Hydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivity

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dc.contributor.authorDuvert, Cen_AU
dc.contributor.authorRaiber, Men_AU
dc.contributor.authorOwen, DDRen_AU
dc.contributor.authorCendón, DIen_AU
dc.contributor.authorBatiot-Guilhe, Cen_AU
dc.contributor.authorCox, MEen_AU
dc.date.accessioned2015-09-09T03:25:47Zen_AU
dc.date.available2015-09-09T03:25:47Zen_AU
dc.date.issued2015-10-01en_AU
dc.date.statistics2015-09-03en_AU
dc.description.abstractIn areas of potential coal seam gas (CSG) development, understanding interactions between coal-bearing strata and adjacent aquifers and streams is of highest importance, particularly where CSG formations occur at shallow depth. This study tests a combination of hydrochemical and isotopic tracers to investigate the transient nature of hydrochemical processes, inter-aquifer mixing and recharge in a catchment where the coal-bearing aquifer is in direct contact with the alluvial aquifer and surface drainage network. A strong connection was observed between the main stream and underlying alluvium, marked by a similar evolution from fresh Ca–Mg–HCO3 waters in the headwaters towards brackish Ca–Na–Cl composition near the outlet of the catchment, driven by evaporation and transpiration. In the coal-bearing aquifer, by contrast, considerable site-to-site variations were observed, although waters generally had a Na–HCO3–Cl facies and high residual alkalinity values. Increased salinity was controlled by several coexisting processes, including transpiration by plants, mineral weathering and possibly degradation of coal organic matter. Longer residence times and relatively enriched carbon isotopic signatures of the downstream alluvial waters were suggestive of potential interactions with the shallow coal-bearing aquifer. The examination of temporal variations in deuterium excess enabled detection of rapid recharge of the coal-bearing aquifer through highly fractured igneous rocks, particularly at the catchment margins. Most waters collected from the coal-bearing aquifer also showed an enhanced influence of weathering during the wet season, which was likely triggered by the water–rock interaction with fresh recharge waters. An increase in both residual alkalinity and carbon isotopic ratios at two locations indicated inter-aquifer mixing between alluvium and bedrock during the wet season. The results of this study emphasise the need for conducting baseline hydrochemical surveys prior to CSG development in order to describe the transient nature of recharge and inter-aquifer mixing processes. © 2015, Elsevier Ltd.en_AU
dc.identifier.citationDuvert, C., Raiber, M., Owen, D. D. R., Cendón, D. I., Batiot-Guilhe, C., & Cox, M. E. (2015). Hydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivity. Applied Geochemistry, 61, 146-159. doi:10.1016/j.apgeochem.2015.05.021en_AU
dc.identifier.govdoc6007en_AU
dc.identifier.issn0883-2927en_AU
dc.identifier.journaltitleApplied Geochemistryen_AU
dc.identifier.pagination146-159en_AU
dc.identifier.urihttp://dx.doi.org/10.1016/j.apgeochem.2015.05.021en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/6183en_AU
dc.identifier.volume61en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectStreamsen_AU
dc.subjectSalinityen_AU
dc.subjectCoalen_AU
dc.subjectDeuteriumen_AU
dc.subjectAquifersen_AU
dc.subjectEvaporationen_AU
dc.titleHydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivityen_AU
dc.typeJournal Articleen_AU
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