MEXICO CITY (AP) — Mexico is pursuing a criminal complaint against the country’s biggest copper producer seeking to force a new remediation effort for a toxic mine spill in the northern state of Sonora nine years ago, an environmental official said Thursday.

The complaint, which was filed in August but announced only on Thursday, centers on remediation funding for eight polluted townships in Sonora.

Mining company Grupo Mexico closed its remediation fund in 2017, arguing that it had met legal requirements.

The government contends that was premature and is asking the courts to order a new fund be established.

“The people, the environment are still contaminated and there are sick people,” said María Luisa Albores González, who heads the government’s Environment Department.

Albores described the August 2014 mine spill as “the most serious environmental disaster in the history of metal mining in Mexico.” Ten million gallons (40 million liters) of acidified copper sulfate flooded from a waste reservoir at Grupo Mexico’s Buenavista mine into the Sonora and Bacanuchi rivers.

The accident, about 62 miles (100 kilometers) from the city of Nogales, has left “alarming” levels of air, water and soil pollution across 94 square miles (250 square kilometers) to this day, according to a government report last month.

Grupo Mexico promised to establish 36 water treatment stations, but only 10 were installed and only two of those were finished, Albores said. Of the latter two, the one in the town of Bacan Noche ran for two years and the other in San Rafael de Aires ran for only a month before both ran out of funding, she said.

The company did not respond to an emailed request for comment on Albores’ announcement, but in a statement it issued last week in response to the government study it said its remediation efforts were successful and legally complete.

The government study “lacks any causal link with the event that occurred in 2014,” the statement said. “They fail to point out other current sources of pollution,” like farm runoff, sewage and other mining, it said,

Albores acknowledged Grupo Mexico’s response speaking to reporters Thursday. “They say: ‘Close the trust, because it has already complied’. It did not comply, it did not fulfill its objective,” she said.

Activists in the affected area were cautiously optimistic after hearing about the government’s legal action. “May there be justice for the people very soon,” said Coralia Paulina Souza Pérez, communications coordinator for local advocacy group PODER.