Ground gas and VOCs Exploring continuous online ground-gas monitoring for accelerated risk assessment

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1 Ground gas and VOCs Exploring continuous online ground-gas monitoring for accelerated risk assessment Steve Wilson

2 The basics Before we cover continuous monitoring let s discuss the basics: Uncertainty and conservatism in risk assessments The Conceptual Site Model

3 Causes of uncertainty in gas risk assessment Poor (or non existent) conceptual site models Not using the CSM to design the investigation or to develop the risk assessment Monitoring in poorly designed wells, deep wells or wells for groundwater sampling The belief that methane (or any other gas) above background concentration in the ground will pose a risk Reliance on advice from gas protection suppliers Belief that gas risk assessment is limited to use of Wilson and Card (GSV) screening method

4 Conservatism Historic use of 1% methane and 5% carbon dioxide as trigger levels for gas in the ground and inclusion in CIRIA C665 and BS8485 When considering above ground development there is no unsafe concentration of gas in the ground How fast can it migrate out of the ground (if at all) pressure and flow rates or diffusion 90% methane in ground may pose no risk to development at ground level Overly conservative assessments when only carbon dioxide is present ( and it is not from a high risk source)

5 BS8485: 2015 Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings Does not apply to retrofit (even if the building is brand new and has just been built)

6 Example CSM Carbon dioxide

7 Example Site undeveloped in past green field with no significant source of methane or carbon dioxide No landfill sites that are credible source of gas 1.2m Made Ground soil with no putrescible material Natural sand and gravel common to get elevated CO 2 No methane Elevated natural carbon dioxide 7.9% One flow rate results at 4.8l/h Defined as CS 2 venting and membrane because of CO 2 concentration Look at the results and the CSM

8 Example natural carbon dioxide CS1 and gas protection is not required

9 Example natural carbon dioxide CS1 and gas protection is not required

10 Continuous monitoring You do not need to use it on every site Only use it where it is going to provide a cost benefit Complete continuous monitoring: Gas or vapour concentrations Flow rates Humidity Temperature Each reading linked to local weather data wind speed, rainfall, air temperature, etc This data can allow a better understanding of the gas regime

11 Complete continuous monitoring Continuous monitoring with flow rates now possible Opens up new and exciting possibilities for ground gas risk assessment where appropriate It can provide value for clients by reducing need to install gas protection, reducing cost of site investigation, reduce scope of gas protection or reduce ongoing monitoring requirements/costs Statistical analysis of distributions and comparison of trends from different gas sources Assessment of well radius of influence Assessment of gas permeability of the ground AmbiSense/EPG will be publishing papers and running seminars showing how you can get value from the data

12 About GasfluX Continuous Gas Monitoring Continuous Flow Monitoring Solar Powered Telemetry Enabled User Configurable Data Integration Connect Sensors & Data Sources CH 4, CO 2, O 2, NH 3, CO, H 2 S, VOCs, Pressure, RH, Temp. Completes the risk assessment equation Maximises service interval Report live data from any location Utilise as an early warning detection system Configure H/W & S/W to match project requirements Integrates with SCADA, EQuIS, MonitorPro etc. Connect external devices & data sources

13 Typical Data Portal

14 Example of benefits

15 Times series of gas concentration and flow outside landfill

16 Outside the landfill the CO2 is from a natural source Background CO2 Outside landfill in migration pathway Inside landfill

17 What are the implications? The time series of carbon dioxide concentration outside landfill shows a relationship with atmospheric pressure Is flare operation influencing gas concentrations? BUT The GSV shows no significant relationship flows are not affected It also shows the flare system is not having any effect on this particular well Partial continuous monitoring without flow rates is misleading Analytics show natural background concentration of CO2 outside landfill Can turn flare off

18 Example Open space over landfill Complete continuous monitoring in wells Consideration of effects on gas flow from atmospheric pressure and temperature Demonstrated that elevated methane did not pose any risk to users of the site by using data to model surface emissions and outdoor air exposure Confirmed by surface emissions mapping and flux boxes

19 Concentrations only CO2 and CH4 have different response Drop in CH4 when atm pressure goes up

20 With flow rates and GSV there is a relationship to atm pressure

21 But temperature is also having an effect

22 Combine the data to estimate surface emission rates for risk assessment confirmed with flux boxes

23 Post construction monitoring of voids Is NOT required on all sites Need to monitoring well into the void not at air bricks Cannot feed pipes through airbricks curl up inside cranked ventilator or end up curling in void Need specific installation drill into the void Cannot treat as a flux box by sealing air vents there is still a lot of air flow via cavities, etc Post construction monitoring gives most benefit when linked with meteorological data (especially wind speed and direction) Also need temperature and humidity in void Compare actual performance with design performance

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25 Example Gas membrane not verified Continuous monitoring of void space below floors GSV for this site was <0.07l/h (no flow detected) with carbon dioxide at 17% (deemed to be Characteristic Situation 2) Source - colliery spoil below site

26 Conclusion void is providing sufficient protection and works to address membrane are not required

27 Uncertainty - VOC risk assessment Lack of CSM Poorly designed monitoring wells Lack of vapour sampling Vapour sampling from wells with groundwater No consideration of building construction in risk assessment model Use of generic models (eg J&E and CLEA) when not appropriate Use of soil data exceeding GAC instigates use of VOC membrane DQRA is not just about changing parameters in CLEA often have to use other models

28 VOC PID limits of detection If you are vapour monitoring for VOCs as a screening exercise ppm detection levels are not suitable where risk is borderline Need to monitor with instruments capable of ppb detection limit Compound Mol Wt. RfC (ug/m 3 ) Concentration (ppb) Concentration (ppm) Benzene Toluene Ethylbenzene Xylene Naphthalene Tetrachloroethylene (PCE) Trichloroethylene (TCE) Cis 1,2-dichloroethylene Vinyl chloride ,1,1-trichloroethane (TCA) ,1-dichloroethane ,2-dichloroethane ,1-dichloroethylene (DCE)

29 Continuous soil or indoor vapour monitoring Ambisense are able to continuously monitor for specific VOCs at low detection limits Eg 1mg/m 3 for TCE 10 minute analysis time Can sample multiple locations (up to 30) Telemetery Applications In situ GW or soil remediation, monitoring internal VOC levels in existing buildings, site investigation if cost of vapour mitigation system is very high and could potentially remove it

30 Conc (ug/m3) Determining Exposure Time 4 % of time above 0.5 ug/m3: ~ 6% PCE st Floor Air PCE Run Number

31 Vaportrail Real-time Contour Plot

32 Summary Always consider the CSM it is not just about gas monitoring data Complete continuous monitoring with flow rates is a game changer and can help you reduce costs for clients Continuous monitoring for VOCs that targets specific compounds is now possible AmbiSense/EPG will be publishing papers and running seminars showing how you can identify when to use continuous monitoring and how to maximise value from the data Early 2018 Thank you for listening