Three Kings quarry owner Winstone Aggregates will soon begin blasting rock on its 15.1ha site, in an operation to last a year.
The explosions at New Zealand's biggest inner-city quarry will start from July, aiming to remove a basalt rock plug so hard it can only be blown apart. Residents are gathering tonight to discuss the proposal.
Winstone Aggregates' national environmental co-ordinator, Andrea Cave, wrote to them about the operation and explained how a siren would warn them first, "to reduce the startling effect of unexpected ground vibration and air overpressure that may be associated with the blasting".
Thousands of people live in the area, which is also home to the Three Kings School, Carlson School and Three Kings shopping centre.
"Due to the geology of Three Kings Quarry, a drill and blast programme needs to be implemented to remove the harder basaltic rocks and the welded scoria," Andrea Cave wrote.
"These rocks need to be fragmented so that they can be stockpiled and then taken to the mobile impactor for further processing. Once processed, this material will be sold as high quality roading/building aggregate."
One resident said he was stunned to be told of the blasting at a pit where operations are due to diminish to prepare for the land to be filled, subject to an Environment Court ruling.
He said he was concerned about pensioners and the fact that house foundations were shifting.
Winstone general manager Bernie Chote said quarrying would continue for about 18 months to two years "with the hope that we commence filling this time next year".
"We need to have management plans completed and a few infrastructural things put in place," he said.
"We haven't had any direct feedback from the community but we are holding one of our normal site liaison group meetings on Monday where we are sure to get feedback."
Winstone raised its own concerns about pre-blast sirens. Under existing conditions, a warning must sound for 40 seconds, starting five minutes before the blast, and continuously for the final 20 seconds before it.
After blasting and when the area is safe, five to 10 minutes later, a siren would give three short blasts.
Winstone said this was out of date with modern blasting practices and would cause residents "unnecessary concern due to the length and noise level that the siren will operate at". It said the siren should not be sounded for so long, and a feedback form had been distributed to residents.
Andrea Cave said forms were also distributed at an open day on May 7.
A Facebook campaign has been mounted against Winstone saying the quarry lies over a large freshwater aquifer of 25sq km, which is a back-up drinking water source for Auckland.
"It will not be a cleanfill operation but one that will use material with elevated levels of contaminants, including arsenic, copper, zinc, DDT and hydrocarbons," campaigners say.
"No one has guaranteed that contaminants from the fill will not leach into the aquifer.
"This may result in the aquifer, a key regional asset, becoming too contaminated to be used as a much-needed water source - why would we be prepared to take the risk?
"If a natural disaster hit in Auckland, such as the Christchurch earthquake, we would desperately need a back-up water source."
Tonight from 7pm to 9pm, Three Kings quarry liaison meeting, Three Kings Primary School hall.By Anne Gibson @Anne Gibson Email Anne