Article Contaminated Land Data Management Instrumentation & Monitoring

Ground Gas Monitoring and AGS Data Transfer Format

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Introduction

Ground gas monitoring and data assessment are often part of a site’s generic quantitative risk assessment (GQRA), as outlined in the Land Contamination: Risk Management (LCRM, 2025) guidance.

The aim of ground gas monitoring and assessment is to understand the risks posed by ground gas sources to relevant receptors and, if needed, to design measures to mitigate these risks. Capturing high-quality data during ground gas monitoring is therefore essential for a robust risk assessment.

AGS data transfer format (further referred to as AGS data or AGS format) enables easy transfer of data between different parties involved in ground gas monitoring and subsequent interpretation of the data. However, this has not been applied in a consistent manner for ground gas monitoring data reporting. This can lead to inconsistencies in data provided by different parties and, in extreme cases, in important data being missed out from the overall dataset.

This article has been written in collaboration between the AGS Contaminated Land Working Group (CLWG), the Data Management Working Group (DMWG) and the Instrumentation & Monitoring Working Group (I&MWG). The article provides an overview of key requirements for robust ground gas monitoring and how to report the acquired data in AGS format. This is to help practitioners involved in ground gas monitoring and risk assessment to gather and manage a good dataset.

Ground Gas Monitoring and Risk Assessment Process

LCRM guidance provides links to further, more detailed, guidance on assessing risk posed by ground gases and design of protective measures for buildings:

Further guidance on dealing with ground gas is available:

It should be noted the list of guidance provided here is not exhaustive.

The listed guidance and standards highlight the need for a conceptual site model (CSM) as a key element for ground gas risk assessment, as it would be with any other risk assessment for land contamination. An initial CSM should be prepared as part of the desk-based risk assessment. This will inform the assessor about the potential sources of ground gas (e.g. coal mines, landfills) and pathways that can lead to the ground gas migrating to the relevant receptor (e.g. foundation piles for a house enabling migration of ground gas into the house). Ground gas monitoring is then typically scoped as part of ground investigation.

Diagrammatical CSM may be useful to understand the interactions between different factors influencing pollutant linkages including those relating to ground gas. Ground model can be created for the site to aid the understanding and support the diagrammatical CSM.

CIRIA C665 (Section 2.6) provides a good overview of factors influencing the migration and behaviours of gases and vapours. These factors comprise of:

  • Driving force, i.e. the potential for gas to migrate from its source as impacted by pressure differential, diffusion along gas concentration gradients and flow within liquids (in dissolved form);
  • Meteorological conditions:
    • Atmospheric pressure (at falling pressure increased emission rates occur);
    • Rainfall and frozen ground;
    • Temperature;
    • Wind;
  • Vegetation;
  • Geology;
  • Anthropogenic influences; and
  • Hydrogeology/tidal effects.

The purpose of the ground investigation and ground gas monitoring is to capture the data describing the above factors. The assessor needs to be able to explain why any potential changes to ground gas flows occur and how these fit into the CSM for the site. They should also confirm whether the expectation from the initial CSM holds and nothing unexpected is occurring, e.g. landfill is sealed, petrol station is regulated.

CIRIA C665 (Section 5) provides more detail on monitoring methodology including recommended data collection, description of a typical monitoring round and suggestions for monitoring period duration and frequency of monitoring rounds.

CIRIA C665 and BS 8485 note that “worst-case” scenario should be captured by the monitoring period. A typical ground gas risk assessment thus comprises data-informed updates to the CSM and worst-case scenario screening value. The gas screening value (GSV, litres of gas per hour) is based on the maximum borehole flow rate (l/hr) and maximum gas concentration (%). The assessment then allows for the selection of a Characteristic Situation and selection of protective measures for the building and/or remediation.

The Data

Collected ground gas monitoring data need to be of sufficient quality to enable subsequent risk assessment as described above.

Ground gas monitoring can be undertaken manually in rounds as mentioned above or as a continuous process over longer periods. A monitoring round can be undertaken over multiple days, especially for larger sites with a significant number of wells to be monitored. Both continuous monitoring and manual ‘spot’ monitoring rounds can be reported in AGS data transfer format. The requirement to report data in AGS format should be added to the ground investigation scope and specifications. The specification should clarify the scope for the provision of the AGS data.

‘BS 8485 also advises that to adopt the worst case as a site characteristic GSV, the assessor should be confident that it is prudent and reasonable to do so and does not result in unnecessarily conservative protection of the development.’ (NHBC guidance)

Data captured prior to monitoring and required for interpretation of monitoring data includes:

  • Location of the exploratory hole
  • Geology encountered during ground investigation
  • Installation details including top and base of the response zone and datum

Equipment calibration details[1] – included in the factual report together with the instrument serial number.

Data captured during monitoring should include:

  • Site name/reference
  • Client
  • Location of site/monitoring wells
  • Date/time of monitoring
  • Monitoring personnel/organisation
  • Instrument type including serial number
  • Atmospheric (barometric) pressure and trend
  • Air temperature
  • On-site weather (precipitation, wind speed etc.)
  • Ground conditions/evidence of contamination (vegetations stress, visual contamination)
  • Any other relevant information such as borehole condition
  • Ground gas flows and concentrations:
    • Monitoring point reference (ensuring this can refer back to the exploratory hole location and its installation)
    • Flow (l/hr)
    • Differential pressure (Pa)
    • Concentrations of relevant specified gases as identified in the CSM.
  • Groundwater monitoring data:
    • Depth to groundwater (m bgl and/or m AOD)
    • Depth to base of the well (m bgl and/or m AOD)

Monitoring personnel details need to be captured as part of the monitoring process to ensure traceability and competency of person undertaking monitoring. However, this information is likely not to be passed outside of the monitoring organisation to ensure adherence to GDPR regulations.

CIRIA C665 provides a proforma for capturing the data on site in Appendix A3, capturing only peak and steady concentrations for the monitored gases. However, we would recommend that raw monitoring data is captured at ‘reasonable’ intervals until equilibrium is achieved (for manual ‘spot’ monitoring). This provides the assessor with additional information about the gas flows rather than just peak/minimum and steady concentrations.

How equilibrium is defined depends on site-specific circumstances but generally two consecutive readings after at least 3 minutes with all parameters within 0.1, 1 or 10% (as appropriate) is, in our experience, usually a good and justifiable rule of thumb. This also means the monitoring team does not have to spend unnecessary amounts of time at every location recording and the process is much more efficient and sustainable.

Typical Ground Gas Monitoring AGS Data Issues

Ground gas monitoring data reported in AGS data format often only includes the peak (minimum for oxygen) and steady readings. This means that some form of interpretation has already been undertaken by the organisation responsible for the monitoring, often a contractor involved in ground investigation for the site. This then limits the assessor in their interpretation of the data. Full factual data as captured during the monitoring should therefore be reported in AGS data as well.

Currently, ground gas monitoring data provided in AGS format also often excludes details on monitoring locations that have been missed for any reason; for example the contractor could not locate the well, open the tap and so on. All this information should be captured and provided as part of the AGS dataset.

AGS Data Structure

There are four main AGS data groups which contain information relevant to monitoring and three additional groups that may contain data that can support interpretation:

  • LOCA (Location Details) contains exploratory hole name, hole type and coordinates
  • MONG (Monitoring Installations and Instruments) providing details of the installation including the depth of response zone
  • MOND (Monitoring Readings) contains all records of the monitoring results – (gas concentrations and groundwater monitoring results), each reading is represented in a new row of data
  • TREM (Time Related Remarks) was originally intended for observations during ground investigation but can be used to record weather observations and ground conditions during monitoring
  • PIPE (Monitoring Installation Pipe Work) provides details for calculating the well volumes
  • GEOL (Field Geological Descriptions) contains geological descriptions associated with depth below ground level and can contain interpretation of the descriptions in the form of geology codes
  • DETL (Stratum Detailed Descriptions) provides detailed observations made within the particular stratum which appear on logs in the form of comments within the geological description.

The above groups in the AGS data format are linked via shared key fields. All parties must ensure that they use exactly the same (capitalisation, spelling, decimal places etc.) key field data relating to the locations of the monitoring points (LOCA_ID, MONG_DIS, MONG_ID).

Example ground gas monitoring data captured in Excel and AGS data format are attached to the article and can be used as a template for creating other monitoring data. Ground investigation data such as encountered geology within the exploratory hole are not part of this article.

According to CIRIA C665, the presentation of ground gas monitoring data should include as a minimum:

  • A site plan with monitoring locations;
  • Raw data captured; and
  • Summarised data.

Site boundary and other spatial data related to the site can be stored in geospatial (GIS) data formats such as geopackages. Further details on geospatial data are not part of this article. Recording the data in AGS format enables easier/automated data manipulation and presentation for reporting.

AGS Data Format Tips

Use the MONG group (Monitoring Installations and Instruments) to understand the details about the installation:

  • MONG_ID and MONG_DIS are used to differentiate multiple installations within the same well

Provide enough details in the MOND group (Monitoring Readings):

  • Use MOND_REF (Monitoring Reference) to indicate the monitoring round
  • Record < LOD instrument value in MOND_RDNG for readings below detection (e.g. < 1) and ‘dry’ for dry monitoring well
  • Record all missed readings leaving the MOND_RDNG (Reading) empty and writing the reason for missed reading in MOND_REM (Remarks)

Record weather and ground conditions in the TREM group.

Check out the AGS website for all relevant abbreviations.

Collect/collate the data only once: Use specialist mobile apps for capturing data on location rather than recording data in a spreadsheet/notebook and then typing into AGS.

Conclusion

Good quality data is essential for accurate interpretation of risks posed by ground gases. AGS data transfer format provides defined structure for consistent reporting of ground gas monitoring data.

The key conclusions and recommendations from this article are:

  • For sites where a plausible risk from ground gas has been identified in the initial conceptual site model, a ground gas risk assessment often including gas monitoring is required.
  • The collection of high-quality data is an essential part of good interpretation of risks posed by ground gases.
  • Ground gas data from both manual ‘spot’ monitoring rounds and continuous monitoring can be provided in AGS format.
  • Full datasets should be captured in AGS format for gas monitoring; not just peak or steady state concentrations and flow rates.

Article provided by Dr Petra Lincoln, Chris Swainston and Geraint Williams

The authors would like to thank the following for their contribution to the article:

Melody Wareing, Neil Chadwick, Phil Child, Leon Warrington, Antony Phin, Chris Hughes, Jonathan Gammon

[1] Calibration details currently cannot be transferred using the AGS format.