Plans to increase stone quarrying are going ahead despite concerns over its impact on the local geology.
Breedon Aggregates, which runs Stowe Hill and Clearwell quarries in St Briavels, can now extract an extra 2.5 million tonnes of aggregated materials.
Clearwell said it understood concerns but insisted it was within strict conditions set out in the application.
Campaigners who fought against it, were now calling for the decision to be reviewed by the Secretary of State.
Newland Parish Council clerk, Richard Crighton said: “Our primary concern… in the local area, was and remains, the very real risk to the integrity of the Slad Brook SSSI (Site of Special Scientific Interest).
“This is a brook which contains hydro-geological features called tufa dams – there’s a very delicate balance of elements in nature and these tufa dams are the best example in the UK and possibly in Europe.”
He added although these arguments had been made before, the site remained “the most environmentally sensitive” in the county.
Residents are also worried about noise, pollution, dust and lorry movements, as well as the visual impact on the Forest of Dean landscape.
The planning application includes the expansion of Stowe Hill quarry by 28 hectares as well as the continuation of operations at Clearwell Quarry.
Under the new planning conditions, up to 600,000 tonnes can be extracted per year across both sites.
A spokesman for Clearwell said: “We’re pleased Gloucestershire County Council has recommended conditional approval of our application, which remains subject to completion of a legal agreement.
“It will ensure that we can continue to provide future employment for our colleagues at Clearwell for many years to come.”
Gloucestershire County Council’s planning committee voted in favour of the plans on 9 July.