The city of Sweet Home will soon accept bids on the fourth phase of its inflow and infiltration reduction project with construction ideally beginning this summer.
Plans for the project include areas across the city where leaking pipes will be repaired at a cost of up to about $6.5 million. The project will include three different parts, which may be included depending on whether the city has enough money to do them, removing from 2.5 to 3 million gallons per day of inflow and infiltration (I&I), officials say.
I&I is water that leaks into the sewer system through deteriorated and cracked sewer pipes or through cross connections to storm drainage. I&I can severely overload the wastewater treatment plant during heavy rains, forcing the city to bypass untreated wastewater into the South Santiam River.
The city needs to reduce I&I by about 5.7 million gallons per day to bring the flows down to levels the wastewater treatment plant can handle, said Public Works Director Mike Adams.
The wastewater treatment plant is rated to handle 7 million gallons per day. The water treatment plant produced an average of 418,000 gallons per day during February.
During the last overflow, on March 28, the wastewater treatment plant handled a flow of 8.78 million gallons per day before the bypass started, said Adams said. During that weather system, the city’s rain gauge showed 1.03 inches of rain on March 28, 1.13 on March 29 and .9 on March 30.
That was the first bypass since December 2007, Adams said.
The city is past its Jan. 1 deadline, set by an agreement with the Oregon Department of Environmental Quality, to eliminate bypasses during five-year rain events. Under the agreement, the city could not be fined for wastewater bypasses.
A request to extend the deadline is under consideration by the DEQ.
Brown and Caldwell Environmental Engineers and Consultants is drawing up the plans for the fourth phase of the I&I reduction project.
The project will include some areas included in previous phases. Areas with previous lateral work will include main lines while areas with previous work on the mains will include laterals.
In the first three phases, the city replaced and repaired sewer mains and private laterals, reducing overall I&I flows from 22 million gallons per day to about 12.7 million gallons per day, Adams said. If a major source of I&I cannot be located, following the fourth phase, the city will need to improve the treatment plant.
Money will be better spent in the plant than the sewer system, Adams said, mainly to bring the city into compliance with the DEQ requirement to handle the remaining 3 million gallons per day quickly enough.
The city could still spend another $10 million in the collection system, Adams said, but it would take even longer to reduce the I&I levels to meet the requirement.
“It gets us into compliance,” Adams said. “It will not fix the I&I problem.”
He added that some I&I work will be necessary to keep the wastewater plant functioning properly.
“We will still have to do repairs in the system to do I&I removal,” Adams said. “If ignored again, it’ll deteriorate.”