A trial to determine the impact of soil washing on coal seam gas (CSG) dam sediments in Queensland

Abstract

Extracting coal seam gas (CSG) is becoming increasingly common in Australia and throughout the world. With the number of wells in Queensland alone increasing from 10 in 1995 to 4,484 by 2013 and 20,000-40,000 more expected to be drilled in the next 20 years, the production of methane from CSG is forecast to become one of Australia’s largest export commodities within the next decade. There is, however, growing disquiet about the potential for CSG to negatively impact the environment because it generates a number of gaseous, liquid and solid waste streams, the composition of which are largely unknown. CSG waste streams include fugitive emissions, drilling mud, chemical fracking fluids, produced chemical fracking fluids, and produced water and brines, some of which are settled water and brines, some of which are settled into large evaporation dams to form sediments. Moreover, minimal data on the chemical and physical properties of these various waste streams resulting from rigorous environmental research have been published or made publicly available, adding to society’s growing concern for CSG as an environmentally sustainable approach to extracting gas from coal. For this reason, the present study examines the chemical properties of two types of CSG dam sediment from the Bowan Basin in Queensland, and investigates the role that conventional soil washing might have in converting these low-level contaminated sediments into a “clean soil” which can be applied in on-site, beneficial reuse projects; the chemical properties of the resultant flushing solutions are also examined. The study found the majority of components in CSG dam sediments are benign, and soil washing removes or partially removes most inorganic contaminant species from CSG dam sediments; the study also found that these contaminants were mostly transferred to the flushing solution, which can be treated separately and potentially reused for livestock drinking water or irrigation water or recycled into the operating circuit. Key words: Coal seam gas, CSG, soil washing, sediment, flushing solution.