IRP IGM

1
IRP - IGM
Ground-gas monitoring the way forward
Dr Mark Todman Urban Vision Partnership Ltd
2
Improved risk prediction from continuous
in-borehole ground-gas monitoring (IRP-IGM)-
project partners

• Salamander
• Project management
• Responsible for hardware design, development and
  production
• University of Manchester
• Project coordination
• Basic and applied science development
• Urban Vision Partnership Ltd
• Stakeholder engagement
• Methodology guidance preparation and adoption

3
Objectives and methods of gas monitoring

• Determine the risk
• Predict how this may change in the future
• This is currently achieved by
• i) Periodic static measurement of gas
  concentrations
• ii) Using boreholes to access the subsurface

4
The evolution of UK risk assessment

• Recent UK guidance moves towards monitoring
  periods based on risk and proposed end use
• Risk assessment is only as good as the input
  data
• Over conservative remediation due to unknown or
  poorly quantified worst case conditions

5
Problems with existing UK best practice

• What is the sampling frequency?
• Sampling frequency currently based on what is
  possible rather than variability of gas in the
  sub surface
• Each borehole is unique
• Variable geology, installation and sampling
  regime
• Is concentration related to risk?
• Risk may be greater when gas generation is
  rapid or when gas flux is high, which might not
  be related to gas concentration

6
Current UK best practice spot sampling data
7
Cost? Benefit?

• 8 years of monthly monitoring
• ..over 300 monitoring visits
• anything upwards of 30,000 gas monitoring
  programme
• to tell you
• not a lot!

8
Adding a new dimension to monitoring
Meeting these requirements

• Determination of sampling frequency
• Characterisation of each borehole
• Definition of the relationship of concentration
  to gas production / movement
• will improve site characterisation and
  understanding of the processes of ground gas
  generation and movement.

9
Adding a new dimension to monitoring

• Understanding of processes will improve the
  ability to PREDICT ground gas concentration and
  reduce uncertainty in Risk Assessment.
• To understand processes temporal resolution of
  sampling must be increased

10
No significant change in monitoring technique?
Technology not available
Poorly understood processes
Technology too expensive
No supporting guidance
11
What has changed?

• Recognition of the need for more representative
  data
• Availability of affordable technology

12
www.gasclam.co.uk

• Key features
• Continuous monitoring of CH4, CO2, O2, H2S,
  barometric borehole pressure and water level
• ATEX approved
• Extended deployment, up to 6 months based on
  hourly sampling
• Robust stainless steel design
• Fits in 50mm borehole
• Easy to use and deploy
• Venting and vented modes

13
Ability to collect ground-gas data

• Develop an understanding of the processes
  controlling ground-gas migration, leading to
  better prediction
• Requires research and field trails
• Marketing effort for a new product and
  methodology
• Requires methodology development and stakeholder
  engagement to develop best practice guidance

14
Continuous Data
995mb
15
Time series data allows temporal variation to be
quantified or accounted for
Borehole with gas only observed at Christmas. A
period of continuous monitoring show otherwise
16
Sampling rate and concentration variability can
be matched gas concentration can vary on a range
of timescales.
Short time scale variability
17
Risk Assessment rather than Risk Recognition

• Time series data allows a meaningful summary of
  concentration measurements
• The only meaningful summary at present is whether
  a borehole ever exceeds a threshold concentration
  

concentration duration curves
18
Concentration duration
Black curves spot sampling simulation
19
Correlations
20
Correlations
Correlation of atmospheric pressure and
concentration
21
Correlations
22
Correlations

• Such relationships could give confidence in
• the prediction of concentration from other
  environmental parameters
• recognising the driving force behind gas movement
• however

23
Correlations

• INVERSE RELATIONSHIP?
• Without time dimension this could be written
  off as error / scatter / poor understanding of
  processes / increased uncertainty

24
Large scatter on data where has my
predictability gone?
25
Hysteresis
A closer look reveals loops of data
Time
26
Hysteresis
27
Hysteresis
28
Hysteresis

• Borehole pressure (RP) is the same in both
  boreholes despite different gas compositions -
  suggests borehole pressure is wholly a
  consequence of atmospheric pressure not gas
  production.
• RP is negatively correlated with AP, however,
  hystereses are apparent.
• Hystereses are anti-clockwise, c.f. clockwise
  hystereses in solute/discharge rating
  relationships.
• Anti-clockwise hystereses - at identical AP,
  higher RP whilst AP is falling rather than rising.

29
Calibrating a borehole

• Ground gas concentration is not measured directly
  because the borehole is an uncalibrated sampling
  device
• Hydrogeologists rely on pump tests to
  characterise production rates of water from
  boreholes
• With time-series gas concentration data a similar
  approach can be adopted

30
Borehole characterisation
31
Borehole characterisation

• To set the context for any subsequent monitoring
  programme every borehole should be characterised
  to allow more reasonable inter-comparison
• A borehole is not an innocent bystander

32
Summary

• Time-series data allows
• A more direct measurement of ground-gas regime
• Characterisation of boreholes
• Improvement of understanding of processes
• Quantification of the real ground-gas flux

33
Developing new a methodology, guidance and best
practice

• Urban Vision experience as a regulator and as a
  consultant
• Best practice to be driven from the bottom up

34
Developing stakeholder engagement

• Continuing to develop network of contacts across
  the public and private sector
• Expert Advisory Group
• Dissemination of application data and methodology
  development through a Gasclam User Group on
  www.gasclam.co.uk

35
Contact details

• Urban Vision Dr Mark Todman
• E mark.todman_at_urbanvision.org.uk
• T 07912 774 934
• University of Manchester Dr Peter Morris
• Project Coordinator
• E peter.morris_at_manchester.ac.uk
• T 0161 275 0183
• Salamander Dr Stephen Boult
• E s.boult_at_salamander-group.co.uk
• T 0845 053 1234