Quarry operators want leave to dig into Christchurch's groundwater table to get more gravel for the rebuild.

Under existing rules quarry operators in the greater Christchurch area are allowed to dig no more than a metre above the highest groundwater level, but they are seeking to have that restriction eased because a number of the large established quarries are nearing the end of their life.

They have lodged resource consent applications with Environment Canterbury (ECan) and the Christchurch City Council seeking permission to deepen their existing quarries by up to four metres. By digging further down they believe they can yield up to 25 to 30 million extra tonnes of aggregate, but they face opposition from those worried that quarrying deeper could lead to contamination of the aquifers that supply Christchurch's drinking water.

Staff from ECan and the city council are working through the consent applications, which will be publicly notified, meaning people will have an opportunity to make submissions.

In their consent application, the quarry operators, who form the Canterbury Aggregate Producers Group (CAPG), said as the speed of the earthquake recovery had accelerated, so too had the demand for aggregates. That demand was predicted to last for at least the next decade.

CAPG believed it would be better from an environmental, social and economic perspective to maximise the resource volumes that could be extracted from the existing quarries rather than establish new quarries.

Their proposal involved extending the depth of quarrying between one and three metres below the highest groundwater level recorded before December 2014 at each of the three quarry areas around Christchurch: Miners Rd in Yaldhurst, McLeans Island Rd in Harewood, and Selwyn Rd in Prebbleton.

"The risk of contamination will be minimised by strict controls on the material that is used to backfill the excavation, timing the deeper excavations to minimise the risk of groundwater rising up into the pits, and monitoring groundwater quality," the CAPG application said.

CAPG chairman Brian Warren said the quarry operators spent three years working on their proposal and they were "extremely confident" it posed no threat to groundwater.

Christchurch Deputy Mayor Vicki Buck does not share that confidence and is worried about the environmental consequences of deepening the quarries.

"I just think groundwater is so important in Christchurch that any incursion into that groundwater is not OK," she said.

"If there is any damage to our groundwater then my supposition is that becomes a cost to the community.

"When this [resource consent application] is notified, it would be excellent if people made their views known."

Green MP Eugenie Sage said the city's aquifers had to be protected.

"We do need more gravel and the operators are saying it is easier to use existing sites than to build new ones but safeguarding the quality of our aquifers must be an absolute priority."