Access 18: Former Britannia Smelting Works, Avonmouth by St Modwen
Shortlisted for Brownfield Awards Category 8 - Best Urban Regeneration and Category 13 - Project of the Year
The Access 18 development is a regionally important urban regeneration project, led by St. Modwen Developments Ltd. The commercial development is situated within the heart of the Avonmouth Severnside Enterprise Area. The site comprises the former Britannia Zinc Smelting Works and covers an area of 212 hectares. There is a historical legacy of heavy industry on the site, dating back over a century.
Avonmouth is Bristol’s most established industrial and distribution area; the Access 18 Development provides a strategic location with excellent motorway links (M5 and M49) in close proximity and nearly 80% of the UK’s population within a four-hour drive.
The aluminium smelting works closed in 2003, with the loss of 400 jobs. After purchasing the site following its closure, St. Modwen commenced the regeneration of the facility. The Access 18 development has created more than 2000 jobs with 19 employers and several thousand further opportunities to come as the phased development progresses. The multidisciplinary team formed by St. Modwen comprises Roberts Limbrick (Architects), Turley (Planning Consultants) and Rodgers Leask Environmental (Environmental Consultants).
The £150m development at Access 18 is an excellent example of multidisciplinary employment generation on brownfield land where St. Modwen have ensured through their design code that worker wellbeing and ecological biodiversity enhancement have been embedded in the development of the masterplan.
Britannia Zinc Limited, an Industrial Legacy
Industrial development in Avonmouth first commenced in the early 1900s, following construction of the Royal Edward Dock. The area to the north of the site was first developed in 1917 and comprised a sulphuric acid plant. It is understood that the plant was also used for the manufacture of mustard gas during the first world war.
The zinc and lead smelting operations within the site began in the 1920s, when a Delplace Roasting Plant was built, owned by the National Smelter Company. The Imperial Smelting Process was first developed at the site and in its heyday was home to the largest and most efficient zinc blast furnace in the world. In the 1990s, the plant was producing 100,000 tonnes of zinc, 55,000 tonnes of lead and 250,000 tonnes of sulphuric acid a year, employing 600 people.
Smelting operations continued until the late 1990s, when smelting ceased due to the economic pressures from global competition. It has since undergone phased demolition, remediation and redevelopment.
Contamination and Remediation
Phases 1 to 7 of Access 18 are located within the footprint of the former smelting works and have been remediated. The ecological enhancement areas are all within Phase 8. Phase 8 comprises undeveloped land surrounding the former smelting works, impacted to a lesser extent by heavy metals. The enhancement areas have been progressed but the earthworks for the development plots have not yet started.
Figure 1: The National Smelter Company Facility 1957
Figure 2: The BZL Smelting Plant in the 1990s
The site is typically underlain by approximately 2m of Made Ground overlying approximately 15m of Tidal Flat Deposits over bedrock of the Mercia Mudstone Group.
The long industrial legacy resulted in varying levels of contamination, principally in the form of heavy metals. In addition, much of the slag (from the smelting operation) and other waste generated during its operational life was discarded in a large landfill adjacent to redevelopment area.
The heavy metals are known to be leachable, impacting perched water in the Made Ground but confined by the upper clays of the Tidal Flat Deposits. The Tidal Flat Deposits retard the downward migration of contaminants within the site and a cut-off wall (keyed into the natural clays) around the whole perimeter prevents lateral migration, with a effluent treatment system removing the metals before discharge to surface water. In the longer term, the presence of hardstanding and positive drainage will greatly reduce infiltration and, therefore, the generation of contaminated perched water. Combined, these measures are protective of controlled waters (piling risk assessments having proved no new pathways will be created).
The intercepted rainfall is transported via a positive, sealed drainage system to surface water attenuation ponds (SWAPs) around the site. These SWAPs are focal points for ecological enhancement, with planting design to provide optimal habitats for various flora and fauna including birds and water voles.
The remediation approach focussed on retention and re-use of all Made Ground within the confines of the site boundary, whilst protecting construction workers and future site users from contamination. Phased mass excavation included a turnover to the base of the Made
Ground to remove smelting works infrastructure and below ground obstructions. This was followed by re-engineering of site-won material to provide a suitable construction platform.
Reuse of Made Ground was a key aspect to the project and the approved Remediation Strategy targeted severing contaminant pathways, rather than source removal (other than where gross contamination was encountered). The reuse of material on site provided many economic and sustainability benefits, including the avoidance of significant import of material to raise levels to achieve flood mitigation levels (the tidal flood risk meant levels needed to be increased by around 1.5m). This approach to the filling operation saved millions of haulage miles as the material reuse volume is approximately 500,000m3 across the various phases.
The remediation used construction materials (sub-base and hardstanding) in combination with clean fill materials to sever contaminant linkages.
Access 18 Masterplan
The Access 18 development offers a modern commercial development built with a focus on biodiversity and the wellbeing of the employees.
The masterplan has been designed to incorporate and adapt the complex system of surface water streams (known as rhines) and smaller ditches to balance high quality commercial space within a parkland setting. The parkland setting offers employees and the public, the opportunity to use the trim trails and cycle paths as part of their commute or lunch break. The wellbeing routes are suitably embedded alongside landscaped attenuation ponds that allow the fauna and flora to prosper.
Phases 1-7 on Access 18 house 22 industrial units ranging in size from 6,000sqft to 150,000sqft. Phase 8, once completed, will include 11 industrial units ranging in size from approximately 8,000sqft to 300,000sqft.
Figure 3: Remediation at the BZL Smelting Works 2018
Figure 4: Illustrative depiction of completed Access 18 Development
Focus on Employment
Since the opening of docks, Avonmouth has been a major employment hub for the south-west of England. Currently, businesses cover a vast area in a series of commercial estates. The main uses reflect the needs of the current day including:
Transport and storage;
Historically, the BZL site was one of the top employers in Avonmouth employing around 600 staff. Based on current employment figures, Access 18 is the workplace for over 2000 people. There are 19 businesses on the development, including Hermes (couriers), catering equipment providers Nisbets and leading healthcare distributor Movianto.
In early 2021, Ocado is due to open a Customer Fulfilment Centre in a recently constructed 151,330sqft unit within Access 18. The largely automated facility will be capable of handling more than 30,000 orders a week, employing 815 people.
Once completed, inclusive of Phase 8, Access 18 will provide a total of over 2,000,000sqft of commercial space. This is anticipated to provide employment space for around 5,000 people.
Figure 5: Construction on Phase 6 2019
Historically, a complex system of rhines and smaller ditches were formed to drain the formerly boggy summer pasture in and around the Access 18 site.
All the watercourses are subject to many man-made pressures such as pollution, building of flood defence structures and their operational control, disturbance, invasive species and development. These pressures, at their worst during the operation of the smelting plant, had a negative impact upon species diversity. However, since the smelting plant closure and development of the three ecological enhancement areas within the Access 18 masterplan, improvement in surface water discharges have been recognised and a number of rare species have returned to these watercourses.
Otters, water voles and dippers are just three of the notable species found here. Otters and water voles are both UK priority species. Kingfishers are also now found throughout the Avonmouth rhine network.
Three Ecological Enhancement Areas provide a green corridor through the development. The areas retain and expand upon the rhine network and are designed to include various habitats to support and bolster local biodiversity.
Ecological Enhancement Area 1 includes three SWAPs, areas of woodland, shrub, woodland edge, wildflower meadow, and tussock and marsh grassland along the ancient Shirehampton Rhine which connects Access 18’s intercepted surface waters to the wider rhine network.
Figure 6: Design for Ecological Enhancement Area 1
Ecological Enhancement Area 2 comprises a new rhine designed to link the ancient Shirehampton Rhine and Kings Weston Rhine. It includes SuDS for Access 18 and ecological habitat including wildflower, tussock and marsh grassland.
Ecological Enhancement Area 3 includes a series of new rhines, interconnecting three SWAPs providing various open water, woodland, grassland and marshland habitats.
The placement of green thoroughfares, cycleways and trim trails, adjacent to the ecological enhancement provides green space for workforce to use and enjoy.
Healthy Design for Employee Wellbeing
In recent years, the importance of maintaining an active lifestyle has become integrated with our working life. Physical inactivity is responsible for one in six UK deaths (equal to smoking) and is estimated to cost the UK £7.4 billion annually.
Exercise has been shown to impact almost every area of health, help with stress management, and promote proper brain function. NICE state that “If the United Kingdom’s 5.7 million small and medium-sized businesses encouraged their workforce to be more active, they are more likely to reap the benefits of having engaged employees who are more productive and are less likely to take time off sick”.
The design of Access 18 incorporates opportunities for the workforce to exercise as part of their working day. The plan helps to promote a modern relationship between exercise and work by providing off-road infrastructure to:
Promote walking / cycling to work;
Encourage employees to take some time out of the workplace to have a walk;
Supporting trim trails for exercise during breaks; and
Promote worker interaction by providing communal outdoor areas.
Bristol is widely regarded as the ‘best UK city for cycling to work’, the ‘17th best in the world’ (COYA 2019). The centre of the Access 18 development is an approximate 10-minute cycle (20-minute walk) from Avonmouth Train Station or the Bristol suburb of Lawrence Western. Once complete, the Access 18 development will include 1.75km of standalone multi-user pathways which will track through ecological enhancement areas and provide easy commuter routes through the area. It will also provide an additional 2.25km of off-road walkways.
The Access 18 Development has been well supported by Bristol City Council (BCC) since St Modwen’s acquisition of the BZL plot in 2004. The Section 106 provided the foundations for the ecology and wellbeing to establish as part of the plan. These were further enhanced by the design team through the creation of the ecological and travel management plans (EMP & TMP) approved by BCC. The delivery of these plans allowed the project to flourish as a commercial development with green spaces that give the impression of a parkland setting.
The support for the development by the authorities has been principally driven by the contaminative legacy of the site and the thorough remediation. Close liaison with the BCC Contaminated Land Officer and the Environment Agency throughout the detailed remediation design, implementation and validation of parcels of land has been fundamental to the success of the project.
Project Summary & Legacy
The development at Access 18 is an excellent example of employment generation on brownfield land in an urban area, where worker wellbeing and ecological enhancement is embedded in the design of the project.
The design benefits are likely to have subtle but widespread impacts on workers lives and the environment. The reduction of haulage miles to remediate the site was significant but a commercial development providing greenways to reduce vehicular commuter journeys and enhance the environment from inception is excellent.
The parkland setting has been designed to provide a choice for a healthier lifestyle and not only improves the health and wellbeing of employees but also benefits the employer through engaged, productive employees.
The redevelopment of a former heavy industry site to the modern Access 18, within an ecological setting of ancient waterways, is exceptional. Once the project has been completed, Access 18 will support a workforce of around 5,000, making Access 18 an excellent example of urban brownfield regeneration.