Sean C. Morgan
An engineer told the City Council Tuesday, Oct. 8, that the city has reduced as much of its inflow and infiltration problem as it can, cost-effectively, by replacing and repairing sewer lines and laterals.
More work would simply cost more for each additional gallon of inflow and infiltration reduced.
Inflow and infiltration is storm water that leaks into the sewer system through deteriorating pipes or cross connections to storm drainage.
Ron Lee of Brown and Caldwell presented the final flow data for Phase IV of the city’s inflow and infiltration reduction project to the council during its regular meeting on Oct. 8 following a tour of the Wastewater Treatment Plant.
When the city faces heavy rains, during one-in-five-year storms, the Wastewater Treatment Plant can receive some 22.2 million gallons of wastewater per day. The plant is designed to handle a maximum of 7 million gallons per day. During dry weather, it handles just 1 million gallons per day, according to Brown and Caldwell’s 2001-02 Facility Plan.
When the plant receives more water than it can handle, operators must bypass untreated wastewater, which enters the South Santiam River. The Oregon Department of Environmental Quality may fine cities for bypassing untreated wastewater. Under an agreement with the DEQ, the city pledged to reduce I&I flows while the DEQ would not fine the city for bypassing.
The city needed to reduce I&I by at least 15 million gallons per day, based on a one-in-five-year storm, and it went to work on the sewer collection system, including both sewer mains and private laterals, each phase followed by additional monitoring.
Following Phase I and Phase II, the city had reduced its I&I flow to 15.8 million gallons per day, based on a one-in-five-year storm. By the end of Phase III, flows were reduced to 13.2 million gallons per day. Following the end of Phase IV last year, flows were down to 11.5 million gallons per day, which leaves the city to reduce flows by another 4.5 million gallons per day.
So far, the city has spent $15 million, including $12 million in construction costs, primarily funded by low-interest and no-interest loans from the state, Lee said. The projects replaced and repaired 35 percent of sewer mains and 30 percent of private laterals. About 7 percent of the system remains in “poor” condition, compared to 25 percent of the system prior to Phase I.
The project cost 47 cents per gallon of reduction in Phase I and Phase II, Lee said. Phase III reductions cost $1.41 per gallon of reduction, and Phase IV cost $2.86 per gallon of reduction.
“We’re losing our cost effectiveness as we move forward out into the system,” Lee said. Now, it’s time to look at the Wastewater Treatment Plant and Facility Plan to see if it can be more cost effective to improve the plant.
The plan will look ahead 20 years and address the estimated need at that time, said Catherine Dummer of Brown and Caldwell, which is developing the new Facility Plan.
Brown and Caldwell has already noted several areas where the plant could be improved.
Among the improvements, the plant has no measurement of influent, Dummer said. The openings in the screens at the entrance to the aeration basin, the first step in the treatment process, are too large, allowing rags and other debris through. Flows from the aeration basin to the three clarifiers are uneven.
The holding tank for solids treatment and disposal is small, requiring frequent treatment; and the belt filter press, used to finish the solids treatment, needs improvement, she said. Landfill disposal is expensive.
She suggested the city may be able to use the solid waste for land application on farms.
That’s something the city used to do, said Public Works Director Mike Adams. Increasing regulatory costs prompted the farmer who used the sludge to stop.
“We’ll do a cost analysis of these (options),” Dummer said. “It might not pencil out.”
Dummer also noted the plant has hydraulic capacity limitations between the filtration system and chlorination steps.
As part of the Facility Plan, Brown and Caldwell will present recommendations to the City Council for the Wastewater Treatment Plant. In the meantime, the city will attempt to find funding and work on extending its agreement with the DEQ, which ended in 2010. At least one additional public meeting will be held.
The city is gathering financial information to figure out how much it can afford and when it can afford it, Adams said. From there, it can put together a schedule for improvements.
The city has not had any bypasses so far in 2013, and that includes the extra wet September, during which Sweet Home recorded 8.74 inches of rain at the plant, Adams said. The city bypassed twice in March 2012, which had 12.95 inches of rain. That was the last time it did so. It also bypassed in January 2012. Before that, it was December 2010 and January 2011 after three months with a lot of rain.
Present at the meeting were councilors Marybeth Angulo, Craig Fentiman, Mayor Jim Gourley, Bruce Hobbs, Greg Mahler, Scott McKee Jr. and Dave Trask.
In other business, the council:
n Appointed Dennis Dean to the Traffic Safety Committee.
n Appointed Charlene Adams to the Library Board.