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

3 Introduction

3.1 General Introduction

During April 2014, a number of cases of ill health were recorded affecting some residents in the former mining area of Gorebridge, Midlothian. An Incident Management Team (IMT) was set up by NHS Lothian to investigate the cases. It was discovered that the residents had been suffering from health issues related to carbon dioxide (CO2) exposure. Radiocarbon analysis indicated that the CO2 was derived from a geological origin indicating that old coal mines were the root cause.

A report was compiled by the IMT (Carbon Dioxide Incident in Gorebridge, Midlothian, April 2014 – final report of the Incident Management Team November 2017) which produced numerous recommendations, some of which were made to Scottish Government and relate to building regulations. Based on these recommendations in the Gorebridge IMT report, the Building Standards Division within Scottish Government commissioned RSKW to address the issues. The project definition was:

“a research project to investigate the prevalence of CO2 from disused mineral mines and implications for residential buildings.”

The aims of the research project are the following:

• Identify organisations who have produced guidance on mine gas mitigation and establish if a review is required;
• Build-up an inventory of similar events in Scotland; and
• Explore the eight issues (detailed in the following section) surrounding the Building Standards system and building regulations.

The project was commissioned in September 2018 and this report presents the outcome of the fact finding carried out via a literature review, stakeholder engagement, a consultation with industry experts, plus an analysis of the main findings and compilation of a number of options to consider for further work in this area.

3.2 Project Requirements

The research project requirements were set out in the contract award sent to RSKW on 3^rd October 2018. The project comprises four main stages:

• Project Start Up
• Stage 1 - Engagement
• Stage 2 – Consultation with experts
• Stage 3 – Analysis & Research Output.

Throughout the process, regular updates were submitted to the Scottish Government (SG). The final project output was to document our findings and further options for consideration/research, as detailed in this report.

The following section sets out the main requirements of each project stage.

Project Start Up

• Project inception meeting – review aims, objectives and identify key stakeholders;
• Project setup and literature review. Provided the project team with the opportunity to review the latest related reports, research, guidance and regulatory requirements.

Stage 1 – Engagement (Section 7)

• Collect views from the Local Authorities (LAs) and regional NHS Boards where CO2 mine gas (shale and coal mining) events have occurred in the last 54 years (the time that has elapsed since national building regulations came into force), extracting as much information about each event as possible;
• Engage with the 32 LAs where applicable to find out how they each scrutinise the possibility of CO2 mine gas migration for new development. Carry out a review of the guidance available on mining gas mitigation in new development; and
• Hold a stakeholder event to collect views and discuss issues.

For this task a GIS map was generated to overlay the areas of former coal workings and the LAs under which they exist. This exercise was repeated with NHS boards to ascertain who to contact for the stakeholder engagement. A generic email invite was sent out along with a series of initial questions and a request for any additional data on similar events in Scotland related to mine gas (particularly related to CO2).

Stage 2 – Consultation with Experts (Section 8)

• Work with industry experts to consider the questions raised to collect unbiased views.

The consultation involved a series of conference calls or face-to-face meetings using a structured list of questions to tease out the information and to ensure conversations remained on topic. Each expert was given time to express their viewpoint in detail with thorough justification to ensure maximum information was collected.

Stage 3 – Analysis (Section 9)

• Bring together the findings from the research to provide a finalised report (No direct recommendations are required as a result of the research, but options to consider have been requested).

A systematic approach to the analysis phase was taken. All the issues that arose during the stakeholder engagement and expert consultation were collated into an issues log. The issues were then grouped to understand where in the process, assessment or mitigation measures, the issues occurred. The issues were paired to solutions and additional detailed comments obtained from the expert consultation to direct the ‘options for consideration’ detailed in Section 11.2 of this report.

3.3 Project Context

3.3.1 Definitions

It is important to understand that the purpose of this document is fact finding in relation to the risks that carbon dioxide (CO2) poses to residential properties from former mine workings. However, this is not to be confused with the more blanket term ‘mine gas’, that tends to include all ‘natural/harmful’ gases produced by coal workings. Table 3‑1 A summary of mine gas terminology delineates the variety of terms used to describe mine gas and to what principal gases or gas mixture they refer. The Gorebridge IMT report uses the term ‘mine gas’ within their report when discussing just carbon dioxide. Within this project, the focus has been on CO2 from mine workings, but we have also considered the related issues from mine gas generally. The key terms that relate to the conditions at Gorebridge (a rise in CO2 and decline in oxygen (O2)) are blackdamp, stythe and choke damp.

Table 3‑1 A summary of mine gas terminology

Word/phrase	Definition	Principal gas(es)
Mine gas(es)	Any of various harmful vapours produced during mining operations.	CH4, CO, CO2, H2S, VOC’s (volatile Organic carbons), Rn
Damps	Damps is the collective name given to all gases or combination of gases (other than breathable air) found in coal mines. The word corresponds to German ‘Dampf’, the name for vapour.	Various
Blackdamp Other names: stythe, choke damp	Reduction in oxygen and increase in carbon dioxide beyond which is capable of sustaining human life. Principally carbon dioxide, with minor denominations of nitrogen and water vapour. (Most dangerous compared to other damps as it provides no warning)	CO2, N2, H2O
Firedamp	Mine gas which is primarily methane.	CH4
Whitedamp	Noxious mixture of gases formed by the combustion of coal (normally enclosed environment). Mainly carbon monoxide and hydrogen sulphide.	CO, H2S
Afterdamp	After an explosion of firedamp. Consists of carbon dioxide, carbon monoxide and nitrogen. Hydrogen sulphide and carbon monoxide also present.	CO2, CO, N2, H2S
Stinkdamp	Mine gas which is predominantly hydrogen sulphide.	H2S

Throughout this document the issue will be referred to as carbon dioxide or blackdamp. Although the research project is related to the risk of exposure to carbon dioxide, this normally coincides with a drop in oxygen (or an oxygen deficient atmosphere). This occurs because there is an inverse relationship; CO2 concentrations increase as O2 concentrations decrease when coal is oxidised on exposure to air (Xu-yao et al., 2009). Therefore, an O2 depleted atmosphere is also included within the scope of a CO2 related incident or similar. Our terms of reference are limited to residential properties in former coal mining areas; commercial properties and public buildings are outwith the scope of this study.

3.3.2 Scale of the problem

The true scale of the issue is unknown because of the distinct nature and effect of CO2 (blackdamp) related events. Section 5 highlights the known incidents related to a rise in carbon dioxide and/or depleted oxygen atmosphere related to former coal workings.

In former mining areas there has always been an awareness of mine gas issues in confined spaces. The surface impacts from underground coal workings either through mine gas releases or subsidence are not new. With the closure of the mines, local regeneration and new housing developments, there are likely to be areas where a combination of a CO2 source in proximity to properties could create issues. With older properties, it is suspected that due to underfloor ventilation and poor air tightness, there is a reduced risk of CO2 build-up over time because CO2 can escape from the building. It has been noted that new build properties in Scotland will be more airtight and may have an unventilated concrete slab floor; therefore, without a form of mitigation in place, they may be at higher risk.

Major fire (methane) mine gas events expose themselves quite readily because the events generally result in an explosion or fire. One notable event, that made national press, was the explosion in Loscoe, Derbyshire. Although this event was related to an adjacent landfill site, the methane emission followed a low-pressure weather event. This mirrors the pattern of methane (and carbon dioxide) releases from former coal mine workings.

Similarly, those events related to hydrogen sulphide (H2S) are detected quickly due to the ‘rotten eggs’ smell produced by the gas at low concentrations (incident data, The Coal Authority).

CO2 is odourless and in combination with depleted O2, causes symptoms that are relatively generic (headache, dizziness etc.) and similar to those of a minor illness. For this reason, an event involving exposure to levels of CO2 that can cause ill-health may be unreported. Unless the symptoms are sudden and/or widespread, such as the case at Gorebridge, or a person is discovered either in a collapsed condition or found dead from exposure as occurred in Northumberland in 1995 (Coal Authority, 2018).

In addition to the potential for under-reporting of chronic events it has been suggested in the IMT report that events like Gorebridge may become more frequent in the future due to changing environmental conditions.

3.3.3 Factors affecting gas generation and migration from mine workings

The factors affecting gas generation and migration from mine workings include:

• Meteorological pressure and temperature changes
• Rising groundwater levels e.g. changes in water levels within former mine workings
• Creation of preferential pathways by anthropogenic activity

The correlation between low pressure meteorological events and an increase in CO2 emissions from abandoned mine workings and landfill sites is well documented (Teasdale et al., 2018; Hendrick & Sizer, 1992). Low pressure weather systems can also cause heavy rainfall; therefore, rainfall can act as a proxy for low pressure events.

There are, however, instances of mine gas emissions which are unrelated to meteorological events (Lagny et al., 2013; Wrona et al., 2016). This is likely to reflect the nature of the mine workings beneath a particular site. Shallow mine workings, such as those found in parts of the Scottish Coalfield and Northumberland, are more likely to be impacted by low pressure events than deeper mine workings (Robinson, 2000).

Global climate change may result in more extreme low pressure events in the future creating the sudden drops in air pressure favourable for CO2 migration (CL:AIRE, 2018) as well as heavy rainfall events.

Rising groundwater levels

Within working mines, pumping of water was used to keep the hydraulic head artificially low to prevent flooding of the workings. Rising water levels within abandoned mine workings have been described in detail (Adams and Younger, 2001; Robinson, 2000) particularly in relation to the impacts on the water environment. Another impact of rising groundwater levels is the potential for an increase in gas pressure as a rising hydrostatic head displaces gas within abandoned mines and reduces gas storage capacity. In the longer term, water levels in mine workings will reach equilibrium with the storage capacity stabilised at a lower level. However, there may be competing factors affecting gas generation, including dissolution of gases from mine waters and the generation of additional CO2 through the interaction of rising acidic mine water within limestones.

Research has been carried out to better understand the potential impact of greenhouse gas emissions from abandoned mine workings on climate change (DECC, 2011). However, there seems to be little recent published research in relation to the impact rising groundwater levels may have on the source of gas within mine systems, particularly around the volumes of methane and carbon dioxide held in solution within rising mine waters and the interaction of rising water within shallower rock formations.

Another factor to consider is that the effects that climate change may have on groundwater levels across the UK are uncertain. According to UK Climate Projections (UKCP09), the UK climate will become warmer due to climate change, winter rainfall will increase by 10 to 30% and summers will be drier. Aquifers will likely be recharged during wetter winters (Jackson et al., 2011), but overall groundwater levels depend upon the balance between winter recharge and summer evaporation, transpiration, and the increased stress on groundwater resources during drier times (BGS, 2019).

Yawson et al. (2019) found that groundwater recharge will likely increase in Scotland, Northern Ireland and Wales whereas groundwater reductions will likely occur in England, which is supported by Herrera-Pantoja and Hiscock (2007). However, the effects of climate change on groundwater are site specific and are dependent on a variety of factors including land use and vegetation types (Jackson et al., 2011). Additionally, location plays a factor as climate change is expected to increase the landward intrusion of seawater into coastal aquifers, which will affect aquifers near the coast (Safi et al., 2018; Abd-Elhamid and Javadi, 2008; Sherif and Singh, 1999).

Therefore, predicting the future changes to groundwater levels in abandoned mines and the resulting effects on gas generation are complex. Further research is recommended to assess the effects of climate change on the interaction of groundwater resources and abandoned mine workings.

Anthropogenic activity

New preferential pathways between mine workings and the surface can be created by a number of anthropogenic activities associated with site development including:

• ground investigations
• abstraction boreholes for water resources
• ground source heating systems
• on shore oil and gas drilling
• geothermal exploration in Scottish coal deposits and abandoned mine workings
• mine stabilisation works
• creation of foundations related to infrastructure or development.

The assessment of many of these issues is referred to in existing standards and guidance, such as BS 8485:2015+A1:2019. Works involving drilling or piling into mine workings and treatment of abandoned coal mine workings for ground stability purposes are subject to Coal Authority permitting (Banton et al., 2015).

Ground sealing as a result of development may also affect ground gas migration from mine workings to its effect on existing passive venting of gases to the surface. Cumulative development over a short time period could be particularly significant. This issue was identified as a concern in the Gorebridge IMT Report and in stakeholder engagement as part of this project and particularly in areas where rapid development is being undertaken in some areas of the former Scottish coalfields.

3.3.4 Planning and Building Standards Process

The Planning and Building Standards systems in Scotland were referred to both by Local Authority (LA) and other stakeholders in the consultation phase of the project. Therefore, in order to provide context, we set out the key elements of the system at national and regional levels as it operates in the development of sites and individual properties.

Building Standards

Responsibility for Building Standards system in Scotland sits with the Building Standards Division under the Scottish Government’s Directorate for Local Government and Communities.

Under The Building (Scotland) Act 2003, Scottish Ministers may make building regulations for purposes including “securing the health, safety, welfare and convenience of persons in or about buildings”. These regulations are published as The Building (Scotland) Regulations 2004.

The Scottish Government publishes several documents covering procedural and technical guidance which are reviewed on a regular basis. They also conduct any necessary research and consult on changes to the building regulations and associated Technical Handbook guidance on behalf of the Scottish Ministers.

Information on the Building Standards system is available via the Building Standards website. Although updated in 2017, it is noted that the current ‘Technical Handbook – Domestic’ document does not provide any information on ground gases, including mine gas. The equivalent document in England titled ‘Approved Document C - Site preparation and resistance to contaminants and moisture’ was reviewed in 2013 and references ground gas risk throughout the document with a small section covering methane and other ground gases.

Although the Building Standards system is overseen by the Building Standards Division, the regulations are enforced at a local authority level. Local authorities are also appointed as building standards verifiers tasked with granting building warrants when they are satisfied proposed work meets building regulations and accepting completion certificates where completed works also comply.

The Building (Scotland) Regulations 2004 implement building standards that are required to be met in the completed building so that there will be no threat to the building or the health of the people in and around it due to the presence of harmful or dangerous substances.

Planning

The planning system in Scotland is overseen by the Scottish Government who is responsible for the development and implementation of legislation and national planning policy (The Scottish Government, 2019).

The primary responsibility for the delivery of the planning services in Scotland lies with the 32 local authorities and the two national park authorities: the Cairngorms and Loch Lomond and the Trossachs.

Planning authorities are responsible for administering the three main parts of the planning system:

• Development planning – setting out how places should change in the future using plans
• Development management – making decisions on planning applications guided by policies in the development plan
• Enforcement – ensuring development is carried out correctly and acting when necessary.

There are also currently four Strategic Development Planning Authorities (SDPAs):

• Aberdeen City and Shire SDPA
• Glasgow and the Clyde Valley SDPA
• SDPA for Edinburgh and South East Scotland – SESplan
• SDPA for Dundee, Perth, Angus and North Fife – Tayplan.

In addition, Scottish agencies, such as Scottish Water, Scottish Environment Protection Agency (SEPA), Scottish Natural Heritage (SNH), Transport Scotland and Historic Environment Scotland, have a duty to engage in the development plan process at different stages.

The Town and Country Planning Act (Scotland) 1997, amended in 2006, forms the basis of the planning system in Scotland. Development plans and planning decisions are guided as appropriate by Scottish Government documents, such as the National Planning Framework (NPF), the Scottish Planning Policy (SPP), Circulars and Planning Advice Notes (PAN).

In this context PAN 33 is particularly relevant as it covers land contamination and related issues including ‘flammable and toxic gases. The PAN also states that one of the key principles adopted by Scottish Government is the ‘suitable for use’ approach. It is the responsibility of the developer to undertake an adequate risk assessment of a site, and to propose measures to ensure that these risks are appropriately addressed. The planning authority and building standards have the role of ensuring that developments are ‘suitable for use’.

In terms of land contamination, to ensure that land is made suitable for the proposed new use, planning authorities should require that applications include suitable provision for site assessment and where applicable, remediation measures.

PAN 33 recommends that “even before an application is made, informal discussions between the developer, planning authority and any other interested party should be beneficial in identifying the likely state of contamination and the most appropriate means of remediation.”

When considering a planning application, a planning officer will need to consider, with specialist advice (from within the authority or externally) whether or not the developer has adequately identified the sources of contamination and put forward a suitable restoration scheme for the proposed use. Planning permission may be granted on the condition that development will not be permitted to start until a site investigation and assessment has been carried out and that the development itself will incorporate measures shown in the assessment to be necessary. Planning conditions are normally included to this effect. If an issue cannot be resolved by imposing a planning condition, it may be possible to do so by concluding an agreement under section 75 of the Town & Country Planning Act 1997.

According to PAN 33, planning authorities, through Development Plans, are expected to promote the reuse of brownfield land, including sites affected by land contamination. Development plans allow authorities to set out their priorities for the reclamation/reuse of contaminated land and to inform developers of the availability of sites and any potential constraints associated with them. Local development plans should set out specific proposals for land use in their area so that opportunities for development are easily identifiable by landowners, potential developers and the community. Planning authorities should not be deterred from allocating potentially contaminated land for development on the grounds that remediation is required, but this should be a material consideration in granting planning approval for a specified development.

The applicant therefore needs to satisfy the planning authority that any unacceptable risks from existing contamination will be successfully addressed through remedial actions with as little impact to the environment as possible during and following the development. Any measures agreed upon concerning the post-development monitoring or maintenance must be presented to any future owner so that they are fully aware of the responsibilities that are tied to the land.

Supplementary planning guidance has been published by a number of local authorities in the Central Belt of Scotland in relation to land contamination issues including mine gas issues (Joint Scottish Contaminated Land Regulatory Officers 2010). A revised version of the joint document is currently being reviewed by Environmental Protection Scotland.

Some individual local authorities, e.g. Falkirk and West Lothian Councils, have also produced their own supplementary planning guidance related to contaminated land.

A major update of planning legislation in Scotland is pending. The Planning (Scotland) Bill was introduced to Parliament on 4 December 2017 and continues to be considered by the Scottish Parliament.

The Bill is intended to strengthen the planning system's contribution to inclusive growth and empowering communities. The Bill sets out the Scottish Government’s proposed high-level changes to the overall framework under which planning operates, in particular the Bill proposes a major update of the way local development plans are taken with a 10 year cycle as opposed to the current five years. This is referred to further in the analysis section of this report.

Figure 3‑1 Scottish Development Planning Process

3.3.5 The Part IIA Regime

Part IIA of the Environmental Protection Act 1990 is the primary legislation in the UK that relates to the assessment and remediation of land contamination under its current use. This was implemented in Scotland through the Environment Act 1995 and the Contaminated Land (Scotland) Regulations 2000. The Statutory Guidance provides details to all parties on how the regime should be implemented (see Scottish Executive, Environmental Protection Act 1990: Part IIA Contaminated Land Statutory Guidance: Edition 2, May 2006, Paper SE/2006/44).

Local authorities are the lead regulators under Part IIA with SEPA responsible for regulating certain ‘Special Sites’ and advising on water pollution cases.

The Contaminated Land (Scotland) Regulations 2005 were implemented by the Scottish Government in April 2006.

The definition of “contaminated land” under these regulations is as follows:

“any land which appears to the local authority in whose area it is situated to be in such a condition, by reason of substances in, on or under the land, that –

(a) significant harm is being caused or there is a significant possibility of such harm being caused; or

(b) significant pollution of the water environment is being caused or there is a significant possibility of such pollution being caused.”

In this context, relevant categories for ‘significant harm’ stated in the Statutory Guidance comprise:

• Human health effects: death, disease, serious injury, genetic mutation, birth defects or the impairment of reproductive functions
• Property in the form of buildings: structural failure, substantial damage or substantial interference with any right of occupation.

The Part IIA regime relates to the current use of land, in contrast to the planning regime which considers proposed future use. Part IIA is therefore the legislation applicable for considering whether existing properties are impacted by CO2 from mine gas.