By Steve Frandzel
By analyzing average daily water flow rates through the Corvallis sewer system and the length of time that pumping stations operated, Mathew Palmer and his Expo project team determined that large volumes of excess water is infiltrating the system through cracks and fissures in underground pipes.

“Whenever it rains a lot, water seeps into the sewer system through these cracks,” explained Palmer, who is graduating with a degree in chemical engineering. “That means the pumping stations have to work longer, and that costs Corvallis money that could be spent on other things.”

The team found that operating the city’s pumping stations to pump out the excess water cost $3,200 annually, and that covered just three of Corvallis’ 19 drainage basins. While that’s not an excessively high amount, Palmer noted other considerations. For example, if pumping stations are overtaxed regularly during the rainy season, the overflow waste would be directly discharged into nearby rivers, and costly additions or modifications to the wastewater treatment plant might be needed.

Right now, the precise location of major intrusions can’t be precisely identified, but Palmer predicts methods to do so will be developed soon. “That’s the ideal, but that level of precision is still a few years away,” he said.

For the short term, the team isn’t too concerned, added team member Aasya Moussaoa, who also is receiving a degree in chemical engineering. “But the scope of the intrusion could increase a lot over the next decade, and that’s when these costs really start to add up,” she said. “When Corvallis considers expanding its wastewater treatment plant to handle increasing capacity, the city might instead determine that it’s more economically feasible to fix these pipes rather than to expand the plant.”

Other team members:
Sam Fusick, chemical engineering