A report from three environmental groups says coal ash stored at the Big Stone power plant in South Dakota, near the Minnesota border, is polluting groundwater.
The report, from the Environmental Integrity Project, the Sierra Club, and Earthjustice says arsenic, boron, lead, and sulfates exceed state and federal standards in groundwater near the Big Stone plant.
Peter Carrels with the South Dakota Sierra Club said the state isn't doing a good job of monitoring the site.
"We know that the pollution problem extends to the property line, but beyond that the monitoring hasn't been as thorough," Carrels said.
South Dakota officials however are disputing the report. They say heavy metals at the site are at similar levels to average South Dakota soil.
Jim Wendte, with the South Dakota Department of Environment and Natural Resources, said test wells show no statistically significant impacts on groundwater.
"There are some elevated concentrations for some parameters, but those elevated numbers are well within average numbers for South Dakota glacial till," Wendte said.
Wendte said his agency tracks pollution from an old pond that stored water-softener-waste, resulting in high sulfate levels.
Storage of coal ash is currently regulated by individual states; the U.S. Environmental Protection Agency is considering imposing federal rules.
There are 11 coal ash disposal sites in Minnesota, but none were cited in the report.