James Baker, manager of the Three Rives Clean Water Plant, said employees discovered a foam-over from one of the treated biosolids tanks early Saturday.
Baker said crews reacted immediately and deployed drain blockers to prevent discharge into storm sewers. An estimated 38 gallons entered into the storm sewer and more than 2,700 gallons spilled around the west side of the Clean Water Plant and Lincoln Avenue.
Crews thoroughly cleaned the street and grounds, Baker said.
Samples were taken from the St. Joseph River on Saturday with results indicating there was no change in water quality between the sampling locations both upstream and downstream from the plant.
Baker said the matter was brought to the attention of the Michigan Department of Environmental Quality.