WATERLOO, Iowa (AP) — Officials say heavy rainfall has overwhelmed Waterloo's sewer system, letting untreated sewage reach rivers and streams.

The Waterloo-Cedar Falls Courier says Waterloo Waste Management Services reported three locations where sewage escaped manholes and six more spots where workers bypassed sanitary sewer lines into street drains to relieve pressure and prevent other spills.

Service director Steve Hoambrecker says the untreated wastewater has been heavily diluted, owing to the nearly 8 inches (20 centimeters) of rain in the past week, "minimizing the sanitary concern."

Rain runoff and groundwater are meant to go into storm sewers, while human waste and other contaminants are go into separate sanitary sewer lines. But cracks in sanitary mains and home footing tiles connected to sanitary lines let groundwater infiltrate the sanitary sewer system during heavy rain.

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Information from: Waterloo-Cedar Falls Courier, http://www.wcfcourier.com