Sean C. Morgan
The Sweet Home City Council approved a plan to go forward with designing a second inflow and infiltration demonstration project last week.
The city is working on the first right now. The current project will cost about $1.4 million and includes the replacement of main sewer lines along 18th Avenue and in an alley between Long and Main streets from 18th Avenue to 10th Avenue. It also replaces private laterals in three different areas.
The projects are aimed at reducing inflow and infiltration and determining the most cost-effective approach to doing it citywide.
Inflow and infiltration is water that leaks into the sewer system, most often during heavy rain. The city’s waste water treatment plant is designed to handle 7 million gallons per day, but heavy rain can sometimes increase sewer flows to 22 million gallons per day. By contrast, the city typically produces less than 1 million gallons of water per day, meaning most of the returning water comes into the sewer system from other sources.
When the waste water plant is overloaded, untreated waste water bypasses the plant into the South Santiam River. The Department of Environmental Quality has fined the city for bypassing in the past.
Now, the city is working under an agreement with the DEQ to eliminate bypasses by October 2007. To meet the requirements of the agreement, the city will need to replace deteriorating sewer main lines and private laterals or expand the treatment plant.
Expanding the plant to handle all of the flow would cost an estimated $17 million. The demonstration project is aimed at determining whether replacement of sewer mains or private laterals will result in the most reduction in inflow and infiltration.
The second demonstration project will replace lines on the west end of town, around Strawberry Heights and the avenues, which show the biggest problem with inflow and infiltration.
The second project will be used to increase the level of confidence in deciding how to meet the DEQ requirement, by replacing mains or laterals or expanding the treatment plant.
If further sewer system improvements are determined to be a cost-effective part of the city’s compliance program, Public Works Director Mike Adams said, the more work down now, the less required in the future and the more likely the compliance schedule in 2007 can be met.
The second project will show commitment and good faith, Adams said. Possibly, if an extension were needed to the agreement, DEQ might be more inclined to grant it.
The sewer system also has significant structural defects and should be replaced before they collapse, forming sinkholes in the streets, John Holland of consulting firm Brown and Caldwell said.
The city received a $2 million loan from DEQ for the first project. The remaining funds will be used to design the second project and within the project, Adams said. The city would need to find additional funding through grants, loans or other sources.
For each $1 million in construction the city ends up spending, it will cost individual rate payers approximately $2.89 per month.
The city expanded the treatment plant in 1990 from 2 million gallons per day to 7 million gallons per day to deal with the extra flows, but it was not enough.
“I don’t think we can build a plant big enough without replacing lines,” Councilman Craig Fentiman said. If the city just expands the plant again, “we’re in the same boat we were in 1990.”
With the condition of the sewer collection system, Holland said, “you cannot go wrong spending money on the pipes in the west side of town.”