Methane contributions from holding ponds
Locating and mitigating sources of any unintended releases of methane are important for addressing community concerns around fugitive emissions from onshore gas production.
This desk-top study evaluated the potential for CSG water holding ponds to be a source of methane emissions. The study found that there is limited and variable information about methane emissions from CSG holding ponds and the true methane emissions of CSG holding ponds in Queensland is unknown.
In this study CSIRO scientists examined published scientific literature for evidence of emissions from gas-industry holding ponds, assessed non-industry water bodies (natural and constructed) to understand the potential of water bodies to contribute to emissions, and used these data as a proxy for estimating potential emissions by gas-industry water bodies.
Potential emissions varied according to pond size, presence of additional carbon and nutrient inputs, and pond location in either temperate or sub-tropical zones.
Potential emissions ranged from 15 milligrams per square meter per day (mg/m2/d) to 30 mg/m2/d. For comparison, reported methane emissions from an urban sewage treatment plant inlet was 28,900 mg/m2/d and reported methane emissions from an 80 ha landfill site was 35,000 mg/m2/d.
While the proxy estimates are likely to be conservative, the concentrations proposed could potentially represent a significant source of methane, given that publicly available data show Surat and Bowen Basin CSG industry holding ponds comprise almost 65,000 megalitres of water with an aggregate surface area exceeding 1,100 hectares (ha).
Further investigation involving field work and microbiological assessment to accurately quantify methane emissions and potentially other greenhouse gases from CSG holding ponds in Queensland is recommended. Key knowledge gaps around organic carbon inputs to holding ponds (particularly ultra-fine coal particles) and the microbial dynamics with respect to methane production and consumption in these ponds should be addressed.
CSIRO’s GISERA has approved two new research projects designed to address knowledge gaps identified in the current study: Methane emissions from CSG water holding ponds in Queensland, which will directly measure methane emissions from CSG holding ponds, and Key controls or contributors to methane emissions from CSG water holding ponds, which will focus on the role that methane generating and eating microbes, algae, brine and sediment play in the methane emission contributions of water holding ponds.
Together the current study and the two new research projects will further refine understanding of the potential of the CSG industry to contribute to emissions in the Surat Basin/Western Downs region of Queensland.