The Illawarra region contains some of Australia's best coking
coal resources. These have been mined since the 1880's, providing
coal for both export through Port Kembla and for use in the
steelworks (now operated by BlueScope Steel).
To maintain supply for steel making, BHP Billiton is
developing the Dendrobium Coal Mine. This underground mine will
recover coal from the lowermost 3.2m of the 9m thick Wongawilli
Seam by longwall mining methods (see an individual chock in the
panel to the right) at a rate of up to 5Mtpa ROM for 30 to 40
years. Coal from the Wongawilli Seam is an essential component of
'Illawarra Blend' premium coking coal, which is known for its
specific steelmaking qualities.
The name 'Dendrobium' is derived from an orchid that
is indigenous to the Illawarra, and which lends its name to the
Parish of Dendrobium where the mine is situated. The orchid appears
in the mine's logo, and Dendrobium is one of the largest families
of orchids - about 1000 species are known. The Dendrobium orchid
family is found only in Australia, the South Pacific, South East
Asia and India.
Dendrobium will mine coal adjacent to Kemira, Nebo and
Wongawilli Collieries - which were consolidated into Elouera
Colliery in 1993. Early images of Wongawilli Colliery are shown on
the front and rear covers, and an electric locomotive used at Nebo
is shown on the rear cover - Dendrobium utilises a re-vamped Nebo
Colliery pit top.
Area 1 of Dendrobium Mine involves mining the
Wongawilli Seam between the footprint of two arms of Cordeaux
Reservoir. This reservoir is one of the major storages of the
Sydney Water Supply, containing 93,640 ML at full supply level.
Longwall panels are to be mined beneath the overlying Bulli Seam
(30m interburden) which has been partially mined. Additionally, the
Wongawilli Seam previously has been mined to the north and south of
Area 1.
GHD Geotechnics are contributing to the Dendrobium
project through: determination of the hydrogeological setting
(southern limit of Illawarra Coal Measures, warped seams due to
doming, igneous intrusives within the seam, dykes at margin of Area
1) employing downhole permeability test results (both current and
historical, over mined and unmined areas); assessment of impact of
past mining activities in both seams; hydrogeological modelling of
caved and upward migrating bed separation; prediction of impact of
longwall mining subsidence, valley closure and upsidence in the
base of the storage reservoir; and risk assessment of uncontrolled
inflow into the longwall panels.
These are all in the context of obtaining approval
from the NSW Dams Safety Committee for Dendrobium to mine adjacent
to one of Sydney's water supply reservoirs.
In addition, Area 2 of the mine is situated adjacent
to the Cordeaux Crinanite complex, upon which Upper Cordeaux No. 2
dam is situated. - see side panel. Current tasks include
engineering geological mapping. This is part of our on-going
involvement to define the challenging hydrogeology of the
Dendrobium Project, so as to preserve the security of Sydney's
Water supply.