More Than One Bypass
The Dunedin City Council has come under the scrutiny of the Dunedin group Protect Our Oceans after they received news
that a further bypass of the Green Island Treatment Plant is already under operation.
The DCC’s Green Island Treatment Plant releases trade waste from PPCS Silverstream after the rest of the waste stream
has been through the secondary treatment process. This means that it is not subject to the biological processing and
disinfection the main waste flow encounters.
The admission comes after confirmation of the construction of a $600,000 pipeline to carry industrial waste from
secondary treated Green Island to primary treated Tahuna.
The Green Island Waste Water treatment Plant currently receives three main industrial sources. PPCS Silverstream, PPCS
Burnside and Colver Mair (a tannery). All three are crudely pre-treated on-site by the industries themselves before
entering the DCC’s sewage system. The by-pass pipeline currently under construction will carry industrial waste from
PPCS Burnside to the Tahuna plant for discharge to sea off Lawyers Head. The waste from PPCS Silverstream will also
continue to bypass the Green Island Plant’s secondary treatment facility as it would enter the waste flow after the
treatment process.
The Green Island Plant has a long history of non-compliance with consent conditions for its discharge to Waldronville.
During the January-March 2001 quarter the median Faecal coliform concentrations discharged from the Green Island WWTP
breached the consent limit set by the Regional Council by 167 times. Although Faecal coliform levels have improved
moderately, annual medians still consistently breach the consent conditions. Ammoniacal nitrogen also breaches on many
occasions.
The Protect Our Oceans (POO) group felt that the general public was not aware that some of the waste going to the Green
Island Plant is not being subjected to secondary treatment. POO Spokesperson Andrew Brown said ‘there has been a long
record of non-compliance with consent conditions at the Green Island Plant but bypassing the purposefully designed
secondary plant is not the answer’.
The consent for the DCC’s Tahuna Plant is currently going through the renewal process. The Tahuna consent application
seeks to increase biological oxygen demand (a measure of organic matter), chromium III, nickel, sulphide and ammonia to
levels 3.9, 22.1, 11.1, 4.1, and 2.2 times greater than the current consent values respectively. Many of these
contaminants are key components of industrial discharges (especially tannery and meatworks effluent). Although these
conditions are higher than what were previously used, they will be the same as those already in operation at Green
Island.
Protect Our Oceans is concerned about the DCC’s comparison to the secondary treated Green Island Plant. Andrew Brown
said ‘This sounds really good as there is secondary treatment at Green Island. However it is cause for concern because
the Green Island Plant has trade waste bypassing the secondary treatment to go directly to sea. It isn’t reflective of
what a well functioning secondary plant is capable of’. The group is also concerned that the waste entering Tahuna
through the bypass pipe will have similar effects on the faecal coliform and ammonia levels as it did in Green Island.
‘Its all very well having consent conditions but if trade waste means we cant meet them they are of little value,
especially if they are not enforced’ Mr Brown said.
The Otago Regional Council hearing for the Tahuna consent will be held on Monday 19th May.