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Former William Blythe Chemical Works, Restoration of landfill site and creation of a country park

Shortlisted for Brownfield Awards Category 13 - Best Biodiversity Enhancement

Organisations: RSK Environment Ltd., RSK Geosciences, Synthomer plc., Gleeson Homes, Buckingham Group Contracting Ltd.

Summary 

The site was a former chemical works near Burnley including a  hazardous waste landfill which was restored over the last ten years  in accordance with an RSK design enabling sale of part of the  factory site by Synthomer plc. to Gleeson Homes for housing  development. Gleeson Homes are mid-way through construction of  the housing development and are currently creating an access  footpath within the landfill (retained by Synthomer) to enable  recreational public access which was an intended benefit of the  landfill restoration.  

The restoration has made safe an area that represented a potential  risk to public health whilst significantly enhancing biodiversity. It also  created a site of clear amenity value to the local community both  within the new housing development and the wider village through  the following: 

▪ Providing a solution to combine landfill closure best practice  with the creation of an accessible public open space on the  doorstep of the new housing development realising an  opportunity to enhance the health and wellbeing of new  residents.  

▪ Competitive tendering and re-measurement were selected to  best apportion the risks and to achieve the most cost-effective,  and durable solution. Selection of a quarry fines by-product for  the restoration soils, provided a sustainable, nutrient poor  subsoil producing optimal conditions for biodiversity  enhancement 

▪ Applying Environment Agency (EA) Construction Quality  Assurance (CQA) guidance to provide a confident solution, in  conjunction with planning conditions, landscaping best practice  and responding to the requirements of the Lancashire  Biodiversity Action Plan.  

▪ Removing a source of concern, the site has been transformed  both aesthetically and as an amenity into an asset for the local  community. The project included extensive consultation and  contribution from the Local Parish Council and the Burnley and  District Civic Trust who awarded a certificate to the project team  in recognition of the community benefits generated by the work  undertaken 

▪ Restoring a chemical works landfill previously producing  leachate, which could only be disposed to foul sewer, to  create a surface water environment providing new habitats  for wildlife, safe spaces for public amenity, and unlocking  adjacent brownfield land for residential redevelopment. 

▪ Selecting design, structure and landscaping to provide a  durable and adaptable solution, evolving over the last  decade to meet the requirements of the EA, residential  developer and local community, the ultimate objective  being that the site is not constrained by any long-term  licence, permit or maintenance requirements.

Timeline and Key Roles

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Former landfill and chemical works

Background

The restored landfill (5 ha) is within the former William Blythe  chemical works (total 15 ha) located on the outskirts of Hapton,  Lancashire, operating on the site adjacent to the landfill since the  mid-1800s. Waste materials generated from the production of  arsenic, lead, tin and zinc and sulphur-based compounds on site were  progressively deposited in the landfill over a period in excess of 150  years.  

The remainder of the land (10 ha) was occupied by the former factory  buildings (now under development by Gleeson) and an area of  undeveloped grassland and woodland, designated as greenbelt. The  waste deposited has a thickness of up to 10m. Due to its age, no  controls such as an engineered liner or capping were in place, with  the waste placed directly over the natural clay. 

Over time, as only parts of the landfill were in use, it had  progressively become overgrown. It comprised some established  mature woodland and a plantation (silver birch) added during a phase  of partial restoration in the 1990s to screen the site from the M65

 

Investigation and Risk Assessment  

The landfill remained in use until 2005. Following the issue of a  Closure Notice by the EA in 2006, RSK was appointed by the site  owner (Synthomer plc) to undertake intrusive investigations and risk  assessments across both the landfill and the wider William Blythe  site. This work developed the site conceptual model and ultimately  the most appropriate landfill restoration strategy.  

The landfill contents include very high concentrations of metals,  arsenic and asbestos which prior to full restoration posed a potential  risk to human health preventing access and potential redevelopment  of the remainder of the former factory site.  

Risk to groundwater (Secondary aquifer within Coal Measures) were  largely mitigated by the presence of a thick layer of low permeability  Till. However, in its unrestored state, the landfill leachate  represented a significant risk to surface waters. The EA were  consulted throughout the process of investigation and risk  assessment to ensure the work undertaken was adequate to inform a  future restoration and monitoring strategy.  

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Placement of mineral layer and drainage stone

Restoration  

Planning consent for the landfill restoration scheme was granted in  2010 and RSK supported the Client in the selection of a remediation  contractor, Buckingham Group Contracting Ltd. RSK developed an  Earthworks Specification for CQA documents and managed the  tender process. The project risks were assessed with the client and  used to develop suitable contract terms. After tender assessment,  RSK recommended a contractor and the contract was prepared and  signed. RSK administered the contract as the Engineer, with the ICE  7th edition remeasurement contract being selected to obtain best  value. 

Various options were explored for a capping material including a  bentonite matting layer. The chosen solution, on the grounds of both  cost-efficiency and proven effectiveness and durability was a 0.5m  low-permeability clay layer, 0.3m gravel drainage and 0.2m  restoration soils comprising a subsoil layer to create a 1.0m thick  barrier. The capping design was established taking account of EA  Technical Guidance on Capping and Restoration of Landfills.  

The capping materials were sourced from local quarries and the  selected ‘subsoil’ was a quarry fines material. This was a by-product  of aggregate manufacture and therefore a more sustainable  construction product. It had an added benefit of being well-draining  and nutrient poor which was ideal for supporting wildflower meadow  species and curbing the growth of grasses. However, it was found  that a balance was needed between enhancing biodiversity and  achieving slope stability: more grass seed needed to be applied  during later re-seeding events for the steeper gradients to help bind  the fine surface material and prevent formation of runoff gullies. 

A soil analyst explored the options for manufacturing soil using  paper production waste or reservoir silt, as a means of reducing  topsoil import costs. Detailed discussions held with the planning  officer confirmed the methods for achieving acceptable soil  depths and conditions for future planting. 

Once the waste had been reprofiled, the mineral layer was placed  and rolled sequentially onto the surface, and keyed into the  underlying natural clay. It was necessary to construct a deep in ground clay barrier along some boundaries to completely tie-in  the cap to the underlying clay and prevent water in adjoining  made ground and historic drainage systems from flowing under  the landfill.  

The selected landform removed existing very steep gradients, is  most efficient at shedding rainwater and takes the form of an  irregular dome surrounded by a ‘V’ shaped drainage ditch,  collecting in an attenuation lagoon prior to passing to foul sewer.  Residual flows of leachate are also collected at two locations and  flow passively to foul sewer. RSK supervised and validated the  restoration work which was completed in 2011/12. The Landfill  Closure Report and validation reports prepared by RSK were  referenced in an updated Environmental Permit. 

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Biodiversity Enhancement  

A Phase 1 Habitat Survey was undertaken by RSK as part of the  planning application for the redevelopment. This identified the  site to be in an ecological setting which includes areas of common  moorland to the east; Pollard Moor, Hapton Common and Bentley  Wood Green. These sites comprise a complex mosaic of habitats  including neutral grassland, acid grassland, modified bog, flushes  and scattered scrub and trees.  

The survey indicated habitats present on site to contain common  and widespread species. They were identified as being easily  replicated and of negligible nature-conservation value from a  botanical perspective. Even those existing habitats that were more  structurally diverse such as plantation, scrub, reed-swamp, and  rush pasture were described as common in the landscape, typical  of former industrial sites and ‘unexceptional’ in their extent or  diversity.  

RSK prepared the landscape design for the landfill, taking into  account the findings of the Phase 1 Habitat Survey and provided a  detailed specification for planting areas and tree and wildflower  and grass species within meadow areas, which was agreed with  Lancashire County Council taking into account the priorities of the  Lancashire Biodiversity Action Plan (BAP).  

The BAP lists several habitats to be considered in the planning  process, which was used by RSK in developing species lists.  Overall, the proposed landscaping and planting has significantly  increased the diversity of habitats and number of plant species  and overall ecological value of the site. The range of habitats  created was also designed to attract several invertebrate and  vertebrate species to the site in the medium term. 

Landscape Design  

The restoration required the removal of the existing poor-quality  trees from within the landfill area, and the planting of over 3,500  new broadleaf native tree species across both the landfill and  surrounding greenbelt area covering a total of 19,000m2. A  donation of trees was also made by Synthomer to the Parish  Council to improve existing amenity areas within the village of  Hapton.  

The three main landscape features and habitats identified in the  landscape plan were:  

Tree and Shrub Planting  

Proposed structural tree and shrub planting to screen detracting  features (including the M65 and electricity pylons) and to improve  biodiversity. 

 

Wetland Habitat  

Improvement upon existing open ditches, to include a flood balancing attenuation lagoon and widened ditches, to  complement existing wetland and moor habitats, when combined  with targeted planting, encouraging the diversity of wetland plant  species in the medium to long term. 

 

Wildflower Meadow 

Most of the landfill capping layer was seeded as a species-rich  wildflower meadow which now provides seasonal interest and  colour, as well as supporting insects and birds. 

Habitat management measures were incorporated to mitigate for the  loss of habitat due to the clearance of the site including;  

enhancement of habitats and areas of transition (including woodland  and wet woodland, ditches, reedbed, hedgerows, grasslands, ponds;  bat foraging and bird nesting habitats) 

Damaged perimeter hedgerows were replaced and the incorporation  of attenuation for rainwater runoff in the form of  

widened ditches and lagoons provided opportunity to create  1,900m2 of wetland habitat and marginal reed swamp habitat  (500m2). 

 

RSK continues to manage a landscape management contract  which has ensured the successful establishment of tree and  grass planting on both the landfill and surrounding areas (see  images).

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Enhanced planting within greenbelt land and landfill beyond

Monitoring and Aftercare 

 

Since the restoration completed in 2011, RSK has undertaken  aftercare monitoring of the landfill and its environment. RSK provides  annual reports, providing records to the EA of monitoring of  environmental media, slope stability and landform settlement. RSK is  also in the process of assisting Synthomer in securing surrender of  the Environmental Permit for the landfill.

 

 

Gleeson Redevelopment; fulfilment of long-term  planning requirements  

Investment in restoration of the landfill by the client, Synthomer  which, as well as responding to regulatory requirements, enabled the  sale and redevelopment of the adjoining former factory plot. The  area was sold in 2016 to Gleeson Homes who proposed the  construction of over 200 homes.  

The planning determination for this development included a Section  106 agreement stipulating the creation of access to the restored  landfill, so that the area could be used by the residents of the housing  development as a public open space amenity. This was agreed by  Synthomer and the EA and a licence granted to enable formation of a  series of footpaths across the landfill.  

This has taken effect in 2021, the work carefully observed by RSK to  ensure integrity of the landfill cap and monitoring infrastructure is  maintained. 

 

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Attenuation lagoon with coir netting reinforced banks (top image taken in 2011, bottom image taken in 2021)

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Access footpaths being placed by Gleeson

Conclusion


In conclusion, restoration of the former industrial site and landfill at Hapton is considered an exemplary case study of best practice in long-term planning and delivery of site restoration to achieve biodiversity enhancement and social/ amenity value.