Te Arawa Ki Tai Trust undertook their own independent investigations, which included working with Te Arawa professional diver Joe Te Kowhai who worked on the Deep Horizon (BP) oil spill in the Gulf of Mexico in 2010.
"The remnants of the wreck have integrated themselves really well into the structure of the reef because there is a lot of fauna," Mr Te Kowhai told TVNZ's Marae Investigates.
He said bringing in huge structures and machinery to lift the ship out of the water would "literally tear away at the reef."
Advice was also sought from senior Te Arawa elders, and experts' reports that there were no lingering poisons, Mrs Bennett said.
An agreement with the ship owners, dependent on resource consent approval, involved being in control of ongoing monitoring of the wreck and the company paying $1.25 million, which would be used for a Maori marine centre for the protection of the local ecosystem, as part of the cultural mitigation package.
"We had to make a decision, keep wrecking the rock, knowing its removal will wreck it - what's more offensive? Wrecking the rock or leaving it on the rock."
They been criticised by other iwi on their deal.
"This isn't [selling out]. Some of those people who are calling us that have already received payouts," Mrs Bennett said.
"We [the trust] are all volunteers, we have been working on this the best we can. It's all very well to sit on the sideline but [other iwi] have had an opportunity to make a submission, we are carrying out our role of kaitiakitanga (guardianship). Our focus hasn't shifted in these four years in getting the best we can for the environment.
"Even if there was no money involved, we would still have this position," she said.
But Ngati Te Hapu, who represents members of Motiti Island, have said they were disappointed in the actions of the Te Arawa trust.
"Actually disappointed is an understatement, angry is more like it," spokesman Buddy Mikaere said. "We think that's fair enough they have a say over their little piece of coastline but it should be entirely restricted to that, not have a wider say and certainly should not have anything to say about Motiti Island."
Objection has also come from within Te Arawa.
"Te Runanga o Ngati Whakaue ki Maketu was not consulted on the "cash pay-out", spokeswoman Maria Horne said.
"Whakaue Kaipapa Marae was used as the hub for the Rena clean-up operations in Maketu for two months. The Maketu local community and Ngati Whakaue whanau have never been recognised for their efforts. The marae and people were told at that time ' ... the marae should not expect to make money out of this disaster, it should be about cleaning up the beaches,' that's a bit rich from the lady advocating to take the cash," she said.
