Monday numbers: Chapel Hill’s – and the planet’s – coal ash problem

By: - September 12, 2022 12:39 pm


The Bolin Creek Trail near Martin Luther King Jr. Boulevard flanks the coal ash disposal site. (Photo: Lisa Sorg)

In the mid-20th century, Chapel Hill residents unknowingly strolled the streets in a miasma of coal ash. Until federal regulations required the UNC coal-fired power plant to install pollution controls, the ash carpeted the town, its residents — and its residents’ lungs — in invisible particles. In addition, hundreds of thousands of tons of leftover fly ash was dumped, along with other trash, at what is now 828 Martin Luther King Blvd., the home of the Chapel Hill Police Department.

Avner Vengosh, a distinguished professor of environmental science at Duke University, and his colleagues recently released a report analyzing the chemical composition of the ash buried at ‘828,’ as it’s known for short. The property has been targeted for a controversial proposed mixed-use development that would include low-income housing, albeit above the first floor. How to remediate the property, short of excavating the ash, which would create its own environmental hazards, is a problem city leaders and consultants have yet to solve.

Scroll down for information regarding an online forum about coal ash, featuring Vengosh and several more scientists and environmental advocates.

Chapel Hill, where the standard of living has long been out of reach for even many middle-class families, needs affordable housing. And it needs housing along transit lines. 828, proponents say, fills both bills.

Unfortunately, the 828 site has become politicized: One side argues most of the ash can be capped by asphalt (a small amount could require excavation), and that in that encapsulated state, the risk to public health is negligible. The other side says the risks are too great, especially considering the toxic elements the ash contains, and the unknowns related to the use of ash as structural fill.

More than 20 contaminants, including arsenic, thallium, strontium, uranium, radium-226, radium-228, lead, cadmium, are present in the ash, according to an analysis of eight samples conducted by Vengosh and his team last month. The chemical makeup of the ash is consistent with its source — Appalachian mines. The ash particles are also smaller than in modern ash. Without pollution controls to filter those particles, people living in Chapel Hill “were exposed to small particles from flue gas,” until the 1980s, Vengosh said.

Concentrations of arsenic, a known carcinogen, and thallium, a neurotoxin, ranged from just below to exceeding the EPA’s Regional Removal Management Level for residential soils. There are also many exceedances for ecological toxicity, which is relevant because the groundwater at and leaving the site is contaminated.

The cumulative effects of multiple contaminants “may intensify the … effects of individual contaminants or may give rise to interactions… that create new effects,” according to a report by Physicians for Social Responsibility and EarthJustice.

A view from the Bolin Creek Trail, looking up at the mound of ash that has been covered. (Photo: Lisa Sorg)

The following numbers are from the Duke University team’s report:

10-to-30 – number of times higher the concentrations of toxic metals found at the Chapel Hill site are, compared with baseline North Carolina soil

2-to-4 – number of times higher the concentrations of radium-226 and radium-228 are, compared with baseline NC soil

99.4 to 99.8 – percentage of fly ash present in material collected at eight sampling sites at the Chapel Hill site

Surface to 4 feet below ground – depth that ash was found at those percentages

39.5 to 58.2 – parts per million of arsenic in soil samples taken from three locations, ranging from at the surface to 2.5 feet below ground. No amount of arsenic is safe.

120 to 173.7 – parts per million of vanadium, which exceeds the standards for ecological toxicity for birds

2 – rank of coal ash, in amount, among industrial waste in the U.S. Mining is the top industrial waste producer.

Online forum about public health risks of coal ash

When: Thursday, Sept. 22, 7:30- p.m. Register here.
Who: Avner Vengosh, distinguished professor of environmental science at Duke University;
Julia Kravchenko, associate professor of surgery at the Duke School of Medicine;
Kristina Zierold, associate professor in the school of public health at the University of Alabama;
Susan Wind, an environmental activist who lived in Mooresville, in Iredell County, where coal ash was widely used as structural fill. Her daughter is one of several teenagers in the area who developed thyroid cancer. The state Department of Health and Human Services found there is a statistically significant rate of thyroid cancer in two zip codes in Iredell County, but has not pinpointed a cause. Click here to read Policy Watch reporting on this situation.

This map shows the location of three major coal sources in the U.S. Researchers evaluated how fly ash from several coal-fired power plants neutralized acidic runoff in abandoned and active mines. The results were mixed; in some cases, a chemical reaction created secondary contamination. (Map from journal article)

If any of the ash is removed, it will likely be trucked to an out-of-county landfill; without an active landfill, Orange County exports its waste. Fly ash is also used as structural fill, such as base material for parking lots or airport runways. If the asphalt or concrete fails, the fly ash can become exposed, which occurred at a car dealership and a separate parking lot in Iredell County.

“Using it as structural fill puts it closer to the water tables,” Vengosh said. He recommends locking the ash into concrete, at least in the short-term.

Fly ash also has been deployed to neutralize “acid mine drainage” at spent and active coal mines. Acid mine drainage is essentially runoff, produced when water — rain, even snow melt — reacts with coal and sulfur-containing rocks. It leaches metals into the groundwater, rendering it toxic for drinking water wells, irrigation, even industrial uses.

Even after mines are abandoned, Vengosh said, they still generate acidic runoff. “Even those from 50 years ago,” he said. “People think if they stop the coal mining the problem is solved. But there’s an environmental legacy.”

Vengosh and his team of researchers compared fly ash from four areas of the U.S., as well as India. The scientists found that ash from Appalachian coal, used by Duke Energy to generate electricity, does neutralize the acid mine drainage. However, the chemical composition of coal from this part of the country naturally contains higher concentrations of arsenic and selenium. When fly ash is placed into the acidic runoff, a chemical reaction occurs. Arsenic, selenium and metals leach into the runoff, and “the resulting fluids may be highly toxic and, when mixed with groundwater, surface water and soil, may have harmful effects on humans, animals and plants,” the study says.

If mining companies or environmental regulators use fly ash from Appalachian and Illinois coal, the discharge “would further contaminate the environment for some toxic elements,” unless it’s treated, the study says.

Coal sourced from the Powder River Basin, in Wyoming, leaches less contamination, scientists found.

Additional numbers from the Duke University team’s report:

12,000 – miles of streams in the U.S. contaminated by acid mine drainage

8 billion – tons of coal burned globally in 2020

1 – number of known coal mines that operated in North Carolina. The Coal Glen mine, near Farmville in southeastern Chatham County, was the scene of the state’s worst mining disaster. In 1925, an explosion killed 53 miners.

180 – years coal fields near the Deep River were active

1952 – the last year those fields operated

Sources: Rachel Weinburg, Rachel Coyote, Debabrata Das, Zhen Wang, Avner Vengosh “Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the U.S.” NC Department of Cultural and Natural Resources, The News & Observer

“Coal ash legacy in Chapel Hill,” by Vengosh, Wang, Ellen Cohen, Robert Hill and Gordon Williams

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Lisa Sorg
Lisa Sorg

Assistant Editor and Environmental Reporter Lisa Sorg helps manage newsroom operations while covering the environment, climate change, agriculture and energy.