Dust pollution from trucks and other vehicles traveling to and from the proposed Copper World mine on a lengthy dirt road could push a surrounding area into non-compliance with federal air quality standards, Pima County officials say.
Trucks delivering copper concentrate from the mine, and other vehicles carrying commuters to it, will travel a 7.7-mile stretch of unpaved Santa Rita Road to reach the Copper World site on the Santa Rita Mountains' west slope, says the Pima County Department of Environmental Quality. Unpaved roads have long been considered a prime dust pollution source in and near major Arizona metro areas.
In response, Copper World developer Hudbay Minerals Inc. said it acknowledges concerns about dust on that road and is willing to work with government agencies to try to mitigate it.
"A lot of heavy truck traffic for several miles back and forth — that's the concern," Scott DiBiase, director of PCDEQ, told the Arizona Daily Star. "The biggest impacts would be from early morning temperature inversions forming a stagnant air mass. You just kick up the dust and it stays elevated for a period of time. An air inversion holds down the dust. Temperature inversions are typically worst in in the fall and winter."
The department raised these concerns in a Sept. 11 letter to the Arizona Department of Environmental Quality.
Asked by the Star about the letter, the mining company said, "Hudbay acknowledges concerns about traffic and the potential for increased dust on Santa Rita Road as the Copper World project progresses. Because of these concerns, Hudbay has voluntarily offered to help with dust control and has already received authorization to do so" from the State Land Department.
The land department has granted Hudbay a special use permit to use the portion of Santa Rita Road that's under the department's control. That part of the road passes through the Santa Rita Experimental Range, a sprawling area of mesquite, prickly pear and ocotillo that's an ecological preserve and a research haven.
"Hudbay is open to working with PDEQ and other agencies to address concerns," the Toronto-based company said.
In his letter to ADEQ, DiBiase asked that Hudbay prepare a dust mitigation plan in cooperation with the county agency that would include measures to address dust pollution from the mine trucks.
The county staff's concern is that the vehicles will kick up heavy concentrations of large and fine dust particles, which the Environmental Protection Agency says can cause heart and respiratory problems for people.
"Pima County anticipates Copper World-associated elevated traffic flow as the Copper World Project progresses to full operational capacity. This has the potential to drastically increase the amount of fugitive dust released into the nearby communities," DiBiase wrote ADEQ's Air Quality Division.
The county environmental director wrote the letter as part of the county's comments on ADEQ's proposed air quality permit for the mine. But the proposed permit doesn't cover the area outside the mine site that includes the dirt stretch of Santa Rita Road, DiBiase noted. So the agency's air quality permit won't cover the impacts of mine vehicle traffic on that road.
The unpaved stretch extends to East Corto Road south of Sahuarita, he said.
Residents' laments
Several longtime residents who live north and east of Santa Rita Road say dust from the relatively few trucks that traverse the road today are already kicking up dust that's visible from their homes, even though they're up to five miles away.
Jessamyn Tran, who lives in the Entrada Estates subdivision north of the mountains, said she already sees "dust coming off the road constantly, every time they drive" a truck down the road, "let alone when they do blasting on dry days" for the nearby Cimbar Resources limestone quarry.
"When you run 40 or 50 miles a week on the roads, you get a big dose of it," said Tran, who said she's lived in that area 20 years.
Diana White and her husband have lived about 13 years in Entrada Estates. She said she can see dust from the road all the time now, "pretty much every day," although they live three miles from it.
"It just kind of hangs along Santa Rita Road," she said. The whole area has nothing but dirt roads and today she and her husband have to remove dust from their home every two days, she said.
Betsy Riley, who has lived in Entrada Estates 20 years, said she's very upset about the prospect of more trucks coming down that road when and if the mine opens. She said the air quality out there is already not that good, and the haze hanging over her neighborhood is now at times worse than it's ever been.
"Sometimes, you can't even see the mountains," Riley said.
Overview of part of the site of Hudbay Minerals Inc.'s planned Copper World project southeast of Tucson.
"Hudbay is committed"
Hudbay's permit with the Land Department requires it to comply with all federal, state and local environmental laws, but also releases the land department from any liability regarding the environmental laws, DiBiase wrote.
But the permit lacks a detailed dust mitigation plan to address fugitive dust emissions — those not traceable to a specific source — on Santa Rita Road along with a parallel utility corridor and dirt maintenance road, he wrote.
"The dust mitigation plan should include specific control measures that ensure dust generation associated with Copper World traffic on Santa Rita Road are limited and are within Pima County's fugitive dust requirements. Additionally, Pima County requests annual review and revision of the Santa Rita Road dust mitigation plan as needed," DiBiase said.
Asked if it would go along with the county's request on this matter, Hudbay replied, "Yes, Hudbay is committed to reducing fugitive dust and working with the County on appropriate dust control measures."
The mining company added, "Santa Rita Road is a public road and Hudbay will be using it as a member of the public. There are no PCC (Pima County) fugitive dust requirements' that apply to this activity."
The exact number of mine-related trucks and other vehicle trips to be made on Santa Rita Road isn't known yet. Hudbay told the Star, "At this time, it is too early to provide precise traffic estimates for the Copper World project."
DiBiase acknowledged to the Star that the impacts of mine truck dust would be somewhat limited, geographically, "pretty localized, typically within a mile or two of where the dust is generated."
Much if not most of the area near Santa Rita Road there is undeveloped and the dirt road itself is surrounded by open desert in the experimental range on both sides. Exceptions are the 300-home Entrada Estates subdivision east of the road, and a number of other homes lying south and southwest of the road, neighbors say.
The problem is with the area's geography, in which the mountain areas can help trap pollution during temperature inversions in the fall and winter, DiBlase said. They can add to the pollution concentrations, he said.
He also acknowledged that the county hasn't done computer modelling of the area that would produce specific projections of whether emissions would be enough to exceed U.S. Environmental Protection Agency standards.
"But we can expect elevated emissions here and it made sense to provide that comment" to the state," he said. "We are concerned."
Water spraying or other measures
The most effective dust control measures besides a highly expensive project to pave the road would be to spray water or an artificial dust suppressant compound known as a dust palliative on it, he said. Watering the road once or twice a day to hold down the dust would use "a significant amount of water," he said.
A wide variety of dust suppressant compounds exist that typically bind with soils and provide "a pseudo-paved surface," he said. The U.S. Forest Service publishes a guide to them.
But "with heavy truck traffic that doesn't work too long," he added, based on his experiences in 19 years of air quality regulatory work in Pinal County.
Hudbay, asked if it would be willing to apply water to the dirt road for dust control, replied, "Hudbay has voluntarily offered to perform dust control measures, such as watering, along the 7-mile stretch of Santa Rita Road. We obtained the (special use permit) in August which gives us the necessary authority to perform maintenance and dust control on this public road."
