Freeks Farm Landfill Remediation by Soilfix

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

Freeks Farm Landfill Remediation, Burgess Hill, Surrey

Organisations: Soilfix Ltd, IDOM Merebrook Ltd, Countryside Properties PLC

Project Details:

The Northern Arc development in Burgess Hill is a 200-acre Homes England-led project aimed to deliver the construction of 3,600 homes, areas of public open space, habitat creation and archaeology preservation. Phase 1 of the scheme is being delivered by Countryside Properties PLC in partnership with Homes England.

To enable ongoing construction, a new Spine Road was required to unlock access from the surrounding road network to the development. The only viable location for the Spine Road (incorporating a cycleway, surface water swales, multi-use games area, new children’s playground and car park) was situated on part of a closed municipal landfill that accepted household and commercial wastes in the 1970’s and 1980’s. Wholescale excavation & treatment of the landfill material was required to construct a suitable, geotechnically stable platform for the required infrastructure to be constructed. Elevated concentrations of methane and carbon dioxide recorded at the site boundary (in proximity to residential housing) presented another driver for comprehensive remediation of this portion of the landfill site.

The Challenge:

Remediation of the former landfill site presented several challenges requiring unique and creative solutions. These were as follows:

▪ Cost-effective Re-use of soils: For sustainability and economical purposes the re-use of soils contained within the landfill material was considered crucial for the success of the project – the alternative (wholescale excavation and disposal followed by importation of engineering fill was cost prohibitive;

▪ Cohesive Soils: The soil matrix within the landfilled materials was predominantly cohesive in nature, presenting a challenge for effective segregation of wastes from soil, as well as for effective re-engineering;

▪ Reinstatement of soils: Stringent geotechnical compaction targets were set to comply with the high standards required by the adopting highway authority, including compaction greater than 95% dry density;

▪ Available Treatment Area: Remediation required a robust, bunded treatment area for stockpiling / processing of landfilled materials. Due to space limitations, this could only be achieved by constructing a treatment cell within the proposed landfill excavation area itself;

▪ Leachate Management: Perched groundwater (leachate) and surface water ingress during periods of inclement weather had to be managed to facilitate excavation and backfilling;

▪ Live Utilities: The remediation area resided several in-situ live utilities (strategic sewer & water main) requiring protection, as well as overhead HV power lines crossing the excavation area;

▪ Environmental Management: The landfill remediation area was situated adjacent to residential communities and an area of Public Open Space. Robust environmental considerations, including noise, dust, odours, and litter were therefore required; and,

▪ Multiple Project Stakeholder Involvement: This included Countryside, Homes England, Environment Agency (EA), Local Authority, County Highways Authority as well as the local residents.

Development of Sustainable Solutions: Soilfix (Remediation Contractor) worked closely with IDOM Merebrook Ltd (IDOM) (Geo environmental & Geotechnical Consultant) from an early stage to develop a sustainable yet robust Remediation Strategy for the site. The Strategy was based primarily on two phases of site investigation and a treatability trial performed by Soilfix and IDOM.

A key aspect was the sustainable reuse of soils contained within the landfill material, to maximise material retention on-site and minimise off-site waste disposal. Landfill materials undertook a combination of soil conditioning, screening and use of an elevated hand-picking station fitted with high-pressure ‘air knife’ system to segregate landfill waste from the soil. The landfill material ‘treatment train’ was continually adjusted to best suit the variable materials that were encountered in different areas/depths.

Due to the variable, challenging nature of the landfill material, laboratory / field trials and experimentation of the above techniques were performed during works to maximise soil retention from the landfill material while still optimising the processing rate. Processed soils were subjected to further testing to ensure residual organic and a ‘de-minimus’ fine waste content within the soils were at suitably low levels to be reused on site.

Conditioning of soils with Quicklime and subsequent modification with Cement and was carried out to produce a geotechnically suitable fill to be re-used, as well as facilitating effective segregation of waste from soil. Stringent geotechnical targets including moisture content, CBR value, shear strength, maximum dry density and air voids were achieved in accordance with Series 600 Specification for Highway Works, carried out to the satisfaction of the adopting authority.

Spatial limitations can be a challenge for any remediation site. For the Burgess Hill landfill this was particularly challenging due to the restricted available footprint for the landfill remediation & treatment works. The treatment area had to be constructed across one half of the landfill remediation area, while the other half of the landfill was excavated and backfilled. After completing one half of the process, a new treatment area was established on the newly remediated half, to allow the old treatment area to be subjected to be excavated.

To tackle landfill leachate and surface water ingress a bespoke leachate treatment plant was established on site. A temporary sump well and drainage system was installed on site to collect leachate for treatment using settlement tanks, methane stripping and sand/carbon filtration prior to discharging to the nearest foul sewer under temporary consent.

A Materials Management Plan (MMP) was developed by IDOM in accordance with CL:AIRE Code of Practice (DoWCoP) to regulate re-use of processed landfill soils as ‘non-waste’. Early engagement with the local area Environment / Waste Permitting teams of the EA was sought by Soilfix and IDOM.

Based on these discussions and submittal of treatability trials information, the EA agreed that treated landfill materials meeting the reuse criteria would be considered as recovered and therefore deemed ‘non-waste’ and suitable for reuse under the MMP. The EA also accepted that the treatment process could be carried out under Soilfix’s Mobile Treatment Permit, stipulating that segregated waste materials, together with any ‘non-confirming’ soils, must be removed off-site in accordance with full waste Duty of Care.

This proactive dialogue, to enable timely, cost effective and sustainable reuse of materials for the construction project (the reasons why DoWCoP was developed in the first place), enabled the Spine Road and Infrastructure construction to commence on programme. Should the EA have pursued other regulatory options for the treatment/reuse of the materials, such as a Bespoke Recovery Permit, the entire 3,600 home development would have suffered a significant delay, or even shelved by Homes England due to no obvious alternative means of access.

Best Practice Works Undertaken:

The following works commenced in June 2020 and were completed by December 2020:

▪ Removal and stockpiling of 845 m³ topsoil for future reuse in Phase 1 of the Northern Arc project;

▪ Removal and stockpiling of 6,384 m³ of clay capping soils covering the landfill material for future reuse in Phase 1 of the Northern Arc project;

▪ Preparation of treatment cells with engineered leachate containment for storage/processing of excavated landfill material;

▪ Installation of modular processing equipment for separation of waste from soils;

▪ Surgical excavation of 13,890 m³ of landfill material within the remediation area;

▪ Safe standoff distances for excavations maintained away from live utilities;

▪ Conditioning of soil through addition of quicklime where necessary to ensure soil moisture content within satisfactory range of optimum;

▪ Treatment through physical segregation and handpicking of 2,588 m³ waste materials from the excavated landfill material. Wastes were removed to an off-site permitted facility for further treatment and sustainable recovery as Refuse Derived Fuel (RDF);

▪ Additional controlled hand-picking of 8tonnes asbestos cement sheeting fragments and controlled removal of an old (partially insulated) boiler – both non-permitted wastes therefore unforeseen;

▪ Cement stabilisation of treated soils for geotechnical improvement purposes;

▪ Filling to agreed levels based on construction build-up requirements below proposed development levels; and,

▪ Verification testing to fulfil the requirements of the IDOM Earthworks & Remediation Strategy including CBR values 5 - 30%, Air Voids <10%, >95% Maximum Dry Density and Shear Strength >50kN/m².

The final materials balance achieved by the scheme is summarised in the Table below.

Sustainable & Beneficial Re-use of Soils and Segregated Landfill Waste:

Of the 11,000 m³ of landfill soils excavated and processed, 99% of the material was successfully reused on site as engineered fill. The cost of removing all such material to landfill (including standard rate of tax) followed by importation of suitable material was £4.2M. The on-site treatment and re-engineering solution implemented at the site reuse therefore provided a saving of ~£3.0M.

Landfill waste segregated from the soils was segregated into further categories including general mixed waste, tyres and metal to maximise the amount of material recycled. The general mixed waste fraction (mixed plastic, wood, rubber, glass etc) was removed offsite for further treatment at a local waste recovery facility. Recovered plastics, unable to be recycled at this facility, were transported to mainland Europe for recovery as a fuel in Energy from Waste or Refuse Derived Fuel power station plants.

The charts presented overleaf illustrate the volumes of soil and landfill waste excavated and recovered.

Environmental Management:

Great care was given to environmental monitoring & controls during the course of the remediation works, adopting a ‘proactive’ rather than ‘reactive’ approach. The site was sandwiched between a residential development and Public Open Space (including a BMX track) making control of environmental emissions critical to a successful project. Daily qualitative and quantitative environmental monitoring was performed by Soilfix and IDOM, to support the comprehensive environmental controls implemented at all stages of the remediation.

Due to dry conditions during the summer and the use of quicklime for soil conditioning, stringent dust control measures were implemented. Dust was controlled through a combination of misting cannons, jet washers, and towed water bowsers. Verification of control measures was satisfied through fortnightly dust frisbee sampling and respirable (PM10) dust monitoring stations installed on site to produce real-time dust monitoring data. Airborne fibre monitoring and industry-leading Scanning Electron Microscopy (SEM) based techniques were utilised to ensure there was no unacceptable release of asbestos fibres. To control odours released when excavating the landfill, portable independent rotary atomiser’s (PIRA) were installed at strategic site locations to maximise their effectiveness. Litter picking was required throughout the works to manage the spread of light material such as plastics originating from the landfill. Effective control of litter was of particular importance during periods of high winds.

Compliance with Health & Safety / Covid-19:

Site works commenced shortly after the initial COVID-19 UK lockdown. Robust social distancing and hygiene measures in accordance with Government / Construction Leadership Council (CLC) guidance and Soilfix’s Covid 19 Management Plan were implemented on site to ensure the safety of all personal. The remediation works were carried out under the highest standards of health & safety with zero lost-time accidents during the 7-month remediation contract and ~19,300 man hours worked.

Stakeholder Engagement:

Socially distanced outside meetings were held on site on a minimum monthly basis, typically comprising of Soilfix, Countryside, Coinford (civils contractor) & IDOM – also with periodic attendance by representatives of West Sussex County Highways and the Contaminated Land Officer of Mid Sussex District Council.

A close communication was kept with local residents via letter drops and face-to-face engagements prior to and throughout the works. Many of the long-time residents witnessed the construction and operation of the original landfill and were interested to see how it could be successfully reclaimed for such beneficial use. Soilfix supplied regular updates with interested parties and the general public on various social media platforms, documenting the progression of remediation. This included a video of each soil treatment phase and photos highlighting some of the equipment and techniques in use.

Conclusions:

The sustainable, robust remediation & re-engineering of former landfill has enabled timely construction of an access Spine Road, in turn unlocking the 3,600-home Northern Arc development. A new children’s recreational playground and multi-use games area has now also been completed. The remediation approach implemented allowed for the reuse of >99% of segregated landfill soils and the successful recycling the vast majority of the landfill waste, saving over 14,000m³ (23,000tonnes) of material from disposal to landfill.

“We have had nothing but hugely positive feedback during your works on site from all visitors throughout our business and your Site Team were fantastic accommodating us during your works, always taking the time to explain the process, sequence and programme in depth. It’s been a great operation to see and a great success.” Ryan Hughes, Regional Construction Director, Countryside Properties PLC.