Infilling of a Mineshaft

Donor Site

The Donor Site was the former Maliphant Railway Sidings Site in Swansea. The site is being redeveloped for the new Hitachi Trains Servicing Facility (part of the electrification project for the South Wales Main Line).

The main contractor, Volker Fitzpatrick Rail, identified the need to excavate 44,000 tonnes of contaminated and uncontaminated soils from the site as part of the overall development. Volker Fitzpatrick set an environmental target to divert 90% of the material requiring offsite disposal away from landfill.

The Treatment Hub was able to accept the material following a comprehensive review of the waste assessment commissioned by Volker Fitzpatrick Rail (carried out by ESG).

The hazardous / non-hazardous material (circa 16,000 tonnes) was shipped to The Treatment Hub with most of the remaining less contaminated soils being reused as engineering backfill on site. The bulk of the material (circa 14,000 tonnes) was shipped in an eight-week window between April and June 2014. A further 2,000 tonnes were shipped in December 2014.

Receiver Site

The Receiver Site was a small residential development site in the Morriston area of Swansea. The site was located in an identified high risk area associated with historical mining activities. A site investigation undertaken by Earth Science Partnership [ESP] indicated the presence of a mine shaft within the development site – historical reports documented the presence of a 122m winding shaft which had been backfilled in the 1940’s. Further intrusive investigation by ESP indicated the presence of a shaft to a depth of 67m.

ESP undertook further surveys of the shaft and concluded:

  • The shaft diameter was typically circa 2m with local widening up to 5m
  • Groundwater was present at circa 35m below ground level
  • It was concluded that the shaft had a potential void volume of circa 200 – 500m3

The infilling of the mineshaft with suitable geotechnical materials was part of the ESP remit for the site redevelopment – these materials also needed to meet designated target levels in terms of leachability due to the presence of groundwater within the shaft.

ESP recommended utilisation of recycled material in preference to the use of imported virgin material – this was considered to be the most sustainable solution and in addition, it was difficult to obtain locally sourced virgin material. ESP therefore approached The Treatment Hub to provide suitable materials for the infilling process.

Soil Treatment

Based on the chemical and geotechnical specification for the required infill material (stipulated by ESP) and taking into account the chemical and geotechnical properties of the material received from the donor site, a treatment strategy was developed and implemented.

Circa 700 tonnes of materials received from the Maliphant Sidings Site were treated and tested to confirm compliance with the designated specification and suitability for the use intended.

Reuse of Treated Material (Recycling)

ESP produced a Material Management Plan [MMP] documenting the whole recycling / reuse process (i.e. donor – treatment – reuse). The MMP was signed off by a Qualified Person in accordance with the requirements of the CL:AIRE Code of Practice prior to the infilling works commencing.

The treated material was then reused by the appointed contractor for the infilling of the mineshaft.

Conclusions

The Treatment Hub enabled the recycling / reuse of material accepted from the donor site. The treatment / recycling process was fully compliant with the ‘End of Waste’ requirements enabling reuse of the material as a product in accordance with the designated specification as stipulated by ESP.

The recycled materials were provided at a very attractive commercial rate.

The Treatment Hub was therefore able to offer a sustainable and economic alternative to the use of virgin material.

The sustainable reuse of significant volumes / tonnages of soils resulted in Volker Fitzpatrick Rail being awarded the CIWM 2014 Award for Sustainable Construction and Demolition. The CIWM Award Press Release is shown in Figure 5 below.

ESP stated the following in relation to the use of recycled materials from The Treatment Hub:

‘Significant social, economic and environmental benefits had been realised through the importation, e.g. reduced use of virgin aggregates, carbon footprint and creating affordable homes in Morriston’.

 

Case Study Details

mineshaft-infilled

Donor Site

Maliphant Sidings Site, Swansea

Receiver Site

Residential Development Morriston, Swansea

Quantity Recycled

700 tonnes

Environmental Consultants

Earth Science Partnership

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The Treatment Hub

Advanced Material Treatment, Remediation And Recycling. The Treatment Hub is a landfill Tax Exempt Hazardous Soil Recycling Treatment Facility based in South Wales.

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