Richborough Energy Park by Sanctus
Shortlisted for Brownfield Awards Category 12 - Best Infrastructure Project
RENEWABLE ENERGY FROM THE ASHES OF AN INDUSTRIAL PAST
Background
Prior to its rebirth as the ‘Richborough Energy Park, the site was originally home to a coal fired power station with constructions starting in 1958 with power generation commencing in 1963. In 1971 the power station was converted to burn ‘residual fuel oil’ and required additional heating infrastructure, heavily insulated pipework and additional storage tanks, boilers, and pressurised pumping equipment.
Further alterations were made in 1987 to enable the burning of ’Orimulsion’, a proprietary product comprising and oil and water emulsion imported from Venezuela. Following closure, the plant underwent decommissioning with the cooling towers and chimney being demolished in early 2012.
The multiple chapters in the history of this site created a unique combination of chemical processes and contamination sources at a hugely complex and geotechnically compromised site which left a hugely challenging industrial legacy to resolve for the site to have a viable future.
A Brighter Future
As a result of its proximity to continental Europe developers had identified the site as a potential receiving station for renewable energy generation. The concept of the ‘Richborough Energy Park’ was born seeking to connect the UK to Belgium via a 130 km long undersea link known as the ‘Nemo Link’. This connection allows transmission of up to 1000MW of electrical between the UK and Europe, as well providing connection to the offshore Thanet Windfarm.
Scope of Works
Sanctus were tasked with site wide remediation, specialist demolition of remaining structures, clearance of all subsurface obstructions, provision of an engineered platform, treatment of contaminated soils, management of asbestos containing materials, as well as contaminated soils and surface water within the intertidal limits. Each of these individually complicated environmental engineering challenges had to be managed, set against unfavourable local hydrogeology and a unique and challenging commercial and political landscape.
Remediation
Sanctus mobilised to site under an agreement that the full 6ha of the site would be available, for stockpiling and processing of excavated soils. However, following mobilisation it became apparent that the majority of the agreed area was unavailable and occupied by additional contractors working on a different phase of the project, more than halving the available working area from 6ha to 2.5ha. This change meant that the materials processing or materials now had to be carried out within the same footprint as the full works package, greatly increasing the risk of excavation and processing works disrupting one another as the works progressed. The redesigned system operated throughout the programme to treat material on site ensuring that more than 99% of all material could be reused on site.
Sanctus’ extensive experience and unparalleled expertise in ground engineering in brownfield environments meant that we could develop a material specification, testing criteria, approach to placement and compaction which maximised reuse and removed the need for expensive and environmentally impactful geotextiles and stabilisation admixtures in the final design. In this way we achieved a closed loop on materials and fully embraced the principles of the circular economy throughout the project.
Specialist Demolition
A number of surface structures remained on site including the former turbine hall, large steel frames, surface mounted pipework and storage tanks. The specialist demolition of these feature required an array of specialist plant ranging from 13t to 71t long reach excavators. The reinforced foundations of the former turbine hall was uniquely challenging requiring the use of the largest mechanical breaker in the country (at the time), which still only succeeded in removing 10m3 of concrete per shift, a perfect illustration of the structural integrity of the former power stations construction.
Historically, more than 4,000 piles were used in the construction of the power station meaning they were ubiquitous across the development area. Where impracticable to remove, each pile was reduced to level and its location recorded, in agreement with the clients’ design team. This allowed them to adjust their foundation design based on the known residual ground risk across the site, eliminating the need for full scale removal. In total some 20,000m3 of heavily reinforced foundations and piles were recovered and a further 4,000m3 of material from the cooling tower base and associated foundations was broken out and processed for reuse on site.
One of the key deliverables for the project was the turnover of the entire development area to 2.4mAOD, with all soils being screened to remove any oversize materials. It was during this part of the project where the extent of missing information became clear as multiple cavernous interconnected, reinforced basements were discovered. This meant that specialist confined space procedures had to be implemented to allow the basements to be accessed and surveyed. Having determined that these areas contained ACMs, Sanctus produced detailed plans of work and submitted a notification to the HSE ahead of undertaking licensed removal works. All excavated materials were assessed for visual and olfactory contamination and argillaceous materials removed and processed into general fills/engineering materials. All oversize material was crushed and screened to form compliant fill.
Civil Engineering Solutions
The client requested that the basement structures outside of the development footprint be sealed at the CDM boundary and kept in situ where possible rather than being broken out or fully infilled.
Sanctus engineered a gabion basket solution adjacent to the remaining basement walls measuring ~4m high and 3m wide at is base, which supported the remaining foundations of the basements. This provided security to the client ensuring the site boundary was resilient even if basement structures outside of the site boundary were removed at a later date. The gabion baskets allowed for a full reinstatement of the area up to the site boundary and met the hugely demanding load tolerance requirements.
Some remaining below ground structures also underlay transit routes across site and therefore required significant remedial works to stabilise them to prevent collapse during the importation of large items during the construction phases of the project. The former cooling water pipes, some 2.5m in diameter and 300m in combined length, running beneath the area of the original turbine hall were removed up to the CDM boundaries and near to sensitive structures.
Where pipe work could not be removed they were filled with an expanding ‘Bacel’ Resin Foam. The sealing of pipes was undertaken using modular reusable formwork to ensure optimal filling and density removing future risk of compaction. The particular resin was selected for its resistance to residual contamination and salt water from the tidal influences. The pipes being up to 2.5m in diameter were weighed down and strapped to concrete mass foundations up to 5mbgl, during pipe removal and infilling, all works were undertaken under confined space controls with all operatives equipped with respirators and gas detectors to ensure safe working practices.
A by-product of the use of this resin was the release of formaldehyde into the residual waters present in the base of the pipe. Sanctus used Air-Sparging to force the formaldehyde out of solution as well as passing the water through granular activated carbon pods removing any residual risk.
This combination of ground and civil engineering interventions was hugely important as the solution allowed record-breaking vehicle movements and plant to safely transit across the site, including what was at the time the largest (by weight) import and road going delivery in the UK. Eventually four power converters were delivered fully assembled to site on a 28-axel lorry over Sanctus’ retaining structure and reengineered ground improvements.
Soil Treatment
A large component of the soil improvement works involved separating argillaceous material from site won fill and pre-processing it to reduce its compressibility. The screening, crushing and improvements turned the problematic material into a competent fill, achieving a minimum of 5% CBR. This processing allowed Sanctus to reduce thickness of the pile mat, virtually eliminating the need to import material, achieving significant
financial and environmental improvements. Sanctus were able to process and re-engineer 65,000m3 of material to or above the client’s original specification – achieving 5% CBR at formation and 10% for the piling mat.
Water Treatment
As the site was founded on former tidal flats, dewatering, water treatment and management were a defining feature of the works. Unfortunately, due to the commercial / political landscape of the project Sanctus were unable to engage in advanced permitting discussions with regulators which could have caused significant permitting delays. Sanctus therefore developed a dewatering solution, comprising the use of the former cooling tower bases as temporary reservoirs to store treated water until a discharge consent was granted. The cooling tower bases were surveyed, and confirmed to be watertight before being used to store some 6000m3 of groundwater. Once the discharge consent to the adjacent river was granted, water was pumped across site and passed through our bespoke parallel series of water treatment plant before being discharged to the river.
In total Sanctus treated and safely discharged nearly 19,000m3 of water into the River Stour with the discharge monitoring demonstrating that we successfully achieved an environmental betterment.
Asbestos Management
Asbestos containing materials were prevalent across much of the development, therefore Sanctus opted to process contaminated soils on site allowing them to be reused in accordance with the clients’ specification (reuse at depth). This process comprised the excavation of all soils found to contain asbestos within the CDM boundary, and passing them over a picking station where specially trained operatives removed the asbestos fragments by hand.
This exercise allowed virtually all soils to be retained on site with only bulk asbestos containing materials and impacted PPE picked being disposed of offsite.
Material Reuse – Application of Circular Economy
The only materials to leave site during the project were materials considered unsuitable for reuse including materials that would degrade over time such as metal, wood and vegetation and bulk asbestos products and PPE.
All concrete broken out was recycled on site to a 6F2 grading allowing it to be reused on site, hugely decreasing the volume of aggregates required to be imported to site to form the 25,000m2 piling mat.
The overall cut and fill earthworks comprised re-use of 69,000m3 material (45,000m3 of Made Ground and 24,000m3 of site won recycled aggregate).
Environment Protection and Improvement
Throughout the works, extensive and varied environmental monitoring was carried out including water quality monitoring as well as reassurance air monitoring around the perimeter of all asbestos works.
Ahead of our works, concerns were raised regarding the potential level of vibration that would be caused by the demolition activities. Sanctus therefore placed high sensitivity vibration monitors at key locations across the site and monitored frequently to demonstrate there was limited risk of effecting the adjacent transformers adjacent to the southern boundary.
Additional monitoring and protection measures were also implemented during higher risk activities such as throughout confined space works where operatives were fitted with real time multi gas monitoring equipment and alarm systems. All of which demonstrated that the controls being implemented by Sanctus were suitable to protect people, wildlife, and the environment.
Conclusion
This previously derelict parcel of land formerly used as a coal and oil-fired power station should never have been recoverable as it was simply not technically possible, commercially viable or environment suitable to do so.
As a result of our all-risk approach to contracting, the site has been transformed into a glowing example of international connectivity and cooperation, providing a strategically significant infrastructure asset for the country. By reusing almost all materials on site Sanctus was able to make the development commercially viable but perhaps more importantly environmentally appropriate. The small volume of materials leaving site were able to be recycled and where possible, sent to local facilities for repurposing. The only unrecoverable materials comprised degradable vegetation/timber and bulk asbestos and impacted PPE. It was especially pleasing to achieve a betterment to the local water environment through our treatment of groundwater impacted by decades of contamination.
Throughout our time on site Sanctus were able to adapt to an ever-changing commercial and political situation managing to complete the works to the required standards on budget and within the final programme.
