Case Study 1:
London Remediation Project, Leap Environmental May 2017
This project involved demolition of existing structures on a site in London and remediation for residential development. During the site investigation phase, preliminary basic gas monitoring indicated a risk category CS1. During remediation, an old in-filled pond was discovered containing organic material, likely to cause a gas risk and thus likely to require additional gas protection measures. To fully investigate this, further gas monitoring was required. Doing this with spot monitoring would take between 6 – 8 weeks, slowing down the project with no guarantee that the data would prove the gas risk conclusively. Doing this with other forms of continuous monitoring equipment without the capability to measure flow-rate would not provide a full appreciation of the gas risk.
3 units were installed around this part of the site, measuring bulk gases and flow-rates and data from a local meteorological station was integrated from Weather Underground to further contextualise the gas readings. The deployment ran for 1 month to cover a range of atmospheric pressure conditions to include a period of falling atmospheric pressures.
Upon installation, the client saw large fluctuations in CH4 which gradually reduced over time. These large fluctuations saw methane recorded at levels up to 15 – 20% & as low as 1%. If the same measurements had been taken with spot monitoring devices, the difference in potential results could have quite an impact on the project.
Throughout the project, very low flow-rates were evidenced. When coupled with the gas readings this allowed for much more accurate gas screening values to be calculated, given the higher density dataset available. In fact for most of the readings, the flow-rate recorded was negative, showing that the dominant meteorological conditions actually mitigated against potential gas migration. This provided huge confidence in terms of assessing the risk and recommending appropriate gas protection measures to be installed.
The live data also meant that by the time the project was completed, the consultant had a thorough understanding of the site and was in a position to advise their client accordingly. This sped up the site investigation process considerably, allowing the customer to provide an answer to their client much sooner than would be typically possible.
Fig.2 Client data display, customised to their requirements
Case Study 2:
Historic Landfill Divestment – Enitial Ltd. March 2017
The site is a former landfill, filled in the 1970s & 1980s. It is adjacent to an airport and an industrial estate in the Midlands and as such is prime development land. enitial were approached to do continuous monitoring to support divestment of the site. The data gained was also acquired to support final permit surrender.
One GasFlux™ unit was deployed measuring bulk gases, flow-rate and was integrated with a water level logger to provide ground-water level information online alongside the gas readings; another Gasflux™ unit was installed on a secondary location. The deployment ran for 1 month to cover a range of atmospheric pressure conditions to include a period of falling atmospheric pressures.
The GasFlux™ data was reported live using the AmbiSense web platform, allowing the client to login daily to see the results. This enabled a much more proactive site investigation process as the customer could adapt their assessment program based on live gas readings and hence expedite the site investigation. The ultimate result was that the land could be sold to a developer immediately after the project was completed, removing the liability from the balance sheet of the previous owner.
Case Study 3:
Assessment of Risk (Local Authority Site) EPG & Enitial, December 2016
The site was a former sandstone quarry and subsequently a domestic landfill site in the 1980s. Capped in topsoil in 1994, gas was found to be migrating out of the site through the surrounding ground in 2005. A comprehensive gas management system was since installed to extract and flare the landfill gas. Consideration is now being given to permanently shutting down the active gas controls and replacing them with a passive system. Complete continuous monitoring data was collected to inform the decision-making process.
3x GF units deployed onsite measuring bulk gases and flow rates over a 2-month period. Half-way through the project, the gas control system was switched off to understand the potential impact of doing this on a permanent basis.
When the gas control system was switched off, this was found to have a marginal effect on the gas migration around the site, proving that switching it off would have no major impact on the site.
Look at the graphs, the methane concentration shows that there is a correlation with atmospheric pressure. This could suggest that methane emissions increase in low atmospheric pressure. However, the GSV graph shows no significant correlation that would affect risk and therefore no increased emissions in low atm pressure. This allows the consultants to conclude that, on this site, time series data of concentration alone (i.e. without measuring flow) can be misleading.
Fig 4: Time Series of CH4 and GSV (source: EPG ltd)