Churngold and RPS won Best conceptual design in the BB Remediation Innovation Awards for work on the former ICI facility at Thornton.
Churngold was selected to carry out the remediation of part of the former ICI Burnhall Facility, Thornton, which is being developed as part of the to enable the construction of a composting facility. Churngold worked alongside RPS Planning & Development and Waste 2 Resources (W2R), the principal contractor for the project, in developing a remediation strategy for the site.
Site investigation works by RPS identified hotspots of MCB, DCB, TCE and PCE, totalling just over 0.7ha. The contamination was within the saturated zone, both as DNAPL and dissolved phase contamination. The key receptor at risk was a non-tidal ditch that forms the northern boundary of the site.
Assessment of the remediation options
A Site Characterisation Model was designed to assess the remedial options. This considered the geology of the site (low permeability and heterogeneous), contaminant properties and concentrations, limited timeframe and logistical restrictions and the depth and geometry of the treatment zones.
Process design
The most favourable technique emerged as In-Situ Chemical Oxidation (ISCO). ISCO relies on contact between the oxidant and contaminant. As contamination was partitioned within soil and as NAPL often lies in organically rich silt sand bands, conventional methods of injection would not be sufficient to achieve this.
An innovative method of delivery and selection of the most appropriate oxidant in order. The solution offered was based on an innovative combination of soil mixing and high strength oxidants, which would offer the following advantages:
- increased contact through mechanical mixing as well as injection
- variable treatment intensity
- rapid process that can cover large areas and also target specific areas
- no waste streams or VOC emissions generated.
Selection and refinement of the oxidant (lime activated persulphate) followed preliminary experiments, a pilot study and a further laboratory study.
The addition of lime aided the dissolution of the contaminant in the dissolved phase (owing to its surfactant properties) and also aided the geotechnical stability of the treated soils by reacting with any by-products to form benign minerals.
Cost effectiveness
Churngold gathered further data on the vertical distribution of the contaminant via a MIP investigation, which enabled treatment to be highly targeted. This was key to the success of the project as very little oxidant was wasted, making the process highly efficient.
Reduction of pollution
Baseline mass balance calculations estimated that approximately 17,400kg of contamination was partitioned in soil and NAPL, with a further 210kg in groundwater. Post-remediation calcuations indicated that 11,715kg of contamination was destroyed in-situ as part of the process.
Philip Block, the technical manager for FMC, who hold the worldwide patent on the use of persulphate for remediation purposes, suggests "...that this is one of the largest, if not largest, destruction of contamination at any site using persulphate oxidation". Around 48,400 tonnes of contaminated soil were prevented from being sent to landfill.
"Truly innovative" Clive Boyle
