Overwhelmed plant dumps sewage during storm

Heavy rains two weeks ago caused the Port Washington wastewater treatment plant to release 3 million gallons of untreated and partially treated sewage into Lake Michigan.

City Engineer Roger Strohm said that the city received more than seven inches of rain on Saturday night and Sunday morning, Aug. 9 and 10, which overwhelmed the sewer system.

“We received more flow than we could handle,” he said, due to rainwater that entered the system through inflow and infiltration.

Inflow is when surface water enters the sewer system through direct connections such as floor drains or sump pumps while infiltration is when groundwater seeps in through leaks and cracks in pipes, joints or manholes.

The plant can handle a maximum 4 million gallons of wastewater a day, Strohm said, but during four hours that night the flow was measured at 15 millions gallons a day.

“We very well may have been receiving more than 15 million gallons,” he added, noting that is the maximum flow measured on the plant’s meter.

The plant typically handles about 1 million gallons a day, Strohm added.

Strohm said the lead operator at the plant was overseeing operations until about 2 a.m., when he headed home.

About 4 a.m., he said, “his phone started blowing up with alarms from the plant.” 

The operator returned, along with the rest of the operations crew, and found that multiple tanks and operations were overflowing, Public Works Director Rob Vanden Noven said.

They opened a bypass channel that leads to the ultraviolet disinfection, where about half the water that was released received some treatment, he said.

However, the flow was too great for the UV processes to handle it all so about half the water did not receive any treatment.

“The guys did what they could,” Strohm said.

Strohm said that the operators tested the water entering the plant and found the suspended solids level was 24 milligrams per liter, less than the 30 milligrams allowed under the city’s permit.

“The sewage was so diluted with water it met our discharge limit,” Strohm said. 

While the water wasn’t disinfected, he said, most of the bacteria it contains dies when exposed to sunlight.

Strohm said the city reported the bypassing to the Department of Natural Resources but has not heard anything from the state. 

He added that he does not expect the state will require any corrective measures, noting many lakefront communities experienced the same issues.

“It’s an extreme event,” he said.

But, Strohm added, one of the city’s long-term goals has been to reduce the amount of water entering the sewer system through inflow and infiltration, efforts that will likely be bolstered by the bypassing.