 |
| Titel |
A multi-tracer study in the Hutton Sandstone aquifer, Australia: How “wrong ages” give us deeper insights into aquifer structure and effective deep recharge to a double porosity system |
| VerfasserIn |
Axel Suckow, Andrew Taylor, Phil Davies, Fred Leaney |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142265
|
| Publikation (Nr.) |
 EGU/EGU2017-5865.pdf |
|
|
|
|
|
| Zusammenfassung |
| Depressurisation of coal seams in the Walloon Coal Measures in Queensland, Australia, may
influence aquifers both over- and underlying the formation. The Gubberamunda Sandstone
aquifer, which overlies the Walloon Coal Measures, is the starting point of the Great Artesian
Basin (GAB) flow system and has been the focus of numerous recharge studies. In
comparison, the Hutton Sandstone aquifer, which underlies the Walloon Coal Measures, has
received much less attention. This aquifer however, is the main supply of stock water for the
beef industry in the area.
A multi-environmental tracer study of the Hutton Sandstone aquifer was undertaken at the
Mimosa Syncline and was complemented by a few samples taken from the underlying
Precipice Sandstone aquifer. This multi-tracer study (comprising 18O, 2H, 3H,
CFCs, SF6, 14C, 36Cl, and 4He) demonstrated that the Hutton Sandstone aquifer
behaves as a double porosity system. At the regional scale, the system features a
relatively small fraction of conductive rock within a fairly large fraction of low
permeability rock. Tracer migration therefore occurs mainly by advection in the
conductive fraction and mainly by diffusion in the low-permeability fraction of the
aquifer. Groundwater flow velocities, derived from exponential decrease of 14C and
36Cl concentrations with distance, differ by a factor of ten and therefore do not
indicate the real groundwater flow velocity. However, accounting for a double porosity
interpretation of the tracer data leads to a single groundwater flow velocity that is consistent
with all observed data. Advective velocity in this double porosity model differs
from face value flow velocities derived from 14C and 36Cl by a factor of 4 and 40
respectively.
As a consequence of this interpretation, the deeper groundwater flow system
of the Hutton Sandstone aquifer is estimated to receive only ~3% of the recharge
previously estimated using the Chloride Mass Balance approach at the intake beds. The
other ~97% is assumed to be rejected recharge which discharges through spring
complexes in the Surat Basin and contributes to base flow of the Dawson River. This
interpretation also suggests: 1) that the Hutton Sandstone aquifer is potentially
more vulnerable to impacts from groundwater abstraction, including from stock and
domestic water supply and coal seam gas production, than previously anticipated;
2) that other “groundwater age records” around the world likely observe similar
double porosity effects and their apparent ages may be similarly distorted; and 3)
that the multi-tracer approach used here is a suitable method for identifying other
previously unknown double porosity aquifer systems and can potentially quantify
deep effective recharge where important water resources are subject of economic
development. |
|
|
|
|
|
|