Old Oak Common Station Work Package for Heathrow Express Depot (HEX) Demolition and Associated Ground Remediation works.
John F Hunt Regeneration (JFHR) were instructed by BBVS JV to undertake the site preparations of the last remaining strategic land parcel to facilitate the construction of the new Old Oak Common Station – the UK’s large rail hub linking HS2 with Cross Rail and the Great Western Mainline.
Scope
- Carefully managed dismantling/deconstruction of the former Heathrow Express Traincare Facility.
- Enabling works to clear the site of foundation substructures, legacy refuelling and drainage infrastructure.
- Extensive delineation investigations to target and confirm the presence or absence of ground contamination.
- Forensic excavation of grossly contaminated Made Ground and soil materials impacted with petroleum hydrocarbons and asbestos containing materials.
- Deployment of mobile plant for crushing and preparation of some 16,000m³ site won recycled aggregates.
- Establishment of an on-site Water Treatment Plant to intercept and mange perched groundwater and Non-Aqueous Phase Liquid (NAPL) / residual fuel and oil from historic rail operations.
- Bulk earthworks for a ground level reduction and delivery of temporary works to facilitate the construction of the new Great Western Mainline Station Box.
- Careful coordination and interfacing of the works with other subcontractors.
- Installation of temporary works infrastructure including haul roads and reinforced concrete aprons for wheel cleaning operations.
Deconstruction
JFHR undertook supplementary Hazardous Materials Surveys and a thorough environmental clean prior to commencement of demolition. This ensured potential risks associated with insulation materials and fire retardants were confirmed and the correct due diligence applied for selection of suitable pathways for re-use, recycling and recovery in accordance with the waste hierarchy.
An extensive environmental clean was implemented to ensure operative exposure risks to traces of asbestos from brake linings etc were minimised. The staged carefully managed approach to deconstruction enabled recycling/ recovery of:
- Circa 750 tonnes of ferrous metals
- More than 5 tonnes of non-ferrous metals
- 3,000m³ of ‘clean’ concrete to be segregated and processed as secondary aggregates (6F2) for re-use on site.
Delineation Investigations
With 100 + years of former use as railway land, including servicing and maintenance of Great Western’s High Speed Trains (HST) – a diesel powered fleet, extensive residual fuel contamination was anticipated and confirmed. Sporadic low intensity contamination by asbestos containing materials including Asbestos Insulation Board debris was also encountered found to be present.
More than 70 machine excavated trial pits formed the basis of a phased programme of detailed delineation investigation and site characterisation.
This was carefully planned, sequenced, and delivered by our team of experienced trained scientists, engineers, and asbestos trained operatives.
We also seized opportunities to gain early information of ground conditions through our proactive approach to collaborative working with other subcontractors including those installing new track bed drainage infrastructure serving the existing great western mainline.
This offered opportunities for:
- More accurate forecasting and logistics planning
- Balanced and appropriately resourced approach to implementation and delivery
- Flexible and adaptive approach to working and problem solving
- Assisting the main contractor and HS2 achieve greater sustainability targets
Bulk Excavation & Materials Management
To facilitate these works, a Water Treatment Plant was established on site incorporating Primary Settlement, Oil Water Separators and Granular Activated Carbon.
This provided capacity to manage both perched water and groundwater, to minimise and control polluting run-off during the remediation excavations and also allow the safe discharge of surface runoff to foul sewer during the works. The earthworks material balance did not offer opportunity for on-site re-use beyond recycled secondary aggregates within temporary works platforms, and haul roads for the construction work.
Where possible we always strive to embrace the waste hierarchy and avoid consigning materials to landfill. The bulk excavation works involved the management of some 7,700 m³ of hazardous soil materials. Less than 5% was directly removed to landfill with more than 95% successfully accepted for treatment at a suitably permitted hazardous waste treatment facility.
5,553m³ of non-hazardous soils were also disposed as part of the works package. A significant proportion was removed to a local permitted rail hub as a more sustainable disposal option to transport via road. A large quantity was also beneficially disposed of as part of a quarry restoration project.
Waste Minimisation and Conserving Resources
More than 17,000m³ of site won recycled aggregates were generated. Segregated bulk concrete and masonry arising from the demolition and site enabling were processed to achieve 6F2 grading requirements for re-use including the placement of an extensive protective capping layer across the earthworks formation.
In line with the WRAP Quality protocol, a diligent recorded Watching Brief was in place to ensure material feedstocks subject to initial pulverising/particle size reduction were free of visible asbestos contamination or gross petroleum hydrocarbons.
This was augmented with a robust regime of sampling, for lab based geochemical analysis (asbestos screens and sulfates) and materials classification testing.
All materials movements were fully logged and recorded by land surveyor. Those materials re-used in the reclamation of the works were subject to a robust programme of validation sampling and testing to ensure Suitable For Use status for the proposed development. Materials classification testing and end product compaction testing was completed to ensure robust engineering standards were maintained, and construction platforms conformed with engineering project requirements.
Recent technology in the form of UAVs/drone was used to record the progress of the works, provided updates on site levels, and allow the safe and accurate assessment of the volumes of material stockpiles to be completed.
In addition to serving the needs of the JFHR works package, through our flexible and collaborative approach, JFHR were able to assist the Contractor with the greater needs of the wider infrastructure construction project to be met. Accepting surplus bulk concrete from the wider site for processing under JFHR mobile plant deployment avoided as significant quantity of waste being consigned for processing off-site at an alternative suitable waste management facility.
This conferred a number of benefits to the wider project including:
- Reduced impacts on the local air quality associated with lorry movements and emissions
- Reduced congestion, nuisance risks and hazards for potentially vulnerable road users
- Reduced pressure on site resources for wheel cleaning.
The project was completed on time enabling BBVS JV to achieve a significant project milestone despite a number of logistical challenges and variations to the original forecast programme and scheduled activities.
Challenges
The most substantial challenge to the works with HS2 and BBVS would be coordination with others on such a large-scale government led contract and the intense document control required by a central government funded high profile project – we have excelled in these areas, undertaken intense training, employed specific personnel and tactics to fulfil this demanding aspect of this project.
Successes
Winning BBVS Safety Awards on two occasions in May and July 2022 – unheard of for a contractor to win two within a short period on such a large project.
