Mine Gas Risk Assessment, Sunderland CC
Mine gas risk assessment for existing building
Name: Site in Washington
Date: November, 2019
Local Authority: Sunderland City Council
Gas Risk Assessment
A planning application to change a warehouse into a leisure facility was frustrated by the fact that the building was on a former colliery site and, it was thought, very close to an old mineshaft. Concerns were raised about potential mine gas emissions from the shaft had been raised by the local authority, but with the building soon to be opened a quick resolution to the issue was required.
EPG began the assessment by undertaking a comprehensive desk study that looked for sources beyond the usual Envirocheck reports. EPG used map and aerial photograph overlays as well as looking at local history and Coal Authority information. Interpretation of the desk study information identified that the shaft was actually further away from the building than originally thought. An assessment of the ground conditions showed that the Coal Measurers were capped by Glacial Till, which would limit the risk of gas emissions from the shaft reaching the building. Further desk study indicated that the shaft had been filled and capped and the groundwater levels in the area were known to be fully recovered. There were no shallow workings and the former deep workings were flooded. This minimised the risk of gas emissions up the shaft.
A programme of continuous monitoring of gas concentrations immediately below the concrete floor slab was designed by EPG and completed via a vapour pin installation. This method allowed sufficient data to be collected over a short period, including suitable drops in barometric pressure, which is the key driver for mine gas risk in this site. This was demonstrated using the approach described in CLAIRE Technical Bulletin TB17 Ground gas monitoring and ‘worst-case’ conditions, written by EPG’s Technical Director Steve Wilson and Australian Director James Lucas.
The continuous monitoring data was collected by Ambisense units and analysed using the Ambilytics platform; providing further evidence that there was no risk of carbon dioxide emissions occurring from the shaft and affecting the building. The Ambilytics platform provided correlation plots, heat maps and 1D partial dependency models to show the absence of correlations. When combined with the other site information sets it helped provide multiple lines of evidence showing no risk from mine gas.
The Gas Risk Assessment provided by EPG was extremely cost effective as the Local Authority quickly approved the recommendations and the facility was opened on time and without the need to retrofit costly gas protection measures.