Residents reassured during factory remediation
During remediation of a site used to make viscose rayon, Akzo Nobel did a complex risk assessment, which included 228 houses and a nearby lough. Richard Thurgood reportsE&RS and its partner ESI were appointed by multinational corporation Akzo Nobel to investigate a site in Northern Ireland for contamination by carbon disulphide, a substance used in the manufacture of viscose rayon.
Carrickfergus Industrial Estate is on land adjacent to the Belfast Lough, and was formerly used by Courtaulds for the production of viscose rayon fibres between 1950 and 1981.
Although the site had been closed for 17 years when Akzo Nobel acquired Courtaulds in 1998, the firm's regular environmental assessment process prompted a desktop study and visit.
A similar site in England had previously been found to be contaminated with a substance called carbon disulphide, used in the manufacture of viscose rayon. Initial investigations showed that carbon disulphide had been both made and used at the Carrickfergus site. Akzo Nobel wished to undertake a full investigation voluntarily, in line with its corporate social responsibility policy. The objective was to ensure protection of all site users, residents, and the local environment by determining and assessing the extent and risk of any contamination.
The Carrickfergus site was large and complex. Historically, the 111-hectare site included a sulphuric acid and carbon disulphide manufacturing area to the north, a main operations area, and an effluent treatment area. Landfilling had taken place to the north and east of the site.
On closure by Courtaulds, the site was sold off and later split up. At the time of the site investigations, the former chemical manufacturing plant and effluent treatment plant had been demolished. But the main site buildings were largely intact, and either derelict or in use by light industrial or commercial operations.
The west of the site comprises a 228-property residential estate, constructed by developers after closure and disposal by Courtaulds, on what was undeveloped land. This residential estate was adjacent to the former carbon disulphide plant.
Carbon disulphide is a challenging contaminant to investigate because of its properties. It is extremely flammable, has a very low ignition energy, and can pose a vapour explosion risk. When impure, it has a strong, unpleasant odour. It was vital that all of these issues were addressed during the investigation planning process.
The conceptual model showed a number of potential sources, pathways, and receptors, including the potential for contamination to reach the Belfast Lough, making ecological receptors an important consideration.
E&RS was commissioned to manage the project, including coordination of site investigation and management of resident liaison. In turn, it appointed ESI to undertake the site investigation works and to manage the extensive dataset that would result. TAL, a construction company based in County Antrim, was selected as Principal Contractor to facilitate the site investigation and ensure health and safety targets were met. Physalia, a consultancy that specialises in forensic ecology, undertook the ecological assessment of the Belfast Lough. The project took 18 months from start to finish.
The investigation was undertaken with the knowledge and consent of the current property owners. The Environment and Heritage Service, part of the Department of the Environment Northern Ireland was kept fully briefed throughout the investigation.
Carrickfergus Borough Council provided support to the communication process with the residents, as well as undertaking its statutory role. The residential estate comprises 228 large detached or semi-detached properties.
In each rear garden, at least five holes were drilled using a Geoprobe. And typically three to four soil samples taken from each hole.
Groundwater samples were collected where encountered. Two drilling teams meant that two gardens could normally be completed each day. Great care was taken to minimise damage to the gardens. Once completed, the holes were backfilled and the garden reinstated.
Soil samples were screened for asbestos by the laboratory and analysed for VOCs, including carbon disulphide. In addition, 10% of samples were analysed for a full suite of chemicals. Samples were also taken from the roads on the estate, to identify any migration pathways.
Representatives from the project team and Carrickfergus Borough Council visited each household to explain their results and provide a copy of the report. If residents had any queries about the investigation, they were encouraged to call the project information lines operated by E&RS and the council. The project received consistently good feedback for the standard of its garden investigations and general communications. And it received no complaints from the residents or occupants of the industrial estate.
Geoprobe and cable tool rig drilling on the industrial area was concentrated around the potential sources or pathways, including the carbon disulphide production and recovery plants, waste tips, and former site drainage and effluent plant.
Geophysics was used effectively on the effluent plant and waste tip to determine shallow subsurface structure, thereby minimising disturbance of wastes and allowing the investigation to be more focused.
Risk assessments carried out by the team indicated the potential for direct effects of contamination or long-term migration to the Belfast Lough as a receptor. Localised elevated concentrations of some contaminants were found, and further investigation was considered necessary to determine whether this material was migrating into the lough. Forensic ecology was therefore carried out on nearshore surface water and sediment samples from the lough.
Forensic ecologist Physalia was commissioned to carry out an ecological assessment of the status of intertidal communities present in the Belfast Lough adjacent to the former Courtaulds' factory. Interest centred on establishing whether materials that had been used in processes at the factory could be detected in the nearshore habitats and if these were associated with identifiable ecological effects.
The study combined analyses of communities of microscopic invertebrates, known as meiofauna, with investigations of growth patterns and bioaccumulation studies in mussels.
The community study identified and described diverse assemblages of invertebrates comprising more than 100 species and at total densities of up to almost four million animals per square metre of shore.
The assemblages included several sensitive, stress-intolerant animals as well as species that feed and depend on populations of sensitive bacteria and algae. The presence of these species argued against the existence of adverse environmental conditions in the shores adjacent to the former factory.
Detailed statistical analyses of the clusters of these communities identified natural environmental factors as the principal determinants of the community structures.
Analyses of the mussel shells was combined with statistical techniques. The mussels collected from the sampling station next to the former factory site and nearest to the stream and outlet of the closed-off drain onto the foreshore were not significantly different from any of those sampled along the north shore of the lough. This supported the findings of the community studies and argued against the existence of significant localised effects.
It was concluded that, despite the initial concerns over migration, the marine communities were healthy, and that there was no evidence of actual ecological effects caused by the former factory.
This was one of the most diverse investigations carried out for carbon disulphide, using a wide range of techniques and methods across a large and diverse site to provide data that was tailored to meet the needs of risk assessment for each of the different receptors identified for each area of the site.
An effective communications strategy ensured the investigations went smoothly, particularly with regard to the sensitive issue of investigating residential properties. This minimised distress and detrimental impact on property values.
Ecological risk assessments are often overlooked in site investigation programmes. In this case, the ecology of the lough was considered part of the investigation from the outset and the results of the ecological study helped support the findings from the terrestrial investigations.
Risk assessments can often be rather conservative, relying on the use of models to predict outcomes from a given set of data. A key advantage of the ecological assessment was that it looked at the true effect the former site was having on the ecology of the lough, which in this case was insignificant.
Richard Thurgood is technical director at E&RS.