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A rare stormwater tunnel inspection

For the first time in more than a decade, the U.S. Army Corps of Engineers is undertaking the process of drawing down the Lower St. Anthony Pool of the Mississippi River in Minneapolis to investigate its lock and dam and related infrastructure. Barr and the Bassett Creek Watershed Management Commission took advantage of the drawdown to perform a condition survey of the Bassett Creek stormwater tunnel, the outlet of which is normally submerged by the river. The drawdown process took three days to reach a maximum drawdown of twelve feet and then kept the river at that level for two days. Refilling to normal operation will also occur over three days.

To conduct the work safely, Barr closely coordinated with the USACE, Minneapolis Public Works and Fire and Rescue, the Minnesota Department of Transportation, Minneapolis Park & Recreation Board and Rescue Resources, a private confined-space and standby technical rescue team. A crane with a basket and the standby rescue team were positioned at a nearby upstream access shaft 90 feet above the tunnel to provide secondary access and emergency egress. The four-person inspection team was equipped with gas meters, waders, an alarm system, personal flotation devices, harnesses, communication radios, hardhats and lights, and of course, masks due to COVID-19.

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