Solid Energy has mothballed its $10 million water treatment
plant at Stockton opencast mine after about five years of
use, but says the plant wasn't a mistake.
Communications manager Bryn Somerville said the plant
operated from late 2007 until recently, treating black water
- water holding coal fines from the company's working and
For a time it was also used to remove other sediment like mud
fines from the water.
It had made a substantial contribution to Solid Energy's
programme to reduce the impact of the mine on the Ngakawau
River, Mr Somerville said.
Solid Energy had mothballed it because the catchment, the
Mangatini, no longer needed it. Mining had moved on and the
company now had alternative means of meeting targets without
using the plant.
That area of the mine was only receiving overburden from
other areas being shaped and readied for final
rehabilitation. This produced brown water, where sediment and
low pH were the main concern. They could be corrected more
cheaply by the Mangatini Sump - which was built after the
treatment plant began operating - and by lime dosing.
Parts of the treatment plant, including a specialised system
for raising the pH level of water, were still being used, he
Solid Energy redesigned its mining processes, built
reservoirs and the treatment plant, and began lime dosing
after community concern in 2004 about its environmental
"In simple terms, the aim we agreed with the community around
Stockton was Ngakawau River water quality that supported
native fish life," Mr Somerville said. "The later resource
consents reflected that aim."
Mr Somerville said Solid Energy had realised in November last
year that it could work without the now mothballed plant and
scaled back the plant's role.
- By Kim Fulton of the Westport News