Groundwater quality

Groundwater salinity increases with the depth from fresh and brackish in alluvial aquifer (EC = 387 to 5810 μS/cm), brackish to saline in shallow bedrocks (EC = 3867 to 9371 μS/cm); inter-bedded sandstone-siltstone water-bearing zones (EC = 2395 to 6100 μS/cm) and coal seams (EC = 3014 to 4999 μS/cm) (Parsons Brinckerhoff, 2012a; 2012c; 2013a). Similar salinity patterns were also observed for the Stratford, Duralie and Rocky Hill coal mines located in the Gloucester Basin (Australasian Groundwater and Environmental, 2013; Heritage Computing, 2009; 2012).

The stable isotope values of groundwater, collected from all formations, indicated that all tested water samples are of meteoric (rainfall) origin and that no enrichment has occurred due to evaporation. In terms of the age, the oldest water was identified in the inter-bedded sandstone/siltstone water-bearing zone (mostly aquitard) and the youngest in alluvium. This corresponds with the EC/salinity trend. The stable isotopes, aging analysis and EC values are likely to indicate that high salinity in the older groundwater is likely to be related to in-situ water mineralisation.

In SRK (2010), iron (Fe), fluorine (F), phosphorus (P) and mercury (Hg) were identified as typical elements occurring in coal seams, which can potentially assist analysis of aquifer interactions. Only Fe and P were included in water quality monitoring, and P concentration was particularly elevated in all formations, which is not typical for groundwater. Total organic carbon levels increased with water age and methane concentrations were, on average, 10 µg/L, 140 µg/L, 12,789 µg/L and 21,931 µg/L in alluvial, shallow bedrock, inter-bedded sandstone-siltstone and coal seams respectively.

Last updated:
5 January 2018