HYDROCHEMICAL AND ISOTOPIC INDICATORS OF HYDROLOGICAL PROCESSES WITHIN COAL SEAM GAS FORMATIONS AND ADJACENT AQUIFERS, CONDAMINE RIVER CATCHMENT, QLD. Daniel Des Rex Owen BNatRes MSc (Research) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Earth, Environmental and Biological Sciences Science and Engineering Faculty Queensland University of Technology 2016 Keywords Aquifer interactions; Bromide; Carbon isotopes; Chloride; Coal seam gas; Coal bed methane; Compositional data analysis; Dissolved Organic Carbon; Hydrochemical indicator; Hydrogen isotopes; Inverse modelling; Isometric log ratios; Lithium; Major ions; Methane; Methanogenesis; Multivariate statistics; Sodium-bicarbonate groundwater; Stable isotopes of lithium; Stable isotopes of chlorine; Thermodynamic controls Hydrochemical and isotopic indicators of hydrological processes within coal seam gas formations and adjacent aquifers, Condamine River catchment, QLD. i Abstract In areas where a range of industries and economies rely on the extraction of water, aquifer connectivity can be a controversial issue and in some cases it may lead to water resource conflict- and management-challenges. Recently, the expansion of the coal seam gas industry has raised concerns about the risks to aquifers adjacent to gas-bearing aquifers because water needs to be extracted from the coal seams in order to release the sorbed gas. Consequently, there is a need to: a) understand aquifer connectivity in particular areas; and b) critique the effectiveness of different parameters that can be applied to understand interactions between coal seam gas formations and adjacent aquifers. This study provided a hydrochemical and isotopic assessment within and between a coal measure aquifer (the Walloon Coal Measures) that is being exploited for coal seam gas reserves, and a large, agriculturally- important alluvial aquifer (the Condamine River alluvium), in south east Queensland, Australia. This study had two main aims: 1) To understand solute and gas transport within and between the coal seam gas-bearing and adjacent aquifers; and 2) To determine the effectiveness of a number of potential hydrochemical/isotopic indicators in coal seam gas-related aquifer connectivity studies. Two distinct coal seam gas groundwater facies from the gas reservoir were described: one dominated by HCO3 and the other by Cl. These facies accompany respective shifts in F and Ca and Mg concentrations. This can be explained by variability in the lithological and coal matrix. Using multi-variate statistical analysis in combination with inverse geochemical modelling, similar Na-HCO3 water types were also shown to evolve in-situ in the alluvium via a number of hydrochemical pathways including the recharge of rainfall or river water or the evolution of basalt- derived discharge. A novel hydrochemical ion ratio index (the CCR index) was proposed as a simple method for delineating Na-HCO3 water types in large, highly variable data sets and a number of potential areas of aquifer interaction were noted. However, delineating coal seam gas groundwater and associated pathways within and between bedrock aquifers using conventional techniques remained challenging due to the occurrence of Na-HCO3 water types in all aquifers. This was addressed using a compositional data analysis approach. Hydrochemical and isotopic indicators of hydrological processes within coal seam gas formations and adjacent aquifers, Condamine River catchment, QLD. iii Coal seam gas groundwater in the Surat and Clarence-Moreton basins (Condamine River catchment) and other basins around the globe were shown to exhibit subtle, yet distinguishing, compositional attributes. These attributes can be defined by the relative proportion of ions in the simplex and expressed as simple linear or quadratic models of isometric log ratios. These models are a novel and more informative alternative to conventional means of characterising “water types” based on the dominant ions. Two isometric log ratios that represent the relative proportion of HCO3 to Ca and Mg, and Cl to SO4 were found to successfully delineate groundwater associated with high biogenic gas in the Condamine River catchment, as well as in other basins worldwide. These isometric log ratios are proposed as a new, informative and universal method for characterising and delineating coal seam gas hydrochemistry. For the Condamine River catchment, the compositional variability of coal seam gas groundwater and the occurrence of gas and the associated hydrochemical attributes were found to be spatially inconsistent within the coal measures. The collective hydrochemical information presented above informed a strategic sampling program that employed: a) CH4 and the associated isotopes of carbon and hydrogen; and b) a conservative ions and a multi-isotope approach to further assess aquifer connectivity. Peak CH4 concentrations were found in the coal measures (95 – 25000 µg/L). In the gas reservoir (200-500 m) a limited CO2 pool and significant 13 biogenic methanogenesis leads to relatively enriched δ C-CH4 (-58‰ to -47‰). In 13 contrast, in the shallower coal measures (<200 m) the δ C-CH4 was typically depleted (-80‰ to -65‰). Small concentrations of CH4 (10-535 µg/L) were also 13 found in the alluvium with a similar δ C-CH4 range (-80‰ to -50‰). By combining 13 2 data on δ C-CH4, δ H-CH4, salinity and redox, and dissolved organic carbon, complex hydrochemical and thermodynamic controls associated with in situ generation of CH4 was observed for both the shallow coal measures and the alluvium. This study reported the first observation of acetoclastic methanogenesis in the Walloon Coal Measures of the Surat Basin which accounted for the most 13 enriched δ C-CH4 sample (~-50‰) in the shallow coal measures. Data do not show any evidence of gas migration, either from the deep gas reservoir to the shallow coal measures or from the shallow coal measures to the alluvium. Results highlight that Hydrochemical and isotopic indicators of hydrological processes within coal seam gas formations and adjacent aquifers, Condamine River catchment, QLD. iv the isotopic description of the CH4 from the gas reservoir is not necessarily the appropriate isotopic-CH4 end member to use in aquifer connectivity studies. The final component of this research used a combination of Cl, stable isotopes of water, δ37Cl, 3H and 14C, Cl/Br and Li/Cl ratios and δ7Li were used to assess the origins of conservative solutes within and between aquifers. 14C provided ambiguous results due to the effect of methanogenesis, and potentially due to the dissolution of carbonates, in both the coal measures and the alluvium. While discrete spikes in Cl in deep areas of the alluvium have previously been thought to be associated with the influx of groundwater from the underlying coal measures, δ37Cl results do not show evidence of significant solute (Cl) migration between the alluvium and coal measures. Using Li/Cl ratios in combination with Br concentrations, a clear delineation between alluvial and coal measures aquifers could be made: this reflects the consistently low Li concentrations in the alluvium (typically ~0.001 mg/L or less), while Li concentrations in the coal measure are distinguished by higher Li concentrations (0.007 mg/L to 0.04 mg/L) that are positively correlated with Cl. Combining Li concentration results with the stable isotopes of Li (δ7Li) peak Li concentrations in the alluvium were shown to be associated with weathering of clays in shallow zones. In addition, some interactions between the basalt aquifers and coal measures were observed. Moreover, this study found no evidence of large-scale gas or solute transfer between the alluvial aquifer, the Condamine River alluvium, and the underlying Walloon Coal Measures in the upper Condamine River catchment. The most effective hydrochemical indicators used in this study were: 1) isometric log ratios that describe the relative proportion of ions: these can be used to delineate particular water types and groundwater associated with high gas concentrations; and 2) Li concentrations (Li/Cl versus Br plots) in combination with δ7Li. Li and its associated stable isotopes (δ7Li) shows particular promise as a hydrochemical tracer in coal seam gas-related studies due to conservative properties and because this ion is generally unaffected by pH and redox conditions and biological processes. The use of CH4 as a tool to understand aquifer interactions requires complex biogeochemical processes to be understood at the catchment scale. Researchers are encouraged to collect 13 2 13 2 comprehensive data sets, including δ C-CH4 and δ H-CH4, δ C-DIC and δ H-H2O Hydrochemical and isotopic indicators of hydrological processes within coal seam gas formations and adjacent aquifers, Condamine River catchment, QLD. v as well as hydrochemical data to describe redox and salinity conditions prior to making inferences about CH4 origins at the catchment-scale. The findings of this study have direct applicability to future studies concerned with aquifer connectivity and/or water resource management associated with unconventional gas development worldwide. More broadly, the techniques and approaches used here provide informative insight into the effectiveness of hydrochemical and isotopic parameters to delineate particular groundwater end members and/or to be used as indicators of aquifer connectivity in in future hydrogeological studies. Hydrochemical and isotopic indicators of hydrological processes