Wangaloa Coal Mine opened in 1945, and by the time of
its closure in 1989, had produced 750 000 tonnes of coal and disturbed an area
of 75 ha. The original mining licence required land rehabilitation to exotic
forestry, however the current owner, Solid Energy, has worked with Crown
Minerals and local councils to write a new rehabilitation objective. The site is now being stabilised
and replanted with native species, and may be available for
public use before the coal mining licence expires in 2007. Site discharge
permits expire in 2017, and by that time, it is anticipated that discharge
water chemistry will be similar to background levels. MWH are currently contracted for
management of the mine rehabilitation project.
The Kaitangata coal unit mined at Wangaloa is sulfurous lignite with
associated pyrite. Kaitangata coal contains 3.2 wt per cent sulfur, which is
higher than most New Zealand coals. Initial analyses at Wangaloa indicate low pH
(2.56.2) values in soil, groundwater and surface waters as a result of acid rock
drainage (ARD) processes, leading to increased metal mobility and challenging
conditions for vegetation. Pilot studies indicate pinus radiata needles contain
up to 67 mg/kg boron, and elevated As, Cu and Zn concentrations in surface
waters. The main lake at the site has a pH of approximately 4.9, despite lime
dosage in 2002.
There is a real need for a complete geochemical model of the Wangaloa coal
mine. Such a model could be applied to similar restoration projects, and would
assist by pinpointing geochemical processes and toxic metal relationships most
harmful to the receiving environments. Using this model, rehabilitation in the
future will be targeted and more efficient. This project is part of a larger
scheme to characterise and model the Wangaloa mine site restoration, including
waters, soil, vegetation, geology and invertebrates.