Project: Former Chrome Plating Works
Timescale: 2 years
Poor working practices at a former chrome plating works led to repeated spillages of chemicals containing hexavalent chromium (Cr VI), causing considerable contamination of the soil and groundwater. A site investigation revealed Cr VI contamination concentrations below the site of up to 25,000 mg/kg in the soil and up to 5,000 mg/L in the groundwater.
A multi phased approach was developed and agreed with the Environment Agency to quickly reduce contamination levels on-site and reduce the risks to the wider environment, whilst minimising the impact of site works on neighbouring companies and their employees on the surrounding industrial estate.
In the first phase of treatment, over 700 tonnes of heavily impacted soils containing up to 25,000 mg/kg Chromium were removed from within the former plating works building footprint and transferred for disposal via a licenced treatment facility. Prior to backfilling with clean infill, exposed contaminated groundwater was treated with reducing agents to convert the toxic Cr VI to its insoluble and less harmful trivalent form (Cr III).
The site investigation had indicated smeared contamination at depth. In a second stage of remediation, deeper groundwater was accessed via the pump and treat method, reducing groundwater contamination from up to 500 mg/L Cr VI to less than 20 mg/L. This method also encouraged ‘flushing’ of the subsurface with clean groundwater, significantly reducing the contaminant load within the area and minimising migration of gross contamination.
Once these works were complete, a third and final phase of treatment took place, where In-situ Chemical Reduction (ISCR) was used to treat areas of residual groundwater contamination which had spread outside the building’s footprint. Chemical reducing agents were delivered to the subsurface using direct push injection facilitated by ERS’ rigs and injection equipment. This enabled the targeted application to specific permeable horizons which were deemed potential pathways to a nearby river. Over 40 locations were targeted, delivering over 1500 kg of reagent to the contaminated zones.
Despite the complex geology underlying the site, the third phase of treatment successfully reduced the Cr VI concentrations in groundwater to below 1 mg/L, whilst the in-situ method minimised further disruption to other users of the busy industrial estate.