Landfill at Emerson’s Green, Bristol
Details of the Site
The Site at Emerson’s Green comprised a 2.3ha historic landfill located within the boundary of a larger 99ha site in South Gloucestershire approved by the local planning authority for a mixed-use development called Emerson’s Green Urban Village being constructed by a consortium of national housebuilders. The landfill was a former valley in the natural topography that was infilled under license granted by the local authority with approximately 52,000m3 of commercial and industrial waste in the 1980’s. The site was covered with a clay cap and restored to grassland in the early 1990s.
Following removal of the landfill capping materials, excavation for off-site disposal of the entire volume of landfill waste and reinstatement of the resultant void with inert material to construct a development platform would have involved in the region of 26,000 haulage vehicle movements on local roads.
To avoid the disruption posed by this approach, a remediation strategy comprising excavation of the landfilled waste for on-site processing to recover materials that are suitable for re-use to construct the development platform (soils, gravel, rock, brick, masonry, concrete) was proposed. Materials unsuitable for re-use on-site would still require off site disposal, however their quality (by virtue of the processing to remove all adhering soils) would render them suitable for recycling (with regard to metals and rubber) and energy production (with regard to wood, textiles and paper/cardboard). The resulting material shortfall to construct the development platform would comprise imported soils generated from foundation and drainage excavation arisings across the wider 99ha development area, which would otherwise have required off-site disposal as a potential waste.
Prior to commencement of this project, landfill remediation projects that involved treatment of site-won materials for on-site re-use had been undertaken using a mobile plant permit to Regulate excavation and treatment of the waste in conjunction with the CL:AIRE Definition of Waste: Code of Practice (DoWCoP) as a mechanism to demonstrate that the recovered materials intended for re-use were not a waste. This regulatory approach was akin to that adopted at many sites affected by land contamination (other than landfill sites) that regularly undergo remediation to enable redevelopment through the Planning regime.
However, at the time that VertaseFLI began pre start discussions with Regulators (January 2018), it became clear that there was a shift in focus with regard to the most appropriate Regulatory regime for landfill remediation projects in England and Wales. Specifically, it was recognised by the Environment Agency that, whilst being a valuable tool to the land remediation industry, the CL:AIRE DoWCoP was not really intended for materials that had been previously intentionally discarded into landfill (and were thus already classified as a waste). This contrasted with land affected by contamination, where the Environment Agency considered it plausible that the contamination was a result of accidental release as opposed to intentional discard, and thus the contaminated materials were not necessarily already classified as a waste.
Instead, the Environment Agency’s preferred mechanism to Regulate the Emerson’s Green landfill remediation project was a bespoke Waste Recovery Permit whereby permanent deposit of the waste to land was the mechanism of ‘recovery’. This Regulatory position was understandable due to the unambiguous evidence that the landfilled material was already a waste. However, in the absence of case histories (at that time) of landfills being remediated under this permitting regime, both the client and VertaseFLI were concerned about the ongoing viability of the project via this Regulatory route. Primary concerns were around the following:
The timescales to obtain the permit to commence the works;
The timescales to surrender the permit upon completion of the remediation and whether they were compatible with the build and sales programme for the new development (i.e., would mortgage lenders lend to home buyers if the permit was still active at the time of conveyancing);
The apparent hazard-based approach underpinning the waste permitting regime, which is a stark contrast to the risk-based approach underpinning the assessment and remediation of land contamination set out in best practice guidance (e.g. Land Contamination Risk Management guidance published by the Environment Agency on .gov.uk);
The potential tendency for the Environment Agency waste permitting team to view the remediation activity as creation of a new landfill, rather than a strategy to break pollutant linkages and render land affected by contamination suitable for proposed new use under the Planning Regime.
Notwithstanding the concerns, VertaseFLI proceeded with an application for a site-based (bespoke) waste recovery permit for the permanent deposit of waste to land, which was successfully obtained eight months after submission of the application and confirmation that it had been ‘duly made’.
Importantly, the permit application procedure shaped the remediation and re-use strategy in two key ways:
Firstly, the waste permitting regime put significant emphasis on ensuring the permitted activity did not lead to a deterioration of environmental quality relative to baseline conditions (a key requirement to satisfy the legal test for permit surrender).
Therefore, rather than the derivation of risk-based remediation/re-use criteria for contaminants in soil and groundwater, the remediation criteria for contaminants of concern were underpinned by background/ baseline conditions to ensure that a net deterioration in quality could not occur. This required comprehensive documentation of the baseline site conditions from previous site investigation reports and additional site investigation prior to commencement of the remediation activity.
Secondly, the permitting regime put significant emphasis on ensuring ‘pollution control measures’ (temporary and permanent) were incorporated into the works (also a key requirement to satisfy the legal test for permit surrender). The most significant of these for the remediation strategy was the requirement to use of a minimum 1000mm thick low permeability engineered geological barrier at the base of the development platform constructed from inert engineered clay. The intention of this geological barrier, from a Regulatory perspective, was to minimise the downward migration of contaminants from recovered wastes into the groundwater beneath the site. Arguably, this represented a measure that was unnecessary had a risk-based approach to the derivation of remediation criteria been accepted. Furthermore, construction of this barrier using inert clay sacrificed valuable void space for the re-use of site-won recovered materials from the landfill waste.
Importantly, none of the above associated with the Permitting regime precluded the more typical Regulatory checks and balances undertaken by the Local Authority Environmental Health department and the National House Building Council (NHBC) to ensure that risks posed by contaminants and ground gas were adequately addressed by the remediation measures. The remediation measures included the on-site treatment of contaminated soils (source reduction), use of a cover system in gardens and open spaces (pathway interruption) and inclusion of ground gas protection measures in buildings (pathway interruption).
Furthermore, a Geotechnical Design Report was produced in accordance with the now withdrawn HD22/08 guidance on managing geotechnical risk published by Highways England to ensure the geotechnical suitability of the development platform constructed using recovered materials for its intended purpose of road, infrastructure, and residential construction.
Implementation and Material Re-Use
The recovery of materials from the landfill waste that were suitable for re-use on-site to construct the development platform was undertaken using a combination of waste separation technologies including selective excavation, mechanical screening, density separation, and manual sorting. Images of the waste being excavated from the landfill, and of the on-site waste processing area, are shown in Figure 1 and Figure 2, respectively.
The waste shown in Figure 1 illustrates the typically high soil/mineral content of landfilled waste deposited using the ‘controlled tipping’ method whereby a daily cover of soil/soil-forming material was used at the end of each working day to minimise wind blown waste dispersion and to discourage scavenging vermin.
Figure 1. Waste being excavated from the landfill for haulage to the on-site waste processing area.
Figure 2. Waste processing area where unprocessed waste is separated to enable recovery, recycling and re-use.
Quantities of materials excavated and recovered for re-use or disposal from the site are summarised in Table 1. Of the total volume of waste excavated from beneath the capping for on-site processing, 80% was recovered for re-use on-site to construct the development platform. This material comprised soils and crushed aggregate that underwent rigorous geochemical and geotechnical characterisation to confirm suitability for proposed use in accordance with agreed re-use criteria.
A key re-use criterion related to the degradable organic content of the material. Demonstrating compliance with this criterion involved building on the methodology published by CL:AIRE in Research Bulletin 17 for the forensic characterisation of the processed waste to confirm that the degradable organic content was below levels that would generate unacceptable levels of ground gas.
Of the 20% of excavated waste that was not suitable for on-site re-use, none was sent to another landfill. Instead, the wastes were further separated allowing approximately 109 tonnes to undergo recycling and 23,156 tonnes to undergo recovery for energy production (Table 2). Whilst off-site disposal involved haulage, recycling and energy recovery facilities were identified that were close to the site of excavation, thus minimising haulage distances as much as possible.
Table 1. Summary of material quantities excavated and recovered for re-use or disposal.
Table 2. Summary of material quantities recycled or used for energy recovery.
Surrendering the Permit
The bespoke waste recovery permit was surrendered in April 2021 after successfully demonstrating that the legal test for permit surrender (as set out in Regulatory Guidance Note 9 published by the Environment Agency dated May 2013) had been met. As the recovered waste had been well characterised during the remediation works in terms of its leaching and gassing potential (culminating in a comprehensive set of waste acceptance records), a case was made by VertaseFLI for ‘low risk surrender’ of the permit. This took the form of a detailed remediation verification report tailored to the requirements of the surrender process which compared post-remediation data with baseline site condition records to show that the permitted remediation activity had not led to a deterioration in environmental quality.
Shaping the Future
To the best of VertaseFLI’s knowledge, this Site represents the first example of the remediation of a commercial/ industrial landfill to enable residential development which has been Regulated by the Environment Agency under a bespoke waste recovery permit where the permanent deposit of waste to land (to construct the development platform) is the mechanism of recovery.
Whilst the project almost never went ahead due to initial confusion and uncertainty caused by the Environment Agency’s decision to Regulate the scheme via this approach, following acquisition of the permit and VertaseFLI’s mobilisation to Site, the project was completed on time and within budget.
Importantly, this project highlights the intentional limitations of the CL:AIRE DoWCoP and serves as a trailblazing example of the use of an alternative (albeit not ideal) mechanism to Regulate a landfill remediation activity that is aligned with the requirements of the Waste Framework Directive, which must not be undermined when re-using materials as part of remediation projects.
Building on this experience, VertaseFLI feel that there is an opportunity to improve the permitting regime for the remediation of historic landfill sites (where the re-use of site won materials forms a key part of the remediation strategy) and have had initial discussions with Regulators to share our experience and offer constructive suggestions for improvements. These discussions are ongoing at the time of writing (May 2021) and, if successful, are expected to provide benefits to other practitioners and the wider remediation industry in the future.