Overview

In May 2021 a SoBRA sub-committee was established to develop guidance to help practitioners in the land contamination sector to account for climate change effects in controlled water risk assessments (CWRA) in a robust and consistent manner.  The sub-committee has representatives from geo-environmental consultancy and UK regulatory bodies (a full list of contributors is provided at the end of this article).  The full guidance entitled “Guidance on assessing risk to controlled waters from UK land contamination under conditions of future climate change” (V.1.0, dated August 2022), will soon be available for download from the SoBRA website[1].

Context

Climate change is expected to alter the frequency and distribution of rainfall, increase atmospheric temperatures, and increase the frequency and severity of extreme weather events, leading to longer periods of drought and more extreme rainfall events with associated rising groundwater and surface water levels causing flooding and coastal inundation. Furthermore, long-term changes in climate are forecast with the Meteorological Office projecting that by 2070, on average across the UK, summers will be between 0.9 and 5.4 ᵒC warmer, and winters will be between 0.7 and 4.2 ᵒC warmer[2].  Precipitation is also expected to be affected, with a -47% to +2% UK average change during the summer months, and a -1% to +35% change during winter months[3].  The projected pattern of rainfall across the UK is not uniform and will continue to vary on seasonal and regional scales into the future – see information provided by the Met Office[4] for seasonal and regional variations.

Changes in recharge rates, and to a lesser extent atmospheric temperature, can be important factors in determining the outcome of CWRAs[5]  being completed to assess the impacts to receptors from contaminant sources.  Climate change could therefore alter the risk posed to controlled waters (including to groundwater resources, surface water bodies, marine bodies, and groundwater-dependent terrestrial ecosystems), and the required management of these risks.

The need to incorporate the predicted effects of future climate change into qualitative and quantitative risk assessments has been recognised but rarely implemented in practice. This need is set out within the Environment Agency’s 2010 “Managing and reducing land contamination: guiding principles (GPLC2) FAQ 8”, and within the National Planning Policy Framework (NPPF) for England and Wales and LCRM. It is understood that the National Planning Framework 4 and WAT-PS-10 in Scotland will also in future include the need to consider climate change within land contamination risk assessments. Within the recently published BS21365[6] there is a requirement to consider and identify ‘possible foreseeable events’ within CSMs that could affect contaminant impacts or create new exposure pathways, e.g. flooding, rising groundwater or seawater levels and extreme weather which all go hand in hand with climate change. The absence of published UK guidance has resulted in variable ways of inclusion of climate change effects into CWRA, or, more usually, the influence of climate change being ignored entirely.

Effect of Future Climate Change on Controlled Waters Risk Assessments

All CWRA are underpinned by a conceptual site model (CSM), which synthesises the key physical, chemical, and biological processes that characterise the system, and establishes any potential Source-Pathway-Receptor linkages (i.e. no linkage, no risk).

Figure 1: Indicative CSM considerations based on a climatic shift to ‘wetter’ weather.

Future climate change could foreseeably affect any given CSM.  For example, an increase in precipitation could lead to increased recharge resulting in rising groundwater levels; source (e.g. soil) erosion; or overland flow.  It can further be seen how these scenarios could affect the pathways from source to receptors e.g. unsaturated zone thickness, hydraulic gradients and dilution factors, or the introduction of new pathways e.g. from overland flow, or previously unsaturated drains/culverts acting as new preferential pathways (see Figure 1).  As a result of the change in pathway, the number and type of receptors may also be affected, all of which could change the calculated ‘risk’ posed to controlled waters[7].

Figure 2: Indicative CSM considerations based on a climatic shift to ‘drier’ weather.

By way of another example, an increase in extended periods of hot dry weather or drought i.e. as predicted for the summer months, could result in reduced overland flow; falling groundwater levels which could, for example, change the pathway length by increasing the unsaturated zone thickness or increase dependency of baseflow to rivers; source drying increasing the risk of wind erosion/dust generation, and the development of desiccation cracks creating preferential vertical flow paths; changes in water demand e.g. through the installation of new abstraction wells or enhanced drawdown.  All of which could again alter the calculated ‘risk’ posed to controlled waters (see Figure 2).

In line with industry standards (e.g. LCRM[8]), the SoBRA guidance recognises that any change to a CSM (due to future climate change effects) must be determined by a suitably qualified and experienced professional, using evidence-based reasoning, and that the risk assessment process should only progress to higher tiers (i.e. generic quantitative and detailed quantitative) if the risk cannot be determined ‘acceptable’ at the preliminary stage.  The SoBRA guidance supports practitioners in doing this by setting out “What-if” scenarios for source, pathway, receptor CSM components that could be affected by climate change, in order to guide evidence-based reasoning. This is in line with the approach detailed in BS21365.

Adequacy of Available Datasets

The current best source of information for understanding future meteorological (e.g. temperature and precipitation) and sea level rise projections is the Met Office UK Climate Projection (CP) 18[9] dataset. This dataset was primarily developed to inform water resource management and flood risk assessment and as such the data modelled under the worst case high emissions scenario (RCP 8.5) is the most comprehensive, particularly when considering effects at the local scale. Projections are available until the end of the century. The projections consider average effects and do not necessarily include the effects of extreme events.

The Enhanced Future Flows and Groundwater[10] (eFLaG) Project, which is based on UKCP18 meteorological data, is the most up to date source of information detailing projections to recharge and river flows. This may be a more useful data source in relation to understanding changes to the hydrogeological CSM in relation to future climate change.

The choice of data set used to understand future climate change influences on the CSM is ultimately the responsibility of the risk assessor and should be suitably justified with uncertainties and limitations clearly stated. As the effects of climate change vary seasonally and spatially across the UK, careful consideration should be given to the site setting when choosing the appropriate climate model output for use in risk assessment.

Adequacy of Available Modelling Tools

Commercial modelling tools used in the higher tiers of risk assessment e.g. the Remedial Targets Methodology worksheet (‘P20’)[11], and ConSim[12], currently assume environmental conditions remain constant, however, the effects of future climate change are projected to vary over time, and so therefore will the established pollutant linkages.

This poses a challenge for practitioners with tools ill-equipped to model changes to the values of parameters over time.  Although distributed flow models exist (e.g. MODFLOW and FEFLOW), in addition to compartmental modelling environments (e.g. ConSim), the data requirements, time, and computational and staff resources required to develop and run these models is unlikely to be proportionate to most routine land contamination risk assessments.

It is therefore evident that further tools need to be developed (or current tools adapted) to model the transient effects of future climate change.  However, until such time, the SoBRA guidance recommends that existing tools are employed, except where risks are borderline acceptable (in which case an existing transient modelling approach may be most appropriate).  The SoBRA guidance sets out recommendations for how this can be achieved using commercially available tools.

SoBRA Sub-Committee Members

David Drury (Golder Associates / WSP); Emma Evans (Arcadis); Emma Hipkins (Golder Associates / WSP); Emma Khadun (The LK Group); Helen McMillan (RSK Geosciences); Isla Smail (The Scottish Environment Protection Agency); James Wilson (Atkins); Jesse Davies (Ramboll); Jonathon Atkinson (The Environment Agency); Katie Gamlin (WSP); Leon Warrington (Hydrock); Roisin Lindsay (WSP); Sarah Poulton (Natural Resources Wales); and Suzanne Blackman (Mott MacDonald).

We would also like to thank Simon Cole (SoBRA chair) and the wider SoBRA Executive Committee for their support and contributions in making this guidance possible.

[1] https://sobra.org.uk/

[2] UK Climate Projections: Headline Findings.  July 2021 (available at https://www.metoffice.gov.uk).  Values presented are based on Met Office high emissions projections (RCP8.5) for 10% and 90% probability levels.

[3] Where a negative value denotes a reduction in precipitation.

[4] UKCP18 Climate Change Over Land (available at https://www.metoffice.gov.uk).

[5] Controlled waters is a term used in legislation in England and Wales. Its equivalent in Scotland is the water environment. It is understood that Northern Ireland use both terms. Throughout this article the term ‘controlled waters’ is used to refer to regulated groundwater and surface water throughout the UK.

[6] BS EN ISO 21365:2020 Soil quality – conceptual site models for potentially contaminated sites

[7] Changes to a Conceptual Site Model can also be envisaged because of increases in the frequency and duration of extreme cold weather events, changes to wind intensity and duration, pluvial or groundwater flooding, marine inundation, and river or coastal erosion.

[8] Land Contamination Risk Management Guidance.  Available at https://www.gov.uk/government/publications/land-contamination-risk-management-lcrm

[9] https://www.metoffice.gov.uk/research/approach/collaboration/ukcp

[10] https://www.ceh.ac.uk/our-science/projects/eflag-enhanced-future-flows-and-groundwater

[11] https://www.gov.uk/government/publications/remedial-targets-worksheet-v22a-user-manual

[12] http://www.consim.co.uk/

Article provided by Dr. Emma Hipkins, Helen McMillan, and Isla Smail on behalf of the wider SoBRA Climate Change and Controlled Waters sub-group.

The UK Government has committed to Net Carbon Zero by 2050 Net Zero Strategy: Build Back Greener – GOV.UK (www.gov.uk).  Underpinning this goal is a 10 point plan encompassing the following areas:

• advancing offshore wind
• driving the growth of low carbon hydrogen
• delivering new and advanced nuclear power
• accelerating the shift to zero emission vehicles
• green public transport, cycling and walking
• ‘jet zero’ and green ships
• greener buildings
• investing in carbon capture, usage and storage
• protecting our natural environment
• green finance and innovation

Whilst this puts a focus on the energy industries, this does not mean that the construction industry and associated industries are exempted. Indeed, according to the UK Green Building Council, around 10% of the country’s carbon dioxide emissions are directly associated with construction activities. The number rises to 45% when taking into account the whole of the built environment sector.

Therefore, members of the AGS and their clients have an obligation to change behaviours, practices and methodologies to meet the challenge of net carbon zero. The clock is already ticking and changes need to be made sooner rather than later if the 2050 deadline is to be achieved.

There are a number of instigators and drivers which trigger a starting point on this journey. This could be an internal commitment from senior management or funders requiring businesses to meet a standard or set commitment, such as ‘Pledge to Net Zero’ Home | Pledge to Net Zero or ‘SME Climate Commitment’ Commitment – SME Climate hub. These schemes trigger baseline carbon footprinting and structured planning towards  the 2050 (or earlier) target.  Alternatively, the trigger could be external through commercial 3^rd party requirements. The whole supply chain is affected by the Government Pledge and therefore public client bodies will be requesting evidence from suppliers of they will meet the current targets. We can expect that these requirements will also be seen from private clients, especially as they develop their carbon reduction requirements beyond Scopes 1 and 2 and into Scope 3[1], which requires assessment of the supply chain.

Having established a driver and committed to reducing carbon, the next step is to measure the business’s carbon footprint and establish a comparable metric. This will vary between business types, but there is much guidance and support available from organisations such as the Carbon Trust. The process can be started small with simple assessments related to energy usage and develop complexity with time , especially as the ‘wins’ and reductions become harder to achieve.

Beyond business carbon footprints sits project carbon footprints.  PAS 2080:2016 “Carbon Management in Infrastructure ” is already 6 years old and was designed to help organisations in the construction industry move to a sustainable future by identifying areas for improvement and utilising sector best practice. The PAS2080 framework looks at the whole life cycle carbon management when delivering infrastructure assets, aiming to reduce carbon and reduce cost through more intelligent design, construction and use. There are also multiple tools to assist in assessing carbon footprints and opportunities for carbon reduction through good design and construction practice. The EFFC/DFI’s Carbon Calculator for foundations allows contractors to establish their carbon footprint on site and determine a benchmark against which reduction can be assessed and where the carbon intensity is within a project. The Federation of Piling Specialists (FPS) plans to mandate that all projects over £1m in value require EFFC/DFI Carbon Calculator calculations to be submitted. For projects less than this, the FPS is considering a simple ‘rule of thumb’ calculation that can be applied to give an approximate carbon value. This process can be adapted to some site investigation driller techniques.   Similarly, structural engineers Elliott Wood have developed ‘The Structural Carbon Tool’ in conjunction with the Institution of Structural Engineers to enable assessment of embodied carbon in structures. This includes geotechnical structures such as basements, retaining walls etc.  On the contaminated land side of geo-engineering, SURF-UK has developed guidance towards Sustainable Remediation which includes a number of Environmental Indicators such as ‘Emissions to Air’ and ‘Natural Resources’ and will expand to carbon measurement. Use of such tools is increasing and we can expect it to become a normal part of ‘value engineering’ or ‘options appraisals’.

What could reduced carbon methods may look like?  Each business will have different effective solutions. A big part is having the relevant technology available commercially, which is a work in progress for plant and commercial vehicles where battery power is currently limited in scope and range. In the meantime, sustainable fleet management and driving is already established as good practice .eg FORS, which provides a measurable starting point.   Electric drilling rigs have been available for some time, but often require a commercial electricity supply which is problematical, especially whilst the electricity supply infrastructure is not in place to support demand.  Technology is continually developing and changes to support carbon reduction can be expected to become more frequent and more available.

Also think about office related improvements. Switching energy suppliers to green non-carbon based suppliers where possible, committing to zero waste to landfill/ recycling and resourcing eco-friendly supplies from re-cycled/recyclable materials will provide first steps to carbon reduction.

For businesses who believe they can carry on as always and simply off set their carbon without fundamental changes to processes, this is the equivalent of putting a plaster on a wound that needs surgery.

The drive to reduce carbon is no longer a ‘wish-list‘ item.  Being able to demonstrate how your business and designs or procedures contribute to carbon reduction is becoming both a technical and commercial requirement.  It will soon be a ’must have’ and geo-engineers need to be thinking ahead to meet the needs of both Clients and Government drivers. If everyone starts to think about what they could do to manage their carbon footprint and plan towards it and put relevant demands on their supply chain, the goals will be achieved sooner.

[1]  Scope 1: Direct emissions that result from activities within your organisation’s control. This might include on-site fuel combustion, manufacturing and process emissions, refrigerant losses and company vehicles. • Scope 2: Indirect emissions from any electricity, heat or steam you purchase and use. Although you’re not directly in control of the emissions, by using the energy you are indirectly responsible for the release of CO2. • Scope 3: Any other indirect emissions from sources outside your direct control. Examples of Scope 3 emissions include purchased goods and services, use of sold goods, employee commuting and business travel, outsourced transportation, waste disposal and water consumption (Ref. www.carbontrust.com)

Article provided by Jo Strange, Technical Director at CGL