Remediation of a former timber yard Brookwood, Woking

Remediation of a former timber yard Brookwood, Woking

Located in a prime position opposite a mainline rail station to London, this site was formerly used for the treatment of fence panels with creosote for over 40 years. Conditional planning permission for the development of 28 flats was secured.

Ahead of the required remediation, our site conceptual model indicated a creosote dip tank was the likely primary source of a creosote plume identified between 1 and 2.5 metres below ground level. Identified contaminant pathways included surface water run-off, surface water drainage systems and flow through the underlying aquifer following the natural hydraulic gradient. Complaints of odour and observations of oily streams emenating from the site, had been received by the local council over a 20 year period. Protection of an adjacent surface water receptor, a canal, was critical.

Project Details

Remediation method

Remediation of this site with minimal disturbance to site neighbours was a pre-requisite of this project and demanded the development of an innovative, sustainable in-situ treatment technology. We examined a range of remediation options for the site. Soil stabilisation was selected as the most suitable method because it provided the ability to meet our remedial target of removing 95% of the mobile contaminants onsite, whilst avoiding the associated odour or extended operating periods of other options. In-situ treatment technologies – such as SVE or surfactant flushing – were examined but deemed inappropriate due the identified heterogeneity of site soils (sands interbedded with low permeability clays). Off-site disposal was discounted due to concerns regarding odour generation, safety of village residents and sustainability issues (>100 lorry movements off-site, through a quiet village, with unnecessary landfill use). Extensive lab trials were carried out in our in-house  laboratory, prior to mobilisation. Trials were utilised to evaluate appropriate binders and their ratios. Trials also examined site specific oxidant performance and oxidant dosing specification. Observations of physical properties of the monoliths were made (any crumbling/ cracking) and a pressure test applied. Following this, binder ratios were optimised to identify the optimal amount of binder required to achieve the desired physical properties. Less binder equated to a significant cost saving for the client and CO2 reduction. The photographs below show a comparison of the non-treated baseline soil versus a stabilised soil sample. Extensive in-house laboratory trials enabled us to demonstrate effective mass removal/stabilisation to key stakeholders, including our client, the Environment Agency and the Local Authority, engaging them in the recommended in-situ treatment strategy.

Remediation outcome

We achieved a 99.8% reduction in mobile contaminants utilising applied stabilisation/oxidation techniques. Permeability within the stabilised monolith was reduced by four orders of magnitude. Total mass of contamination was reduced by between 51% and 87%, with the greatest percentage reductions being achieved in more toxic polycyclic aromatic hydrocarbons (PAH) and phenol compounds. The main works were completed within a two week timeframe. No off-site disposal of creosote contaminated soils was required as a result of the in-situ technique applied, saving over 100 lorry movements offsite, providing a cost saving of £250,000 to our client. Contamination at the site had represented a significant source of concern for local residents for decades. The communications plan implemented by QDS was successful in engaging the community in our proposed method of works. A single complaint of odour was received during the entirety of our occupation of site. During the previous tenants’ occupation of the site, up to 10 complaints a day were received by the council.

Experience gained globally and delivered locally captures what you get when you engage FLI QDS.

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