This article was published on: 10/30/13 12:00 AM
The best option for Bend to treat the water from Bridge Creek is membrane filtration, not ultraviolet light.
This has been a debate for years in Bend. The Bend City Council is getting close to making a decision.
Bend gets about half its water from a surface water intake on Bridge Creek. The other half comes from wells.
The federal government requires filtration for surface water systems to protect the public from nasty things in the water that can make people sick, such as cryptosporidium.
Both membrane filtration and ultraviolet light are perfectly capable of treating the water.
Membrane filtration is basically like a coffee filter. It’s a physical barrier to keep the bad stuff out of the water.
Ultraviolet zaps the water with light, scrambling the DNA of the things in the water rendering it harmless.
One issue is that the water Bend gets from Bridge Creek sometimes has high levels of particles in the water — turbidity. When turbidity levels are high enough, UV can’t penetrate the water well enough to be effective.
Other communities, such as Baker City, have opted for UV filtration. But Baker City has 11 intake points for its water supply. Bend has one diversion point at Bridge Creek. That means if there is a problem with turbidity, Baker City can switch around its diversion point. Bend cannot.
The most severe risk to the Bridge Creek Watershed is fire.
Membrane filtration might enable Bend to continue using water from Bridge Creek in the event of a fire, which can cause high levels of turbidity. Pall Corp. says its membrane filtration system for Bend will operate for 10 years and treat water with very high turbidity levels. The actual filters may have to be replaced after those 10 years. That should protect Bend from many extreme events.
With UV, Bend would have to stop relying on Bridge Creek at much lower levels of turbidity and use wells.
The option of UV and adding wells has advantages, too.
Bend will likely need to build more wells in the future to serve any increased demand for water. Using more wells leaves more water in-stream for wildlife. Well water is not currently required to meet the same treatment standards as surface water.
A membrane would also be more expensive than UV. The city says that an average customer’s bill, membrane will cost about $2 more a month than ultraviolet.
But the $2 more a month is worth it.
It provides more certainty that Bend will be able to have access to two sources of water. That flexibility could be important as regulation and the environment change.
It also provides more certainty that the city will get something out of its $24 million investment in a new Bridge Creek pipeline and intake.
The council should support membrane filtration.