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Kent, Former Landfill
The Challenge:
A former landfill dating from the 1930s-1960s covered the northern third of the site. Landfill contained extraneous waste items such as ceramic, glass, brick, wood, metal and fabric. The soil was also contaminated with hydrocarbons which were leaching through the ground and impacting local watercourses. The depth of the waste varied with a maximum recorded depth of 5.5m bgl. The landfill required remediation to treat hydrocarbons and geotechnical improvements to make it suitable for redevelopment. The remainder of the site required bulk earthworks to form stable construction platforms.
The Approach
Cognition was contracted to undertake the remediation and earthworks. The key elements included;
- Excavation, screening, segregation and bioremediation of contamination hotspots within landfill;
- Dynamic compaction to improve geotechnical properties of fill, prevent differential settlement, and reduce disposal volumes;
- Construction of clay cut-off wall and permeable reactive gates to treat groundwater;
- Screening of excavated landfill to segregate and remove all waste and deleterious material, and reuse treated material under MMP
- Stabilisation and formation of piling mats;
- Cut and fill of landfill material to meet development topography;
- Roads cut across the site and recompacted using the deep impact roller to ensure the subgrade material met the CBR target for road formation;
- Geo-environmental testing and validation reporting to regulators.
The Outcome
The remediation and earthworks were carried out in accordance with Cognition’s remediation strategy and proved to be a highly sustainable project delivering significant savings to the client and bringing a problematic sloping landfill site back into use. A total of 8,000m3 of landfill material and 35,000m3 of soil material was excavated and treated using a combination of segregation, ex-situ bioremediation, enabling re-use on site and reducing disposal costs. The clay cut-off wall and permeable reactive gates will protect the local watercourses from potential residual hydrocarbons within the saturated landfill. The dynamic compaction and stabilisation not only delivered firm construction plots and piling mats, but also formed a suitable subgrade for road construction for the new development.
