COLUMBIA -- An environmental group has sued a South Carolina utility, saying the company broke state law when it discharged arsenic and other contaminants into a river.

South Carolina Electric & Gas Co. operates a 700-megawatt, coal-fired power plant near Eastover, about 25 miles southeast of Columbia, and stores a coal ash byproduct in earthen lagoons near the Wateree River.

In a lawsuit, filed in federal court Thursday, the Catawba Riverkeeper Foundation said that wells near the ponds have been found to contain arsenic levels of five times the legal limit.

The lawsuit also said the ponds sometimes leak, sending "streams of arsenic-contaminated water out of the riverbank and into the Wateree River."

"For 40 years, these coal ash waste lagoons have been polluting South Carolina's waters," said Frank Holleman, an attorney for the Southern Environmental Law Center, which is helping the foundation with the lawsuit. "They're a disaster waiting to happen, perched on the banks of the Wateree River."

According to federal filings, SCE&G reported that in 2009 it disposed of more than 2.7 million pounds of toxic substances at the Wateree plant, including 3,100 pounds of compounds containing arsenic.

In the lawsuit, the foundation said SCE&G "continues to operate Wateree Station without a permit for its ongoing discharges of arsenic and other contaminants from the coal ash impoundments into waters and groundwaters of the State."

The foundation also said SCE&G signed an agreement with state environmental regulators in 2001 that acknowledged the pollution going into the Wateree River but didn't require that it stop.

Last year, in a private agreement signed with the state, SCE&G said it would remove all ash from the ponds by 2022, a move the foundation said shows that the utility is capable of moving the ash byproducts but doesn't have to do so for a decade.

An SCE&G spokesman said the company already is working to move ash from the ponds to a new landfill, and it closely monitors ground and surface water at the site.