Soil excavation makes way for remedial capping layers, to remove contamination ‘hotspots’ or simply just because there’s excess material generated during development, contributes to carbon-intensive removal of large volumes of soil that may not actually require treatment or off-site disposal. This also results in unnecessary vehicle movements, landfill use, and overall environmental impact. A thorough contaminated land risk assessment which assesses the risks to human health and the environment can mean the difference between overly cautious or blanket remediation (such as soils removal), and remediation that’s genuinely necessary, and helps to support more sustainable land management and development.
One such site where a thorough and detailed risk assessment helped save unnecessary soils removal to landfill is located to the west of London and has been redeveloped as a warehouse facility. This site is located in an area of mixed commercial, industrial and residential land uses and was historically occupied by a small-scale engineering works and van hire facility.
The site is located in an environmentally sensitive area due to the presence of Principal aquifers and its location within a groundwater Source Protection Zone.
During demolition and removal of hardstanding across the site, a small area of residual hydrocarbon contamination was encountered in the shallow soils. It was initially proposed to remove this material and dispose off-site as hazardous waste as part of a ‘dig and dump’ exercise. However, given the amount of material that was intended for removal (approximately 65m3) and the associated costs, additional soils sampling and analysis, and Detailed Quantitative Risk Assessment (DQRA) was undertaken to confirm whether the identified contamination actually posed a significant risk to the underlying groundwater and would therefore require removal, or if the contamination posed a low risk and could remain in-situ.
The DQRA demonstrated that the risk to the underlying aquifers was low and the impacted material could remain in place, thus eliminating the need for unnecessary material removal, transport and disposal to landfill.
It was estimated that 2.2 tonnes of carbon was saved thanks to limiting lorry movements and landfill disposal.
Options for the reuse of soils can also be considered subject to certain conditions, preventing the unnecessary removal and / or importation, and associated movement of materials.
This was the case for a residential development in West London, that had been previously occupied by a public house and meadow which had become overgrown and was no longer being maintained. The re-development comprised the construction of residential properties and retention of the meadow which was to be re-contoured and brought back into use as an area of public open space.
The meadow was surrounded by a large pre-existing soil bund. Parts of this bund required removal to accord with Local Planning Authority requirements relating to flooding. In addition, construction of a swale and a change in levels in the residential development area meant that a significant quantity of soil arisings was to be generated.
Contaminated land assessment was undertaken across the site which confirmed that soils in areas to be excavated did not pose a significant risk to end users of the site, the underlying aquifer and the adjacent stream. Following agreement with the Local Planning Authority and the Environment Agency, excavated soils were re-used as part of the recontouring works in the meadow, under a Materials Management Plan and in accordance with the CL:AIRE Definition of Waste Code of Practice.
Approximately 2735m3 of soils was saved from off-site disposal, saving around 80 tonnes of carbon from lorry movements and disposal to landfill.