By: Stuart Phillips and Thomas Lobsey
Date Published: October 27, 2021
Land Contamination Risk Assessment
In-ground risks can cause significant issues for a development in terms of costly overruns and time delays. “Getting out the ground” as it is referred to, on-time and with no surprises, forms an important part of the construction planning process.
Stuart Phillips, Associate Environmental Director at AESG, provides an insight into the scoping processes required to ensure that in-ground risks are appropriately considered via a comprehensive geoenvironmental assessment.
Scoping for a specific project should always start with the first question, “what is the client looking to achieve?
No site is ever the same in terms of environmental context and objectives, and we receive a wide variety of enquiries. Some clients may be looking to purchase or sell a site and want to know the key risks (this is called environmental due diligence) or perhaps they already own the site but require support on obtaining planning permission. Other clients may come to us when they’ve started construction but have come across specific challenges on site such as in-ground obstructions.
Engaging with the client as early as possible in the scoping stage is imperative to fully understanding their needs and project objectives. Essentially, assume nothing!
Commonly we discover that it’s not just contaminated land and geotechnical support that is required when you discuss the site in greater context.
Other aspects such as Unexploded Ordnance, Underground Service location and Topographical Surveys can all form part of a more comprehensive assessment when the wider environmental context and client’s objectives are known. Undertaking these assessments under a single commission can often provide the client with better value for money in the long term.
Once we have ascertained the client’s aims and objectives, we can then start to scope the works required. For contaminated land works, this is undertaken in accordance with Land Contamination Risk Management Guidelines (LCRM) published in October 2020 and updated in April 2021, which replaced Contaminated Land Report 11 (CR11). For geotechnical assessments “BS5930 Code of Practice for Ground Investigations” is generally used along with various Eurocode documents.
The first stage for a contaminated land assessment is typically a Preliminary Risk Assessment (PRA), mostly commonly known as a “Phase I Desk Study” within the industry.
The aim of a PRA is to determine potential contaminant linkages using something known as the ‘source-pathway-receptor’ Conceptual Site Model(CSM). An example of a CSM is presented to the right.
The PRA also typically includes the procurement of a commercial third-party data search. The data search report provides detailed and accurate information on environmental and geological datasets and provide information on previous land use through high resolution historical mapping imagery.
A site visit is generally undertaken to support the desk based review of information and the production of the PRA report. Site specific risks such as storage of fuels or chemicals, which may not have been picked up in the data search alone, can then be risk assessed. Once we know what unacceptable risks are likely to be present from the PRA, a ground investigation can then be scoped to assess each link more closely. The findings are then included in a Phase II Environmental Site Assessment.
A ground investigation typically comprises the logging and sampling of soil or rock. Various sampling methods are available with the most common in the UK being window sampling, trial pitting, cable percussive drilling and rotary drilling. Ground gas and groundwater monitoring / sampling wells can also be installed once the boreholes are formed. Samples collected from the investigation are then scheduled for laboratory analysis and along with the other findings are compiled into a report. Conclusions are then made in determining whether any unacceptable risks remain and whether any remediation is required.
In addition to contaminated land aspects, the client may also require geotechnical information for aspects such as foundation option appraisals (shallow foundations, piles etc), sustainable drainage systems (SuDS),concrete design and in-ground obstructions from previous site uses.
Having a competent and experienced ground investigation supervisor on site is key to really finding out ‘what lies beneath’. Having spent the first 6 to 7 years of my career supervising ground investigations across the UK, one thing is for certain, nothing is ever as you expected!
As such, we need to ensure we capture all of the information without having to re-mobilise to site and that for the most part comes from experience in terms of understanding the context of what is found on site.
Teamwork is the key to success, and we work collaboratively across each role. The key aims and objectives are identified at the project planning stage to ensure everyone in the team is aligned including drilling crews, monitoring technicians and those describing the soils or rock encountered.
This in-turn then enables AESG to report early findings to the Client. Once the ground investigation works are completed, an interpretative report is compiled, where our findings are presented and summarised to the client.
Although much of the technical data and interpretation is required by Statutory Regulators, for example for planning purposes, none of the findings should be a surprise to the client if you’ve communicated effectively with them all of the way through the project.
Stuart shares some of the interesting things he’s come across on site
Former gas work sites were fascinating to investigate across the UK, given the number of historical structures and processes. I spent just over a year on site at the former Gasworks in Southall, West London which has been developed for housing.
We also came across an animal burial ground on a rural site in the south-east, where livestock had been slaughtered and buried because of foot and mouth disease. Supervising the excavation of those was a unique experience for everyone involved.
We’ve also worked on a site recently where a lost river of London passed beneath the site and posed a significant in-ground risk in for pile design.
Unmapped underground services can also pose a significant constraint to a development, as diversions can cause time delays and additional costs.
Determining what lies beneath can be a complex constraint. Engaging with an experienced geo-environmental consultant at an early stage in the process enables ground risks to be appropriately considered and managed.
How can AESG help?
AESG is a specialist consultancy, engineering and advisory firm headquartered in London, Dubai and Singapore working on projects throughout Europe, Asia and Middle East. We pride ourselves as industry leaders in each of the services that we offer. We have one of the largest dedicated teams with decades of cumulative experience in sustainable design, fire and life safety, façade engineering, commissioning, data management for the built environment, waste management, environmental consultancy, acoustics and carbon management.
Associate Environmental Director, AESG
Stuart is AESG’s Associate Environmental Director leading geoenvironmental projects in the UK. Stuart’s specialism is within the geo-environmental sector. He has over 22 years of experience in the UK in advising residential, commercial and industrial clients on various aspects of development including purchase / divestment of sites, planning, construction and sign-off.
With his passion for environmental consulting, he has a drive to constantly enhance industry standards and practices. Stuart is committed to supporting clients with his comprehensive knowledge of the UK industry and his technical expertise.
UK Country Director, AESG
Thomas is the UK Country Director at AESG. Thomas’s position within AESG is to support the growth and success of AESG into theUK market, including business development, team leadership and project delivery.
Formerly based in Sydney Australia, Thomas previously worked as Operations Manager and General Manager for a fast-growing multi-disciplinary engineering and environmental company, operating across the east coast of Australia. Thomas specializes in environmental and contaminated land investigations and remediation and has strong experience within geotechnical engineering, occupational hygiene and hazardous buildings materials. Thomas has a passion for effective project delivery, business strategy, growth and organization development, with a drive towards operational efficiency through a balance of structures, leadership and culture.
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