Hertfordshire county councillors have deferred a decision on whether to build a quarry on the former aerodrome site in between Hatfield and St Albans at a meeting on Wednesday.

Brett Aggregates have drawn up plans to extract up to eight million tonnes of sand and gravel from the 87.1 hectares aerodrome site, which sits between Smallford and Ellenbrook.

But concerns have been raised about the impact that could have on the contamination of water below ground.

That's because a 'bromate plume' - attributed to a leak from a former chemical works in Sandridge - flows close to the site.

And there are fears that any disturbance by the quarry could impact on the flow of that 'plume' and could lead to contamination of drinking supply.

Brett Aggregates - who hope to begin work on the site in 2021 - have insisted the measures they will take will mean there is no risk of contamination.

And the Environment Agency have said that the proposed operations - and the required planning requirements - would "reduce and effectively manage the risk".

But the county council's development control committee refused to take a decision without further information from the Environment Agency.

Leading calls for the deferment, county councillor Seamus Quilty said the decision was a "balancing act" - and that it was "an absolute disgrace" that the Environment Agency was not present.

He said the EA's references to reducing and managing the risk meant that there was a risk and asked the watchdog to give a professional guarantee that there would be no contamination to the public water supply.

"Not having them here is ridiculous," said Conservative councillor Quilty. He also asked that the director of public health Jim McManus was on hand to answer their questions.

They also asked that the EA must attend the next hearing.

Conservative councillor Michael Muir said it was the most difficult decision, in his 16 years on the committee, and added that he couldn't make the decision on "one-sided evidence".

Earlier councillors had heard from Ellenbrook Area Residents' Association, Welwyn Hatfield Borough Council, Smallford Residents Association and on behalf of the owners of Popefield Farm.

As well as the pollution from the bromate plume, their concerns included the implementation of a previous Section 106 agreement for a country park on the site, the cumulative effect of the quarry, such as traffic, and the direct impact on Popefield Farm.

Councillors were also addressed by Brett Aggregates' planning director Simon Treacy and Peter Rowland from SLR Consulting, who is project manager for the Hatfield site.

Mr Treacy, from Brett Aggregates, pointed to the importance of mineral extraction and he said the scheme had been designed to the highest standards.

He said the company had undertaken considerable research to understand the physical properties, extent and behaviour of the bromate plume.

And he said their plans had been independently scrutinised by the Environment Agency and Affinity Water.

When asked if he could guarantee that there would be no contamination of the water supply, he said: "Yes, we can".

Mr Treacy also said the country park would remain open to the public during the phased extraction of the sand and gravel as he understood the importance of its provision.

Meanwhile project manager Mr Rowland said the bromate plume was "static" and in answer to a question he said the risk of it leaking into the water supply was "low".

The meeting heard that work on the Green Belt site - which would be split into seven separate four-year phases - would run with restoration for up to 32 years.

It was also reported to councillors that the Environment Agency had specified that no minerals should be extracted from within the existing plume and that activities close to the plume should neither change the water flow or interfere with the remediation of the bromide and bromate pollution.

And according to a letter submitted by the Environment Agency, the planned operations and the recommended planning condition will "reduce and effectively manage" the risk to ground water.

Following the meeting on Wednesday (December 18) Simon Treacy, planning director for Brett Aggregates, said: "We are disappointed that the committee has decided to defer consideration of the application today.

"But we respect the decision that has been made and we look forward to hearing the committee's decision when it takes places in the future."