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Paul L. Hayden / Lake Superior Magazine
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Still under construction during its first test with an April shower, the sanitary sewer overflow tank in Canal Park should eventually be blended with landscaping and a growing roof cap. The tanks location was the most cost effective for handling two trouble areas and uses gravity for collection.
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MSA PROFESSIONAL SERVICES
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It’s not exactly pretty, but when it comes to keeping sewage from reaching Lake Superior, Duluth’s new $20 million tank looks good.
The 8.2 million gallon tank at the edge of the Lakewalk in Canal Park is part of the city’s out-of-court settlement with the U.S. Environmental Protection Agency and Department of Justice to stop sanitary sewer overflows by 2016. The Western Lake Superior Sanitary District (WLSSD) is under the same directives.
The new tank, along with four others that raise the holding capacity by slightly more than 15 million gallons, can “handle a rain event that has the odds of occurring once every 25 years,” says Eric Shaffer, Duluth’s chief utilities engineer. That essentially means a downpour of 2 inches in a single hour.
Past problems have arisen whenever the city is drenched in precipitation that overwhelms the sanitary sewage system, causing overflows that go into the lake. Older home sump-pump systems that pump rainwater into the sewage system have contributed and the city has taken steps to have homeowners reroute or disconnect those systems.
The new systems got a work out with a 2- to 3-inch rain in April that occurred over about 12 hours. The Lakewalk tank held back 2.5 million gallons of water. Once in the tank, the water can be pumped into the regular WLSSD system when it has less water to handle.
For now, the city is pleased with the tank, which worked even before being completed. “We were very pleased that we were able to have a big rain event and not spill a single drop into Lake Superior,” Eric says.