Residential asbestos ground investigations: a Part 2A case study

The site, formerly a large factory built in the 1930s and demolished prior to development in the early 1970’s, covered an area of 33 hectares containing over 800 residential properties of mixed types and ownership.

The investigations and remediation required over the years on the site has seen the Council work with specialists in many fields. Many phases have been cutting edge, from assisting in developing new remediation techniques, to being a catalyst in the understanding of the issues and dangers of asbestos containing material (ACM) in residential soils. The project has played a role in the significant changes in how site investigation and remediation of asbestos in soils is now addressed across the country.

The main scope of the works included the removal of asbestos-contaminated soils from the front and rear gardens of 81 properties determined under the Part 2A Environmental Protection Act. At tender stage the client supplied two extensive Ground Investigation (GI) reports with highly detailed laboratory testing suites. The reports focused on assessing the long-term risk to local residents and identifying gardens with Significant Possibility of Significant Harm (SPOSH).

The two GI’s fulfilled their remit but lacked detail regarding the lateral and vertical horizons of asbestos contamination to allow the identification of waste segregation/consignment and mitigation measures during the remediation works. Because of the residential setting, such classification could not be undertaken during remediation due to the high likelihood of encountering significant fibrous asbestos contamination. There was no scope to segregate, stockpile and test the waste during the remediation works, so to allow the remediation contractor to segregate efficiently, and ensure appropriate disposal, the waste had to be assessed in-situ.

Hydrock undertook GI’s within each of the 81 properties (six trial pits/property) to further assess the depth, extent and type of asbestos in made ground, sub-soils and top soils. All arisings were visually inspected by a BOHS P402 trained asbestos surveyor for ‘clearly identifiable’ asbestos and tested (gravimetrically) for visually unidentifiable asbestos fibre. The GI provided an opportunity to assess the soils for waste consignment and to update the Preliminary Risk Assessments (PRA) in accordance with the Control of Asbestos Regulations 2012 (CAR2012-Reg 6) and the Conceptual Site Model (CSM).

By assessing the risk of fibre release for the more disruptive works, the excavation methodology, disposal routes and requirements for control measures could all be designed and tailored for each garden to avoid wasting time and resources. It also provided an opportunity to meet residents, address their concerns and discuss the works required in a calmer setting.

Because the maximum depth to be remediated in each rear garden was 0.6m, hand dug trial pits could be used to delineate the varied horizons and check for additional issues such as concrete slabs, voids or significant metal work.

In general, the trial pitting identified three separate waste streams:

• 0 to 100mm topsoil with turf and root system (high organic content, but no asbestos);
  
• 100 to ~300mm subsoils with asbestos fibre <0.1%w/w (no visible ACM);
  
• ~300 to 600mm made ground with asbestos fibre >0.1w/w (with visible ACM)
  

These horizons were identified within all six trial pits within the same garden, indicating that the segregation of the material into these three categories was plausible. Within this garden, ~50% of material would require removal as hazardous with very stringent control and transport conditions, while the remaining ~50% being removed as either non-hazardous, inert (for restoration) or waste with a high organic content.

Excavation and segregation allowed the waste to be sent to appropriate landfills under the correct European Waste Catalogue (EWC) code. The waste could also be packaged according to risk, with the highest-risk material being consigned in specialist containers.

The GI works permitted the works to accord with the Definition of Waste Code of Practice (CL:AIRE) and the Control of Asbestos Regulations 2012. Otherwise a high proportion of the waste would automatically have been sent to landfill as hazardous without accounting for the opportunity to segregate.

In summary, this case study highlights that on projects where the key contaminant of concern is immobile in soils and highly variable within short distances (like asbestos), the need for further detailed and reliable visual assessments may provide disposal routes that will permit significant cost savings. Such data will ensure that wastes can be segregated, consigned and disposed of safely, even if, initially, the historical site investigations seem to be sufficiently robust.

For more information, please contact the co-authors:

James Macfarlane Technical Director (Asbestos), Hydrock Consultants – for advice on asbestos site/ground investigation , and

Anna Spinks Waste and Environmental Protection Manager, City of Wolverhampton Council, for more information on the project as a whole.

This article is reproduced with the kind permission of the CIWEM (Chartered Institution of Water and Environmental Management) and was first published in their Contaminated Land Network Newsletter in June 2018.