During consent hearings, the Christchurch City Council's town planner said the effect on residents' health of the 30-year-old quarry's expansion would be "minor or less than minor".
However, since then residents have reported a long list of health issues, including coughing, shortness of breath, runny eyes, and asthma.
One man says he has been prescribed an inhaler despite never having a history of respiratory illness.
Annell McDonagh and her teenage children were given Prednisone by their GP, a drug that fights severe bronchial asthma.
Bob Cross and Vicki Christofferson felt forced to sell their home of 20 years.
They weren't prepared to stay next to Winstone's quarry extensions, which ran almost the length of their boundary.
McDonagh fears her family, living with 140m of quarry operations, might have to do the same.
"If there's health issues you've got to think of your family," she said.
The Christchurch City Council gave the company consent to expand in 2014, despite evidence from multiple sources, including the company's own dust expert, suggesting that quarries shouldn't operate within 250m of a dwelling.
Council town planner Helen Bealey quoted the Victorian Environmental Protection Agency during consent hearings.
"Dust impacts are a function of separation and distance, with the Environmental Protection Authority Victoria (EPA Victoria 2013) recommending a separation distance from quarries to sensitive activities of 250m," she wrote.
"In addition, the greatest intensity of dust impacts will typically be within 100m of a source. There are two dwellings which are around 100m from the proposed quarry."
The Victorian EPA suggests a boundary of 500m when dust produced from a quarry contains 30 per cent crystalline silica.
Winstone Aggregate's dust consultant, Richard Chilton wrote in the company's resource consent: "It is my experience that coarse dust impacts will typically be within 100m of a source."
Yet, the quarry was granted consent to expand and operate within 200m of about six homes.
Last May, Cabinet Minister and MP for Selwyn Amy Adams pledged her support of the residents of Yaldhurst.
She said: "It is my clear view no quarrying should be permitted within 250m of an existing residential property and that quarrying inside this buffer zone should be a prohibited activity."
Environment Canterbury said it would step up efforts to mitigate dust from the quarry once it knows how much people's health is affected.
ECan service delivery manager, Brett Aldridge said the agency was waiting for a letter from Canterbury's medical officer of health, Alistair Humphrey, detailing the seriousness of the situation.
"There's a risk and we need to understand the magnitude of it and what kind of exposure levels raises that risk," he said.
Humphrey said yesterday that a health assessment being conducted by respiratory, toxicology and public health professionals is expected to be completed by Wednesday.
The residents are eagerly awaiting a meeting with Adams, chief executive Bill Bayfield and Commissioner David Bedford at the ECan offices on March 28.
Meanwhile, GBC Winstone general manager Ian Jones said the quarry had been operating since 1988 and was following the conditions of its resource consent.
"We are committed to continuous improvement and, with this in mind, have appointed an independent air quality expert to review our systems and see if there is anything else we need to do," Jones said.
The company has increased staff training and made a number of improvements including installing a wheel wash on site.
