First Union said Channel Infrastructure was a heavy industrial site that has been subject to significant contamination over Refinery NZ's many decades of operation.
"We therefore remain concerned that, as it stands, once the resource consent expires, Channel Infrastructure may go bankrupt and the cost of site remediation will fall on the taxpayer," the union told the select committee.
"This represents an ongoing liability for the New Zealand people that needs to be addressed."
But Channel Infrastructure said it would bear the remedial cost— a fact confirmed by NRC.
"We are often asked about the state of our land and our plans for remediation of the site, and have been very open about how things stand, as we have a very good understanding of the condition of our site.
"Importantly, unlike other heavy industrial sites, we do not have stockpiles of waste or byproducts that we need to remove now that we have shut down the refinery process plant."
Through the consent process and decommissioning studies, the spokeswoman said Channel Infrastructure had undertaken extensive independent assessments of the effects of past site contamination and these demonstrated there was minimal impact beyond the site boundary, including the surrounding marine area.
As has been well-publicised, including when the company undertook the resource consent application, she said the site did have legacy groundwater contamination present from the historic refinery operation.
"While we have shut down the refinery, an important condition of our resource consent is that we will continue to operate the groundwater recovery network – at our cost – which is continuously remediating groundwater and we will prepare a site remediation plan in the future, if we were to discontinue operations on the site.
"We have a long-term commitment to continued operations at Marsden Point, and while we recently changed what we do, that doesn't mean we are completely shutting down and vacating the area.
"Quite the opposite actually - we are actively pursuing new and innovative ways for us to contribute to New Zealand's future fuel requirements as these evolve and change in coming years."