City water plan update includes main replacement, new wells
The city of Woodburn has completed an update to its water master plan for the next 20 years, from 2017 to 2037.
Major components of the plan address future deficiency in water production, assessing the growth in demand that will arise with Woodburn's development boom and urban growth boundary expansion, and replacement of old water mains.
A critical part of the plan is rehabilitating and replacing the city's wells, which pump groundwater from the Troutdale Aquifer. Two of the city's six wells begin pumping sand out of the aquifer if run at too high a volume, and one well is operating a reduced capacity due to buildup of iron bacteria in screens and pipes. All three will have to be rehabilitated in the future.
Well rehabilitation is not completely effective however, and only returns about 90 percent of a well's capacity. One well continues to diminish in capacity after several rehabilitations and needs to be replaced.
Summer production at all the city's wells is reduced by irrigation wells which also draw water from the aquifer. The city does not know the magnitude of the impact of irrigation wells, and is hiring an outside consultant to assess potential new well sites, according to Public Works Director Eric Liljequist.
Demand for water is expected to increase to more than 4,000 gallons per minute (gpm) by 2037, while well capacity will continue to decrease to less than 2,500 gpm by 2037. The plan predicts that additional wells will be required to address the decline and provide for future growth.
The plan forecasts that while new wells will be necessary, overall the city's storage capacity will be sufficient to provide for the thousands of residential houses being built and industry developing in the city's expanded urban growth boundary.
The city's elevated storage tank, which provides pressure to the water system through gravity, needs some minor repairs. The tank's altitude valve is stuck in the on position and will need to be replaced, while the exterior of the tank needs to be recoated.
The expanded development and industrial area west of Interstate 5 was also taken into account in the plan. The city should have enough water supply to meet consumption needs for businesses and residences west of I-5, but an additional I-5 service crossing will be required to address fire flow demands. Fire flow is the amount of water necessary to provide fire protection throughout a municipal region.
A major cost to the city over the next 20 years will be replacing and repairing water mains. Water main replacement is estimated to cost the city $16,380,000 over the next 20 years, not including associated costs of excavation, dewatering, property easement and acquisition, and specialty construction. Five to 10 percent of the city's water mains are candidates for replacement based on age and condition, according to Liljequist.
Total capital improvements for the water master plan are forecast to be $27,895,000 over the next 20 years, at an annual cost of around $1,454,000 per year.