Once every two years, stormwater causes sewage to overflow onto city streets and can cause combined stormwater and untreated wastewater to be discharged into Guemes Channel.
That, according to a memo from the Public Works Department to the City Council, “violates the conditions of the city’s National Pollutant Discharge Elimination System permit.” It last happened on Feb. 4, 2018, according to a Public Works presentation Monday before the council.
The council gave a head nod supporting one of four options presented by Public Works to improve the city’s ability to handle stormwater flows and improve discharges into the channel during heavy rains.
The improvements including increasing the treatment plant’s capacity to better treat combined effluent and stormwater year-round, and installing a new outfall.
The projected cost is about $25 million, which Public Works Director Fred Buckenmeyer said would likely be covered by a bond repaid from the Public Works budget and sewer rates. The project would take three to five years.
Although not a formal vote on the project, the council’s consensus by head nod — Mayor Laurie Gere was away at a Sister Cities event and Councilman Brad Adams was absent — cleared the way for Public Works to proceed with the engineering report for the preferred option.
“There are a number of milestones and decisions and discussions later,” Buckenmeyer said. “Tonight’s consensus would allow us to proceed with the preparation of this final engineering report for this solution. We then would be able to enter the project into our capital facilities plan, and after that we’d be able to begin design and permitting.”
Buckenmeyer said the new outfall would be sufficient to accommodate the city through build-out.
Two existing outfalls would be abandoned — the wastewater treatment plant outfall, which carries treated wastewater to Guemes Channel; and the combined sewer outfall, which carries a mix of stormwater and untreated wastewater to the channel during heavy rains to keep the wastewater treatment plant from being overwhelmed.
The city’s stormwater and wastewater systems are largely separate. Stormwater is discharged directly into surrounding waters and is not treated at the city’s wastewater treatment plant. However, “Areas within the City of Anacortes are served by a partially combined sewer system where both the storm and sanitary sewer systems are joined,” according to the wastewater treatment plant website. Those combined systems — on B Avenue and Q Avenue — have “the potential to allow untreated wastewater combined with stormwater to discharge to Guemes Channel during extreme storm events.”
The wastewater treatment plant has an average daily flow of 1.89 millon gallons per day and is permitted for up to 4.5 million gallons per day, according to a wastewater treatment plant report. During a 32-hour rainstorm Feb. 3-4, 2018, the plant released 1.7 million gallons of overflow into the channel via the combined sewer outfall, according to the report.
Under the new system, stormwater discharging into Guemes Channel would be cleaner. According to the proposed plan, the new outfall would use fine screens to separate solids and debris from flows going into the channel.
“There may be additional primary treatment,” said Eric Bergstrom of HDR, an engineering and environmental sciences firm. “Those are still in negotiation with the Department of Ecology at this time. We’re not certain of the level (of additional treatment).”
Bergstrom pointed out that the new outfall pipe is only part of the solution.
“The pipe doesn’t increase the outfall capacity. You have to be able to get the flow into that. We’re looking what are the best ways to address that,” he said.