Details

Autor(en) / Beteiligte

• Cendón, D. I.
• Hankin, S. I.
• Williams, J. P.
• Van der Ley, M.
• Peterson, M.
• Hughes, C. E.
• Meredith, K.
• Graham, I. T.
• Hollins, S. E.
• Levchenko, V.
• Chisari, R.

Titel

Groundwater residence time in a dissected and weathered sandstone plateau: Kulnura-Mangrove Mountain aquifer, NSW, Australia

Ist Teil von

• Australian journal of earth sciences, 2014-01, Vol.61 (3), p.475-499

Ort / Verlag

Taylor & Francis

Erscheinungsjahr

2014

Quelle

Taylor & Francis Current Content Access

Beschreibungen/Notizen

• Groundwater residence time in the Kulnura-Mangrove Mountain aquifer was assessed during a multi-year sampling programme using general hydrogeochemistry and isotopic tracers (H 2 O stable isotopes, δ 13 C DIC , 3 H, 14 C and 87 Sr/ 86 Sr). The study included whole-rock analysis from samples recovered during well construction at four sites to better characterise water-rock interactions. Based on hydrogeochemistry, isotopic tracers and mineral phase distribution from whole-rock XRD analysis, two main groundwater zones were differentiated (shallow and deep). The shallow zone contains oxidising Na-Cl-type waters, low pH, low SC and containing 3 H and 14 C activities consistent with modern groundwater and bomb pulse signatures (up to 116.9 pMC). In this shallow zone, the original Hawkesbury Sandstone has been deeply weathered, enhancing its storage capacity down to ∼50 m below ground surface in most areas and ∼90 m in the Peats Ridge area. The deeper groundwater zone was also relatively oxidised with a tendency towards Ca-HCO 3 -type waters, although with higher pH and SC, and no 3 H and low 14 C activities consistent with corrected residence times ranging from 11.8 to 0.9 ka BP. The original sandstone was found to be less weathered with depth, favouring the dissolution of dispersed carbonates and the transition from a semi-porous groundwater media flow in the shallow zone to fracture flow at depth, with both chemical and physical processes impacting on groundwater mean residence times. Detailed temporal and spatial sampling of groundwater revealed important inter-annual variations driven by groundwater extraction showing a progressive influx of modern groundwater found at >100 m in the Peats Ridge area. The progressive modernisation has exposed deeper parts of the aquifer to increased NO 3 − concentrations and evaporated irrigation waters. The change in chemistry of the groundwater, particularly the lowering of groundwater pH, has accelerated the dissolution of mineral phases that would generally be inactive within this sandstone aquifer triggering the mobilisation of elements such as aluminium in the aqueous phase.