The Illinois Pollution Control Board (IPCB) has allowed a lawsuit against NRG Energy over groundwater issues to be expanded in light of newly-discovered coal ash ponds near the company's active coal-fired power plants in Illinois.

Coal ash is a toxic byproduct of electricity generation discharged from coal-fired power plants.

The IPCB's ruling issued Thursday means the complaint filed by citizen and environmental groups -- which alleges NRG's Waukegan, Joliet, Romeoville and Pekin coal plants are "causing or contributing to violations of public health protections for groundwater" due to their associated coal ash repositories -- can be amended to include additional coal ash dumps that have recently been identified.

"As more documents were uncovered in litigation, attorneys representing the citizens' groups discovered old ash dumps where Midwest Generation - the previous owners of NRG's coal fleet - has disposed of or stored coal ash waste," reads a news release from the groups behind the lawsuit, including the Sierra Club, the Environmental Law & Policy Center, Prairie Rivers Network and Citizens Against Ruining the Environment. "These previously undisclosed ash dumps are suspected of contributing to significant groundwater pollution at all of NRG's coal plant sites in Illinois."

The lawsuit in question was initially filed shortly after the Illinois Environmental Protection Agency issued violation notices in 2012 for high levels of harmful chemicals found in groundwater near the Waukegan, Joliet, Romeoville and Pekin plants.

Since taking over Midwest Generation's plants last April, NRG has thus far "made no long-term commitment to the communities to ensure full remediation of these sites," according to the organizations.

"[The] decision by the Illinois Pollution Control Board to allow an expanded lawsuit and investigation into NRG's coal ash disposal methods brings us one step closer to making sure local communities and bodies of water around these plants are adequately protected," said Holly Bender, an attorney with the Sierra Club Beyond Coal Campaign. "While NRG asserts that it is building the utility of the future, it is still operating dirty coal plants across Illinois that are discharging toxic waste like a utility of the past. Real commitment to change is needed and we have no time to spare as Illinois' rivers and lakes are at risk."