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Horley, Sewage Works
The Challenge:
Cognition was contracted by Wates to remediate a former industrial site in Whitmore Way Horley for a residential development. The site was occupied by the sewage treatment works and garages. Landfilling of pulverised waste had also taken place on a portion of the site in the mid 20th century. In the 1980’s vehicle repair workshops were present on the site. Site investigations showed made ground exhibited elevated levels of arsenic, copper (both marginal), zinc, PAH, benzo (a) pyrene, TPH, and xylene. The contamination posed an environmental risk with potential impact on the shallow groundwater. The soils also posed a moderate human health risk to future residents and required stabilising and relocation beneath clean capping soils to be installed in gardens and soft landscaping within the new development.
A number of brick built buildings were present on site and were subject to tight ecological controls due to the presence of bats. Reptiles were also found in abundance in the overgrown areas of the site.
The Approach
The key elements of these works included;
- Ecological management including habitat creation for reptiles and management of ecological surveys;
- Instigate environmental monitoring around site boundaries;
- Removal of existing services on site;
- Demolition of all buildings and break-up of existing tarmac roads with materials segregated and crushed for re-use;
- Demolition of old sewage works filter beds and disposal of clinker;
- Delineation of contamination hotspots, excavation and ex-situ bioremediation of TPH contaminated soils;
- Stabilisation/encapsulation of heavy metal contaminated soils
- Cut and fill to reprofile site for new development;
- Stabilisation, backfill and re-use of processed and treated soil;
- Construction of stabilised building platforms for new development.
The Outcome
Cognition completed the works with minimal off-site disposal and maximum re-use. The contamination hot spots were treated to meet re-use criteria; hydrocarbon contaminated soils were bioremediated and heavy metal contaminated soil stabilised to reduce leachability and environmental risk.
The site was reprofiled and treated soil stabilised to form construction platforms. The site has since been re-developed as the first phase of a larger residential scheme planned in this location.
