PORTLAND, Maine (WGAN) Portland Water District officials say nearly 4 million gallons of wastewater spilled into Casco Bay due to a malfunction caused by a power outage last Sunday.

Officials closed down East End Beach that day after a power outage led to a malfunction at the wastewater treatment plant. Water tests showed that the water was safe, and the beach was reopened, but officials were still not certain exactly how much waste spilled into the bay until Friday.

An investigation revealed that a backup generator had failed after the plant lost power, due to multiple bolts that had become loose inside the generator.