HIGH SPEED 2 (HS2) ENABLING WORKS CONTRACT – CURZON STREET STATION GROUND REMEDIATION
Shortlisted for Brownfield Awards Category 1: Best Project Preparatory Work
High Speed 2 (HS2) Enabling Works Contract - Curzon Street Station Ground Remediation
The New Curzon Street Station is located in the heart of Birmingham’s industrial past with a plethora of former land uses including railway termini, a railway goods station, iron foundry, burial ground and a locomotive engine shed roundhouse possibly the first of its kind in the world. WSP helped balance the needs of the project and the views and requirements of numerous stakeholders against the sensitive historic environment requirements and produced a Remediation Strategy which has provided an integrated approach to development of the site. The preparatory work completed by WSP has allowed Laing O’Rourke and J. Murphey & Sons Ltd Joint Venture (LM JV) a seamless transition into site works and allowed re-use of approximately 200,000m3 of Made Ground while meeting strict programme requirements set by High Speed 2 (HS2). The robust strategy provided a sustainable remediation framework for re-use and recovery of materials with flexibility to deal with unexpected finds such as five previously undiscovered Underground Fuel Storage Tanks (USTs) and a network of asbestos cement drainage pipes.
WSP was appointed by LM JV to develop a ground remediation strategy for the New HS2 Curzon Street Station, the first brand new intercity terminus station to be built in Britain since the 19th century.
HS2 and LM JV are committed to managing their environmental impact and providing a sustainable and economic remediation design was paramount from the outset. Works were commissioned under the Enabling Works Contract (EWC) which has the ultimate aim of de-risking the site in advance of handover to the Main Works stations and civils contractors. Providing a robust and agreed Remediation Strategy and Materials Management Plan (MMP) within the programme was crucial to delivering the ground remediation works which were largely completed over a 16 month period re-using approximately 200,000m3 of Made Ground.
Curzon Street Station is located to the eastern side of Birmingham City Centre and covers an area of approximately 10 hectares, comprising derelict land and areas of public open space / car parking. The site has a variety of historical land uses including: historical railway termini; Park Street Gardens burial ground; underground bonded stores; basements; tunnels; culverts and one of the world’s first locomotive engine shed roundhouses from the 1800’s.
Developing the Ground Investigation Strategy
WSP undertook a detailed Desk Study and a Gap Analysis including review of existing geotechnical Ground Investigation (GI) data collected by HS2 in 2016. Scoping of an additional targeted Phase 2 GI focused on Principal Areas of Concern (PAoC) largely driven by historical land use activities and a preliminary data review. Due to the rich industrial heritage of the site a variety of publicly available information sources were utilised to develop the preliminary Conceptual Site Model (CSM) including Goad Fire Insurance Plans, historical aerial photography, railway archive material and church records. WSP were keen to utilise Geographic Information System (GIS) layers hosted by HS2 to aid interpretation of historical land uses allowing production of drawings including multiple historical Ordnance Survey layers over which publicly available historical station layouts were placed (see Figure 1).
Figure 1 – Example site plan utilising Client hosted historical mapping and publicly available historical station layouts to aid conceptualisation
A Ground Investigation Strategy and Ground Investigation Specification were prepared (in accordance with BS 5930:2015+A1:2020) providing a rationale for proposed exploratory holes and associated testing which facilitated tender of the Ground Investigation to a number of Contractors and help achieve value for money for the Client.
Following delivery of the GI, WSP prepared an Interpretative Land Quality Assessment Report and Detailed Quantitative Risk Assessment (DQRA) which utilised and compiled existing 2016 GI data and contemporary data into a single ground model and AGS database. This ensured all data was utilised and assessed as one, a vital requirement set by HS2 and LM JV to ensure the benefit of early geotechnical information was utilised. Again, GIS software was utilised to aid presentation and understanding of results which was particularly important given the number of stakeholders reviewing and approving the reports. Development of the ground model and various geological contour plots (see Figure 2) and geological cross-sections ultimately helped LM JV estimate and budget soil re-use at the site and assisted the tender process greatly.
Figure 2 – Made Ground thickness contour plot utilising historical and contemporary data points
The refined Conceptual Site Model (CSM) is included as Figure 3 and details various contaminative sources including potential Underground Storage Tanks (USTs), an historical underground coke vault and complex geology in proximity to the Birmingham Fault and Digbeth Branch Canal in the east.
During production of the DQRA, detailed liaison with the various Enabling Works design teams, Station Designers and Main Works Designers was required to generate realistic input parameters with varying station finish levels and varying rates of infiltration for different construction periods taken into account. The detailed desk based research, GI and presentation of interpretative results allowed for approval of the DQRA by relevant stakeholders (including the Environment Agency) to enable preparation of the Remediation Options Appraisal (ROA) and Remediation Strategy / Remediation Specification (in accordance with Land Contamination Risk Management).
Figure 3 – Refined Conceptual Site Model (CSM) drawing
Developing the Remediation Approach
The ROA was prepared in accordance with the SuRF UK framework with sustainability key to ensuring the developed Remediation Strategy for the site was robust and achieved an appropriate balance between the benefits of the remediation programme and the effects of undertaking the works.
Pivotal to the process was stakeholder consultation and this was achieved through multi-stakeholder workshops. Given the large number of stakeholder interests within HS2, enabling works, main works and station design teams and the complex heritage and legal compliance requirements associated with the hybrid bill, workshops contained over 40 interested participants and a structured approach was required to ensure that all views and opinions were voiced and acknowledged as part of the development of the remediation options.
As part of the remediation workshops, remediation scenarios were “played out” to develop a consensus led “best for project” approach and this enabled the development of 6 agreed remediation objectives that could be adopted for the Remediation Strategy.
As part of this process, the remediation objectives were screened against a number of project specific drivers (see Figure 4) to act as a remediation decision record and document and record how effective the remediation objective would be in delivering against a number of project factors.
Thank you very much for the workshop this morning, which I think marks a great step forward in clarifying “best for project” remediation scope for Birmingham Curzon Street. I thought the meeting was extremely well structured and presented, and Richard did a great job of controlling the large number of interested and enthusiastic stakeholders in the room!
Well done, and my thanks again……
Verity Doust | Project Manager, Sector N4, Area North Stations | Phase 1 Directorate | HS2 Ltd
Figure 4 – Remediation Objectives Assessment of Benefits undertaken during the ROA
Scope of Remediation and Advanced Validation
Whilst potential contamination hotspots and unexpected issues were considered likely, the site characterisation had established that the site was generally suitable for use and the primary focus of the remediation work would be to enable the site, removing obstructions and impediments to the follow on main line and station construction activities.
To accelerate the site turnover and limit double handling wherever possible, WSP completed statistical analysis of the site investigation data and presented and agreed with the project stakeholders an advance validation investigation and sampling strategy designed to remove the requirement for stockpiling and limit testing of soils during the site turnover while facilitating a watching brief and discovery approach to managing unexpected and/or significant contamination delivering significant programme (3 to 4 months of earthworks activities) and site operational efficiencies.
The developed Remediation Strategy and Remediation Specification allowed a smooth transition into delivering the site works and re-using significant quantities of Made Ground with realised sustainable and economic benefit for the project. Providing clear procedures to follow in the event of unexpected contaminative sources being identified benefitted the programme greatly as a total of seven USTs were identified during the works (only two USTs were anticipated) with LM JV and their Contractors following the assessment and validation process to facilitate removal of the tanks and associated pipework and ensure no unacceptable risks were posed during and post the works.
Provision of a CAR 2012 (and applicable parts of CAR SOIL and CIRIA C765) compliant Asbestos Management Plan (AMP), CL:AIRE DoWCoP declared MMP and clear agreed site-specific assessment criteria by WSP prior to the remediation commencing facilitated re-use of Made Ground containing asbestos fibres and provided a framework to follow in the event of bulk asbestos being identified. Such an instance arose whereby an asbestos cement drainage network was removed without delay from beneath a former distribution warehouse on the eastern half of the site.
Figure 5 – Exhumations being undertaken at Park Street burial ground
Historic Environment Interface
The New Curzon Street station is located at the heart of Birmingham’s Industrial past as signified by incorporation of the existing historic Old Curzon Street building with links into the New station’s eastern concourse. To prepare for remediation, desk based research into the history of the area and interface with the WSP and LM JV Historic Environment teams was paramount to understand the potential for archaeological remains to exist beneath the site. The desk based research identified a complex narrative of a previously densely populated area that has been adapted and altered through time, to meet with the changes in industry.
One of the biggest challenges was the excavation of the Park Street burial ground (see Figure 5), located in the footprint of the new station. The early investigation and planning of the works consisted of a geophysical survey, and trial holes, feeding into the design of the larger excavation of the burial ground, which took place over 12 months, and identified up to 10,000 individuals.
As part of the historic environment research, and early trial trench investigations, archaeological remains relating to the previous Station were identified within the footprint of the new station, the early investigations works were fed into the final design for archaeological mitigation. The mitigation led to the identification of structures relating to the Grand Junction Railway and the London to Birmingham Railway, of most significance was the identification of Curzon Roundhouse (a locomotive engine shed, turntable and coke vault) (see Figure 6), which is likely to be the first of its kind in the world. Due to the significance of the Roundhouse and collaboration between LM JV and WSP, the ability to adapt the design of the remediation works allowed for the preservation in-situ of the Roundhouse (including significant consultation with Historic England and following ‘Preserving Archaeological Remains, Appendix 5 – Materials for Use in the Reburial of Sites), a feature that highlights the impact of industrial revolution on Birmingham.
Figure 6 – Curzon Roundhouse archaeological remains which have now been preserved in-situ
Early preparatory work undertaken by WSP and extensive engagement with numerous project stakeholders provided a sustainable remediation framework for the completion of the remediation and enabling earthworks at the New Curzon Street Station. LM JV were able to transition to site works smoothly and achieve strict programme deadlines for the new rail scheme. WSP was able to:
Review a wide range of desk based information and compile historical information into engaging and easy to understand drawings and develop a targeted GI Strategy;
Incorporate existing GI information into the ground model and produce a comprehensive refined CSM;
Through stakeholder engagement achieve the required approvals and develop an integrated strategy which helped prepare the site for follow-on works with clear Verification requirements; and,
Meet Historic Environment requirements and help discover and record the impact of the industrial revolution on Birmingham and the West Midlands.