WASHINGTON  – Environmental watchdogs say the power industry’s own data show widespread groundwater contamination near sites storing coal ash, a toxic byproduct of burning coal to generate electricity.

Groundwater monitoring wells near coal ash storage sites used by 265 coal power plants reveal unsafe levels of arsenic, lithium and other pollutants in most of them, according to an assessment by the Environmental Integrity Project, Earthjustice and other environmental groups being released Monday.

The report, which provides the most comprehensive look yet at the potential hazards from coal ash ponds and landfills, makes use of groundwater monitoring data that companies are required to disclose under a 2015, Obama-era regulation that the Trump administration has weakened.

“Coal plants are poisoning groundwater nearly everywhere they operate,” said Earthjustice senior counsel Lisa Evans. “This is a wake-up call for the nation.”

Each year, US power plants produce about 100-million tons of coal ash, generally stashing it in landfills and disposal ponds. Although the overall toxicity of coal ash has long been debated, it generally contains arsenic, mercury, lead, chromium and other substances that can cause irreversible brain damage, cancer and other serious health problems.

Occasional ruptures have sent toxic slurry surging into rivers and, in some cases, even smothering homes. Last year, floodwaters from Hurricane Florence overwhelmed a storage site near Wilmington, North Carolina.

But the new report underscores the risk of groundwater contamination even in the absence of a spill or emergency. Unsafe levels of coal-ash chemicals were documented in groundwater near storage sites used by 91% of the power plants examined.

According to the assessment, unsafe groundwater levels of arsenic, a neurotoxin that even at non-lethal levels can impair the brain of a developing child and cause cancer, were recorded near sites used by 52% of the plants examined. The reported data also showed groundwater near coal ash sites used by 60% of the plants had unsafe levels of lithium, a chemical that can cause nerve damage.

The report cites particularly high levels of contamination near the San Miguel Power Plant south of San Antonio, Texas; near Duke Energy Corp.’s Allen Steam Station in Belmont, North Carolina; and at the Brandywine landfill in Maryland, 19 miles southeast of Washington.

More than 550 individual coal ash ponds and landfills were covered by the analysis of 4 600 monitoring wells used to sample groundwater. But it doesn’t include information about sites tied to roughly a quarter of the nation’s coal-fired power plants, where disclosure requirements have been waived or extended.

And the federal monitoring requirements don’t apply at all to older, closed coal ash dumps that no longer accept new material -- a vulnerability environmentalists say should be addressed.

While the analysis factored in naturally occurring levels of the compounds, it’s possible some contamination came from other sources.

According to the Environmental Integrity Project, fewer than 5% of coal ash waste ponds have waterproof liners to keep material from seeping into aquifers. And some 59% were built beneath the water table or within five feet of it, the group said.

The new data provide convincing evidence the US should be moving to enact stronger protections, said Abel Russ, the lead author of the report. But instead, he said, the Environmental Protection Agency has been moving in the other direction.

Under President Donald Trump, the agency revised the 2015 requirements so that industry would have more time to stash coal ash in unlined ponds and other sites. The EPA’s changes effectively added at least a year of usable life to some existing ash ponds while also giving utilities and states more flexibility in deciding when they have to be cleaned up.

Under the EPA changes, state regulators also can suspend groundwater monitoring mandates for some coal ash disposal sites and are empowered to certify whether the facilities are adequate.