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Project Wellesley, Worthy Down by Keltbray and SKANSKA

Shortlisted for Brownfield Awards Category 8 - Best Use of Materials

Introduction

Keltbray and SKANSKA have completed the remedial works at the Worthy Down Camp (5km north of Winchester, Hampshire), consisting of approximately 52 hectares (ha) of land occupied by an existing MOD facility and an area of agricultural land adjacent to the existing residential dwellings in west of the main camp site. The works formed part of Project Wellesley, the redevelopment of land and the existing military training camp (Worthy Down Camp).

Image 1 – Worthy Down Camp (2017) 

SKANSKA was awarded the contract by the Defence Infrastructure Organisation (DIO) to redevelop the Worthy Down site in May 2014. Keltbray was brought onboard in 2015 as the specialist remediation contractor to develop Remediation Risk Assessments and the Plan of Works to deliver the agreed strategy. Ground Investigation commissioned as part of the sites re-development of the Worthy Down Barracks site identified wide spread Asbestos Containing Materials (ACM). As well as free asbestos fibres in excess of acceptable human health concentrations were identified in the made ground and shallow soils across the site. Hotspots associated with specific point sources, such as underground storage tanks, were also identified with elevated concentrations (above relevant screening criteria) of Poly Aromatic Hydrocarbons (PAHs). Additionally, Total Petroleum Hydrocarbons (TPHs) and Lead were identified and required remedial measures to mitigate the ongoing and future risks from these contaminants. 

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Image 2 – Typical Made Ground Encountered at Worthy Down Camp

The overall goal of the remediation was to break the Pollutant Linkages (PLs) through the widespread excavation of the impacted made ground, which in turn allowed for the installation of a certified break / engineered cover system to be installed within the construction makeup. Earthworks levels essential in facilitating onward redevelopment of the site were used to guide excavation depth, with reference to the minimum thickness of engineered cover system that was required.

 

In addition to the engineered cover system, remediation was required within ‘service corridors’ to allow 3rd party contractors to install services and general utilities, without the risk of encountering potential asbestos containing materials. 

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Image 3 – Excavation Works Under Controlled Conditions At Worthy Down Camp

The Worthy Down ‘Project Wellesley’ Scheme represents the largest in a number of enabling and remediation schemes currently and historically delivered by Keltbray (as a specialist Sub-Contractor) and SKANSKA (as Principle Contractor). 

 

The waste hierarchy is embedded within both Keltbray and SKANSKA’S management procedures and policies, not just through simple procedures such as ordering the correct quantity of products needed, but through ensuring that the waste procedures and targets in the plan are adhered to and that all personnel are aware of their duty of care and responsibilities, and ‘buy into’ the sustainable construction ethos. 

 

The aspiration for all projects we work on together is to deliver appropriate and sustainable reuse of materials, which we as a joint Project Team (Keltbray and SKANSKA) feel we have achieved on Project Wellesley. Across Project Wellesley, material reuse, recycling and recovery was and is still maximised where reasonably practicable with our project targeting >99% recycling rates, and aiming for zero waste to landfill. This was reinforced to the site teams through the inclusion of waste management and the waste hierarchy in site inductions and Toolbox Talks, ensuring opportunities to eliminate waste onsite were sought throughout the project by everyone involved, not just the management team. 

 

Keltbray’s involvement in the scheme has lasted for 5 years, after Keltbray was awarded the first phase of the remedial works package - ‘Tranche 1’. Keltbray remained onsite until February 2021 following the completion of Tranches 2 (commencing 2017) and 3 (commencing 2019) of the bulk remedial works, and also to manage the material movements and re-use of materials. This prolonged presence and relationship (between Keltbray and SKANSKA) has enabled the sustainable re-use of vast quantities of suitable materials. 

Remediation & Materials Management 


Since 2016 three Definition of Waste Code of Practice (DoWCoP) declarations were made across the project. Two of the declarations were for the re-use of material on the site of origin and associated to the “main earthworks and remediation”, as design changes and an extension to Keltbray’s contracted works saw the predicted volumes increase by greater than 10%, therefore requiring a new declaration for the volume increase. At the completion of the works a total of approximately 335,000m3 of material was excavated and re-used across the remediation element of the project.

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Image 4 – Placement Of Treated Made Ground At Worthy Down Camp

Included within the 335,000m3 was the demolition arisings, existing hard standing, obstruction and oversized aggregates from the material processing, which was further processed under a Quality Protocol (WRAP - End of waste criteria for the production of aggregates from inert wastes) and re-used by Keltbray and other contractors across Project Wellesley.  Approximately 75,000m3 of site won material was processed under a WRAP protocol and reused across the Worthy Down Development. With the excess quality protocol material (approximately 4,600m3) moved off-site by SKANSKA to support other local developments. 

 

Of the soils excavated and processed onsite, approximately 1,000m3 (93 No. loads) was not suitable for re-use and was sent offsite for recovery at suitably licensed facilities (where possible recovery facility were preferentially chosen). This equates to the re-use of 99.7% of all soils and aggregates excavated as part of the remedial and enabling works. With respect to the wider demolition works <10% of demolition arisings were sent for disposal at a suitably licensed landfill. 

 

Of the waste generated by Keltbray activities, only asbestos fragment and insulation were sent for disposal at suitably licensed Landfill facilities. 

 

The project team constantly looked at ways to increase the sustainability of the project, this resulted in the third DoWCoP (‘Direct Transfer’) declaration after a local source of suitable topsoil was identified, allowing the import of approximately 3,500m3 of suitable topsoil, material which would have otherwise been imported from a virgin source.   

 

To reduce the requirement for materials import and to maximise materials reuse in the Parade Square (where a higher geotechnical performance and reduction in frost susceptibility of materials was required). Keltbray successfully completed a number of stabilisation and compaction trials of the site-won remediated made ground with different blends of lime and cement. The results from the trials identified two mix designs for the lower and upper layers of the construction which far exceeded the performance requirement set out in the design documentation, ultimately saving a further 3,000m3 from being sent off site and the same volume of aggregate from being imported.

Image 5 – Aerial Image Of The Main Materials Management Area At Worthy Down Camp

Closing Statement 

The overall volume of waste generated through out construction phase was limited to just below 5.5t/100 m2, through the conscious management of waste and material. This is a great achievement that would receive 2 credits in Waste 01 of BREEAM, historically a difficult benchmark to meet. This was achieved by developing and reinforcing a culture of focusing on the elimination, reuse and the recycling of waste from design stage through to construction stage of the project.

 

The project team’s commitment from the outset of the project to retain and re-use as much suitable material onsite as possible had a hugely positive impact on both the project but also the local community. By reusing 335,000m3 through thorough material segregation, characterisation and treatment, an estimated 60,000 lorry movements were saved, which equates to an estimated reduction of 14,880 tonnes in Carbon Dioxide emissions (calculated through SMARTWaste). Not to mention the lower impact on the local village of Worthy Down on the outskirts of the camp. 

 

In addition to the environmental benefits outlined in this entry, it is estimated that the re-use of material reduced the cost of the development and to the DIO by approximately £30,000,000.