A few years ago, American Canyon’s wastewater treatment plant operators began to question high concentration levels of metals and other compounds in the city’s sewage.

After a four-year investigation, city officials announced Friday a settlement of nearly $7.6 million against AmCan Beverages Inc., a bottling plant owned by the Coca-Cola Company in the Green Island industrial area. By signing the settlement, which includes a $3 million civil penalty, AmCan Beverages admits to no fault.

The settlement came after city investigators, lawyers and employees at the wastewater treatment plant compiled enough documents in the course of their investigation to fill half-a-dozen banker boxes. City Attorney Bill Ross said the city recorded 2,000 alleged city permit violations from January 2005 and September 2007 and November 2007 and May 2008.

City councilmembers on Friday thanked the staff for their efforts.

“This has been a lengthy process,” Mayor Leon Garcia said before the City Council voted unanimously to accept the terms of the settlement. City Councilman Ed West, who was in Reno Friday, voted by phone from his hotel room.

The dispute between the city and the company, which bottles sports drinks and other non-alcoholic beverages on Mezzetta Court, centered on the quality of AmCan Beverages’ sewage — used waters the company sends to the city’s wastewater plant.

AmCan Beverages, the city’s biggest water customer, pre-treats its wastewater before it enters the city’s sewer system.

The city launched an investigation after city sewage showed high pH, and high concentrations of sugars, polymers and metals including zinc and copper, according to the city. From May 2007 to September of that year, the city said it discovered contaminants at levels that interfered with the city’s wastewater treatment process and posed an environmental threat. These levels were much higher than those AmCan Beverages had reported to the city during the same time period, the city said.

City Manager Rich Ramirez praised the staff at the city’s wastewater treatment plant for their persistence.

“They knew something was wrong,” he said. “(And) they stayed with it.”

The settlement money was wired to the city Wednesday, Ramirez said.

Representatives from the Coca-Cola Company’s headquarters in Atlanta visited American Canyon on several occasions, he said.

“Their cooperation was very much appreciated,” Ramirez said.

As part of the settlement, the company agreed to pay three water quality monitors for up to three years.

The city will use $800,000 to pay legal fees, staff time and investigators, with the lion’s share going to the city’s fund for the city’s wastewater and water systems. The city will also use the money to recoup the $66,000 fine state officials imposed on the city in 2006 for violating clean water laws at its wastewater treatment plant.

Coca-Cola spokesman Ray Crockett on Friday said the bottling plant will remain open. Coca-Cola takes great pains to make sure its plants comply with all applicable laws, Crockett said.