The $16.5 billion LNG development, off the coast of Karratha, was given the go-ahead by Woodside and partner BHP in November.
A Supreme Court hearing which continued on Tuesday, has been told the EPA amended the project approvals in mid-2019. The changes allowed additional gas sources to be processed at the existing Burrup peninsula plant - including from third parties - with then-EPA chairman Tom Hatton approving the changes on the same day he received them.
The Conservation Council of WA, which brought the court action, argued this would extend the life of the project and significantly increase greenhouse gas emissions.
But Steven Penglis SC, representing the EPA chairman, told the court that was "patently wrong".
"If you're at a shop, and you're selling ice-creams and you're just selling Streets, then all of a sudden you're allowed to sell Peters, (the idea) that you're going to sell more ice-creams. It's just wrong," he said.
Woodside's submissions use per annum emissions estimates - rather than whole-of-life - and make no reference to extending the 30-year lifespan of the LNG plant, he added.
"That's a huge assumption that (CCWA) can't make. You've got no evidence about the capacity of this plant," Mr Penglis said.
The Conservation Council, represented by the Environmental Defenders Office, claim the Scarborough project will result in an extra 1.6 billion tonnes of carbon emissions over the next 25 years.
The group's lawyer Henry Jackson SC told the court on Monday the EPA chairman did not give proper "intellectual consideration" to environmental impact before granting his approval.
But government solicitor Alan Sefton on Tuesday said the "attack" on Dr Hatton was unwarranted, as he had multiple meetings with Woodside, and had a habit of annotating project documents for further assessment.
"The inference is that ... Dr Hatton considered amendments, but decided none were necessary," he said.
Mr Sefton also acknowledged Woodside "flexibility", including extra gas sources access to its Pluto gas plant, but only to "foreshadow" the future use of the facility.
"Although this isn't a proposal seeking for the use of other gas fields, things are being designed ... with that in mind," he said.
Mr Jackson said there was "no retreat" from the CCWA's claim the amended approvals would extend the life of the project.
"There is no end date to a ministerial statement ... some of them say works must commence by a date, but there is no end date."
Mr Penglis also called for the matter to be dismissed based on the statute of limitations, usually six months for civil cases in Western Australia.
"The whole purpose of the six-month period is to allow parties ... to rely upon decisions of public authorities which have been made in their favour," he said.
The EDO had previously argued the nature of "judicial review as a last minute resort" meant the group pursuing out-of-court resolution with the EPA should serve as a valid reason to delay the filing of legal action.
The council is also challenging the approvals for the expansion of the Pluto LNG plant in a separate Supreme Court action.
The hearing is set to run until Wednesday, with a decision expected next year.
