The Supreme Court has reserved judgment over whether An Bord Pleanála acted properly when approving the first phase of Apple's planned €850m data centre in Athenry.

Two objectors to the permission appealed to the Supreme Court after the High Court dismissed their challenge to An Bord Pleanála's decision.

The appeal was brought by Sinead Fitzpatrick who lives near the proposed data centre, and Allan Daly of Athenry.

Last May, the tech company decided not to go ahead with the Athenry data centre project, but the court's decision could affect how the board would consider a similar development.

The objection was opposed by An Bord Pleanála and the State.

Michael McDowell SC, for the objectors, argued the board had "radically misapplied" the law when it granted permission for the first phase, without considering that the data centre could be expanded to a total of eight data halls.

He said the it cannot allow "a salami style slicing and dicing" of big projects to avoid "hard questions" and a "genuine environmental impact assessment of such projects, particularly the impact of their energy demands".

He argued that eight data halls would increase the total demand on the national grid by between 6% and 8% but the board conducted an Environmental Impact Assessment (EIA) for just one hall, not eight.

Without assessing whether this was a sustainable development from an energy point of view, the board inspector took the view employment considerations outweighed whatever doubt exists on the energy front, he said.

The Industrial Development Authority had estimated that about 300 construction workers would be employed and the project would involve total investment of about €850m over the estimated 15 years it would take to build all eight halls.

Mr McDowell argued that if jobs are to be weighed against energy issues, there must be an effort to balance out the two and there was no effort to show how 300 jobs justifies a 6% increase in energy requirements.

Apple had said the centre would be powered by 100% renewable energy, but the inspector had concluded the best that could be secured was average renewability figures over the 15 years, he added.

Nuala Butler SC, for the board, said it was required "to take into account as far as practicable" the potential build out of the Apple "masterplan" for eight data halls.

The board took the masterplan into account "on a broad level" but disputed an EIA on the entire masterplan was required, she said.

There was no "deliberate project splitting" and "nothing curious" about how Apple applied for permission. The board had conducted no EIA on the masterplan because it was not granting consent for the masterplan, she said.

All eight data halls were not intended to come on stream until sometime between 2030 and 2035, and it would have been completely inappropriate for the Board to decide in 2015 what was going to happen in 2035.

Energy demands were considered and while Apple could not show it would use 100% renewable energy, that situation but could be different in 2035, she added.

James Connolly SC, for the State, supported the board's position and also maintained there was no requirement to carry out an EIA on the entire project.