Treatment technologies in the mix

Contaminated land clean-up specialist, Celtic, explores the development of in-situ remediation technologies, and the importance of an integrated approach.

The recent introduction of the Landfill Directive and the increasing requirements for the provision of sustainable redevelopment solutions has significantly increased the use of innovative on-site technologies. This has driven the development of in-situ techniques, of which Celtic has vast experience, having pioneered the first UK air sparging project in the late 1980s.

As a result of the new demands for on-site, in-situ treatment, recent Celtic schemes have typically included; high vacuum extraction, air sparging, soil vapour extraction, oxygen release compounds, bacteria injection and oxygen infusion techniques.

The choice of on-site treatment technologies can only be considered within an integrated approach to meet the demands of site-specific circumstances, rather than the demands of a particular technique. The commercial benefit afforded by this approach to site remediation is the flexibility to integrate traditional engineering solutions with multi-technology schemes for on-site treatment.

High vacuum extraction

Examples of recent on-site treatments include a High Vacuum Extraction (HVE) system at a former landfill site.

Combined with riverbank stabilisation works, a HVE system was used to minimise the long term environmental risks of a former industrial landfill. A HVE is an in-situ technology that uses liquid ring vacuum pumps to remove various combinations of contaminated groundwater, separate-phase petroleum product and hydrocarbon vapour from the sub surface. Extracted liquids and vapour are treated and collected for disposal or re-injected to the subsurface (where permissible). Water ring vacuum pumps were utilised to deal with the pumping of potentially explosive vapours. The well heads and pumps on the system were controlled via a telemetry control to ensure continuous process monitoring. The monitoring was undertaken from a remote location, enabling customers to access the information and reducing overall project costs.

Approximately 27 tonnes of hydrocarbons were recovered from the site in a seven month treatment period. Site close out was achieved with the Environment Agency in a minimum time period.

Air sparging

Following excavation and disposal works, air sparging was used to treat deep contamination within the River Terrace Gravel, London.

The treatment strategy was fully co-ordinated with redevelopment requirements, resulting in system installation and operation during site construction works. Air sparging is an in-situ remedial technology that reduces concentrations of volatile constituents in petroleum products that are absorbed to soils and dissolved in groundwater. The technology involves the injection of contaminant free air into the subsurface saturated zone, enabling a phase transfer of hydrocarbons from a dissolved state to a vapour phase, the air is then vented through the unsaturated zone.

As a result of the correct technologies being implemented the construction of the building was not delayed and the contamination effectively treated.



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