol is continuing to occur.

 

Barry oxidation remediation