Development of Former Council Depot, Colchester, Essex

Green Earth Management Company (GEMCO) provided environmental consultancy and remediation works at a former Council Depot in Colchester on behalf of a regional home builder.
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GEMCO’s services included; investigation risk assessment and design of a Remediation Strategy (including validation and verification proposals) which was approved by Colchester Borough Council and the Environment Agency. The site had previously been a local borough council depot until 2008. The site was redeveloped for a residential end use including houses with private gardens and 2 (no.) 3 storey block of flats with associated infrastructure.
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The development also included a new public car park. GEMCO discovered a number of contamination sources on site. These included underground fuel tanks, a weighbridge pit, inspection pit, vehicle wash down area and associated interceptor. The site is underlain by River Terrace Deposits sand and gravels overlying London Clay. GEMCO’s site investigation and risk assessments confirmed that there were high levels of TPH and VOCs. The level of contamination at the site had the potential to pose a risk to human health and the environment.
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GEMCO undertook remediation works with the aim to break pollution linkages. On completion GEMCO undertook validation of the works and concluded that the site is suitable for the intended proposed residential end use.

Design of Remediation Works

GEMCO’s remediation strategy was to remove sources of contamination and provision of capping layers and barriers. The works included the removal of existing hard standing, removal and disposal of buried tanks and contents off-site and the excavation of visually impacted and highly odorous soils from the tank excavation. Contaminated soil and groundwater was bio-remediated in-situ. GEMCO designed a 600mm capping layer in gardens or public soft landscaping. GEMCO also carried out monitoring of the gas and groundwater conditions pre-and post-remediation.
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Post remediation ground gas and vapour monitoring proved that the risks had been successfully mitigated. No special gas protection measures were required.

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