Galilee Basin Mining and Groundwater

Transcription

1 Galilee Basin Mining and Groundwater Impact on the Great Artesian Basin John Hillier

2 Acknowledgements Some diagrams used in this presentation have been obtained from: EIS for proposed mining ventures A Report by RPS Australia East Pty Ltd : Galilee Basin - Report on the Hydrogeological Investigations A Report Hydrochemistry and implied hydrodynamics of the Cadna-owie Hooray Aquifer, Great Artesian Basin by Bureau of Rural Sciences

3 Galilee GAB Basins

4 Stratigraphy AGE BASIN FORMATION CRETACEOUS ( Myr) EROMANGA (GREAT ARTESIAN BASIN) JURASSIC ( Myr) ROLLING DOWNS GROUP (e.g. Winton Formation, Wallumbilla Formation, etc) CADNA-OWIE FORMATION HOORAY SANDSTONE WESTBOURNE FORMATION ADORI SANDSTONE BIRKHEAD FORMATION HUTTON SANDSTONE TRIASSIC ( Myr) GALILEE (GREAT ARTESIAN BASIN) MOOLAYEMBER FORMATION CLEMATIS SANDSTONE REWAN FORMATION (includes Dunda Beds) PERMIAN ( Myr) GALILEE BASIN BETTS CREEK BEDS (Includes Bandanna Formation and Colinlea Sandstone) JOE JOE FORMATION

5 GAB Geology

6 Mining Leases

7 Galilee Coal Sequence

8 Groundwater Impacts Obviously, coal mining cannot take place without removing groundwater as access has to be achieved Groundwater will flow in from surrounding areas, but mostly from the same geological formation, or those hydraulically connected to it Some nearby formations, like the Great Artesian Basin aquifers, are not well hydraulically connected to the coal bearing formations

9 Geological Outcrop

10 East West Sections

11 Location Section B - B

12 Galilee GAB Section B - B

13 Groundwater Use 1. Bores in unconsolidated/semi consolidated sediments i. e. In alluvium or tertiary sediments 2. Bores in coal bearing formations - i. e. Colinlea Sandstone or Bandanna Formation 3. Bores in Rewan Formation or Dunda Beds 4. Bores in Clematis Sandstone 5. Bores in Great Artesian Basin proper

14 Bores tapping the Colinlea Sandstone

15 Bores tapping the Rewan Formation

16 Bores tapping the Clematis Sandstone

17 Bores tapping the Hutton Sandstone

18 Bores tapping the Hooray Sandstone

19 Groundwater Flow Darcy s Law Q = KiA where Q is the volume in cubic metres K is the permeability or hydraulic conductivity in cubic metres / day / square metre (under a unit gradient) i is the actual gradient in metres /metre A is the section of aquifer of flow in square metres

20 Groundwater Flow From Darcy s Law, the velocity of groundwater flow can be determined V = Ki Where V is the groundwater velocity in metres/day K is the permeability or hydraulic conductivity in cubic metres / day / square metre (under a unit gradient) i is the actual gradient in metres /metre

21 Flow towards Barcaldine (through aquifer) Permeability of aquifer cubic metres/ day/square metre = 0.5 m/day Distance outcrop to Barcaldine 105 km Fall in altitude 170 m (approx. fall in water level) So Velocity = K (0.5 m/day) x i (170m/105km) = 0.5 x = m/day = 0.3 m/year Time to travel to Barcaldine = 315,000 years

22 Groundwater travel time (Bureau of Rural Sciences, Canberra)

23 Possible impact of Mine on Gab

24 Geological Outcrop

25 Possible impact of Mine on Gab Closest aquifer = Clematis Sandstone Distance approx. = 30 km Intervening formation between Clematis Sandstone and coal bearing formations (Bandanna Formation and Colinlea Sandstone) is the Rewan Formation/Dunda Beds

26 Possible impact of Mine on Gab Rewan Formation Lake Galilee Petroleum Exploration Bore Rewan Formation is: 323 metres thick 276 metres of shale and siltstone, K m/day (horizontal) and m/day (vertical), based on USQ work in similar strata in the Surat Basin

27 Possible impact of Mine on Gab Rewan Formation Maranda 1 Petroleum Exploration Bore (near Jericho) Rewan Formation is: 193 metres thick, mudstones and shales with minor interbedded siltstone and silty sandstone. Probable K value vertically through this layer m/day

28 Rate of flow of groundwater through Rewan Formation If the average Permeability or Hydraulic Conductivity of this strata is about metres/day (or m 3 /day/m 2 ) From Darcy s Law, the rate of vertical movement V = Ki V = x 1 V = m/day or metres/year

29 Possible impact of Mine on Gab In the two Petroleum exploration bores the Rewan Formation has 276 m of shale, and 190 m of shale with minor sandstone. Say an average 190 m in the Rewan. At a groundwater movement rate of m/year, it would take over 10,500 years for any water to move through this Formation.

30 Conclusion The Clematis Sandstone, being the deepest aquifer and the closest to coal mining, is not likely to be impacted. Other GAB aquifer will not be affected Movement of groundwater through faults and fractures in the Rewan Formation is most unlikely. Faults will be filled with weathered material and act an as impediment to flow

31 Conclusion Impacts on groundwater resources will be limited to the Formations that are mined and need to be dewatered, and to the shallow sediments that overlie them.