Contemporary mine wastewater flows are subject to stringent water quality
standards before discharge to local waterways. Strict criteria are often applied
as a result of fears of extensive acid mine drainage; a feature of the many
abandoned mine adits around the Coromandel, Central Otago, and the West Coast.
In most cases the USEPA water quality criteria have been used to set treated
wastewater discharge water quality standards. In future it is possible that the
recently published ANZECC water quality criteria guidelines will be used for
this purpose. The ANZECC guidelines also provide for the establishment of
discharge criteria at specific sites, rather than accept the trigger values.
The use of site-specific criteria for treated wastewater mine discharges was
pioneered at the Golden Cross gold mine, near Waihi, in the late 1980s. The
procedure used to derive water quality criteria was based on USEPA guidelines.
In developing the Golden Cross criteria, only species that occur, or are similar
to those that occur in the Waitekauri River were used.
The mine commenced discharge of treated wastewater in 1991, and
macroinvertebrate communities in the vicinity of the discharge point have been
regularly monitored twice a year for the past 12 years. Despite fluctuations in
community composition and abundance over that period, no permanent significant
changes in the macroinvertebrate communities occurred between sites above and
below the treated wastewater discharge.
The success of the site-specific criteria at Golden Cross has shown how the
application of this methodology can result in the protection of aquatic life
while allowing for the discharge of treated mine wastewater.