Inferring groundwater dynamics in a coastal aquifer near wastewater infiltration ponds and shallow wetlands (Kwinana, Western Australia) using combined hydrochemical, isotopic and statistical approaches

摘要: Abstract A proposal to increase wastewater infiltration at the Kwinana Wastewater Treatment Plant (KWTP) an unconfined aquifer near a groundwater flow-through wetland (The Spectacles) in Western Australia, prompted study of geochemistry and water levels identify types develop conceptual model for flow geochemical evolution. Within catchment, table has dramatically declined (e.g up −70 −90 mm/yr over three decades) due drying climate increasing demand groundwater. Annual rainfall by 9 mm/decade on average or about 1.4% annual mean last decadesWastewater began 1975 increased current rate 4.7 thousand cubic meters per day. Groundwater-surface interactions were interpreted using multivariate statistical analysis major ion stable isotope (δ18O, δD) data. Rainwater infiltrating through interacts with carbonate minerals while flowing westward produce Ca-HCO3 type (Group 1). Below wetland, evaporative signature 2) that higher concentrations TDS (>1 g/L) distinctively δ18O (>2.5 mil) than derived from 3). The ratio ions (K:Cl) was used understand mixing quantify proportions site. Water samples collected 2014 reveal high proportion (>34%) within uppermost 30 m generally decreasing distance away source. Further investigation Spectacles balance hydrochemistry is needed optimally manage prevent degradation quality. Proposed increases recharge may continue help offset impact lake levels.