Thousands of cubic metres of sludge from the Auckland Super City will be dumped at a site just outside the Hauraki Gulf marine park under a 35-year permit being sought.
Coastal Resources Limited is applying for consent to up the amount of "slops" to be dumped on the seafloor north of a Repanga (Cuvier Island) Nature Reserve.
Although the material to be dumped was described as largely consisting of sand, gravel and clay, contaminants would also be present at some level.
"Contaminant levels at the source sites have on occasion breached the ANZECC ISQG- Low (ISQG-Low) threshold," an EPA report on the application said.
Some 250,000m3 per year from Auckland City infrastructure spoils, marinas in Auckland and Waikato, Ports of Auckland dredgings and a proposed America's Cup village at Hobsonville Pt would be dumped just outside the 12 nautical mile zone.
This bypasses the country's obligations under an international protocol to which New Zealand is a signatory, which the resource consent application acknowledges.
The London Convention demanded all practicable steps were taken to prevent pollution of the sea by dumping of wastes and other matter.
The consent, if approved, will replace the current upper limit of 50,000m3 from existing or proposed marinas in Auckland and Waikato each year under a consent due to expire in 2032.
As well as marina dredgings, the ocean site would be a dump zone for spoil from Ports of Auckland, any future works to upgrade Auckland City's stormwater outfalls or other infrastructure needed for the Super City, and proposed marine works including an America's Cup Village at Hobsonville Pt.
The dump site covers about 7 sq km and is approximately 25km east of Great Barrier Island and 22km north of Cuvier Island, a culturally significant site for founding tribes of the Te Arawa canoe.
The site was initially identified due to there being "no obvious sites of cultural significance", according to CRL's application.
However, it was traditionally believed ancestors of the Te Arawa tribes landed at the island before continuing to settle New Zealand.
"It's being turned into a rubbish tip," says Ngāti Hei Kaumatua Joe Davis. "Among other things, our concern is that it's a 35-year consent, so what does that mean? How do we know we're not going to end up taking China's waste?"
He said he was concerned that the site would be used to dispose of contaminated material that Auckland produced as a byproduct of its projected growth.
"With the population increasing by so much in Auckland, there are many 'don't knows' over what happens to all the stuff Auckland doesn't want anymore."
Among the concerns raised by agencies and iwi are the introduction of invasive species such as Mediterranean fanworm and Eudistoma through larvae in the material.
"Monitoring results in the Bioresearches Ltd assessment show the presence of invasive species in the marinas where dredging occurs," the MPI submission said.
"The establishment of these species on Great Barrier, which is closest to the disposal site, would present a novel biosecurity risk to the environment."
According to the application, barges would dump the contaminated sediment using propellers or tug boats, building an undersea mound.
Measures have been introduced to watch out for passing Humpback, Southern Right and Grey's Beaked whales that have been sighted in the area.
Submissions and feedback to the EPA closed on Monday. If the application is declined, it is unlikely that an alternative will be found, according to the CRL application.
Dredged material was first dumped at the site in 2010, in a test under Maritime New Zealand.
Since then, between 100 and 130 barge loads have been dumped each year from dredgings at the Pine Harbour, Half Moon Bay, Sandspit, Hobsonville, Hobsonville Pt and Whitianga marinas.
CRL says in its application that no other practical alternative for disposal were identified then or since, except for reclamation within the Ports of Auckland which turned the sludge into "mudcrete" to build Fergusson Wharf terminal.
With no further consented reclamation projects at the Ports of Auckland, this option now no longer exists.
In an economic impact report, the impossibility of getting consent to deal with the spoils on land was highlighted, along with the cost and number of tankers needed to transport the sludge.
CRL was part of the Kaipara Ltd group of companies. On its website, it said it had ''over 20 years' experience in delivering completed marine projects to the Auckland, Northland and Bay of Plenty regions''.
Asked to respond to claims by iwi in the Coromandel a spokeswoman from Kaipara Ltd said in an email ''we have been advised not to make comment on the application while it is going through the consent process''.