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Landfill at Emerson's Green

Shortlisted for Brownfield Awards Category 8 - Best Re-Use of Materials

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. 

Remediation Strategy 

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. 

 

Regulatory Context 

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. 

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Figure 1. Waste being excavated from the landfill for haulage to the on-site waste processing area.

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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. 

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Table 1. Summary of material quantities excavated and recovered for re-use or disposal. 

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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. 

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