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Repair workers began installing a new, wooden pedestrian and bicycle path across the Highway 43 bridge last week, and expect the span to be finished sometime this week, with the fencing to be erected sometime the week after.
The walkway, which will consist of timber pretreated with petroleum-based creosote, which brought questions from some area people as to whether it was a good choice. Exposure to creosote has been found to cause respiratory tract irritation, while consuming large amounts of the substance has been found to have caused problems from skin irritation to death, according to the U.S. Department of Health and Human Services Agency for Toxic Substances & Disease Registry. The International Agency for Research on Cancer has determined that coal tar creosote is “probably carcinogenic to humans,”and the U.S. Environmental Protection Agency has found the substance a “probable human carcinogen.”
But the Minnesota Department of Transportation (Mn/DOT) has said it’s mitigated much of any risk because the wood has been weathered, and that most of the creosote treatment has already washed off. Mn/DOT spokeswoman Kristine Hernandez said that the wood planks have been used for other temporary bridge decking in other districts for over 18 months, and that the “largest amount of creosote washes off the wood in the first 12-18 months of its life cycle,” and that this wood has been in service longer than 18 months.
Hernandez said that Mn/DOT prefers creosote over metal-based treated wood when it’s near bodies of water, and that it currently considers creosote as the best option for such treated wood. “One of the reasons for the preference is that creosote is petroleum-based so that it is biodegradable,” she said. She said that Mn/DOT’s office of Environmental Services and the Bridge Office in St. Paul have approved the materials.
The work is expected to be completed mid-October, as contractors are also working to paint gusset plates to help prevent corrosion during its final days. The bridge replacement, scheduled for 2014, will cost between $175 million and $250 million. Current repair work will cost just over $1 million.
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