New Low Level Waste Facility

CEEQUAL Excellent (84.1%) – Whole Project Award
Version 4, May 2018 | Dounreay, Caithness, UK

Client: Dounreay Site Restoration Ltd
Designer: Mott MacDonald
Contractor: Graham Construction

Assessors: Lianne Rafferty (Graham Construction)

 

Near Completion

Project Summary

The project involved the Design and Build of two sub-surface vaults for the disposal of solid low-level radioactive waste from the Dounreay facility. This development is an essential part of the infrastructure needed to complete the decommissioning and closure of the former nuclear research site.

Construction activities conducted on the project included;

  • Groundwork preparation and deep excavation work in bed rock
  • Access roads; street lighting; perimeter securing fencing; footpaths; landscaping
  • New concrete and HRA pavements
  • Structural Concrete
  • Power supplies (substation including HV cable from local infrastructure), LV Power Distribution, lighting

Project Management

The Project Team had a wealth of experience and were able to deliver the project in a safe, efficient and environmentally friendly manner. The CEEQUAL assessment recognised the expertise of the site team and the comprehensive procedures in place with this section scoring 88% during the assessment process.

An Environmental Impact Assessment (EIA) was undertaken for the project which assessed the potential risks on the surrounding environment and detailed the control/mitigation required during design, construction and operation to eliminate and minimise adverse environmental impacts. The maintenance of the comprehensive CEMP (Construction Environmental Management Plan) and a suite of supporting plans, including Site Waste Management Plan, helped to ensure the highest possible standards were maintained. To complement the experienced site team, specialists from the SHE Department and Community Liaison Officer worked closely with the site to maximise compliance and implement best practice whenever possible. Maintaining positive working relations with the various stakeholder was another important aspect of the overall project management.

The project involved mass excavation of material in order to construct the sub surface vaults. This would require the excavation of 31,414m3 of topsoil, 51073m3 of subsoil and 278,212m3 of rock. Pecking was originally planned for the breaking out of the rock; however, the Project Team conducted a detailed study into the use of blasting. The study demonstrated that blasting would be acceptable under stringent controls. This would offer several benefits to the project including cost and programme surety. Efficient programme delivery minimised the longevity of any nuisance on adjacent properties and neighbours.

Land Use

During construction, GRAHAM ensured that land use was effective and that temporary greenfield land utilised during construction was not adversely impacted. Fencing was erected around areas that did not need to be traversed, footpaths were created to direct operatives and site visitors, clear demarcation of site compound and material storage areas and haul roads were created for all vehicle movements on-site. These measures ensured that a significant proportion of the site remained free from interference during construction of the vaults.

Conservation of soils and on-site mineral resources formed part of the employer’s requirements for the contract. During construction, topsoil and subsoil was stripped and stored – being re-used within the soft landscaped areas. Excavated rock was assessed as being a fundamental requirement for the proposed development as this will be used as the engineered cap once vaults are full. Rock material was stored on-site, soiled and grassed to ensure it reflected the surrounding landscape, ready for re-use upon closure of the vaults.

Ecology and Biodiversity

In the years preceding the start of construction works on the project, kestrels occupied an area adjacent to the site, suitable for nesting. During the construction works, site staff were excited to see the return of the nesting kestrels in the area.

The return of the nesting kestrels was demonstrative of the conscientious manner in which works were carried out so the breeding pair were not deterred and remained on the site throughout the construction activities.

A series of Ecological surveys were undertaken prior, during and after construction works on-site. A botanical survey of the site identified Scottish primrose (primula scotica) present on-site. This flowering plant species is endemic to the north coast of Scotland therefore plans were adopted to translocate this species out-with the site footprint in order to conserve the Scottish primrose. Prior to translocating, 2257 plants were identified. Translocation was undertaken in July 2011, with 3817 plants translocated. The 4th monitoring visit was undertaken in June 2012 on the success of this translocation, finding that the majority of plants to be very healthy. A total of 4872 plants were observed.

Ecological value of the site was also enhanced during the project. This was in the form of the Geosphere Enhancement, which involved a layer of site won excavated material being placed across the existing ground surface between the vaults and the coast, to ensure the water table lies well below the new ground surface after closure of the vaults. The geosphere was seeded with a mix comprising predominantly of native species, which are established in the area and adapted to local conditions. The mix was suggested and obtained from local agricultural contractor as being a mix that would be similar to the local farmland and was sowed locally.

Water resources and the water environment

Silt prevention measures were adopted at the Low Level Waste Facility to prevent the movement of silty water out-with the site boundary and discharging into the North Sea. Four settlement ponds in total were constructed. The settlement ponds were designed to ensure that all open drains/ditches within the site boundary ran into these ponds where the silt was allowed to settle at the base of the pond. As the water level rises in the settlement pond, it leaves via the outlet that flows towards the northern boundary and out to the north site over the coastal cliffs.

The design philosophy for the drainage system implemented the commitments of the Environmental Statement as detailed in the Drainage Design Justification Report which comprised the following:

• Gravity flow will be used wherever possible, taking advantage of the natural slope of the site.
• Re-create natural drainage patterns using a SUDs approach, dispersing flows and ensuring velocities are reduced to avoid erosion and promote sediment deposition through the site.
• Easily maintainable and inspectable open channels will be used and proprietary systems will be avoided where possible.
• Design drainage elements in the vicinity of the vaults for a 1% probability storm event and drainage elements downstream of the vaults for a 3.33% probability storm event.

In order to reduce water consumption during the construction phase water was stored in a water cube for cleaning tools throughout the scheme. This ensured water was reused and mitigated the need to use fresh water.

Energy and Carbon

A study into ventilation options for Dounreay Low Level Waste (LLW) store was carried out by the Designer as there was a strong desire to naturally ventilate the structure in order to reduce operational maintenance and services requirements.

The study was principally concerned with natural ventilation therefore reducing the energy consumption and carbon emissions of the scheme during operation.
The location of the underground vaults was reviewed and the selected option resulted in the vaults being located in closer proximity to the supporting grouting facility therefore reducing energy consumption through transport energy consumption in operation.

Rock blasting (as descried above) was the chosen option for rock removal. This had added benefits; shorter timescales for excavation and a reduction in the use of rock-breaking equipment. This method ultimately would result in lower energy consumption and was the preferred methodology that was utilised.

A renewable energy source, in the form of solar powered panels were utilised during at the water monitoring boreholes installed across the site – powering the water pumps within.

Material Use

100% of excavated material was retained on site for reuse. Reuse of material was carried out in two ways:

1) Immediate reuse of the material to form the ‘Geosphere Enhancement’ to the north of the site and other smaller aspects of the roads/drainage as part of the permanent works/permanent site formation.

2) Storage of future re-use of the material in the PPC Permit area to the east of the site. Material was stored for eventual re-use in the backfilling, landscaping and finishing of the overall Low-Level Waste Facility site.

Transport

Creation of the Geosphere Enhancement area, in order to reduce the likelihood of artesian groundwater pressures developing on the seaward side of the vault, was constructed using site won material (178,322m3 of rock, 13,601m3 of subsoil and 10440m3 of topsoil). This significantly mitigated the transport impacts in removal of this material from site. ( Refer back to energy/carbon).

Effects on Neighbours

The site was registered with the Considerate Constructors Scheme – in order to ensure the project considered those directly involved on the project, the surrounding environment and the local community. The site team received a Gold Award from CCS, who recognised the works and the efforts made by the team …

With potential dust and noise closely monitored and controlled, and excellent level of safety and site cleanliness, this challenging project created an excellent overall impression of the industry at work

Concrete deliveries comprised larger loads ranging from 8m3 to 11m3 as opposed to the normal lower loads of 6m3 to reduce number of deliveries and subsequent traffic movements.

Relations with the Local Community and other Stakeholders

The Client conducted extensive community engagement during the planning, design and construction of the LLWF. Both the Client and Principal Contractor appointed Communications Manager and Stakeholder Manager respectively to establish and prepare a programme of public engagement and consultation activities to ensure these were implemented throughout the initial design stage and detailed design.

Continuing community relations programme covering all relevant stages of the project has been implemented. Activities undertaken as part of the programme include:

• Resident newsletters
• Project website
• Leaflet drops
• Briefing sessions

Community benefits formed part of the overall GRAHAM management of the project. We got involved with the local community by:

• Helping with grass cutting for the bumble Bee Conservation Trust.
• 9 site volunteers helped extend the garden and play area for Castledown Playgroup and Toddlers
• Donating £500 to boost fund for Thurso youth club
• STEM ‘speed dating’ event at Wick College
• Quarterly meeting with local residents.

Other benefits of using CEEQUAL

A study into the impact of rock blasting found that this would be acceptable for rock removal. This reduced the requirement for pecking out of rock and reduced programme time – therefore providing cost benefits to the project.

The reuse of excavated rock and soils direct on the project footprint removed the requirement for off-site disposal. This resulted in cost saving relating to transport of materials and any associated disposal charges.

Further Information

What were the main challenges for the project and how were these overcome?

The location of the vaults had to be in close proximity to the Dounreay Site – therefore limitations on site placement were present. Ecological and botanical surveys conducted prior to construction found Scottish primrose (primula scotica) – a flowering plant species found only in parts of the North East of Scotland.

To avoid a negative impact on this species, a translocation programme was initiated prior to construction. A total of 2257 Scottish primrose were translocated out-with the site footprint. Monitoring of the translocation 1 year after translocation found 4872 Scottish primrose in the translocation area.

The sub-surface vaults would require substantial excavation works of top soil, sub-soil and rock. Excavation of rock through use of a pecker was assessed to be time consuming and cost ineffective. A study into blasting of the rock was undertaken to assess suitability. This found with the appropriate control blasting would provide added benefits to the project including cost and time saving along with reduced impacts on the environment in relation to energy usage associated with prolonged use of rock pecker.

What were the drivers and perceived benefits for undertaking a CEEQUAL assessment on this project?

The drivers of undertaking a CEEQUAL Assessment for the project was to ensure the successful delivery of essential infrastructure to progress the decommissioning of the Dounreay site; whilst protecting the surrounding environment, reducing the strain on natural resources and helping build a strong community network.

How did the use of CEEQUAL influence the outcomes of the project? What was done differently because of the CEEQUAL process?

The Project Team found the CEEQUAL process to be largely very positive. The requirements outlined within the manual caused staff at all levels to consider their own responsibilities and work practices in an alternative, and generally more sustainable manner- this cascaded down from the Client, Designer and Contractor teams.

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