Prevalence of CO2 from disused mineral mines and the implications for residential buildings: research

Construction techniques

“The Building Regulations are only the minimum standard the public would expect in terms of gas mitigation matters.”

Construction techniques

Concern that the methodology within the building/construction documents is no longer appropriate given the situation that occurred at Gorebridge.

Construction techniques

Building Standards practitioner noted that they were not comfortable in commenting on the appropriateness of current standards and guidance and suggested that perhaps further research is now required.

Construction techniques

“The construction industry will always work to the minimum building standards” LA stakeholder concerned if these standards were appropriate in this area.

Other

“We have a range of discussion groups and formal forums within the environmental health groups (which would discuss mine gasses). These would not include the Building Standards department. So, there are no formal multidepartment discussions covering mine gas risk.”

Other

“The subject matter under discussion today (mine gas) is not one that’s regularly brought up or discussed within stakeholder groups i.e. LABSS.” Suggestion there was no forum for discussions between Building Standards, Planning and EH.

Risk assessment

“The guidance in this (gas risk) area is so specialised that a local authority verifier would tend to get risk assessments peer reviewed/ externally reviewed”.

Construction techniques

“It is fair to say that building regulations are not prescriptive, they are functional standards which set the intention for the mandatory standard and then point towards the guidance documents which sit beneath these.” Issue - Building standards departments can only require the developers to look to the standards and guidance documents. They cannot request additional mitigation if this is not detailed in the standards and guidance.

Construction techniques

“Prescriptive standards would restrict development.” The Stakeholder noted that while a more prescriptive standard would assist with mine gas risk, it may also prevent development in these areas.

Risk assessment

Discussed local authority oversight and understanding of the issues. It was noted that the specialised guidance in this area is outside the expertise of LA staff: “Ground gas risk and fire risk assessments are generally sent for external peer review.”

Risk assessment

Noted that budgets and availability can be an issue when reviewing risk assessments. Consensus that within the individual authorities there is a varied approach in terms of the management and available budget to carry out reviews.

Risk assessment

“Fundamental issue that there is no clear guidance on what unsafe levels of CO2 in properties.”

Mitigation measure

“It’s not sustainable to just demolish affected properties.” Noted that research may be required to test remediation of existing properties. Comments that insurance companies and the Coal Authority require certainty that measures will work and protect the occupants.

Construction techniques

“There has been other contaminated land (not building standards) issues where there has been changes in guidance down south that the Scottish Government has chosen not to pick up on.” Concern that best practice developed in England is not being applied here.

Other

“I don’t see this as just a building control issue. It’s multi agency. The problem is the system in which we work and the way we interact within departments.” Issue raised that responsibility on gas risk lies between separate departments within the LAs which makes it more difficult to ensure that developers are taking gas risk into account.

Construction techniques

“There have been instances where individual local authorities have tried to instigate their own guidance to suit specific conditions within their area. National developers come along, and it turns into a scrap over whether the local authority has the authority to add additional measures.” Perceived issue is that LAs don’t have the power to request any more that the minimum required by standards and guidance.

Other

“As a contaminated land specialist, if I say at the planning stage there should be a membrane in there, and down the line during the building standards verification they discover there’s no membrane included, it’s often too late to flag this up.” It was noted that planning consent requirements are being edited or scaled back during the planning process without reference back to the contaminated land specialists.

Other

Comments from other local authorities about developments going ahead before mitigation is signed off and approved.

Noted that risk assessment/mitigation comes late in the development process and properties are already built before these are reviewed. Concern that developments are built and occupied without suitable mitigation of the risks.

“There are some issues, but it’s difficult for us to discuss these openly as no one wants to shame their own local authority when something goes wrong.”

Other

“Some developers will push the system and work within the existing frameworks to see what they can get away with.”

Concern raised about the capacity of LAs to require sufficient gas monitoring.

Construction techniques

“Concrete slab with no ventilation beneath is perhaps part of the issue.” LA response to the IMT question relating to traditional ventilated solum.

Energy efficiency

LA response to the IMT question relating to energy efficiency–concern over poor ventilation within modern properties.

“There is also an issue with houses becoming more air tight. We have got to the point where we are specifying CO2 monitors in bedrooms.”

Energy efficiency

LA response to the IMT question relating to energy efficiency–concern over poor ventilation within modern properties.

“Airtight houses would appear to be a contributory factor in CO2 issues.”

Energy efficiency

LA response to the IMT question relating to energy efficiency–concern over airtightness/lack of ventilation. “Agree it is a fundamental problem at the moment.”

Energy efficiency

LA response to the IMT question relating to energy efficiency–concern over airtightness/lack of ventilation

“Lack of recognition in the industry that proper ventilation/air infiltration within a property is an important factor”.

Energy efficiency/ construction techniques

Issue raised that stakeholder has seen “new build properties coming in under the designed air tightness value.” Raised concerns over higher risk from mine gas related to new build properties compared with older properties.

Energy efficiency/
construction techniques

Stakeholder raised issue with the chimney effect within an airtight property.

“If you crack the bedroom window open you create this natural draught, which in older properties would have drawn air up from the solum, but in new properties may just draw in any mine gases trapped under the unventilated concrete slab.”

Energy efficiency

Stakeholder raised issue in ventilation and air circulation standards/models.

“Air circulation estimates can vary from what was used in the ventilation design model. Some people will not open windows, some properties will be fully occupied throughout the day.”

Energy efficiency

Stakeholder raised issue with the chimney effect within an airtight property.

Negative pressures creating “a chimney effect with CO2 coming through the service ducts.”

Other

Stakeholder discussed response to research project request for previous incidents/info on concerns raised over CO2. They stated that “it would likely be via the GP’s/NHS board rather than a complaint put to a council planning/ environment department”.

Risk assessment

Stakeholders in LA noted that council contaminated land specialists are comfortable with risk assessment reviews from landfill, but with mine gas it is not their area of expertise.

Risk assessment

Comment from contaminated land specialist on lack of guidance/ understanding of the pathways: “We need more research on how this is happening/what are the pathways we need to look out for?”

Risk assessment

Comment from contaminated land specialist on lack of guidance/ understanding of the pathways.

Stakeholder raised example of landfill over mining area: “how do you monitor how much CO2 comes from landfill compared to how much comes from mines without very expensive lab tests?”

Mitigation measure

Stakeholder discussed retrofit mitigation of radon sumps. They raised the issue that, “this goes against the current regulations as it is an active ventilation system in a dwelling,” adding that if fitted it may be acceptable if the property is “managed” i.e. a housing association.

Mitigation measure

Discussed retrofit mitigation and active ventilation: “There is similar technology available for schools to monitor CO2 and ensure forced ventilation, but for domestic properties the equipment is just not available”.

Mitigation measure

Stakeholder discussed similarities/ differences with CO2 vs radon.

“Radon is a low-level bleed. With CO2 there could be a low-pressure weather event. So you need research to prove that this (radon) system could cope with a large volume CO2 spike”

Mitigation measure

Would radon sumps be an appropriate solution for CO2?

“If there is any suggestion of firedamp then an electric fan is not the way to go.”

“Installation (retrofit active measures) would need to come back to a precautionary risk assessment.”

Mitigation measure/
risk assessment

Stakeholder discussing developers trying to reduce costs on gas mitigation/fitting membranes.

During site zoning “a developer was pushing for certain areas within a site to not require mitigation, when in fact they whole area has the same underlying structure/strata, but gas monitoring was only carried out in one area.”

Stakeholder noted that risks due to the very oldest shallow mine workings are unknown: “As they are very old, there are no records, so you just don’t know what’s down there.”

Mitigation measure

Stakeholder comments on gas membranes: “fine if installed correctly.”

But would be against them being used as “mandatory mitigation” as stakeholder perceived this would provide the developers with a reason not to carry out a proper gas risk assessment.

Mitigation measure

Stakeholder comments on gas membranes: “quality of installation is an issue, the expectation these will be fitted well and validated is variable.”

“Some developers will get in expert installation contractor, but some will leave it to any general labourer to install a gas membrane.”

Mitigation measure

Stakeholder comments on gas membranes: “Verification after fitting is difficult.”

Mitigation measure

Stakeholder comments/concern on gas membranes and the resource available to check/verify these.

“On the verification, are these requirements going to be pushed onto already stretched building standards departments?”

Mitigation measure

Stakeholder comments/concern on gas membrane protection: “When a membrane is fitted are the homeowners made aware of this? Will they be advised not to drill or cut the membrane?”

Risk assessment

Stakeholder comments on risk assessments received within their local authority: “Some are really good/ some are barely acceptable. Very variable.”

Risk assessment

Stakeholder comments on risk assessments received within their local authority: “Some come in too late, if you already have the walls going up, the information provided may not allow the council to make the correct decision.”

Risk assessment

Stakeholder comments on risk assessments received within their local authority: “the developer provides the minimum standard in terms of risk assessment and monitoring, and the council cannot send it back because that would be unreasonable.”

Risk assessment

Stakeholder raised additional concern relating to the issue of CO2 being generated in developments where peat or colliery spoil may be present. “This is not mentioned in the IMT report.”

Risk assessment

Stakeholders commented that the situation requires “long-term monitoring encompassing a wide range of environmental events and application of continuous monitoring techniques as a more standard approach to robustly characterising ground gas conditions in such areas.”

Risk assessment/
mandatory mitigation

Concern was raised that any minimum mandatory CO2 ground gas protection may be unnecessary in some coal reporting areas. Noted that it should not be applied in place of a robust risk assessment. Also, any minimum ground gas protection may not be sufficiently protective.

Risk assessment

Stakeholder noted, “There is adequate guidance available on the ground gas risk assessment process. However, it is rare to review a report that understands that the conceptual site model should be considered in the ground gas investigation strategy, risk assessment and protection, system design.”

Risk assessment

Stakeholder commented that the “gas risk assessment process is probably adequate, but I would suggest it is being wrongly applied.”

“Under the development system, time and money is often a critical factor and risk assessments aren't being carried out properly and monitoring is often a hit and miss.”

“It may be that developers do not understand the time taken to adequately assess ground gas regimes” and/or are “not willing to pay” and/or “the consultants employed are not experienced enough to undertake such monitoring.”

Risk assessment

Stakeholder comment/concern on risk assessments was that “the current risk assessment tends only consider current conditions under Part IIA/PAN33.”

They stated that, “quite often future development plans are unknown at the site investigation stage, the consultant doesn't know e.g. finished ground levels, building/foundation designs etc.”

Concern that the site conceptual model cannot take adjacent sites or foundation design into account.

Risk assessment

Concern raised that larger sites can be developed by different companies with different consultants.

Quite often information not passed on/shared, details overlooked, sites sold, etc.

The stakeholder noted that these “details” may be flagged up by the regulator (if involved), but generally different officers within the regulatory system can deal with various planning applications and this can lead to things being overlooked.

Risk assessment/
mitigation measures

Gas Risk/Mitigation comment: “no holistic approach to either on-site proposals or off-site in the adjacent or wider area.”

Risk assessment

LA stakeholder noted that a significant proportion of CSMs (submitted via planning/building standards) fail to provide sufficient level of detail in regard of the potential pollutant linkage (PPL) associated with mine gas.

Risk assessment

LA stakeholder noted that data gaps and uncertainties in the conceptual site model is common in reports submitted to local authorities.

Risk assessment

LA stakeholder noted that as per issue above the sampling duration needs to be consistent with the conceptual site model, the exposure mechanism(s) and possible temporal/environmental effects. This is not always covered in the reports we receive.

Risk assessment

LA stakeholder noted that “some ground gas risk assessments fail to consider mine gas issues as highlighted by CIRA Report 149.”

Risk assessment

LA stakeholder noted the potential for other interventions affecting the soils to alter the risk of mine gas migration and consequently to render any pre-development assessment redundant.

Stakeholder commented that research/guidance was required: “I do not believe there are other significant literature sources for the risk assessor to seek guidance on such issues.”

Mitigation measure

Comment on gas membrane suitability as protection measure. “It is easy to fit ground gas protection badly. Good integrity across the whole floor area in average weather conditions on a building site is difficult to achieve, and few installers are suitably trained.”

“Even at the design stage, mistakes are made relating to the specification of gas protection because this is new for many house builders.”

Mitigation measure

Comment from stakeholder on gas protection design suitability. “Gas protection systems have to remain effective for the lifetime of the building. I have seen proposals for gas vent trenches and drain-like air vents that would become clogged or covered up with a plant pot within a few years of construction.”

Mitigation measure

Comment from stakeholder on gas membranes. “They have to survive the installation process, which means every worker on site needs to understand the importance of their continued integrity.”

“Examples of accidental subsequent penetration of membranes are commonplace.”

Mitigation measure

Comment from LA building standards inspector on quality of verification reporting. “I am one of a very small number of people in Scotland who has attended the CL:AIRE Membrane Verification course in Doncaster. As a result, I am in the uncomfortable position of being unable to accept at face value any verification reporting I have reviewed (visual/photographic inspection is no verification at all).”

Risk assessment

Concern raised related to gas monitoring and that any discrete monitoring rounds may miss significant changes in the atmospheric conditions.

The stakeholder commented that, “It is my feeling that worst-case conditions may only occur every three to five years and monitoring for this is impractical.” Their view was that a suitable conceptual site model is the best tool.

Risk assessment/
construction techniques

Stakeholder commented that, “One thing that is rarely done properly on site is the decommissioning of existing site-investigation boreholes. This risks leaving a preferential pathway for ground gas.”

Risk assessment/
construction techniques

Stakeholder commented that local authority contaminated land staff are not necessarily qualified to understand foundation design drawings. Care and collaboration required with our colleagues in building standards to ensure submitted drawings show the correct details.

Stakeholder noted that “Builders or their agents often submit drawings that do not conform to the remedial action.”

Risk assessment

Stakeholder raised concern on lack of research/guidance on groundwater rebound. Similar issue with climate change generally.

Other

Stakeholder commented that, “we have uncovered a situation in Gorebridge by unhappy accident.” Concern was to what extent might this problem affect other mining areas?

Risk assessment

Stakeholder comment on risk assessments was that, “there are representatives of other councils who have nobody in posts within contaminated land that are qualified enough to understand whether these reports are good enough or not.”

Risk assessment

Stakeholder comment on gas risk Assessment: “We deal with the difficult ones and ones that are needed to be done quickly in house, but the sheer volume of work is immense.”

Risk assessment

Stakeholder comment on gas risk assessment: “We get a variable quality in reports that come in (some good, some awful). Smaller developers and smaller consultants aren’t willing to do the extra work or don’t have the experience.”

Risk assessment

LA stakeholder commented that small developments don’t understand the process leading to many delays in their developments leading to increased costs.

Risk assessment

LA stakeholder commented that, “I think there should be planning officers here (at workshop) and not building standards officers because that’s the first line of defence. It’s planning applications that give the planning conditions for SI, remediation, everything else. By the time it gets to Building Standards, it’s too late.”

Risk assessment

LA stakeholder commented that if the risk assessment/mitigation is not appropriate it may not get picked up at planning "permitted stage". Once Building Standards pick up on this it is too late.

Risk assessment

LA stakeholder comment on risk assessments: “The reports not as good as they can be, but they’ve improved over the years.”

Risk assessment/
mitigation measure

Concern raised on extensions. Attendee mentioned they were aware of two large councils in coal mining areas where they have stopped consulting on extensions because they do not have the time.

Mitigation measure

Concern raised on extensions: “Quite often there won’t be planning permission required, so the first stop in identifying there is a problem is building standards and we get all the hassle.”

Mitigation measure

Comment that the overall trend is a drop in standards. “In the future, more buildings will not need planning and there’s an indication that some work might not need a building warrant in the future. That might be a problem if there are no checks at all.”

Other

“The key role of a planning department is to determine if the ground in that proposed area is suitable for proposed future use. I don’t think that always happens. There’s some land you probably just shouldn’t build on.”

Stakeholder noted that, “Planning permission is given in some areas it shouldn’t be.”

Other

Concern raised on gas risk was that the planning authority need to appropriately condition a development. This is quite important, and it depends a lot on the experience of the individual planner.

Risk assessment

Comment on gas risk assessments. “We get a distinct variation in the quality of information that is submitted to us. Some can be appallingly bad.”

Risk assessment

Comment on gas risk assessments from LA stakeholder: “Within the last six months we had a housing developer submit a report which had less than 10% of the gas monitoring required. That’s a significant failing.”

Risk assessment

Comment from LA stakeholder that they get developers stating they will install a membrane on all properties to avoid carrying out gas monitoring and a conceptual model.

The LA stated that “We tell them you still have to do your monitoring, risk assessment and conceptual site modelling, because a membrane might not be enough.”

Risk assessment/
mitigation measure

Comment from LA, “there is the assumption that when developers agree to put in gas protection measures, they think that is enough, and they don’t have to gas monitoring and do validation and verification.”

Mitigation measure

There is a legacy issue relating to all the houses and hundreds of sites where verifications were expected or where membranes were fitted, but LAs have never received a report. Several sites where membranes were required have no evidence that the membranes were fitted.

Mitigation measure

Developers have an expectation that membrane verification is to be completed over a very short time period.

Other

Both communications between departments and the quality of responses from developers needs to be improved.

Construction techniques

Site investigation boreholes are a potential pathway if they are not decommissioned and they are routinely lost on site.

Mitigation measure/
risk assessment

Mitigation measures are frequently inadequately designed for the long-term especially when the risk assessment does not cover an extended time period.

Mitigation measure

Ventilation design for vents and trenches needs to be checked as these can become blocked or filled over long timescales. This should be compared with the lifespan of the property.

Mitigation measure

Ground gas ventilation measures are not notified to homeowners. A consequence of this is that vents are becoming blocked. There is a lack of notification because brokers do not want to advertise that a property may have a ground gas issue.

Mitigation measure

Homeowners require notification of mitigation measures such as vents so that they can be maintained and kept clear. A housing association might be able to enforce this, but other organisations may be limited.

Mandatory mitigation

The implementation of a mandatory membrane is good in practice but ensuring installation and verification procedures could prove difficult.

Mandatory mitigation

Creating rules that make installation of gas membranes mandatory is dangerous because it creates an expectation that this is sufficient for the risk. There is a large variety in sites and some may require a much higher level of assessment and mitigation.

Risk assessment

Extremely important that your initial risk assessment is accurate because it supports monitoring, further assessment and mitigation implanted afterwards.

Risk assessment

Gas risk assessments are highly variable, and many monitoring timeframes are too short.

Risk assessment

Some consultants will just conduct six weeks of monitoring. However, this is not necessarily enough time. Occasionally there will be evidence of three or four incidents of spot monitoring. This is unlikely to be robust enough and continuous monitoring should be considered.

Risk assessment

There are issues that consultants are not conducting monitoring correctly. They report that monitoring is complete; however, according to the reports the data is insufficient e.g. three of their six boreholes are flooded for most of the monitoring time, or they couldn’t find a borehole.

Risk assessment

On occasion, developers have submitted plans for monitoring which are artificially low knowing that they are substandard.

Risk assessment

There is no nationwide limit or threshold for CO2. A threshold may help to determine the outcome of a risk assessment or mitigation measures.

Mitigation measure

The verification of mitigation measures is non-existent (particularly with regards to membranes).

Mandatory mitigation

There are no mandatory mitigation measures in our LA.

Mitigation measure

As a method of mitigation, a membrane is limited in the current building standards.

Other

Building standards and planning teams within LAs rarely meet to understand the requirements of a development.

Risk assessment

Focus of coal mine risk is mainly towards structural issues rather than that of mine gas.

Risk assessment

Information from the CA is relied upon to inform planning decisions and frequently this is lacking detail.

Risk assessment

There is an education gap in councils and LAs, personnel are not experienced enough to scrutinise planning and/or risk assessments

Risk assessment

CA may not have a monitoring point or previous gas incident in an area, but that does not mean there is no risk from mine gas (this issue must be iterated in consultants mining reports).

Risk assessment

CA data is limited to what currently exists and what is currently reported. More data is required to support consultants reports and ultimately risk assessments.

Risk assessment

Mining reports requested from the CA frequently state there is 'no record of mine gas,' but the report does not clarify this statement. ‘No record’ does not necessarily mean that there is no mine gas risk.

Risk assessment

CA does not have enough personnel to deal with the issues surrounding mine gas.

Risk assessment

CA does not have enough gas monitoring and groundwater monitoring points to support a robust risk assessment.

Risk assessment

CA coal mine maps are not detailed enough to understand the gas risk and to generate a robust conceptual model.

Risk assessment

The results from consultant’s reports related to mine gas risk are not joined up to the developers plans (for mitigation).

Construction techniques

There is currently testing on properties for noise and tightness, but there is no verification in building standards for the verification of mitigation measures.

Risk assessment

There are currently no specific personnel within an LA that are prepared to deal with mine gas risk. The issue tends to fall to contaminated land personnel.

Risk assessment

Mine gas risk is given enough emphasis in the planning permission.

Risk assessment

There is a lack of knowledgeable people within local authorities/ councils to understand the mine gas risk assessments.

Risk assessment

Mine gas risk is transient, and the monitoring process will not always pick up the environmental changes.

Risk assessment

Gas flow paths are likely to be changed or altered by further developments.

Risk assessment

Risk assessments are reviewed by EHO or contaminated land officers that may lack experience to correctly scrutinise the data.

Risk assessment

There has been loss of experience for councils. Former mine surveyors and other personnel have moved on or to other departments.

Mitigation measure

Generally, the CA’s primary mitigation technique was to demolish a property after a gas 'event'.

Mitigation measure

The developer is not incumbent to check whether the services installation is likely to puncture a membrane (disrupt any mitigation measure in place). A check of the services installation and how this matches up to the mitigation that is installed is required.

Risk assessment

CA mining reports rarely have enough information about mine gas issues.

Risk assessment

The risk assessment is not future proof (not incorporating environmental change).

Risk assessment

Changing environmental conditions are not considered in the risk assessment: climate change, water levels, atmospheric pressure changes.

Risk assessment

The risk assessment process is not incorrect, but it is implemented incorrectly, either at the wrong time or for wrong duration.

Risk assessment

There is significant time pressure on the consultant to monitor for ground gas when it should be conducted over a longer period over periods of lower pressure.

Risk assessment

There is not enough information provided to LAs on the change in ground conditions e.g. site scrape, piling etc. For developments with lengthy development timelines, the conditions are likely to change to adjacent properties.

Risk assessment

There is no monitoring implemented for smaller properties or extensions.

Mitigation measure

The risk assessment relies on the developer to correctly implement the correct gas mitigation measures, and these are not always checked.

Risk assessment

It is possible that mine gas issues are only picked up when there is a large event like Gorebridge.

Risk assessment

Is the current gas risk assessment considering the cost-benefit of demolition as a mitigation method?

Risk assessment

The CA is a ‘reactive’ organisation. This is not the preferred stance for mine gas issues, but more financial support is required if the CA is to provide additional support in this field.

Risk assessment

The CA does not have enough resources to support mine gas monitoring and assessment.

Risk assessment

There is no repository for ground gas data that the CA holds which the LAs can access. All the information comes from the CA reports or information 'on request'. No monitoring data is readily available.

Risk assessment

Often the development has already begun before all the gas risk information has been compiled. This prevents the LA assigning certain mitigation measures because they do not have all the information available to make an informed decision.

Risk assessment

An LA is unable to rectify deficiencies in a development (such as installing a membrane) if gaps are found within the risk assessment or building plans once construction has started.

Risk assessment

There is a conflict between site investigation (SI) reports and council requirements e.g. an SI is undertaken, and the conclusion is that no membrane is required. The council suggests a membrane is required, but once this detail has been raised there is a disagreement as to which choice of membrane based on limited information available/collected.

Mandatory mitigation

There is frequently a conflict between the developer’s choice of mitigation and what the council believe is required. However, there is not enough information to support a particular type or standard of membrane.

Mitigation measure

There is no robust verification process of the mitigation measures or who is taking responsibility for it and who is undertaking the work.

Risk assessment

Information regarding ground gas is frequently submitted too late in the planning process. Any changes, therefore, cannot be implemented.

Risk assessment

LAs struggle to enforce gas monitoring in advance i.e. before planning applications/development plans are submitted.

Risk assessment

The gas risk assessment needs to include parameters such as: climate change, future environmental scenarios, groundwater levels etc.

Risk assessment

Consultants need to utilise and implement the guidance that is available. Currently work that is conducted is substandard.

Risk assessment

Cumulative effects not being taken into account in the gas risk assessment.

Risk assessment

Adjacent develops are generally not considered in the risk assessment.

Risk assessment

Mine gas risk areas need to be identified at the LA planning stage. Frequently there is not enough pre-emptive work completed at the front end of the planning system.

Risk assessment

There is not enough awareness in LAs relating to ground gas risk.

Risk assessment

The risk assessment does not extend to incorporate ground design and the effect of disturbance, piling, etc.

Risk assessment

Gas monitoring should be completed post ground stabilisation.

Risk assessment

CA has no repository of information to be accessed by LAs. The data the CA holds is limited and mainly only available upon the request of the consultants mining report.

Risk assessment

CA monitoring is more general rather than site-specific.

The consultant reports issued rarely help to define the site-specific gas risk.

Risk assessment

Groundwater data is not available on a site-by-site basis. However, this is because there is not a borehole or gas monitoring point nearby.

Risk assessment

CA monitoring data is mainly only available on request.

Risk assessment

Ground improvement and piling assessments are not being reviewed in relation to ground gas.

Construction techniques

Developers are regularly building to the minimum standards.

Mitigation measure

The CA has used membranes as a gas mitigation measure, but they have raised the issue that installations have been inadequate.

Construction techniques

Constructing a solum is frequently easier and more reliable than a membrane as a gas mitigation measure.

Risk assessment

There is significant variation in the quality of reports received from consultants. Much of the work fails to meet the minimum requirement of the guidance. Additional work and evidence are often requested from applicants.

Risk assessment

Off-site gas migration needs to be considered as this is an area currently lacking detail. Measures used for ground stabilisation need to be delineated as these are potential pathways.

Other

Is the training of the professionals sufficient enough that that the chemical and physical processes that influence mine gas are fully understood?

Risk assessment

“Is there sufficient knowledge of the differences in composition/behaviour of mine gas vs ground gas?” More research is required into the characteristic differences between mine gas and ground gas.

Risk assessment

Consultants regularly include gas monitoring as part of the SI, as an assumption, which indicates a failure in the initial CSM development. Gas monitoring may ultimately be required for the site by the CSM, but the potential of mine gas might warrant more sophisticated methods such as continuous monitoring, flow monitoring or sampling for composition.

Risk assessment

TB17 (CL:AIRE, 2018) is a good document but mainly refers to ground gas. The impact of sharply falling barometric pressure is potentially very significant when dealing with mine gas.

Risk assessment

Validation reports are frequently inadequate, and the properties are already completed or inhabited upon discovery of this information. In addition, the planning authorities do not have the resources to chase this issue.

Risk assessment

Concern raised about the responsibility of determining installed mitigation measures on existing adjacent developments.

Q1

Is the current mine gas risk assessment process adequate to correctly determine the level of risk, especially in relation to the requirements for assessing mine gas levels at sub‐surface depths likely to be representative of gas migration potential from underground mine sources?

Q1WS

The results from the risk assessments process and the reports being produced are variable in quality, councils often find that small developers and smaller consultants aren’t willing to do the extra work (monitoring) or don’t have the experience within this area.

Risk Assessments come in too late if you already have the walls going up, the information provided may not allow the council to make the correct decision. In some cases, the developer provides the minimum standard in terms of risk assessment and monitoring, and the council cannot send it back because that would be unreasonable. There needs to me more work on the understanding of the conceptual site model, the risks and pathways.

Monitoring requirements are not long enough–need to cover low pressure events.

There is an assumption from some developers that when they agree to put in gas protection measures, they think that will be sufficient and they don’t have to do gas monitoring, validation and verification.

Concern raised regarding extensions not being risk assessed/ constructed with no requirement for building warrant.

General acknowledgement when dealing with development risks that some councils have robust verification, peer review and good practice policies in place. There was also a concern about a lack of communication between planning, building standards and environmental health departments in this area. Concerns also raised regarding resourcing issues and coal mine gas expertise. Noted that colleagues from planning should be involved in this project as they are key within all of this. Noted that Council Contaminated Land specialists comfortable with risk assessments from landfill, but mine gas is not their area of expertise. We need more research/understanding on the pathways we need to look out for.

Q1R1

There is adequate guidance available on the ground gas risk assessment process (for new developments). However, it is rare to review a report that understands that the conceptual site model (for the scenario of the development and proposed foundation design) should be considered in the ground gas investigation strategy, risk assessment and protection system design. Suitable training courses for practitioners and regulators are required. Technical bulletins are required for raising awareness of mine working issues and for other significant ground gas generation sources (landfill, peat, colliery spoil, radon). Guidance/Technical bulletins on best practice for ground gas protection system design specifications (i.e. material specifications, foundation schematics etc) and how to verify their installation. More information on retrofitting of ground gas protection measures is required. Procedures for Part 11a ground gas investigations and assessing risk are required.

Q1R2

No.

Q1R3

The current mine gas risk assessment process is probably adequate, but I would suggest it is being wrongly applied. Under the redevelopment system, time and money is often a critical factor and risk assessments aren't being carried out properly and monitoring is often a hit and miss. It may be that developers do not understand the time taken to adequately assess ground gas regimes, are not willing to pay and/or the consultants employed are not experienced enough to undertake such monitoring.

Q1R4

BS 8485 notes the framework of ground gas risk assessment (i.e. CLR 11, CIRIA C665, BS 8485 etc) is not prescriptive and professional judgement is required to determine the acceptability of risk and whether there is benefit of more site assessment versus adopting conservative measures in design. Unfortunately, it is the local authority’s experience that the justification and recording of risk assessment decisions throughout the process is often lacking. The key factor to determine if a mine gas risk assessment process is adequate is the appropriateness of the CSM (Conceptual Site Model). From the LA’s perspective, for an area that has been historically heavily mined (at surface and at depth), a significant proportion of CSMs (submitted via planning/building standards) fail to provide sufficient level of detail in regard of the potential pollutant linkage (PPL) associated with mine gas.

In consideration of the generation potential of the source mine gas, this may represent a very low to high risk (as per BS 8576 Figure 6). However, there is often minimal detail presented within the CSM on the nature of such mine workings. In order to provide greater level of confidence in the determination of the generation potential then a detailed CSM is required. The goal to reduce the uncertainty of the CSM, is often absent in reports submitted to local authorities. It is this failure, which causes PPL’s, such as mine gas, to be absent in contaminated land reporting to local authorities. The failure to address data gaps and uncertainties in the CSM is commonly overlooked in reports submitted to local authorities.

The output of the ground gas risk assessment is only reliable if data, and other information (e.g. geology) about the site is sufficient in terms of quality, quantity and appropriateness (BS 8485 section 6.1). It is noteworthy that BS 8485 section 6.1 highlights that any uncertainty (from the CSM/risk assessment) should be reflected in the design of the gas protection system.

Sources and pathways associated with mine gas are highlighted throughout BS 8485 and Environment Agency, Guide to Good Practice for the Development of Conceptual Models and the Selection and Application of Mathematical Models of Contaminant Transport Process in the subsurface, NC/99/38/2, section 3.4.2 and Table A1. This highlights the importance of artificial pathways, such as mine workings, within the CSM. However, reports submitted to the local authority often lack data and discussion on the pathways, e.g. the groundwater system encompassing geology, water table and unsaturated and saturated zone flow and transport.

There is often a lack of acknowledgment in ground gas risk assessments that the sampling duration needs to be consistent with the CSM, the exposure mechanism(s) and possible temporal/environmental effects. Therefore, if the design of the sampling programme is flawed, then the subsequent risk assessment may not be fit-for-purpose (BS 8576 section 10.8.2.1). It appears some ground gas risk assessments fail to consider mine gas issues as highlighted by CIRA Report 149. A re-issuing/ updating of such reports may assist in raising awareness to those undertaking ground gas risk assessments. CIRA 149 section 2.5.5 succinctly notes:

The reliability of measured gas concentrations and emission rates and the uncertainty of predicting future changes is probably the greatest influence on the design and application of gas protection measures. Without detailed knowledge of the gas regime and the long-term behaviour, gas protection measures cannot be fully designed or their performance guaranteed. This is one reason which has led to the adoption of high margins of safety on gas concentrations, the over-design of gas protection measures and the adoption of control systems based on a combination of individual measures.

However, it is worth noting that the standard approach of conducting spot monitoring (empirical, semi-quantitative) of sites to determine a gas screening value has a number of inherent conservative assumptions. It is based on the assumption of directly relating gas monitoring standpipe emission measurements to future gas emissions from a fixed volume of ground around the standpipe (BS 8485 section 6.2.1.1).

Q1R5

It is felt that the current risk assessment process is satisfactory with adequate notification and contact between our department and Planning. However, the quality of reports from consultants vary with a lot requiring further work due to not meeting minimum requirements as per the guidance.

We often must request additional works and evidence from applicants.

There is a worry that Permitted Developments and garden ‘homes’ may be missed from being notified to EH to consider risk factors.

Q1R6

Only if there is sufficient knowledge/expertise within the industry to undertake competent assessments.

Q2

Is the current risk assessment process fit for purpose particularly in terms of taking account of future potential changes in mine gas dynamics and migration risk factors (e.g. due to ground stabilisation measures, additional developments, etc.) that could lead to an increased risk of gas migration into properties over the long term?

Q2WS

The risk assessment should consider the potential for offsite migration of gas but doesn’t always. Adjacent developments are generally not considered in the risk assessments. Where the risk assessment considers the potential migration and identifies that certain measures need to be carried out, the concern is that this may not be effectively completed where a large site is being developed in phases or by different developers.

Guidance and implementation should be stronger. Difficult for cumulative effects (adjacent developments) to be processed into planning applications, would be very hard to deny a planning application based on cumulative risks.

Q2R1

See Response to Q1

Q2R2

No, an additional environmental cause of mine gas risk uncertainty relates to future change in precipitation associated with predicted climate change in Scotland. It is possible that climate change may cause alterations in rainfall patterns in the future; how this will be reflected in groundwater levels is currently unclear. As ex-mining areas complete their groundwater rebound phase, the relative impact of any such change will increase over time. The consequential impact of any climate change related effect on mine gas migration risk is uncertain but could act to increase the overall risk. This is therefore yet another source of uncertainty making mine gas risk prediction more imprecise and another reason for advocating for the adoption of a more highly precautionary stance to future proof mine gas mitigation measures.

Q2R3

No, current risk assessment tends to only consider current conditions under Part IIA/PAN33 and quite often future development plans are unknown, the whole plans for the site are unknown at the site investigation stage, or the consultant doesn't know the finished ground levels, building/foundation designs, etc.

Q2R4

The risk assessor is directed to consider such dynamic and future factors (e.g. flooding, changes in groundwater levels, global warming, extreme weather conditions, the closure of mines, and possible changes to the gas regime caused by future development) by BS 8576 section 6; CIRA R149 section 2.5.5 and EA NC/99/38/2 section 3.3.1 & 3.7. Such factors should therefore be considered within a defensible and robust CSM, where appropriate, by the risk assessor.

Q2R5

Again, we don’t see major issues with the guidance available, rather adherence to this and poor quality of consultant reports which have not considered all factors. Off-site migration is a factor to consider but can be lacking in exploration/detail. Perhaps the ground stabilisation measures area could be flagged more.

Q2R6

I am not aware that sufficient research has been undertaken to identify/quantify these risks, particularly since the closure of the mining industry effectively 20 years ago in Scotland.

Q3

Is there sufficient emphasis in the current mine gas risk assessment process on the potential for other interventions affecting the soils or substructures underpinning any building development, to alter the risk of mine gas migration and consequently to render any pre‐development assessment redundant and inadequately precautionary to protect public health?

Q3WS

Concerns raised on site investigation boreholes not being decommissioned correctly, and foundation design becoming a pathway for gasses. Councils suggested more coal authority involvement in identifying risks required where interventions include permits to break down into coal mines/grouting.

Q3R1

See response to Q1

Q3R2

No

Q3R3

No as per response to Q2

Q3R4

Further to the response provided for point two, I do not believe there are other significant literature sources for the risk assessor to seek guidance on such issues. However, the risk assessor should be cognisant that the CSM is a representation of a real-world dynamic system subject to constant influences via, natural (e.g. geological/atmospheric/biological) and anthropogenic sources.

Q3R5

We feel information on this could be expanded.

Q3R6

I suspect not.

Q4

Are the current criteria used for deciding what constitutes a sufficiently precautionary approach to mitigation appropriate; particularly where there is known to be a potential risk of mine gas migration? Does the process adequately emphasise the need to take account of construction methods that may add to that risk (e.g. the use of vibro-stone underpinnings or solid slab floors that are not separately vented to the outside atmosphere)?

Q4WS

Comments as per Q3 above. Workshop also discussed long term suitability of mitigation measures/ongoing maintenance. Issues where gas trenches are present. Ventilation structures left blocked or not maintained would increase the future risk. Suggestion raised covering Building Standards continuing requirements on building warrant.

Noted that within risk assessments we do see risks related to construction methods on ground improvement and piling for ground contamination, but not covering coal mine gases. Suggestion is contaminated land and ground gas risk assessment should be combined.

Q4R1

See response to question one

Q4R2

No

Q4R3

No. Although the current criteria allow for mitigation measures to be implemented to the next risk assessment level, pre-construction risk assessment is independent of development.

Larger sites/development areas can be redeveloped by different developers with different consultants. Quite often information not passed on/shared or details overlooked, sites sold on, etc. This may be flagged up by the regulator (if involved).

Different officers within the regulatory system can deal with various planning applications and this can also lead to details being overlooked.

Q4R4

This first point (criteria used for deciding what constitutes a sufficiently precautionary approach to mitigation) relates to the robustness of the CSM and risk assessment process. For example, is the precautionary approach based upon a robust data set and detailed logs? Or various unquantified assumptions?

There are multiple sources of guidance within the literature which direct the risk assessor to consider construction methods within their risk assessment framework, e.g. BS 8576 section 6; BS 8485 section A.2 and CIRIA C665 section 2.7.

Q4R5

Yes

Q5

In determining the need for mitigation measures, is the current scope for interpretation of the guidance open to developers at present appropriate?

Q5WS

The guidance under the building regulations is the minimum standard the public would expect in terms of gas mitigation matters. It’s the best published guidance we have now, and it’s those minimum standards that we in local authorities look to when applying the Building Regulations.

There is perhaps a further question as to whether the methodology within those documents is appropriate given the situation that has occurred at Gorebridge.

Perhaps we need some research, but, as a building standards practitioner, I would not feel comfortable in commenting on whether the guidance is now appropriate or deficient in any way.

Acknowledgement that the construction industry will work to those minimum building standards.

Q5R1

See response one

Q5R2

No

Q5R3

Yes. However, there is no holistic approach to either on-site proposals or off-site in the adjacent or wider area.

Q5R4

It is understood that the responsibility for the developer to design (and in doing so interpret the guidance) appropriate mitigation measures. This originates from Scottish Government Planning Advice Note 33 (section Development Control, 4). Therefore, this is a policy question, which is considered out with the technical remit of CLO’s and should therefore be considered by competent Scottish Government/Local Authority Policy Officers.

Q5R5

The guidance appears appropriate. It depends on consultants recognising that this is now a possible pathway.

Q5R6

Yes

Q6

Are construction methods that do not involve creating a ventilated solum beneath the ground floor of a property, inherently more liable to permit the transmission of mine gases to the inside of these properties compared to a traditional ventilated solum construction type?

Q6WS

Solum is always easier and more reliable than a membrane for gas mitigation. Point raised that with suspended timber floors ventilation was fortuitous–it was in place to stop the timber becoming damp–but has now been found to mitigate this other issue. Noted that there is no research into CO2 in existing housing stock so no evidence on solum preventing CO2 in properties.

Q6R1

Unknown–depends on the design and conceptual site model. The ventilated solum is a layer of protection, without it you are relying on the design specification of the other components of the ground gas protection system to compensate (BS8485:2015).

Q6R2

There are other possible methods for gas accumulation and ingress routes.

Q6R3

Possibly yes. However, it is a complex issue and would depend on the quality of workmanship/construction of the floor slab, quality of any membrane installed and its installation.

Q6R4

It is considered likely that the provision of a ventilated solum provides a preferential pathway for gas migration, thereby decreasing the likelihood of direct transmission to the inside of the property.

Q6R5

This is perhaps out with the expertise of Environmental Health, but a ventilated solum can be easy to install in the design stage and monitor thereafter compared to other measures which are more difficult to install and assess.

Q7

Is the drive to improve the energy efficiency of modern properties by increasing the levels of insulation and ensuring they are less prone to uncontrolled air movement (draughts) and are consequently more air tight, a potential factor contributing to the retention of mine gas emissions that manage to penetrate a property?

Q7WS

Airtight houses would appear to be a contributory factor in CO2 issues. Larger issue with ventilation in general and a lack of recognition in the industry that proper ventilation/air infiltration within a property is an important factor. Energy efficiency targets lead to lots of new build properties coming in under the designed air tightness value.

Q7R1

Also, issues with build-up of indoor air pollutants. The building design needs to provide adequate air circulation and ventilation for optimal human health.

Q7R2

Yes, potentially.

Q7R3

Potentially yes. However, it is a complex issue and may depend on air pressure differences being created as the driving forces.

Q7R4

As a CLO, this question is out with my area of expertise. However, the basic premise that increased air tightness within a property could be a potential contributing factor to the retention of mine gas emissions appears sound.

Q7R5

Yes, the increased airtightness is a potential factor.

Q7R6

Whilst modern houses are effectively more airtight, the simple action of opening an upstairs window can institute the chimney effect resulting in a lowering of pressure within the property, thus increasing the likelihood of gas entering the dwelling. Closure of the window then means that the gas is likely to remain for longer periods.

Q8

Would the simplest and most appropriately precautionary solution to the problems highlighted by the Gorebridge incident be to require mandatory gas risk mitigation measures in all new residential and similar developments in areas of Scotland defined by the Coal Authority as former coalfields?

Q8WS

Sounds good in practice but uncertain how this would be implemented. Could pose higher risk with expectation that one solution is appropriate in every situation. Some areas might need much more risk measures than others. In summary, don’t jump into mandatory risk measurements without understanding the specific risk at the site.

From the building standards perspective, everything that we do is evidence based so there has to be evidence for a mandatory requirement.

Q8R1

If it is deemed necessary by the Planning Authority to have areas with minimum level of ground gas protection (CS2?) it must be demonstrated by the developer that this level of protection is adequate. There would need to be a much more rigorous verification process with competent and qualified installers/verifiers being a mandatory requirement.

Q8R2

Yes

Q8R3

Possibly yes. The advantage of this would be that developers/ consultants and regulators would be aware and know what is required. The disadvantage would be that it may not be required in some areas and not be adequate enough in others. It would also depend on the quality of the membrane and its installation.

Q8R4

The proposal does represent a precautionary approach. However, if it was enforced, i.e. mandatory gas risk mitigation measures in all new residential and similar developments in areas of Scotland defined by the Coal Authority as former coalfields, how is the decision derived that the ‘mandatory gas risk mitigation measures’ provide sufficient protection? What is meant by ‘mandatory gas risk mitigation measures’? What specific protection components are mandatory? It is also not evident what is defined as a ‘former coalfield’ by the Coal Authority.

Q8R5

Mandatory measures should be backed up by a robust site-specific investigation which accounts for the source-pathway-receptor analysis whilst considering off-site migration and changes to ground structure during exploration, preparation and installation.

Q8R6

It is nonsensical to require a risk assessment and then ignore its conclusions. If coal workings are found at a depth of 500m under a site, is it necessary to install gas protection measures? Very unlikely unless close to a shaft or drift that intersects those workings.

What would mandatory gas protection measures consist of? Would there then be a temptation to skimp on the risk assessment as a membrane was to be installed anyway? Would there then be a danger of not installing sufficiently robust mitigation measures or not refusing development altogether?

This suggestion in the Gorebridge report is the equivalent of advocating mass medication to reduce the chance of disease (generally resisted by the health authorities). To continue the medical analogy–there may also be side effects!