Surging floodwaters from Florence and its torrential rains, which experts link at least in part to climate change, have released coal ash – a byproduct of coal burning that contains mercury, arsenic and other toxic substances – into the Cape Fear River in North Carolina. The torrent has also overrun several lagoons of pig waste in the state. The mishaps amplified concerns about an array of danger zones including Superfund sites, chemical plants and the region’s large-scale hog farms.

On Friday breaches in a lake at the L.V. Sutton power plant in Wilmington, N.C., opened up, causing coal ash to enter the Cape Fear. North Carolina’s Department of Environmental Quality said it had taken water-quality samples on Saturday but that test results would not be available until later this week. Duke Energy, which owns the Sutton plant, said water tests conducted by the company on Friday showed “little to no impact to river water quality.”

Here is where the dangers lie across the hardest-hit states:

Coal ash ponds

Roanoke Virginia Beach VIRGINIA Norfolk Greensboro Durham Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Flooding reported at Duke Energy’s H.F. Lee Plant near Goldsboro, N.C. Wilmington Columbia SOUTH CAROLINA Spill reported at the Sutton Power Plant Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Flooding reported at Duke Energy’s H.F. Lee Plant near Goldsboro, N.C. Wilmington Columbia SOUTH CAROLINA Spill reported at the Sutton Power Plant Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville H.F. Lee plant: flooding Wilmington Sutton plant: spill Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Source: U.S. Energy Information Administration via Frontier Group

Coal ash is the dusty residue that remains after power plants burn coal to generate electricity. The heavy metals that it contains are linked to respiratory illnesses and cancer.

Energy companies maintain that the way they store coal ash, in earthen pits mixed with water, is safe.

However, last week Duke Energy reported multiple breaches at a lake at its Sutton power plant, in Wilmington, N.C., that caused the inundation of an ash basin on the site. From there the water, which contained coal ash, flowed out to the nearby Cape Fear River.

The Sutton plant has two coal ash ponds, one dating back to 1971 and the other to 1984. The two ponds combined hold 2.1 million cubic yards of coal ash, according to a report prepared for the company. Only one was flooded. It is unclear how much ash has been released.

This was the second breach reported at the site. Shortly after Florence hit, Duke Energy reported a breach of coal-ash storage at the Sutton plant that displaced 2,000 cubic yards of material, the company said, an amount that would fill about two-thirds of an Olympic swimming pool.

Shortly after that, Duke Energy said, three ponds at a plant in Goldsboro, N.C., were flooded but not breached.

The largest spill on record happened in 2008 in Kingston, Tenn., when heavy rains led to the breach of a pond, releasing 1.1 billion gallons of coal ash at a site run by the Tennessee Valley Authority. The cleanup ultimately cost more than $1 billion.

Pig farms

Greensboro Durham Raleigh NORTH CAROLINA Charlotte Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Raleigh NORTH CAROLINA Charlotte Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Raleigh NORTH CAROLINA Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Sources: North Carolina Department of Environmental Quality; South Carolina Department of Health and Environmental Control

Two North Carolina counties in the path of the hurricane’s destruction, Duplin and Sampson, are home the highest concentration of pork production in a state that produces a lot of pork. North Carolina has 9.7 million pigs, producing almost 10 billion gallons of manure annually.

“It’s 500 times the waste produced by the entire population of Washington D.C.,” said Alexis Andiman, an associate attorney with EarthJustice, a nonprofit environmental law firm that has sued the state over its handling of animal waste.

The material is collected in open pits called lagoons.

Ten days after the hurricane, the state’s Department of Environmental Quality reported that waste lagoons at more than two dozen hog farms had discharged at least some of their contents. Five lagoons experienced structural damage and 32 had seen some form of overflow, according to the D.E.Q.’s website.

In 2016, Hurricane Matthew swamped 14 lagoons in the state. And in 1999, the liquid that escaped when Hurricane Floyd flooded dozens of lagoons wound up in waterways where it killed fish and caused algae blooms, which imperil aquatic life.

Superfund sites

Roanoke Virginia Beach VIRGINIA Norfolk Greensboro Durham Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Source: Environmental Protection Agency Facility Registry Service

The Carolinas are home to more than 70 high-priority Superfund hazardous-waste sites, including a former smelting plant in North Charleston near the coast that is contaminated with arsenic, antimony and other substances linked to health problems including cancer.

On Friday, the Environmental Protection Agency reported that assessment teams had completed “preliminary inspections of 62 sites, with no issues identified.” But, on Monday, rivers were still rising and hundreds of roads remained closed. “Teams will move into areas still experiencing flooding and road closures when conditions allow,” the agency said in a statement.

The agency came under fire last year after hurricanes Harvey and Maria inundated Superfund sites in Houston and Puerto Rico.

“Industrial sites have historically been near water,” said Prof. Thomas Burke, associate dean at the Johns Hopkins School of Public Health, who studied chemical exposures after Hurricane Katrina and other storms. “That makes them definitely vulnerable,” he said. “In New Orleans, they caused a toxic gumbo.”

Though cleanup is under way at the Carolina sites, and contaminants like arsenic and lead are already capped to keep them in place, flooding still poses a threat. “With extraordinary surges and inundation of water, you really have to worry about the integrity of these things,” Professor Burke said.

Chemical sites

Virginia Beach VIRGINIA Norfolk Greensboro Durham Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville Charlotte Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. VIRGINIA Raleigh NORTH CAROLINA Greenville Jacksonville Wilmington Columbia SOUTH CAROLINA Charleston Est. cumulative rainfall by Monday, 4 p.m. 5 45 in. Source: Environmental Protection Agency Toxics Release Inventory Program

North and South Carolina are home to more than one thousand sites where toxic chemicals are used or stored, according to a database maintained by the E.P.A.

The region’s paper mills, for example, use various solvents to treat the lumber. Across the country, 2,500 chemical sites lie in flood-prone areas, a New York Times analysis found this year.

“With flooding, will there be damage to storage tanks? These are things we have to watch out for,” said Elena Craft, a senior health scientist at the Environmental Defense Fund. “We’re talking PCBs, dioxins, the worst of the worst,” she said, referring to chemicals known to be harmful to human health.