It should take less chlorine to sanitize city water and there should be fewer byproducts from that disinfection process once a roughly $15.6 million pretreatment system is added to the water treatment plant.
The new process will use millions of tiny air bubbles to float debris to the top of incoming water so as much material as possible can be skimmed off before the water enters the existing filtration system.
Bellingham will be the first city in Washington state to install the pretreatment, known as dissolved air flotation, for drinking water, said Eric Johnston, assistant director of Bellingham Public Works. The process is typically installed at wastewater treatment plants to float a very different type of debris out of water not intended for drinking.
The year-and-a-half-long construction and installation at the treatment plant in Whatcom Falls Park is expected to start this summer, with the system ready to use in 2018.
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Why install pretreatment?
It’s important to install such a system to pull out organics – things like algae, plants and other living or once-living items found in Lake Whatcom – that can clog filters, Johnston said.
In simple terms, the existing system works much like a giant Brita filter: Water comes in from the lake and is poured through carbon and sand to filter out debris and impurities.
With pretreatment, the giant filters will last longer before they need to be back-washed to clear out debris, said Bill Evans, chief operator of the water treatment plant.
After going through the filters, the water moves into a treatment tank where chlorine is added to sanitize it, and after all that, soda ash is added to make the water less corrosive to prevent lead leaching from fixtures and other elements in the water distribution system.
Filtering out even more material before that process will further reduce the amount of chlorine the city has to use, Johnston said.
That’s big news, because using chlorine to disinfect water can create byproducts that some studies have linked with health risks.
The city has seen an increase in those byproducts since the 1990s, partly because of a federal requirement for treating surface water that took effect in 1995, Johnston said. The rule required the city to increase the amount of time drinking water is in contact with the disinfectant before it is distributed to peoples’ homes.
We have a very high standard for our drinking water, for water coming out of the tap, and this project will help preserve and ensure that for many many years to come.
Eric Johnston, assistant director of Bellingham Public Works
“While a longer contact time is necessary to protect public health it was anticipated that the (disinfection byproduct) quantities would increase,” Johnston wrote in an email.
Also playing into the formation of byproducts is a reduction in how much water people use, Johnston said. As less water is used, there is the potential for water to spend more time sitting in the tank with the chlorine while waiting to be distributed.
The levels of those byproducts in Bellingham water are still below the maximum contaminant levels set by the Environmental Protection Agency, according to tests conducted throughout 2015.
Groups who have heard about the plan for the new system have asked, why not just protect the lake? Johnston said.
Reducing phosphorous and other runoff into the lake can reduce plants and algae from growing out of control.
“That’s a very valid concern, but I think both things need to happen,” Johnston told City Council members in an update April 18. “We have a very high standard for our drinking water, for water coming out of the tap, and this project will help preserve and ensure that for many, many years to come.”
The pretreatment, existing treatment plant, and the Lake Whatcom Management Plan are all necessary to keep drinking water safe and compliant with regulations, Johnston said.
No more chlorine gas
Part of the upgrade will include switching from chlorine gas – which currently has to be trucked in and poses a serious and deadly safety risk if anything were to ever leak – to chlorine salt, which can be produced on site.
If you have an accident with salt, you get salt on the road. If a chlorine gas truck spills, you kill somebody.
Eric Johnston on switching from chlorine gas to chlorine salt to disinfect drinking water
“Salt is much safer — there is no impact to the customer and it’s safer for the operators and for the public,” Johnston said.
Using the salt, sodium hypochlorite, is more expensive than using gas, but the city wants to balance the risks and minimize the chances of something catastrophic, Johnston said.
“If you have an accident with salt, you get salt on the road,” Johnston said. “If a chlorine gas truck spills, you kill somebody. We’re willing to spend more to reduce that risk. It was an easy choice.”
Timeline and impacts
The project goes out to bid in May, and construction should start later this summer.
Part of the trail near the treatment plant fence will be closed for the 18-month construction period, and a new trail connector eventually will be installed that won’t require walking on the road to get to the main portion of Whatcom Falls Park .
The project is one of the city’s first to incorporate a 1 percent for the arts requirement that City Council passed in May 2015. The requirement has the city set aside funds equal to 1 percent of capital projects that cost at least $2 million to be used to integrate artwork into the designs. The artwork will be designed over the next year.
The city’s water customers already have been paying for the project for a few years: The more than $15.6 million project was included with a list of other projects when staff calculated utility rates that started going up a few years ago and will continue to increase through 2018, said Ted Carlson, director of Public Works.