Wednesday was another day of heavy haze in her region as the high school science teacher drove into the upper Hunter town of Muswellbrook where she lectures.

"It looked like the whole place had been blown up like a bomb," Ms Wales said. "It was really shocking."

Pollution monitors in the area earlier picked up readings of 103.4 PM10 - particulates of 10 micrometres or less in diameter - at midnight at Warkworth near some large open-cut coal mines.

Residents received an air quality alert from the NSW Environment Protection Authority at 5am, warning PM10 levels had exceeded the national air quality standard of 50 PM10 per cubic metre averaged over 24 hours.

According to James Whelan, spokesman for Environmental Justice Australia, the EPA has issued about 190 such alerts in the Hunter this year. Last month's tally of 72 of the most he had seen in the five years he had been tracking the pollution readings.

"September was extraordinary," Mr Whelan said, adding the jump does not appear to have prompted any steps by the EPA to curtail mine production or seek other remedial step. "It wouldn't make any difference if there were no alerts, or there were 100 a month."

Health impacts

PM10 particulates affects health at any level, with the material absorbed into the blood or lungs. Coal mining is responsible for about 90 per cent.

Coal and Allied's Mount Thorley-Warkworth mine reported emitting 9.2 million kilograms of PM10 in their most recent National Pollution Inventory report, up 12 per cent on the previous year, while nearby Bulga mine emitted more than 5 million kilograms of PM10, up 32 per cent, Lock The Gate said.

Stockton in the Lower Hunter had the worst pollution with its daily average PM10 concentrations exceeding the national standard 36 times so far this year.

Camberwell, Mt Thorley, Singleton NW and Maison Dieu recorded the most exceedances in the Upper Hunter, accounting for 65 of the region's 80 breaches.

Cumulative effects

Fairfax Media asked the EPA whether the September alerts were a monthly record and what steps it had taken to press mines to alter operations.

"The EPA has also required all coal mines to implement best management practice measures to minimise dust emissions via the Dust Stop program," a spokeswoman said.

Mr Whelan said the government's own 2011 commissioned report into best practice stated emissions from material dumping could be minimised by ceasing or modifying activities on dry windy days - weather most of NSW including the Hunter has frequently endured in recent months. Water sprays were another option.

If miners and the EPA had been taking steps, "they were not enough to bring pollution levels down below the [national] standard", he said.

The EJA and Lock the Gate say it is time EPA and NSW's Department of Planning acted on long-overdue recommendations - accepted five years ago - to address and prevent cumulative impacts of open-cut coal mining on air quality.

They say the agencies should tackle the effects of adding more mines when they assess the United Wambo super pit coal and the expansion of the Hunter Valley Operations near Singleton.

"Why is the government still considering more open-cut pits in the worst affected area when they still haven't set basic thresholds to protect people from cumulative health damage?" Georgina Woods, Lock the Gate spokeswoman, said. "There has to be a limit, and we've reached it."

The Department of Planning is currently assessing United Wambo's development application and has commissioned an independent review of its Air Quality Impact Assessment that will include the cumulative mining impacts in the area, a spokesman said.

'Megamine'

Jeremy Buckingham, NSW Greens resources spokesman said the government was failing to account for mining's cumulative impacts from particulate pollution to greenhouse gas emissions, habitat destruction or water.

"The scale of modern open-cut mining turns the surrounding landscape into an industrial area, which is incompatible with sustainable agriculture and healthy communities," he said.

For Ms Wales, efforts to curb develop further down the valley are likely to bring little benefit to her area near Aberdeen where the nearby Mount Pleasant mine is rapidly expanding.

"It's just opening up - it's going gangbusters," she said. "It's a megamine."