MSD had to shut down the main for repairs, which led to overflows at manholes elsewhere in the Chesterfield area, including into Bonhomme Creek and Caulks Creek.

St. Louis Water Commissioner Curt Skouby said the city upped chlorine and carbon at its Missouri River intake after learning of the break.

“We saw an increase in bacteria, but it was nothing that we haven’t seen in other times of the year,” he said. “There’s a tremendous amount of dilution on top of everything.”

About 40 million gallons of water per minute were flowing past the city’s plant when the sewer main broke, he said.

MSD said it found a 12-inch gash on the pipe, which was built in 1983 and is designed to last 25 to 50 years. Force mains deteriorate more quickly, LeComb said, because acidic conditions eat away at the iron.

But he said the area, which MSD took over in 1977, also is “something of a problem child” because of how it was constructed and designed. The district has plans to replace the entire main next year for $6.5 million.