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Former Bowling Terminal, West Dunbartonshire by DEME
Shortlisted for Best Project Preparatory Work
Summary
Typically, preparatory work relates to site investigation, risk assessment and agreement of the Remediation Strategy. However, as demonstrated by this project, to ensure effective delivery “preparatory work” should also extend to facilitate proactive stakeholder engagement, early contractor involvement, change management and an agreed pathway to enable ultimate project closure and sign-off.
Introduction
The former Bowling Terminal comprises an area of 41ha located in West Dunbartonshire on the north bank of the Firth of Clyde, 13 miles northwest of Glasgow. Developed largely on reclaimed mudflats, employing materials dredged from the River Clyde, it functioned as a bulk fuel terminal from the late 1920s to the mid 1990s. The facility was initially operated by British Mexican (Figure 1) before becoming part of ESSO in the 1930s. The eastern section of the site was subject to remediation in 2012-2014. The remaining 35ha forms the subject of this review.
Figure 1 Early Site Development (1927)
Post site closure and decommissioning, numerous phases of intrusive investigation (over 1,200 exploratory locations) were undertaken by multiple consultancies, most latterly by WSP and its legacy predecessors. Significant impact from a wide range of hydrocarbons to both soil and groundwater was identified, reflective of the Site’s legacy as a bulk fuel facility, with asbestos fibres present within demolition rubble in near surface materials. WSP was retained by ESSO to develop a Remediation Options Appraisal, undertake Detailed Risk Assessment to facilitate Regulatory agreement of a suitable Remediation Strategy, and to produce a scope of works for the Remediation contractor to subsequentlydeliver.
Regulatory Involvement
Recognising the value of early Regulatory involvement, the project team undertook an initial presentation to the Regulators (West Dunbartonshire Council (WDC) Contaminated Land Officer (CLO) and Scottish Environment Protection Agency (SEPA)). In addition to setting out the high level aims of the project and a programme for key deliverables, the meeting enabled face to face introductions and an open forum for raising concerns and discussion of Regulator expectations. The strategy presented focussed on the removal of identified hydrocarbon impact within the unsaturated and smear zones, where most source material was located. It was agreed to maintain periodic meetings to facilitate technical review and development/agreement of the Remediation Strategy.
Derivation of site criteria was achieved through completion of Human Health and Water Environment Detailed Quantitative Risk Assessments (DQRAs), allied to technical presentations to the Regulators. A sustainability workshop, attended by both Regulatory parties, was also held. The workshop sought to align the project with sustainable development commitments set out in Scottish national and local policy, with consideration of indicators derived by SuRF-UK to consider Social, Economic and Environmental Sustainability. The primary driver was risk to the water environment via dissolved phase, mobile free phase, and the entry of hazardous substances to groundwater. The open forum permitted the Regulators the opportunity to challenge whilst allowing the client team to provide justification and supporting evidence. Agreement was reached on a site excavation validation criteria, of 9,600mg/kg total petroleum hydrocarbons (TPH), to be protective of risks to surface water from dissolved phase and potentially mobile light non aqueous phase liquid (LNAPL). In addition, a “visual” assessment was agreed to mitigate risk from potentially mobile LNAPL which could impact the Clyde, whereby soils deemed to contain LNAPL would be consigned to soil treatment. A 4,000mg/kg TPH re-use criteria for treated materials, based on the capability of thermal treatment, was also adopted, in addition to human health criteria, based on a commercial redevelopment scenario.
The initially agreed Remediation Strategy identified areas requiring bulk excavation (218,000m3) and proposed thermal treatment of circa 50,000m3 soils, with LNAPL groundwater impact to be addressed by recovery from open excavations. During discussions, the Regulators expressed concern that, whilst an excavation could meet site excavation validation criteria, residual impact may extend beyond the excavation extents. Agreement was reached that a series of verification boreholes would be installed 8m from the excavation base at 40 metre intervals, with each borehole subject to soil sampling, with associated chemical analysis, and subsequent monitoring to further verify the absence of LNAPL. Such collaboration avoided the need for extensive correspondence and streamlined the agreement process, negating the need for protracted document revisions. Murray Dobson (SEPA) summarised the benefits of early and continued Regulator involvement, stating:
“The early and regular open engagement with regulators enabled all parties to positively influence the preparatory works including the development of the conceptual site model, risk assessment, remediation objectives and strategy addressing risks to the water environment. This included early agreement of verification and validation procedures to enable the sustainable re-use of soils as the project progressed. We were also able to anticipate potential regulatory authorisations for the site operations themselves and engage on these proactively with WSP and contractors. Agreeing to continue this engagement through the remediation was a key aspect of the preparatory works.”
Early Contractor Involvement
Following contractor selection, DEME was retained under an early contractor involvement (ECI) agreement. The ECI process allowed the early onboarding of the contractor onto the project team, enabling them to; become aligned to the client objectives; understand the requirements of the Remediation Strategy and Scope of Works; and, to engage with the Regulators ahead of works commencement. As part of the ECI phase, DEME proposed an alternative to visual observations due to the inherent subjectivity of such procedures. DEME proposed assessment of LNAPL mobility using the DEME on-site lab to permit a quantitative assessment, with subjectivity removed. This bespoke approach, illustrated in Figure 2, involved the mixing of a soil sample with water and, following a period of agitation, subsequent centrifuging to separate LNAPL enabling its measurement within the test tube.
Figure 2 DEME Draft LNAPL Mobility Field Test Protocol
The Regulators were receptive to the concept of on-site testing and, throughout the ECI period, DEME undertook site trials to demonstrate its reliability and replicability. A test tube LNAPL thickness of >1mm was deemed to represent a “fail” and, it was proposed that where stockpiles of excavated materials recorded concentrations of <9,600mg/kg but more than >5,000mg/kg TPH, these soils would be subject to the LNAPL test. This approach offered a quantitative assessment, eliminating subjective observation and, by testing all stockpiles recording concentrations >5,000mg/kg TPH, represented a robust approach to the risk of potential LNAPL generation from soils passing the site excavation criteria. The test also allayed concerns over “non visible impact”. During historical operations, the site also handled and stored white oils. Where site soils were found to be impacted with such hydrocarbons, the characteristic black hydrocarbon staining was absent, however, as shown in Figure 3, not all visually unimpacted soils are “clean”.
Figure 3 Clean or Contaminated
DEME also challenged the use of thermal treatment and proposed soil washing as an alternative. Their experience suggested that soil washing requires a lower energy input than thermal treatment i.e., fuel equivalent of 4-10 litres/per tonne treated compared to 60-110 litres/tonne treated for thermal. To further validate this proposal DEME undertook additional site investigation to supplement existing data and to verify the proportions of granular and cohesive materials. This work identified a 60:40 split between granular and cohesive materials, with TPH impact predominantly associated with granular soils (with less than 25% fines) and concluded that the impacted materials were suited to soil washing. Whilst through the generation of filter cake some off-site
disposal would be required, DEME demonstrated significant benefits from the use of soil washing, noting that the disposal (haulage) impact would be outweighed by the significant difference in energy consumption. Following presentations to the project team and Regulators, an “in-principle” agreement was reached, with a reduced treatment target of 3,000mg/kg TPH adopted. The revisions were submitted within a bridging document and once agreed, a revised strategy was issued and formally accepted by the Regulators. The ECI stage was critical in the success of the project by enabling the contractor to; propose and agree value engineering (thermal to soil washing); undertake site-based trials to validate proposed on-site testing methods; and to propose and agree strategy/scope changes.
Following site commencement (May 2021), Regulatory meetings have been maintained, initially on alternate months during site establishment phase before becoming monthly with commencement of remediation works. The meetings have enabled Regulators to stay appraised of project progress, and for Site challenges and proposed variations to the strategy to be openly discussed and, through post meeting site walkovers, viewed at first hand. In addition to the scheduled meetings, an “open house” approach is in place regarding site visits, such that regulators may call in, at any time, to view works and progress.
Sustainability
In addition to early consideration during development of the Remediation Strategy, DEME has also sought to ingrain sustainable practices into the project. A case study, produced for the SocEnv Soils and Stones project, found that the use of on-site treatment saved the equivalent of 6,000 truck journeys transporting materials off-site for disposal or treatment. A treatment efficiency of >90% has permitted reuse of 77% of the materials treated. The project’s sustainability performance is to be verified by BREEAM.
Figure 4 Site Layout Illustrating Active Remediation Areas
Project Closure
The monthly meetings have provided a forum for discussion on the format and contents of Verification reports, with a focus on avoiding duplication and, with over 5,000 soil samples collected and 20,000 on-site tests undertaken, the need for clear presentation of data. With agreement of all parties reached on the format and provision of data, draft reports have been submitted as areas are completed, the intention being to provide succinct documents with a consistent format that minimise review time. As site works complete and the project moves into the verification phase the benefits of an agreed reporting format, allied to involved Regulators who have witnessed project progression, will facilitate prompt review and project closure.
Conclusions
The value of early contractor involvement should not be underestimated and represents essential “preparatory work.” The ECI phase allowed the contractor to become familiar with the requirements of both the contract and remediation strategy, as well as client objectives and client mandated safety systems. Furthermore, it allowed them to close out or limit perceived risk items and, through application of specialist skills and knowledge, to propose and justify change to the strategy and reach agreement with project stakeholders. By introducing regulators and contractors at an early stage, an open dialogue was enabled, where all parties could raise issues/concerns and answer questions directly, enabling prompt resolution.
The open and early engagement with Regulators provided a forum for robust discussion and, through a collaborative approach, ultimate agreement of a suitable remediation strategy. By maintaining such collaboration throughout the project, Regulators have been able to appraise change proposals and provide prompt response, typically in “real time” negating extensive correspondence and avoiding any requirement to unpick verification reports to determine digression from the agreed strategy. Such inclusion has allowed the Regulators to witness the project from the conceptual stage, through remediation implementation and into the verification phase. This process has enabled Regulators to be informed and to participate in a collaborative environment, acting as active empowered stakeholders in the project, rather than passive participants with little project visibility between acceptance of a remediation strategy and receipt of verification reports. Sarah Hamill (WDC_CLO) commented that:
“a key aspect of the project has been the continual dialogue between all stakeholders (landowners, consultants, contractors & regulators), with all parties having a willingness to consider alternative ideas at any stage of the project. This project demonstrates that good project preparation extends beyond the initial stages”.
As one of the largest current remediation sites in the UK, the Bowling project demonstrates the value of “preparatory work” being broadened. By undertaking the preparatory works detailed in the foregoing discussion and, through the active participation of an engaged Regulatory team, the project has successfully navigated many of the challenges and pitfalls that such complex large scale remediation projects typically encounter.