Following new environmental monitoring near a mining waste pile in Cottonwood, state agencies say contamination is not widespread and health risk for the community is minimal. But some residents still have concerns.
For a century, a 50-foot mountain of mining waste, called slag, has sat in the center of town, left over from copper processing in the early 1900s. In the 1930’s, the heap was abandoned. Homes and business sprang up around it.
Now, the slag looms over the Verde Valley Fairgrounds, a playground, a low-income housing apartment complex and the Veterans of Foreign Wars Post.
In 2015, a Tucson-based company started repurposing the slag by breaking the rock apart and crushing it down to make sandy material for industrial uses, like sandblasting.
When Minerals Research Inc. began operating, ADEQ received complaints. Nearby residents reported seeing a “dark colored dust” off the facility’s site. They worried that the mysterious material was accumulating in the corners of their lives and wreaking havoc in their bodies.
After a yearslong saga involving air quality permitting mishaps and environmental testing, ADEQ has finally closed its investigation. At least for now.
Dust from the waste raises concerns about air quality
Two years ago, ADEQ started monitoring air quality at the VFW Post and at a kids park nearby following community complaints. Results from the four- month study showed that PM10, small breathable particles of dust, largely stayed below the National Ambient Air Quality Standard at both locations — except for one particularly windy day in April 2024 at the VFW post, when PM10 met the exceedance threshold.
In March, ADEQ shared new soil and air test results at a community meeting in Cottonwood. Samples taken last year were analyzed for PM10, lead, arsenic, aluminum and other contaminants.
Air quality results from 2024 initially showed high concentrations of lead in the air at the VFW post, but follow-up tests revealed the three-month average was below the federal standards.
Shaida Sina, a naturopathic doctor with an office nearby, still worries about particulates in the air, especially on days that MRI blasts. MRI is authorized to blast 12 times per year; so far the company has blasted 5 times, according to ADEQ. A video taken by ADEQ inspectors in March shows the aftermath of a blast.
The final report, published in March, notes that property owners north of the pile have reported black dust collecting on indoor and outdoor surfaces. Even ADEQ employees noticed visible dust blowing off the MRI property while collecting samples in 2025.
“On March 3, during sampling on the VFW property, high winds also caused observable spreading of dust from these areas of the MRI facility onto immediately adjacent neighboring properties, even with no vehicle traffic,” the report said.
Out of 267 samples tested in a lab in 2024 and 2025, 107 samples exceeded background arsenic levels. The highest concentration was found on a hill where the old smelter stack used to stand — arsenic concentrations hit 1,680 mg/kg, far above the Soil Remediation Level of 10 mg/kg.
The state uses soil remediation levels as risk-based standards based on the total contaminant concentration in the dirt. If a concentration is above the level of 10mg/kg for arsenic, it doesn’t necessarily mean that it needs to be cleaned up, but could suggest further action or investigation.
Of the samples that were flagged for arsenic, not all of them can be linked to the slag. ADEQ proposed three potential sources for the arsenic: MRI’s slag processing, potential previous smelting activity and naturally occurring mineral deposits.
The most recent testing shows that 118 samples shared either an exact or similar “signature” to the slag. Soil taken from the VFW post, from a spot just south of the Verde Valley Medical Center and from the old smelter stack site all share the same unique metals composition as samples taken directly from MRI’s slag. Arsenic concentrations near the VFW post ranged from 32.8 to 174 mg/kg.
State: Avoid exposure to dust, pave over soil
ADEQ’s final recommendations are for residents to minimize exposure in certain hot-spot areas like the VFW by removing soil and replacing it or paving over it. But even if those measures are taken, residents wonder about the dust that will continue to drift from MRI onto properties nearby.
Shea Sorenson, a deputy public information officer for air quality at ADEQ, said the agency is currently working with MRI to address off-property soil impacts related to slag dust.
An Arizona Department of Health Services consultation based on ADEQ’s test data was also published in March to determine if people in Cottonwood have been exposed to harmful chemicals and what that could mean for their health.
Evaluation of areas just north, southwest and northeast of MRI, like the VFW post and some residential neighborhoods, showed potential elevated cancer risk in the case of long-term arsenic exposure based on the soil results. Over the course of many years, exposure could also result in non-cancer health effects, especially in children.
The health department’s conclusion is that exposure isn’t expected to cause health issues, and that health risks are limited to specific locations and exposure situations, not to the entire community. They suggested limiting time outside when it’s windy, keeping windows shut to avoid dust blowing inside and discouraging kids from eating large amounts of dirt.
But it also acknowledged that it was working with a limited data set — samples were taken over a short time frame and from limited locations. Still, officials said they took that uncertainty into account.
Many residents still have questions. Yavapai County Supervisor Nikki Check is among them. On days that the company blasts, she’s noticed dust on her car parked just half a block away from MRI.
“ I think we need more data,” she said. She’s working with the county to install air monitors at nearby sites and do more dust sampling.
Check is also pushing for the county health department to look further into how the dust could be affecting public health by conducting blood or urine tests that trace how heavy metals show up in the body.
‘Citizen scientists’ help monitor sites
ADEQ’s scope of work only covers what happens outdoors. The agency doesn’t test dust that shows up inside buildings. In 2024, residents started looking for someone who could.
“People spend most of their time indoors,” said Lois Polashenski, an environmental science doctoral student at The University of Arizona. “It’s really important to make sure that you have information about what’s happening in somebody’s home.”
Part of Polashenski’s doctoral efforts is Gardenroots, a UA community science initiative run by Dr. Mónica Ramírez-Andreotta that evaluates environmental quality and possible exposure to contaminants near resource extraction and hazardous waste sites.
Based on community concerns, in 2025, the Gardenroots team trained 13 residents to collect samples in an effort to involve the community in the quest for answers. With provided kits and special wipes, the participants collected dust from surfaces inside their homes, set up air monitors outside their homes and gathered soil samples. Those were sent to a UA lab where they were analyzed for lead, arsenic and other heavy metals and metalloids.
“Community members experiencing pollution are bearing witness and have local knowledge,” Dr. Ramírez-Andreotta said. “ We’re all scientists.”
Gardenroots also found arsenic present in the soil. Six soil samples had arsenic levels above the state’s Soil Remediation levels, ranging from 12.05 to 20.48 mg/kg. They are working with community members on more testing.
Now that ADEQ’s years-long investigation is complete, Sorenson said in an email to The Arizona Republic, no further environmental testing or monitoring is needed at this time.
ADEQ has still not yet granted MRI a new air quality permit.
By – https://www.azcentral.com/story/news/local/arizona-environment/2026/04/04/minimal-pollution-risk-found-from-cottonwood-mine-waste/89457921007/