What are the biggest pollution threats as Florence sweeps through SC?

As Hurricane Florence hits South Carolina, government officials and environmental groups are watching a string of contaminated sites that threaten to leak harmful pollutants if heavy rains continue through the weekend.

The biggest worry is that rain will swell rivers so high that they will flood waste sites or that rain will wash toxins off contaminated land into rivers or lakes.

Sites being watched include a hazardous waste dump near Lake Marion, hog lagoons in the Pee Dee, contaminated coal-ash disposal basins near Columbia and Myrtle Beach, an unlined nuclear waste dump in Barnwell County and an atomic fuel factory in Richland County, near Congaree National Park.

Federal regulators also are keeping an eye on four S.C. nuclear power stations, as well as nearly a half-dozen federal Superfund cleanup sites.

S.C. residents like Mary Jackson Kirkland and Andrea Williams hope the heavy rains don’t overwhelm polluted sites like the one near their homes, southeast of Columbia.

That site, the Westinghouse nuclear fuel factory on Bluff Road, has a more than 30-year history of groundwater pollution that many people just learned about this year.

This past summer, uranium leaked through a hole in the plant’s floor, contaminating soil with high levels of the radioactive pollutant. Regulators later said they discovered uranium leaks had occurred as far back as 2008, previously unknown to the public. Uranium is a toxic radioactive material that can cause kidney damage in people exposed to large enough amounts.

“I’ve tried not to think about it; it’s just that concerning,’’ said Williams, who along with Jackson Kirkland, co-chairs a citizens’ committee formed recently to monitor Westinghouse. “We know the contamination threat is very viable.’’

Congaree Riverkeeper Bill Stangler said the Westinghouse site bears watching because of its past. Stangler said he has found evidence that a catastrophic flood in 2015 caused pollution to leak on the Westinghouse property. That could be repeated with Florence, he said.

“It is on my hot-spot list,’’ Stangler said. “We just recently learned about the significance of these spills.’’

Westinghouse spokeswoman Sarah Cassella said the company has closed the plant until next week as a precaution.

But the U.S. Environmental Protection Agency said the threat was important enough to dispatch staff members to Columbia to keep track of nearly a half-dozen federal Superfund cleanup sites in South Carolina.

Additionally, one site that is of concern to many is the Pinewood hazardous waste dump, a 279-acre facility on the shores of Lake Marion. That dump, established in 1978, has been closed for years, but must be monitored for leaks.

Rob Kerr, an attorney who oversees management of the site, said extra personnel are being brought in this weekend to monitor the landfill. Inside the dump are poisonous metals and other industrial refuse that could hurt people or wildlife if released into the environment.

“We have deployed manpower out there; we’ll have somebody at the site 24/7 until Monday,’’ Kerr said.

Kerr expressed confidence that barriers and operating systems at the landfill will prevent any leaks during heavy rains.

The site, for instance, has synthetic liners over the top and bottom of its closed waste pits, and a system to pump out polluted water from below ground, he said. If the site loses power, it has generators that can operate for up to seven days, pumping the contaminated water out of the landfill. If the water builds up, it could cause leaks to spring out of the landfill.

Kerr said the site was pounded by 18 inches of rain during a historic 2015 flood but did not leak.

“Pinewood holds up very well in those kinds of storms,’’ he said.

Whether heavy rains flood hog lagoons remains to be seen, but the state’s riverkeepers are watching some animal farms for signs of runoff or that a waste pond has broken, said Tonya Bonitatibus, the Savannah riverkeeper. Concerns center on harmful bacteria contained in animal waste.

The state has nearly 1,200 animal agriculture facilities, most of them large chicken or turkey farms. Some are located in flood plains.

The state also has more than 100 hog farms, according to DHEC’s website. Many are clustered in Dillon, Marion, Horry, Sumter and Clarendon counties, some of the county’s hardest hit by Florence’s rain..

Unlike poultry farms, many hog farms dispose of manure in ponds, or lagoons, that are held back by dams. In North Carolina, which has a substantially larger hog industry than South Carolina, lagoons have flooded or lagoon dams have broken during past hurricanes.

Aside from concerns about farm pollution, riverkeepers also are watching coal ash ponds that lie along river banks. Those include ash ponds on the Wateree River, southeast of Columbia, and on the Waccamaw River at Conway. The ponds are being cleaned out by the utilities that own them, but some contamination remains. Contamination includes arsenic, a pollutant that can make people sick if they are exposed to it.

The state-owned Santee Cooper power company issued a statement Friday saying it was working to secure ash ponds it is responsible for. With record flooding expected on the Waccamaw River, the company said workers have built a temporary dike to protect part of the area that has already been cleaned. They also are pumping water into ash ponds to help relieve pressure on the dikes, company spokeswoman Mollie Gore said in an email.

Tom Clements, an anti-nuclear activist from Columbia., said he’s also concerned about how heavy rains would affect Barnwell County’s low-level nuclear waste landfill, an aging facility that in the past leaked radioactive tritium into groundwater.

Unlike the Pinewood hazardous waste dump, the Barnwell County landfill still is operating, and some of its unlined burial trenches remain open and exposed to rainfall.

“Those could be fully inundated’’ by rain, Clements said. “That means more penetration (into) groundwater, which would be carrying radioactive materials.’’