Under the Maritime Transport Act (MTA), the Rena was no longer a navigation hazard or what could be defined as a hazardous ship.
More than $500 million had been spent by the owners over the past four years on a lengthy salvage operation - making it the world's second most expensive after the grounding of the cruise ship Costa Concordia - and the owners had gone beyond what was required of it under the MTA to address concerns, Mr Casey said.
"The owners' approach throughout has been to do what is right for the community and the environment," he said.
"While it can not turn back time and prevent what happened, it can do, and has, responded by addressing issues of concern and de-risking the wreck so that what remains is as environmentally benign as possible."
Mr Casey said it could not be assumed that if consent was refused, the wreck would be removed.
"While it may be convenient to compare aspects of the proposal - and the environment - with the hypothetical situation of what it might be like if the wreck was removed, it can not be assumed that such an outcome is an alternative against which the proposal is to be assessed."
It was also important to bear in mind, he said, that if consent was declined or not exercised, the existing contaminants would remain there and there would be no monitoring, contingencies or other mitigation to address them.
"The environment and the community will be no better off - and possibly worse."
Mr Casey also spoke of shipping's importance to New Zealand - last year, 1,612 vessels had visited the Port of Tauranga, delivering a throughput of 19,737,000 tonnes of cargo and before-tax earnings of $142.6 million.
The contaminants
Mr Casey said "uncertainties" had been raised about the applicants' position around contaminants from the wreck, particularly copper, tributyltin (TBT), PAHs (oils and other hydrocarbons) and possibly cryolite.
The owners accepted that the effects of copper could be considered, regardless of whether it is discharged.
While the owners' application had originally assumed most of the ecotoxic copper was still contained within the wreck - a key report prepared independently for the commissioners estimated 20 tonnes of copper clove remained in a crushed hold 50m below the water - it now seemed to have been discharged, or at least in part, Mr Casey said.
Further, the TBT, which was contained in anti-fouling paint on the Rena's hull, had already been discharged in the form of paint flakes, but some remained in parts of the hull, sandwiched below other paint layers.
There were no longer oils or other PAHs "in such quantities as to be of concern", Mr Casey said, while the cryolite had all been discharged and was in the environment.
"The wreck is now in a state where the potential for harm to the environment or to human health is minimal, and any remaining risk will be addressed by conditions of consent."
In the independent report, consulted experts had asked that the copper clove be removed unless it was impossible, and that TBT levels and possible pollution from the "multiple stressors" of combined low-level contaminants be monitored.
Mr Casey told the panel the rest of the Bay of Plenty would be unaffected by the proposal, and described its environment as being "well on the way to recovery".
The only physical reminder was the occasional re-emergence of plastic beads - 86 tonnes of them had been stowed in four containers - and no further flotsam or other debris had come ashore for more than two years.
"Shoreline debris monitoring and recovery will continue to respond to any debris that might show up over the next 10 years."
The wreck site
All that remained of the Rena was now the wreck of the ship and some of its contents, he said.
"It joins the pantheon of wrecks around the New Zealand coast, understood to number as many as 3000."
Effectively, the Rena remained in two main chunks since splitting apart during a violent storm that sunk it in early 2012.
The bow section of the ship, around 60m in length, remained wedged at the top of the reef while the aft-section had slid further down the reef to a depth of 56m below the sea level.
Mr Casey said that before salvage operations to clear a surrounding debris field, the Rena 's wreckage occupied around 1ha, or two per cent of the reef's total area - salvage work had now meant that 98 per cent of the reef would be unaffected by the owners' proposal.
Expert witness Roger King, a Master Mariner with TMC Marine who has been involved with the salvage operation since the grounding, said nearly 3,500 tonnes of cargo debris had been removed from the site, along with a further 84 tonnes dislodged during Cyclone Pam in March, and 0.9 tonnes of copper.
There were now no intact containers or loose flotsam left at the wreck site, he said.
The 75m-high reef was in a "very exposed and dynamic" marine environment, and the effects of wave action, storms and currents on and around it had played a "significant part" in the Rena's fate since the grounding, Mr Casey said.
While the owners' sought to abandon the wreck in its present state, they did not seek "exclusive occupation" of the seabed, such as for a dive site, and would not be regulating access to the wreck site or managing it.
"Extensive analysis has been undertaken and work has continued so as to leave the wreck in a state where the potential for adverse effects has been reduced to the minimum that is practicable," Mr Casey said.
"While not being promoted as a dive site, the wreck will inevitably attract diver interest and so it has been made as safe as practicable for recreational divers."
Response to iwi concerns
Other than its popularity as a fishing and dive site, the applicants had "not found widespread knowledge and awareness" of the cultural significance of the reef before the grounding, Mr Casey said.
The grounding had focused attention on the reef and its cultural and ancestral associations.
Mr Casey however acknowledged the "most significant effect" of the proposal was that the reef had important cultural connections for tangata whenua, especially those who whakapapa to nearby Motiti Island and for Te Arawa ki Maketu.
Other iwi and hapu were also acknowledged as having associations with the moana, or ocean.
"The owner and applicant have worked hard to earn the trust and respect of these groups and to address their values and concerns," he said.
"As a result, it now has the support of iwi and others representing Te Arawa ki Maketu and many from Motiti Island."
However, many iwi groups remained opposed to the ship being left on the reef, with its cultural significance and mauri, or life force, underlying their concerns.
The owners will continue presenting evidence until Thursday, followed by the Bay of Plenty Regional Council, the Crown, and dozens of other submitters.
The Rena Saga
2.14am, October 5, 2011:
The Liberian-flagged MV Rena, with 1368 containers on board, crashes into the Astrolabe Reef. A storm a week later spills container debris and 350 tonnes of heavy fuel oil into the ocean.
January 2012:
More containers and debris are sent overboard as a violent storm breaks the Rena in half and it begins sinking.
May 2012:
Rena captain Mauro Balomaga and navigator Leonil Relon are jailed for seven months for offences including altering the ship's documents.
October 2012:
Rena owners Daina Shipping are fined $300,000 in the Tauranga District Court for discharging harmful substances.
December 2013:
Failings in Maritime New Zealand's initial response to the grounding are highlighted in an internal audit. A scientific report states minimal lasting effect on the environment.
June 2014:
The Rena's owners lodge a resource consent application to leave much of the ship.
December 2014:
The Transport Accident Investigation Commission inquiry details concerns, including crew training and international conventions.
Today:
Hearings on the owners' consent application begin in Mt Maunganui.
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