Presenter: Marcus Wright & Terry Widdowson, Golder Associates (NZ)

Presentation title:  Ground gas – it’s not just a landfill issue!

same scale as other more populated industrialised countries. Consequently, issues associated with ground gases (namely methane, hydrogen sulphide and carbon dioxide), have received little or no comment in New Zealand contaminated land guidance and are often overlooked. Redevelopment in Christchurch and more intensified housing development in other parts of the Country have resulted in increased use of brownfields or development in close proximity to former fill sites.  These have the potential to encounter ground gas issues that may pose a risk to the development and as such should be investigated. The investigation is then expanded by the NES and HAIL process requiring potential issues from neighbouring sites to be considered – which clearly requires potential ground gas migration onto site to be considered.   The purpose of this paper is to raise awareness of the risks of failure to investigate sites potentially impacted by ground gases and identify measures required to mitigate against or allow for its secondary effects. The paper will also present some perspective regarding its risks or lack of in relation to ground gases.    The paper will outline the basics of ground gas reporting, from its source-pathway–receptor approach and investigation design related to a conceptual site model (CSM) (the CSM requiring both an environmental, geotechnical and construction understanding of the site) through the how and when to monitor (equipment, procedures, atmospheric conditions, and when not to monitor), what to record (and understanding its implications), evaluating risk (technical guidance- both broad and analytical) and risk mitigation (remove the source and so remove the gas is not always feasible).      In summing up, the paper will present experience of the actual occurrences of incidents caused by ground gas.


Event: WasteMINZ Conference 2013

Date: Wednesday 23 October 2013