According to Fairfax media, which broke the story on Saturday, the Santos-commissioned test results detected uranium at a level of 335 micrograms per kilogram - well beyond the 17 micrograms per litre, which is the national drinking guideline amount.

Lead, aluminium, barium, boron and nickel levels in the aquifer were also found to be too high, although the Environment Protection Authority reportedly said the detected metals occurred naturally in the surrounding soil and water.

Santos reportedly said the affected aquifer was localised and not linked to regional aquifers.

The contamination event, revealed by Santos to the EPA nearly 12 months ago, was blamed on a "poorly constructed" wastewater pond that was decommissioned by Santos in late 2011, not long after it acquired the project from Eastern Star Gas.

"Despite legislation allowing for a maximum fine of $1 million for corporations that pollute water if the matter is heard in court, the agency decided a $1500 penalty notice was appropriate," Fairfax reported.

"This was based on ‘evidence which showed that environmental impacts were minimal and that Santos had reported and responded to the incident quickly'."

The groundwater contamination event was eagerly criticised by green groups, which already oppose the NSW government's moves to fast-track the Pilliga CSG project.

The incident also sets an industry precedent for aquifer contamination caused by CSG-related activity.