Bioremediation of hydrocarbon impacted soils - Marchbanks, Dundee

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Courtesy of Soilutions Ltd

Client: Dundee City Council

Objective: Bioremediation of hydrocarbon contaminated soils to achieve compliance with the Waste Acceptance Criteria (WAC) for Mineral Oil (C10 – C40); with the intention of re-using the soils to Riverside Recycling Centre to be used as a capping layer.

Challenge: Approximately 2,800 m3 of hydrocarbon impacted soil was stockpiled at the rear of Marchbanks Recycling Depot in Dundee. WAC testing and speciated petroleum analyses indicated that there was a mild to moderate contamination from heavier fraction hydrocarbons. In consultation with SEPA, bioremediation was selected as the most appropriate form of remediation required to achieve compliance with the WAC data.

The Solution: Soilutions Ltd acted as the principle contractor for this bioremediation project. Contaminated materials were excavated from the stockpile and screened for large or non-biodegradable materials using an Allu bucket attached to a twenty tonne 360 excavator prior to forming the windrows. The oversized screened material was sorted and placed into appropriate skips i.e. timber, concrete. The excavated contaminated material was then placed into three windrows which were lined underneath with polythene sheeting. This polythene sheeting was put in place to prevent any contamination to the material beneath each windrow. After completing the windrows they were covered with folio to prevent probable rain penetration.

During the construction of the windrows samples were collected to assess the nutrient status, pH, and indigenous microbial and degrader populations of the soil in order to identify any constraints to bioremediation. Regular monitoring of the windrows was carried out for the duration of the works. The windrows were ‘turned’ using an Allu bucket at intervals determined from data taken during monitoring visits, this allowed the soils to be aerated and chemically amended to enhance the bioremediation process.

On completion of the bioremediation process, with all concentrations of Mineral Oils (C10 – C40) being WAC-compliant to below 500 mg/kg TPH, the remediated soil was transferred under the registered Waste Transfer Scheme to the Riverside Recycling Centre for use as a capping layer.

Duration: 15 months.

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