A delegation from the agency appeared before a meeting of the joint Oireachtas committee on transport and communications and was quizzed over the awarding of a research contract to a consortium, headed by CDM Smith Ireland.
The EPA had been commissioned by the Government to undertake a two-year study into the controversial gas extraction method.
Due to be completed in July 2016, it will examine if fracking can be undertaken in Ireland without causing significant damage to the environment.
The EPA, the Department of Communications, Energy and Natural Resources, and the Northern Ireland Environment Agency awarded the contract to the consortium in August of last year.
The consortium comprises CDM Smith Ireland, the British Geological Survey, UCD, Queens University Belfast, AMEC Foster Wheeler, and Philip Lee Solicitors.
Sinn Féin’s Michael Colreavy said it was an “extraordinary decision” to appoint CDM Smith and questioned how anyone could trust a study where the lead company in the consortium was “a cheerleader for fracking”.
“That’s [fracking] how they make money. That’s what their shareholders expect. Get it into Europe, get it into the US, and now get it into Ireland,” he said.
Fianna Fáil’s senator Paschal Mooney said there were “serious questions” about the independence of CDM Smith given the company was “at best in sympathy” with the fracking process.
He pointed out that the company had been involved in fracking projects in the US and Europe.
“You would get the impression from the EPA notes that they haven’t been involved in fracking,” he said.
However, deputy director general of the EPA, Dara Lynott, defended the appointment of CDM Smith, stating it was part of a wider consortium .
Mr Lynott said the decision was made following an open tender process where six tenders were evaluated by 27 people across a range of bodies such as An Bord Pleanála, the environment departments both north and south, and the HSE.
He said the research was publicly funded and would not be published until it had been fully peer reviewed.
Roscommon Independent TD Denis Naughten stressed such a wide range of bodies would not join a consortium unless they had confidence in its ability to produce a robust report.
“They are all putting their names on the line here. There is no doubt that they wouldn’t put their names on something they can’t stand over,” he said.