environmental SCIENTIST | Challenging perceptions in land condition | February 2018
The mention of asbestos often strikes fear in the thoughts of many people, including professionals in the construction industry, their clients, and members of the general public. Considering there were approximately 5,500 asbestos related deaths in the UK during 20141, those fears are not without basis. Every fibre inhaled into the lungs increases the potential for asbestos related illnesses to develop, typically many years to decades later. That risk is reflected in Part 2, 11(1) of The Control of Asbestos Regulations (CAR) 2012 which state an employer must:
“Prevent the exposure to asbestos of any employee employed by that employer so far as is reasonably practicable; and where it is not reasonably practicable to prevent such exposure, to take the measures necessary to reduce exposure to asbestos of any such employee to the lowest level reasonably practicable”2.
What many people are unaware of is that asbestos fibres are present in the air that we breathe in every day, with concentrations normally higher in urban settings than in rural environments. The construction and demolition industries have progressively been improving standards. Various bans on the use of asbestos products have culminated in the Asbestos (Prohibitions) Regulations 1999. In contrast, going back to the last century, reports in the geo-environmental industry, particularly prior to the 1990s, often did not feature asbestos as a possible contaminant. Even as asbestos started to be included in the analysis of soil as a potential contaminant, there was little industry consensus on what level of risk asbestos in soil posed. For example, what level of asbestos in soil is acceptable in residential garden topsoil and would a regulator agree? Since 2014, that situation has dramatically altered and those changes are currently changing industry practice.
While the CAR 2012 Approved Code of Practice2 kept its focus on the construction and demolition industries, it was initially the CIRIA (2014) Asbestos in Soil and Made Ground: A Guide to Understanding and Managing Risks3 and then the CL:AIRE (2016) CAR-SOIL4 that led to a much greater understanding of the approach to assessing and managing asbestos in soil. Asbestos in soil has gone from being a forgotten aspect, to a feared and misunderstood contaminant, to one that is much better understood and can be properly assessed.
There are four categories that work with asbestos falls into:
- licenced work;
- notifiable non-licenced work;
- non-licenced work (not notifiable); and
- outside of CAR 2012.
WYG's Geo-environmental team recently managed the remediation of two sites in Leeds (at Leeds Arts University and at Quarry Hill) where asbestos was the key contaminant of concern, and sustainability of the remediation was a major driver in the cost and programme of both projects. The licenced remediation project at Leeds Arts University won a Brownfield Briefing Award in 2017 for best reuse of materials. Quarry Hill, in central Leeds, was a remediation project in which the asbestos works were non-licenced.
Case study 1: Licensed remediation
Leeds Arts University is located close to Leeds city centre, opposite the main entrance to Leeds University. The 0.27 ha constrained site comprised of a car park where planning permission had been granted for the construction of a new teaching block. The Phase I geo-environmental desk study identified that a former school had been present on the site which was built in 1896 and demolished by 1978. Architectural records showed the former school to have had two basements, the lower of which included a swimming pool, a boiler room and heating ducts.
What was not immediately obvious was that:
- the boilers were of a type that had sprayed asbestos insulation;
- the heating pipework through the ducts was covered by lagging, which had degraded to spread loose asbestos fibres through the ducts;
- the swimming pool was surrounded with asbestos insulation board which had degraded through decades of being left underground; and
- material containing asbestos including degraded asbestos insulation board had become mixed through the subterranean demolition rubble.
Any one of these aspects was sufficient to classify works that disturbed these features as being licenced work, but this site had all the worst forms of asbestos containing materials (ACMs) combined. Enabling works were required to remove the sub-surface structures, voids, and the uncompacted made ground. The area was backfilled to an engineering specification using site-won material to provide a suitable founding stratum for the new building, which was to be piled with a suspended ground floor slab. The remediation specification for the works was being developed as CAR-SOIL 20164 was being released, so it was important that the remediation contract adhered to the new guidance. Few earthworks and remediation contractors hold an asbestos licence, so even leading remediation contractors had to partner with other companies in order to be considered for the work. Sanctus Limited, a remediation contractor with an asbestos licence, was appointed to undertake the works. The site was located adjacent to one of the main routes into Leeds city centre with no potential for heavy goods vehicles (HGVs) to turn on-site. Therefore, bringing HGVs onto site to remove material for disposal or off-site treatment would have resulted in traffic management difficulties. Waste disposal of soils containing ACMs classifies them as hazardous waste5, and would have been prohibitively expensive. The only feasible option was therefore to treat the soils, demolition materials and excavated underground structures on-site. This involved hand picking out any ACMs from the rubble, and licenced works to remove the lagged pipework and associated ducts, and the boilers and boiler house.
Materials were then screened, crushed and processed on-site enabling:
- the re-use of soils and crushed materials in the earthworks to meet the engineering specification for the slab;
- the reduction of risk to the piling contractors should they decide to use piling methods which generated arisings instead of driven piles; and
- the upper one meter of soil to have a complete absence of ACMs and asbestos fibres where the piling mat, piling caps, landscaped areas, service trenches, movable soil access ramps, and the lift shaft base were to be constructed.
At the end of the works, approximately 10 t of asbestos had been removed from the ground in a city centre environment adjacent to housing, offices, and a main road. The works had included a 9 m deep excavation adjacent to the road on one side of the site and a 4–5 m retaining wall up to the houses on the other side. Only 0.1 per cent of soils were disposed of to landfill (10 m3) because the soils had been in direct contact with degraded lagging, so it was considered safer to dispose of them (despite no visual ACMs and the laboratory sample recording asbestos below the level of detection). Excluding asbestos waste which was disposed of, 97.4 per cent of all processed material was reused on-site and 99.9 per cent was reused or recycled in total. The maximisation of reuse of material on-site saved some 1,850 lorry movements against a disposal and import option; it also saved costs and was a sustainable remediation approach. A critical reason this was achieved was because the risk from asbestos had been understood in light of CIRIA C7333, and the remediation specification was innovatively written, agreed with the regulator and amended to reflect the progress of the works in conjunction with the contractor and with the client’s agreement, in order to maximise reuse of materials. Both Sanctus’s and WYG’s teams were highly committed to the sustainability of the scheme, in recovering the asbestos, and maximising reuse which allowed them to adhere to the programme and avoid financial implications from any delays to the construction programme.
Case study 2: Non-licenced remediation
Quarry Hill flats previously housed around 3,000 people close to Leeds city centre, but were also demolished in 1978 before asbestos demolition surveys were industry practice, and before asbestos was stripped out of buildings prior to demolition. Demolition rubble had been left for decades on this development site where many mature trees had grown. To develop the site for an 11-storey new college, 17,600 m3 of material needed to be removed from the site in order to access the development platform. That material largely comprised of the demolition rubble, in which the ground investigation by WYG had identified the presence of ACMs. The condition of these materials classified the earthworks as non-notifiable non-licenced remediation works.
Historically, it would have been possible for a contractor to have simply taken all the material to landfill. However, given the landfill tax escalator and WM3’s guidance5 on classification of soils as hazardous waste, landfill was not a financially feasible option. Off-site treatment, without the programme constraints of the site, enabled reuse of the material such that the majority was reused elsewhere. The removal of all the ACMs was critical in the minimisation of the generation of hazardous waste since a very small presence of ACMs can classify a waste material as hazardous according to WM35. Therefore, hand picking techniques to remove the ACMs can be very cost effective. This was undertaken off-site in accordance with the CL:AIRE Definition of Waste: Development Industry Code of Practice6 to allow re-use of the material elsewhere. The absence of ACMs in a waste stream can be confirmed via undertaking just Stage 2 of the ‘Quantification Test’, where a soil sample is spread out on a tray and visually inspected for the presence of ACMs and fibre bundles (offering a time and cost saving compared to undertaking the phase contrast optical microscopy (PCOM) Stage 3 test.
WYG wrote the specification for the remediation works using a re-measurable contract, in conjunction with a materials management plan, such that the remediation contractor, Keltbray, was required to minimise the waste and the associated costs via processing the material into seven different disposal, waste treatment, and recycling streams. The volume of hazardous waste was reduced by 97 per cent to 576 m3 by processing the soils off-site. Keltbray worked with Biogenie at the soil treatment facility at Skelton Grange, Leeds to process soils. Allied Plant in West Yorkshire, were also involved in producing a 6F2 material for re-use.
Simon Eden is part of the WYG Leeds Geo-environmental team. He was designer & consultant for both projects and teaches about asbestos in soils for CIRIA.
Patricia Gill is Director of the WYG Leeds Geo-environmental team.
1. Health and Safety Executive (2014) Health and Safety Statistics 2013/14. http://www.hse.gov.uk/statistics/overall/hssh1314.pdf
2. Health and Safety Executive (2013) Control of Asbestos Regulations 2012. Approved Code of Practice and guidance (L143 2nd Ed.). http://www.hse.gov.uk/pUbns/priced/l143.pdf
3. CIRIA (2014) Asbestos in soil and made ground: A guide to understanding and managing risk C733. https://www.ciria.org/ItemDetail?iProductcode=C733
4. CL:AIRE (2016) Control of Asbestos Regulations 2012. Interpretation for managing and working with asbestos in soil and construction & demolition materials. Industry Guidance (CAR-SOIL). https://www.claire.co.uk/component/phocadownload/category/36-asbestos-in...
5. Environment Agency (2015) Waste classification. Guidance on the classification and assessment of waste. Technical Guidance WM3. https://www.gov.uk/government/uploads/system/uploads/attachment_data/fil...
6. CL:AIRE (2011) The definition of waste: Development industry Code of Practice. https://www.claire.co.uk/component/phocadownload/category/8-initiatives?...