Posts by Katie Kennedy


AGS Magazine: November 2023

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The Association of Geotechnical and Geoenvironmental Specialists is pleased to announce the November 2023 issue of their publication; AGS Magazine. To view the magazine click here.

This free, publication focuses on geotechnics, engineering geology and geoenvironmental engineering as well as the work and achievements of the AGS.

There are a number of excellent articles in this issue including;
AGS Photography Competition 2023 – The Results – Page 6
AGS Annual Conference Details – Page 8
Some insights into the geotechnical implications of pyrite and its consideration and management – Page 16
Unconscious bias in recruitment – Page 24
Assessing the possible Sustainability Benefits of using Instruments and monitoring on site – Page 26
Inside: HUESKER – Page 30

Plus much, much more!

Advertising opportunities are available within future issues of the publication. To view rates and opportunities please view our media pack by clicking HERE.

If you have a news story, article, case study or event which you’d like to tell our editorial team about please email Articles should act as opinion pieces and not directly advertise a company. Please note that the publication of editorial and advertising content is subject to the discretion of the editorial board.



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Name: Dave Woods

Job title: Technical Manager

Company name: Huesker Ltd

What does the company do and what areas does it specialise in?

Manufacturer and designer of geosynthetics.

Where is HUESKER located?

UK office in Warrington, production facilities in Germany, USA & Brazil

How many people does the company employ?

10 UK employees, 600+ globally

How long have you worked at HUESKER?

Approaching 4 years

What is your career background, and what enticed you to work for HUESKER?

Civil / Geotechnical Engineer with 30 years of experience in UK, Asia and Europe. Geosynthetics have always been a major area of interest and expertise for me, and Huesker were a company whose materials I had known and worked with over my entire career from my very first project widening the M25 motorway.

What is your current role within HUESKER and what does a typical day entail?

Technical support for sales and design of the company products, advice on site installation, business development, external training through CPDs, conference papers and presentations, university lectures etc and representation of the company and industry on industry and technical committees. No two days are alike.

What are the company’s core values?

Imagination, Progressiveness, Excellence, Attractiveness & Reliability.

Are there any projects or achievements which HUESKER are particularly proud to have been a part of?

We are proud of all our projects from small retaining walls and foundations to huge infrastructure schemes. Most recently the development and implementation of geogrid with integrated fibre optic cables to monitor ground movement and warn of sink holes prior to failure on HS2 and the development of active composite textiles which treat contaminants within soils in situ rather than condemning them to landfills.

How important is sustainability within the company?

Sustainability is at the core of all we do. Our products offer up to 85% reductions in embodied carbon content versus conventional construction methods whilst we continue to lead the market with advances in the use of post-consumer recycled materials in our products and increasing use of renewable energy in our production facilities.

How does HUESKER support graduates and early career professionals who are entering the industry?

Where possible we offer external lectures to students at undergrad and postgrad level within universities globally. We seek to employ the very best young engineers and through continuous internal training, mentoring and the sponsorship of Masters and PhDs seek to advance the careers of our employees to reach their full potential.

How has COVID-19 impacted HUESKER today? Are there any policies which were made during the pandemic that have been kept to improve employee wellbeing and productivity?

Options for remote working and flexibility of working hours were always part of Huesker’s working practices, but during and post Covid, these options were made available to more staff members. The increased use of video conferencing has reduced both in house and external face to face meetings helping to improve sustainability and increasing productivity whilst introducing more regular global meetings and training sessions to better share individual knowledge.

Why do you feel the AGS is important to the industry?

The AGS is a valuable source of information and networking opportunities within the geotechnical field through in person events, webinars and published guidance.

What are HUESKER’s future ambitions?

To continue to innovate within the geosynthetics field with an aim to improving the sustainability, safety and economy of geotechnical projects whilst providing solutions to both existing problems and questions which are yet to be asked.

Article Instrumentation & Monitoring Sustainability

Assessing the Possible Sustainability Benefits of using Instruments and Monitoring on Site

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The AGS has asked each of its working groups to discuss sustainability issues at their meetings and the Instrumentation and Monitoring Working Group is no exception. From the Group’s perspective there are obvious sustainability, cost, time and carbon benefits in not having to go to site regularly to monitor Geotechnical or Geoenvironmental parameters. Instead, remote monitoring equipment can be installed, and the data downloaded periodically or streamed in real time to your office computer.

Such a philosophy is also very much in keeping with the AGS data management philosophy – require input of data only once and get the most appropriate person (ideally the producer) to do it.

Unfortunately, many practitioners have had bad experiences with continuous remote monitoring, which can be tricky to establish, maintain and interpret effectively without sufficient experience. Regulators may also not accept on-site analysis of data without prior approval (difficult to obtain with current regulatory response delays), significant oversight and complementary analysis.

There remains a seeming lack of understanding on the part of some practitioners and regulators as to what can be done these days with remote monitoring, the range of equipment that is available and what guidance is available for the use of that equipment (usually precious little and out of date…). The skill lies in the ability to determine exactly what to do and what equipment to use for any particular project, depending on one’s perspective, competence and defined sustainability goals.


In terms of sustainable development, the Brundtland report (UN Report of the World Commission on Environment and Development: Our Common Future, 1987) defines sustainable development as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’.

Sustainability is the combination of several different considerations including environmental, economic and social factors, which can sometimes be even more important than simply reducing carbon. Offsetting is a commonly misused word in the context of sustainability as it rarely is in practice and most people will only come across it in relation to carbon footprints, credits and the fuel in the plane that takes you on holiday.

In fact, the basic concept underlying sustainability is that it is best achieved using a process involving quantification of a combination of potentially related factors from each of the identified key areas as expressed for example in UN sustainability guidance.

This process lead methodology and approach is absolutely key to determining and calculating the positive and/or negative elements identified and quantified to achieve the “best” result – for a given value of “best”.

There have been several attempts to undertake sustainability calculations by both AGS members and others, and several more attempts are currently in the process of being determined, tested and calculated, including at least one for UK regulators. This is in part a response to the engineering sustainability initiatives being developed within the development/building industry at the request of groups like ICE.

However, this is far from a simple task in practice, especially when one starts including considerations of total life cycle carbon, recycling and waste elements, which are very difficult aspects to attach precise and accurate quantifications to.


So, how does one actually go about proving or justifying the use of on-site methods, equipment, analysis, remote monitoring and costs against more traditional methods such as laboratory analysis?  One of the easier ways to at least start the process is to determine the benefit primarily on the basis of cost, especially as the carbon intensive travel to site element is becoming ever more expensive.

For example, six gas monitoring visits (minimum recommended by CIRIA document C665 ‘Assessing risks posed by hazardous ground gases to buildings’ for residential low risk) may cost in the order of £3,000 and 1.2 tonnes carbon dioxide emissions.

Compare this with a remote continuous monitoring system at two visits (one to install and one remove) over a week of falling low pressure continuous monitoring at a total cost in the order of £2,200 and 0.2 tonnes carbon dioxide emissions.

Issues Identified

However, if the regulator treats the CIRIA C665 requirements (for example) as strict requirements and not as guidance, they may not accept the possibility of remote monitoring data and conclusions as continuous monitoring for gasses largely postdates the original publication of that guidance.

This could increase the costs beyond that for the proposed six visits. This is where the socio-legal aspect of the sustainability calculation comes in, along with our professional duty of care to our clients, and perhaps explains why this is not taken up as much as it could and should be, to improve the sustainability of the industry when using newer technologies and alternative, but equally valid and proven methodologies.


As a regulated industry, we can fail on sustainability when it comes to presentation, guidance and especially the regulation itself, which is often many years behind the current realities of what can now be achieved on site.

We hope that this article will provide an initial spur to tackling some of the issues raised by the working group and that with the help of its members and others, the AGS can produce influential and informative guidance to practitioners, clients and UK regulators regarding the options available, new ways and examples of how to achieve regulatory compliance, and how remote monitoring and analysis can contribute to the overall sustainability of our Client’s projects and the industry as a whole.

Whilst in fact the determination process can be fairly simple (at least in theory), to determine what is probably the best, greater or more sustainable method of undertaking current site tasks and analysis, it may not be attainable using a method currently accepted by the appropriate UK regulator or society.

The Instrumentation & Monitoring Working Group will be exploring this topic further and will aim to provide additional case studies and examples of how this can be successfully achieved in practice. If any AGS members have relevant examples, case studies and critiques on any of the above or related topics then please send them to the group via the AGS Secretariat and thanks for listening.

Article provided by Chris Swainston on behalf of the AGS I&MWG

Article Business Practice

Unconscious bias in recruitment

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Whether we think so or not – we are all biased. Decisions we make about people are impacted by our unconscious bias without us even being aware of it. This can have consequences when we are recruiting people into the workplace as well as in appraisals, training and development, networking and mentoring.

Things we notice about a person when we meet them for the first time include their skin colour, age, gender and disability. Our experiences and influences (such as family, peers, media, education) lead us to unconsciously group people into categories which form the basis of stereotypes*, which can lead to prejudice and discrimination. Once we acknowledge our bias, we can take action to reduce its influence.

There are several types of unconscious bias which can strongly influence who we recruit. A couple of examples include:

Affinity bias: where you unconsciously favour someone because you share similar interests, backgrounds and experiences. We feel more comfortable around people who are like us.

Confirmatory bias: where we look for evidence / information that confirms our beliefs and values and we ignore evidence that disproves them.

When it comes to recruitment, examples of how our unconscious bias could influence our decisions include:

  • Employing someone who is not the most qualified;
  • Not recruiting people with differing views;
  • Following ‘status quo’ as a ‘safe’ option;
  • Not asking someone to interview due to a name not sounding ‘English’;
  • Not recruiting someone because they are not a good ‘cultural’ fit;
  • Assuming that a mother won’t be able to commit enough time to work;
  • Assuming an older worker will not be open to learning new skills.

If we want to create an inclusive environment where everyone can flourish, we must address unconscious bias.

There are a number of ways to reduce unconscious bias in recruitment:

  1. Define the job role;
  2. Redact information on the application form / CV that identify key characteristics of a person such as age, gender, ethnicity. This will remove unconscious bias while short listing potential candidates.
  3. Have a diverse hiring / interview panel.

Even by following these steps, it is unlikely that we will be completely unbiased.

Unconscious bias can sometimes be difficult to self-identify and to assist with that there is a test called the Implicit Association Test (IAT). The IAT measures the strength of associations between different groups of people and your immediate thoughts and unconscious stereotypes about those groups of people. The test’s purpose is to specifically highlight bias, this does mean that you may be confronted with some results that you may find upsetting or do not agree with; however, it can be a great method to understand your unconscious attitudes and beliefs.

You can take part in the anonymous test or learn more about it here:

*Stereotype: a fixed idea or image that many people have of a particular type of person or thing, but which is often not true in reality and may cause hurt and offence

Prepared on behalf of the Business Practice Working Group by Vivien Dent (Groundwater and Land Quality Technical Specialist, Green Growth and Delivery, Environment Agency) and Bradley Falcus (Senior Geo-Environmental Administrator, Central Alliance Pre-Construction Services Ltd)


Some insights into the geotechnical implications of pyrite and its consideration and management

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The assessment of ground aggressivity and suitability of construction materials are fundamental aspects of geotechnics. Ground hosted sulfide and sulfate minerals are known to produce unwelcome implications for ground engineering. Confidence in selection of the most appropriate form of construction and mitigation methodology, must be based on the results of meaningful site-specific material characterisation and assessment of performance in the likely construction environment. It is apparent that many ground engineering practitioners do not fully appreciate that certain rocks and soils are liable to contain sulfur species that may negatively impact ground engineering projects. In practice assessment procedures are often followed without a clear understanding of the issues and how to best manage them. This approach is not always suitable for managing the extensive variability encountered in the UK. Furthermore, an appreciation of how the construction activities may bring about undesirable changes are necessary for design of appropriate mitigation and long-term management. This short article discusses some of the issues that may occur, particularly where pyrite is concerned and considers how these characteristics and associated risks may be managed.

Causes of construction groundwork damage brought about through physical deterioration of ground and engineering materials are attributed to a wide range of factors that involve physical, chemical, and biological processes. In the UK a high proportion of such occurrences in the engineering environment result from the presence of sulfate ions in groundwater, brought about through dissolution or reaction of sulfur compounds. Pyrite and gypsum are the most commonly occurring sulfur compounds likely to be encountered during construction works.  In certain locations, the source of the sulfate ions is clearly through dissolution of evaporitic deposits, but in many cases, covering a much wider geographical area, these are derived from the oxidation of iron sulfide minerals, particularly pyrite. Pyrite, and the other infrequent iron sulfide minerals are unstable in oxidising and damp atmospheric conditions typical of the construction environment and will rapidly weather, producing insoluble orange-brown hydrous iron oxide, with release of hydrogen (H+) and sulfate (SO42-) ions into solution as mobile sulfuric acid. This has a significant negative impact for ground engineering when reaction occurs consequent of ground disturbance, creating conditions that are aggressive to ground material including buried steel and concrete and, in some cases, raising sulfate to harmful levels.

Reaction of the sulfuric acid with other calcareous minerals such as calcite or concrete, give rise to selenite-gypsum as discrete crystals, and this involves expansion. The replacement of pyrite and calcite by selenite involves a volume increase of around 103%, developing ground stresses and causing differential heave due to indiscriminate crystal growth. This chemical alteration is frequently accompanied by rapid deterioration in engineering properties of the host material and the volumetric gain often causes disturbance in filled ground, and failures of foundations, earthworks, underground excavations, tunnels, and slopes. Observations have also documented abiotic pyrite oxidation where the pH of pore fluids was around pH >12, indicating that this reaction mechanism can also occur when pyrite bearing ground is treated using lime and cement.

The oxidation of pyrite is complex, it occurs through various reaction stages, at different rates, which conclude in a range of products. Ultimately reaction depends on various aspects including the crystalline form and grain size of the pyrite, the mineralogy and fabric of the host, and environmental conditions, including the exposure to weathering brought about by the engineering work. To manage any negative impacts to design and construction, the possibility of changes promoting the potential for pyrite oxidation during and after construction needs to be considered.

Sulfur is an abundant element in the Earth’s crust and occurs in geological materials of all ages and origins, in a variety of forms. Sulfur is highly reactive and readily combines with most non-noble elements, particularly under reducing conditions, to form metallic sulfides of which the iron form, pyrite (FeS2) is the most widely occurring, along with its less common dimorph marcasite (FeS2), and occasional pyrrhotite (Fe1-xS where x = 0 – 0.2). Gypsum tends to be the most widely occurring sulfate mineral and is frequently encountered during ground works. Gypsum occurs as a primary accumulation in evaporite deposits such as the Mercia Mudstone Group and forms through evaporation of saline waterbodies. But it is more widely occurring as the crystalline ‘selenite’ form, which tends to develop as a ‘secondary’ product of contemporary weathering action on pyrite in the presence of calcite. The oxidation of pyrite will also give rise to high concentrations of sulfate ions which are mobilised by groundwater. Not all forms of sulfur are troublesome in engineering situations, although this depends upon the environmental conditions. Some recalcitrant mineral sulfates, such as barytes, celestine, and organic sulfur are relatively stable in weathering environments, and do not contribute to the sulfur present in groundwaters, unless conditions are unusual, so they are unlikely to impact significantly in construction and geo-material applications. Therefore, knowledge of the likely occurrence and attributes may help to manage potentially adverse conditions that could occur during and after construction.

Pyrite is remarkably widespread in its occurrence and is found as a minor constituent in a wide range of naturally occurring materials. It occurs in rocks and engineering soils, ranging from ancient sediments to Recent deposits, igneous and metamorphic rocks and hydrothermally deposited mineral veins. Pyrite occurs as diverse forms including variously shaped grains, nodules, and well-formed crystals, ranging from microscopic to several cm across; the morphology of pyrite has an influence on its potential for atmospheric oxidation. Therefore, its appraisal may help to determine its potential reactivity and the suitability of pyrite bearing ground and geomaterials for particular applications.

The different forms of pyrite and their combinations all share the same internal arrangement of iron and sulfur atoms but conditions during formation affect the crystal form. Well-crystallised pyrite occurs in the brass-yellow macroscopic form as large masses, veins or as large discrete often striated cubic, octahedral or pyritohedral crystals a few millimetres to a few centimetres in dimension and are commonly referred to as the ’non-reactive’ form of pyrite.  Typically, these are found in rocks that are well indurated and / or have been subjected to moderate to high-temperatures and pressures.  These well-crystallised forms of pyrite have a densely packed structure and relatively small specific surface area such that they tend to respond slowly in weathering environments. Macroscopic forms of pyrite occur extensively in igneous and metamorphic rocks and some hard-rock limestones, sometimes in substantial concentrations distributed through the host and tend to be relatively stable in construction environments.  These deposits are widely worked in the UK for construction aggregates in which slow oxidation or combination with cementitious binders may lead to problematic chemical reactions. In less-well indurated sedimentary rocks, pyrite may occur as visible nodules or smooth faced crystals, but more typically, it takes the form of disseminated microscopic framboids that are very difficult to recognise.

The microscopic framboidal form of pyrite is of greatest concern to ground engineering. Framboidal pyrite tends to form in sedimentary environments under anoxic reducing conditions through microbial activity where it remains stable, but when exposed to oxidising and damp atmospheric conditions it may rapidly deteriorate with consequentially detrimental effects.  It is commonly found in dark coloured (grey and dark grey), fine-grained sedimentary deposits including clays, mudstones, argillaceous limestones, siltstones, sandstones, and low-temperature hydrothermal deposits. The microscopic reactive forms of pyrite may also occur in newly formed sediments, including marine sands and gravels and river flood plain deposits, which are widely used as construction aggregates. Framboids are raspberry-like spherules, typically 2 – 80 μm diameter, comprising of ordered agglomerations of microcrystalline pyrite grains that are themselves <0.3 – 2 μm in diameter. They occur as disseminated spherules, clusters, or dark greenish-grey coloured concentrations along partings. The framboidal structure results in grains with a large surface area in proportion to their volume, making them highly susceptible to oxidation in an oxygen and water bearing atmosphere and oxygenated water.  This reaction may be mediated and greatly accelerated by microbial intervention from bacteria such as the ubiquitous Acidithiobacillus sp., which rely on electron transfer between Fe2+/Fe3+ for their metabolic process and this functions as a key mechanism in the oxidation reaction. In the ground engineering discipline, this form of pyrite is often referred to as the ‘reactive’ form of pyrite.

It is cautioned that the allusion to the visible form of pyrite as ‘non-reactive’ is not strictly true, the well-crystalline macroscopic forms of pyrite are still susceptible to oxidation following exposure, but depending on their surface condition, reaction generally will occur over a much slower timescale and may not be considered significant where construction is concerned, although it may be expedited where physical damage occurs to the crystals and through reaction of less stable forms. Therefore, potential reactivity must be assessed, with judgement also relying on previous experience of that material.

In the UK, framboidal pyrite is widely found in the dark coloured deposits of marine and fluvial origins of Carboniferous, Jurassic, Cretaceous and Eocene age. These account for a large part of the near-surface stratigraphy that contains many major urban centres. Through weathering, sulfate minerals can be present at shallow depth, whereas sulfide minerals may predominate at greater depths where oxidation has not occurred. Weathering involves physical and chemical changes to the natural material as it adjusts to different overburden pressures and the presence of atmospheric gases.  The change in pressure results in development of fissures and joints which facilitate the movement of oxygenated groundwaters. Water movement promotes chemical adjustments including hydration, dissolution and alteration of certain minerals and the formation of other minerals.  The distribution of sulfate varies within the weathered zone, with the top few metres having negligible amounts due to removal by rain leaching, but elevated levels may be present at the base of the root zone at around 2 to 3 metres depth, decreasing towards the base of the weathered zone, and this is identified by presence of brown staining on fissure and bedding surfaces, and presence of selenite. The weathering state is revealed by the colour changes of the iron forms present. In weathered horizons, the orange-brown colour of ferric iron predominates, whereas with depth the grey colour of ferrous iron represents less weathered lithology and indicates an increase in the presence of unreacted sulfide minerals.

Although British, European, and other standards promote good practice in carrying out investigations, potential problems are often not adequately anticipated and catered for. Historically the Building Research Establishment have provided guidance for routine UK assessment of potential ground aggressivity based upon water and acid soluble sulfate content and acidity of soil and groundwater samples. This worked well for many decades with few instances of sulfate attack on buried concrete reported.  However, following investigation on several cases of sulfate attack on construction materials and disruptive ground heave during the 1980s-1990’s, it was realised that the consequences of pyrite oxidation were not being considered and had been attributed to various other assumptions. Precipitation of new minerals such as gypsum provoke possibilities of ground heave. As the process of dissolution and precipitation will not generally occur in the same location, both expansion and void creation may produce differential movements and heave causing structural damage. This necessitated revision of testing standards, and guidance advocating a staged approach based on initial review of the geological setting, followed by a planned investigation programme and detailed ground assessment. This requires an awareness of potentially aggressive material and importance of focused chemical testing. The severity of pyrite oxidation depends not only on the crystal form but also on the permeability and chemistry of the host deposits as well as the groundwater conditions. The site investigation may confirm the presence of significant quantities of pyrite, gypsum, and calcite but these values alone do not facilitate assessments of the reaction rate and significance to construction. Assessment also requires that the consequences of the construction activity and weather-related issues in the construction period and beyond are fully addressed to provide an adequate basis for the design of structures.

The consequences of pyrite reaction may become a significant hit for the construction budget and progress when unsuspected. The oxidation of pyrite bearing deposits during earthworks and construction has been observed to progress rapidly over a matter of weeks or months, producing conditions chemically aggressive to engineering materials. Therefore, to avoid or manage potential problems attributed to pyrite oxidation it is necessary to know not just that it is present, but also its distribution, its form and reactivity. Investigations and construction may overlook the potential for material deterioration, but this can be determined at a site level through observation of changes following exposure and targeted chemical testing. The distribution of sulfur compounds in soils and rocks can be highly variable so testing must ensure that sulfur-bearing horizons are not missed, and a suitable characteristic value selected for design. Material selected for laboratory testing should focus on the construction zone but also evaluate other strata that may be affected.

Knowledge of the mechanical behaviour of the host material and the changes brought about through exposure during construction may expedite management of the construction process by facilitating re-use of a favourably weathered product that would otherwise constitute an unsuitable material. Ultimately, management of material avoiding costly offsite disposal, may be achieved through informed investigation with pre-weathering of pyritic fill to mitigate the risk of heave through conversion of pyrite to selenite or by blending, encapsulation, or provision of targeted drainage and impermeable barriers.

Article provided by Mourice A. Czerewko, Associate Engineering Geologist, AECOM Ltd


AGS Photography Competition 2023 – The Results

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In March 2023, the AGS launched their fourth photography competition.

Members of the AGS Executive and Business Practice Working Group including Vivien Dent, Sally Hudson, Jo Strange, Bradley Falcus and Steve Hodgetts took on the challenging task to judge the images by scoring across the following criteria;

  • Originality
  • Composition
  • Colour, Lighting, Exposure and Focus
  • Overall Impression, Impact and Visual Appeal

Four images were shortlisted, and we’re pleased to announce that Shannon Wade of Strata Geotechnics was the overall winner of the competition and won a luxury Fortnum and Mason Hamper.

Our three runners up, who each won a bottle of Champagne are Shannon Wade (Strata Geotechnics), Matthew Cook (Environmental Protection Strategies Ltd) and Aaron Stokoe (Brownfield Solutions Ltd).

The AGS would like to thank all those who took the time to enter the competition.


Shannon Wade, Strata Geotechnics

Image description: Truly highlights the highs and lows of rural GI. An additional scheme of work for The Coal Authority at the site of the Esgair Mwyn, Metal Mine near Pontrhydfendigaid to again improve water quality and prevent it leaching through metal mine spoil. The weather had been foul for days with limited shelter, our team worked their hardest in the conditions to get the works done safely and on time and were rewarded by a little bit of sunshine and a glorious rainbow.


Shannon Wade, Strata Geotechnics

Image description: Working nights with our Comacchio 305 on the M1 Southbound, J35 for National Highways undertaking works to inform design for addition PRS lay-bys on our existing Smart Motorways network.


Matthew Cook, Environmental Protection Strategies Ltd

Image description: The drilling of windowless sample boreholes at an RAF site in Cambridgeshire with RAF jets in the background, boreholes were being drilled to to provide information for use in improvements to site.


Aaron Stokoe, Brownfield Solutions Ltd


Second Generation Eurocode EN 1997: Where are We and Where are We Going? Webinar summary

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On 20th September 2023, the AGS held a webinar entitled Second Generation Eurocode EN 1997: Where are We and Where are We Going?. The webinar was chaired by Chris Raison (Director at Raison Foster Associates) and included presentations from Dr Andrew Bond (Director at Geocentrix), Matthew Baldwin (Independent Consultant) and Stuart Hardy (Technical Leader – Geotechnical at Laing O’Rourke).

The webinar was split into two parts, the first part which was presented by Andrew Bond focused on preparing for the Second Generation Eurocodes and gave a clear timeline for publication. Andrew also provided information about Second Generation Eurocode EN 1997: Geotechnical design – Part 1: General Rules.

In the second half of the webinar, Matthew Baldwin presented on Second Generation Eurocode EN 1997: Geotechnical design – Part 2: Ground Properties, explaining the changed content and layout of this part of the standard.

Stuart Hardy provided an overview of Second Generation Eurocode EN 1997: Geotechnical design – Part 3: Geotechnical Structures and covered the changes which have been made to the clauses and what has not changed from current UK practice.

If you missed the webinar, the recording is now live on the AGS website and is free for AGS members and £30 for non-members (Ex. VAT).


AGS Magazine: September 2023

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The Association of Geotechnical and Geoenvironmental Specialists is pleased to announce the September 2023 issue of their publication; AGS Magazine. To view the magazine click here.

This free, publication focuses on geotechnics, engineering geology and geoenvironmental engineering as well as the work and achievements of the AGS.

There are a number of excellent articles in this issue including;

Use of chemical preservation – the importance of quality in sampling and analysis – Page 16
Surface Emission Surveys – Page 21
Mitigating the risk of asbestos when using vacuum excavators in made ground – Page 24
Inside: Geosense – Page 28
Q&A: Bradley Falcus – Page 32

Plus much, much more!

Advertising opportunities are available within future issues of the publication. To view rates and opportunities please view our media pack by clicking HERE.

If you have a news story, article, case study or event which you’d like to tell our editorial team about please email Articles should act as opinion pieces and not directly advertise a company. Please note that the publication of editorial and advertising content is subject to the discretion of the editorial board.

Article Safety

Mitigating the risk of asbestos when using vacuum excavators in made ground

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Vacuum excavation[1] is widely used in the ground investigation industry as a means of excavating inspection holes and trenches to check for utility services prior to drilling or probing.  The significant safety benefits of vacuum excavation compared to hand digging are that the operatives are not as close to any exposed utility services and that the hazards associated with damage to utility services by hand-held digging equipment are significantly reduced from the activity, a true reduction of risk through engineering controls.

Urban and brownfield sites typically contain made ground and industry suggests that asbestos is detected on most brownfield sites that are investigated[2]. A recent SOBRA report indicated that the asbestos detection rates in soil samples submitted for laboratory analysis vary from 1.4% to 20%[3].  SOBRA concluded that: ‘Anecdotal information from the industry suggests that asbestos is detected at the majority of brownfield sites that are investigated. This data suggests that, on average, asbestos is detected in a small (but nevertheless potentially significant) proportion of samples from those sites.’  Excavation on brownfield sites could therefore encounter asbestos in soil both as visible asbestos containing material (ACM) or as loose fibres, which are not visible to the eye.

The Construction Plant-hire Association (CPA) guidance1 states that if asbestos is suspected during vacuum excavation, work should stop so advice can be sought, and that disturbance of asbestos should be prevented.  It suggests that suitable documented control measures and in some cases specialist or dedicated suction/vacuum excavator machines are required for the removal of asbestos impacted soils.

To comply with the Control of Asbestos Regulations 2012, CAR-SOILTM and AGS Guidance, the CPA recommended that where asbestos is suspected additional controls should be introduced which include: use of suitable PPE and a grade P3/FFP3 face mask; working with a water lance (not air lance) which is less likely to cause asbestos fibres to become airborne; cleaning and disposal of outer clothing; good hygiene; and decontamination of the machine.  The guidance indicates that if asbestos was seen, a laboratory could attend site and undertake monitoring of the machine’s exhaust air, at the downwind public boundary, as well as personal monitoring and swab testing of the machine including the filter. These control actions are reliant on the presence of asbestos being identified or suspected by the Vacuum Excavation operatives or pre-notified to them.

As asbestos in soil can be difficult to identify and loose fibres would not necessarily be visible to the naked eye, the principles of the Construction Design and Management Regulations 2015 (regulation 12.2 including Schedule 3 & 12.4) should be followed. Those employing vacuum excavator should set out the arrangements for controlling risks within the construction phase plan, Schedule 3 ‘Work which puts workers at risk from chemical or biological substances constituting a particular danger to the safety or health of workers or involving a legal requirement for health monitoring’. In addition, where members of the public could be at risk from vacuum excavation of impacted soils within an urban or residential setting, the requirements of the Health and Safety at Work Act 1974 Section 3 ‘General duties of employers and self-employed to persons other than their employees’.

It is therefore a requirement for any contractor adopting vacuum excavation to provide to sub-contractors suitable and sufficient information about the risk of asbestos being present within the target area soils and the controls required to mitigate this risk.

Therefore, for those proposing to use vacuum excavation in environments where soils contain or are suspected of containing asbestos; it is recommended that:

  • they notify operators of the vacuum excavation equipment of the presence (or potential presence) of asbestos in the soil.
  • they consider adopting mitigation controls (in addition to those identified by CPA described above) such as would be required for asbestos in soils environments e.g. using controlled wetting, mist curtains, etc.
  • the control measures within the CPA guidance are adopted for all brownfield sites until the risks to workers and the public from airborne asbestos resulting from the use of suction/vacuum excavators are better categorised; and
  • asbestos in air monitoring is undertaken to support the use of vacuum /suction excavators on brownfield sites including both personal monitoring, boundary monitoring and monitoring of exhaust air to better understand the risk levels to workers and the public.

The CPA guidance suggests that exhaust air emissions could impact other workers and the nearby public, highlighting that the type of filtration used within vacuum excavators does not capture and contain asbestos fibres. While it is possible to dampen the soils entering the vacuum excavator, the mechanical action of the vacuum causes the excavated soil to be dried and could therefore facilitate fibre release, both at the location being excavated and also at subsequent sites using the same plant, prompting a need for thorough decontamination of the plant (in line with the requirements of the Control of Asbestos Regulations 2012) when it is used to extract asbestos impacted soils.

The management of waste is also a consideration when undertaking vacuum excavation where the presence (or potential presence) of asbestos in the soil is known. In such a scenario, the extracted material and plant decontamination washout, cleaning and swabbing materials should all be treated as waste, handled, transported, and disposed of in line with legislative requirements.

The use of vacuum excavators to expose utility services or to disprove the presence of utility services remains a lower risk than conventional machine and hand dug excavation and remains a preferred excavation method when excavating made ground with on urban or brownfield sites where there is a risk of utility services. However, careful planning of these activities is required to ensure that the significant physical risk posed by the utility services is not replaced by a significant health risk posed by potential asbestos release.

By following the principles of good task planning; communicating potential risks, assuring safe systems of work, waste control and staff competence, suitable and sufficient risk mitigation for the use of vacuum excavators on made ground can be achieved.

There will, however, be some conditions which limit the ability and effectiveness of these controls measures to mitigate the risk of asbestos, especially when working within heavily populated areas. In such cases careful evaluation of available risk controls effectiveness is required.

[1] Industry guidance ‘Safe Use of Suction/Vacuum Excavators, Good Practice Guide, Construction Plant-hire Association, Safety Publication Series, SAVESIG GPG1, January 2019’ describes suction/vacuum excavators as ‘items of plant utilising a powerful fan or pump to cause a pressure reduction in a suction hose in order to excavate pre-loosened earth and granular materials, and draw them into a temporary store in a receiving hopper for subsequent discharge. As the spoil reaches the hopper, it is separated from the moving air by cyclonic and other filtration methods, with cleaned air exhausted via an outlet system whilst the spoil is contained within the sealed hopper.’  Ground engaging tools that break soils can be utilised with suction/vacuum excavators and ‘air or water pressure through a lance is considered a safer system than manually breaking soils and allows quick and easy displacement of material around sensitive areas of services. The use of a lance minimises the need for the operator to be at the edge of or within an excavation.

[2] The Distribution of Asbestos in Soil – what can the data mining of sample results held by UK laboratories tell us? Discussion Paper by the SoBRA asbestos sub-group, March 2020

[3] The March 2020 SOBRA paper considered asbestos test results from five laboratories across different time periods since 2011. The origin of the soil samples was not known, and the test methods varied.

Article by Madeleine Bardsley, Technical Director at WSP and Jon Rayner, Director SH&E at AECOM

Image credit: AECOM

Article Contaminated Land

Surface emission surveys to measure ground gas

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Surface emission surveys are used to measure the rate that ground gases are emitted into the atmosphere, which can be quantified in order to determine the risk to the environment or other receptors, such as a property and human health. The concentration and flow of ground gas can alter depending on the location of a monitoring point, source material, geology, atmospheric conditions and groundwater levels. Therefore, an emissions survey can be a useful line of evidence to better conceptualise the actual concentration/volumes of ground gas that may be impacting a given receptor.

Surface emission surveys are commonly used on landfill sites following the placement of a temporary or permanent capping layer, in order to confirm compliance with the environmental permit or conditions. Guidance on this subject can be found in the Environment Agency’s document LFTGN07 V2 (2010). A useful precursor to a survey, and requirement of landfill surrender is to visually assess any evidence of vegetation stress or dieback that could be caused by ground gas, as well as note the condition of the surface layer i.e. note any defects in the capping layer that may allow a route for ground gas to escape.

A surface emissions survey typically comprises two elements:

  1. A walkover survey taking gas readings just above the ground surface, and landfill infrastructure (which is often referred to as the surface emissions survey)
  2. flux chamber tests at selected locations based in (i) or on a grid.

The walkover survey uses a handheld instrument, such as a flame ionisation detector (FID) or tuneable laser diode, which detects organic compounds such as methane at very low concentrations (0.1 parts per million). This again can be used to assess any defects in the capping layer and leaks from landfill infrastructure. The EA guidance states that if a FID survey records concentrations of over 100ppm over the capping layer, or 1000ppm next to a discrete feature such as a monitoring well, then remedial action should be undertaken. The survey results should be geo located and typically contour plots of the data are produced.

The flux chamber survey is used to quantify the volumes of methane emitted from a landfill to confirm that any active gas venting systems are working correctly and to minimise the amount of methane emitted into the atmosphere, a requirement of the Landfill Directive (1999). In the UK it is most common to use a static flux chamber. Essentially a flux box is a vessel of a known area/volume where the concentrations of gas can be monitored (using a FID or other monitoring device with an equally low detection limit) over a period of time in order to calculate the emissions based on the flux in concentrations (see Pictures 1/2). However, it is important to note that the flux box, like any other gas monitoring method, has its limitations. It can be difficult to create a good seal between the flux box and underlying ground, therefore a level surface with the vegetation removed is necessary. Also, a flux box can provide skewed readings if placed over preferential points such as cracks or on the edge of a capping layer where gas can escape, so the survey requires careful design involving multiple points spread across an area, based on the initial surface emissions survey.

With respect to contaminated land investigations where the principal objective is to assess the risk to an existing or future development, a surface emission survey is a valued line of evidence to confirm calculated rates using measured borehole data, along with empirical data. In relation to calculated rates, the ‘Peckson method’ is often cited, which assumes that borehole’s zone of influence is 10m2.  However, this method does not consider differences in the permeability of the underlying geology (leading to over conservatism) and potential preferential pathways such as services. A more detailed assessment to calculate the movement of ground gas via diffusion or advection can be undertaken using Ficks or Darcey’s Law.

A flux box survey can also be useful technique where there is a shallow source of gas / where shallow groundwater levels limit the use of monitoring wells (flooding the response zone, which prevents the ingress of gas), assuming the conceptual site model indicates a viable risk. Other lines of evidence, including visual description of the source material and soil testing for organic matter, should always be used alongside the emissions test to provide robust risk assessment. The flux box test is not well suited to assess risk from deep sources, or if new pathways for ground gas migration are introduced by the development from foundations or services.

With regards to monitoring, the placement of shallow monitoring wells (<5m) over a deeper source can aid characterisation of the risk if there are intervening cohesive layers that limit the vertical migration of the gas, or in establishing flow dynamics in historical landfills by contrasting the results with deeper wells. Careful consideration should be given to the existing and possible future pathways of gas migration when designing the monitoring positions ideally placing them at some significant point between the source and receptor. The use of continuous monitoring devices that record gas concentrations and flow (depending on the device) along with atmospheric conditions (typically every 1 hour) have become a well-established method of monitoring ground gas. They are extremely useful for rapidly assessing any trends in concentrations and the ‘worst-case conditions’, the results of which can be used when calculating the emission rate.

In summary, emission surveys are commonly used on active landfill sites to ensure compliance with the environmental permit. These techniques can also be used as a line of evidence when assessing the risk to a development from ground gas. However, these surveys do have limitations and should not be used in isolation.  Anyone using the approach should ensure that the design of the survey is relevant to the CSM for the site. Further technical guidance would therefore be beneficial to the contaminated land industry to ensure consistency of approach in different ground model and risk assessment situations.

Picture 1 Continous monitoring device

Picture 2 Example of Flux Box

Picture 3 Example of Flux Box


  • The Ground Gas Handbook, Steve Wilson, Geoff Card and Sarah Hains, 2009.
  • LFTG07: Guidance on measuring landfill surface emissions, Environment Agency, 2010.
  • BS8576 Guidance on investigations for ground gas – Permanent Gases and Volatile Organic Compounds, British Standard Institute, 2013.
  • Ground gas – an essential guide for house builders, NHBC, 2023

All images provided by RSK.

Article provided by Andrew Tranter, Principal Environmental Consultant at RSK


Article Contaminated Land Laboratories

Use of chemical preservation – the importance of quality in sampling and analysis

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Geraint Williams, ALS Laboratories and Tim Rolfe, YES Engineering, both members of the AGS Contaminated Working Group, discuss how representative samples should be collected to ensure subsequent laboratory analysis is robust and reliable


This article covers the preservation requirements for common contaminants and key chemical indicators of Monitored Natural Attenuation (MNA) including metals, ammoniacal nitrogen, cyanide, sulphide and manganese II.  It provides practical guidance for those involved in groundwater monitoring and surface water sampling and is relevant for risk assessors, remediation contractors and regulators.

In September 2022, members of the contaminated land group were invited to complete a short questionnaire.  This survey highlighted inconsistencies in the use of chemical preservation.  AGS received comments about a lack of confidence in laboratory results where preservation has not been used, the need to follow established practice and a call for more scrutiny and oversight: “I would have no confidence in the data…”.  Other direct quotes include: “we review reports where preservation has not been used and have to conduct further rounds of monitoring to obtain better quality data”.

Taking account of the concerns highlighted in the previous survey, the following article provides more information on why preservation is so important.

Dissolved Metals

Dissolved metals can be impacted by many physical and chemical factors, particularly redox conditions, pH or temperature which can trigger changes due to precipitation, co-precipitation, sorption or dissolution of particulate matter.  These factors can cause significant positive or negative bias to dissolved metal concentrations.

Samples are acidified to prevent precipitation of metals, especially iron.  Once precipitation has occurred there is no way of knowing how much metal was in solution, or in suspension, at the time of sampling.  The only way of resolving this is to filter out suspended metals in the field, placing the filtered sample in a dedicated nitric acid bottle to ensure that all metal dissolved at the time of sampling remains in solution.

Ferrous Iron

Ferrous iron, once sampled, will generally rapidly oxidise to ferric iron and precipitate as ferric oxyhydroxide.  Hydrochloric acid is used to fix the ratio of ferrous and ferric iron.  Adding the acid in the laboratory is not an acceptable substitute since the ferrous iron is highly likely to have oxidised in transport.

The concentrations of ferrous and ferric iron are used as supporting evidence for the presence of MNA of organic contaminants by biodegradation, therefore measurement of the correct species is essential to understanding the aquifer conditions.

When iron precipitation occurs in a sample, other metals can co-precipitate, causing substantial changes to the overall dissolved composition of metals.  Co-precipitation of metals is covered in more detail in a previous AGS magazine article published back in August 2020.  It highlights how concentrations of arsenic, lead and cadmium can be significantly affected with losses of between 80 to 97% reported.

Manganese II

Samples for manganese II require filtering in the field to remove insoluble Mn IV compounds before adding to a bottle containing hydrochloric acid.  The acid prevents oxidation of Mn II to insoluble Mn IV.  Mn II acts as an indicator of anaerobic degradation of organics, where manganese IV acts as an electron acceptor.

Ammoniacal Nitrogen

Ammoniacal nitrogen includes both the ionised form (ammonium, NH4+) and the unionised form (ammonia, NH3).  An increase in pH favours formation of the more toxic unionised form (NH3), while a decrease favours the ionised (NH4+) form.  Temperature also affects the toxicity and form of ammonia.  This relationship is detailed in the Table 1.

Table 1 Percentage Un-ionised Aqueous Ammonia (0-30°C, pH 6-10)

Source: Canadian Council of Ministers of the Environment (CCME) (2010) Canadian Water Quality Guidelines for the Protection of Aquatic Life.

It is possible to simply measure the ammoniacal nitrogen, and then to calculate the ammonia, if the pH and temperature of the sample were measured at source.  As illustrated above, at the range of pH typically encountered in groundwater samples, the percentage of the more toxic un-ionised ammonia can increase approximately threefold between a sample temperature of 10oC and a room temperature in the laboratory of 20oC.

Because of the volatility of ammonia, the action of nitrifying bacteria, and the changing equilibrium between ammonia and ammonium, groundwater and surface water samples must be collected using sulphuric acid to fix the ammoniacal compounds to prevent further change.  Sulphuric acid reduces pH to <2.  The acid will convert the ammonia to ammonium and the results are reported as ammoniacal nitrogen.  This prevents microbial degradation and off-gassing of ammonia.


Laboratories use sodium hydroxide to keep the water alkaline and the cyanide in solution.  If the water is not preserved and is slightly acidic, the cyanide may convert to hydrogen cyanide and be lost from the sample.  The reported concentration from the laboratory will therefore underestimate the cyanide present in groundwater or surface water, and where speciated cyanide analysis is being undertaken the concentration of the more toxic ‘free-cyanide’ will be most affected.


Sulphide oxidises to sulphate in contact with oxygen. The industry standard technique for preservation of sulphide utilises zinc acetate.  Zinc ions from zinc acetate react rapidly to form zinc sulphide, an insoluble precipitate, sequestering the sulphide species and preventing off-gassing and oxidation.  Ensuring that the correct proportions of sulphide and sulphate are reported is essential to assessments of concrete design classification and of aquifer conditions for MNA decisions.


How samples are collected and analysed is crucial to the reliability of human health and controlled water risk assessment and in assessing the effectiveness of MNA.  Chemical preservation is required to ensure that samples are representative of field conditions.  Samples collected for analysis of unstable contaminants, that have not been preserved, are unlikely to provide valid, consistent, or defensible analytical data.  This article is written in advance of guidance being published by Contaminated Land: Applications in Real Environments (CL:AIRE) on MNA.


  • AGS Guide to Environmental Sampling, Association of Geotechnical and Geoenvironmental Specialists, 2019
  • BS EN ISO 5667-3: 2018 Water quality: Sampling – Part 3: Guidance on the preservation and handling of samples
  • BS ISO 5667-11: 2009 Water quality. Sampling. Guidance on sampling groundwaters
  • CCME (2010) Canadian Water Quality Guidelines for the Protection of Aquatic Life. Publication No. 1299; ISBN 1-896997-34-1
  • Society of Brownfield Risk Assessment (SoBRA) Practical Tips to Share: Improving Risk Assessment – Field to Desk

Image credit to ALS Laboratories (UK) Limited

Article provided by Geraint Williams, ALS Laboratories and Tim Rolfe, YES Engineering


Q&A with Bradley Falcus

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Full Name: Bradley Falcus

Job Title: Senior Geo-Environmental Administrator

Company: Central Alliance Pre-Construction Services Ltd

I’m an early career professional who believes that the power of people can never be underestimated, nor should it be underappreciated. Over the past four years since my masters degree, I have become experienced in the geotechnical sector working in archaeology, geophysical exploration and ground engineering. I have quickly adapted to a management role within this timeframe, developing a team of trained geo-environmental and business administrators before the age of 30. I am passionate and driven to make a difference in the geotechnical sector, be that business-by-business, or wider reaching to the AGS’ members.

Are there any projects which you’re particularly proud to have been a part of?

I suppose my answer to this is split into two, one for my role within Central Alliance and one for my role within RSK. Working as one of the Data Managers on the Wales and Western Framework (Network Rail) has been a fantastic opportunity for me to learn and develop. The role is multifaceted and requires a great attention to detail and seems to continue to grow arms and legs with every week that passes. I enjoy working with my colleagues at Central Alliance on framework projects like this, it gives me the opportunity to work closer with them as part of the project management team and share in the delivery of great results to our client.

Within the wider RSK Group, I am a co-chair of the RSK Pride Network, an employee ran network which supports and welcomes LGBTQ+ people in the workplace. In July 2023, RSK were one of the sponsors of Bristol Pride. We brought together staff members from across the UK and had a wonderful celebration of our RSK Family. I can honestly say it has been an amazing event to organise and run – hopefully we’ll have more like it in the future and maybe we can extend the invite to other AGS members.

What are the most challenging aspects of your role?

Time! I think with a role like mine, it’s quite easy to forget when to switch off. Some days it will be nine hours of meetings, some days it will be nine hours of tender compilations, some days it will be nine hours providing training. Every day is different from the one before it; and even though that makes it interesting, it can be overwhelming if you don’t have the right procedures in place. Best advice from me is to make sure you take time for yourself, in and out of your work hours – don’t be a martyr to Ground Investigation by slaving away for hours and hours.

You have recently joined the AGS Business Practice WG to help develop Equity, Equality, Diversity and Inclusion within the AGS. What are your aspirations for the AGS?

Two of the UN Sustainable Development Goals are Gender Equality and Reducing Inequalities; these are targets that we as an industry have to take seriously going forward. I believe that trade associations like the AGS have a fundamental role to play in changing the attitudes of businesses across the UK and internationally on how we can be more equal and inclusive. I really do have aspirations that the AGS will be able to champion employment equality and equity, increase graduate opportunities and to represent the underrepresented. I hope that we can, as the BPWG, spark conversations around the topic of reducing inequalities across our industry and continue to welcome generations of new bright minds to the fold.

What do you enjoy most about being an AGS Member?

I love being able to connect with so many intelligent and interesting people that are part of the AGS. It’s inspiring as a young professional (I think I qualify for that title) to attend conferences and webinars to learn from the vast amount of experience there is in the group. Personally, I cannot wait for the next in-person meeting and hope to see many friendly faces there.

What do you find beneficial about being an AGS Member?

Being able to keep on the pulse of all the updates from the geotechnical and geoenvironmental sector – rules, regulations, guidance and procedure change so quickly, it’s always good to be part of the movement than behind it. Also being able to interact with the different working groups is invaluable, by attending conferences and meetings you have the opportunity to shape the future of the geotechnical industry.

Why do you feel the AGS is important to the industry?

The AGS is one of the best platforms for collaboration in our industry –  Helen Keller, an activist for disabled rights, said that ‘Alone we can do so little, together we can do so much’ and I think about that quote quite a lot and what it means for us. It’s important to know that we aren’t as secular or ‘alone’ as we sometimes believe to be. The AGS is a shining example of fantastic minds, creative people and keen advocates coming together for the future of our sector.

What changes would you like to see implemented in the geotechnical industry?

In my dreams? I would love to have collaborative networks created between AGS member businesses which minority communities (for example: POC, LGBTQ+, people who are neurodivergent, people who are disabled, etc) would be invited to join. These networks could have regular meetings, chaired by the AGS, where they would be able to give direct feedback and guidance on what the industry can improve upon. I’d hope we could create a welcoming space for all people to join us from all backgrounds and ensure that their voices are heard. In the meantime, I would love to see guidance from the BPWG on tackling unconscious bias and good hiring practices in our industry as a fundamental step in the right direction.