Ignoring the thundering jackhammers and the roar of gravel being dumped by the truckload, a crane with a red cab slowly lifted another crumpled piece of metal out of the Mississippi on Friday and turned to set it down on a barge. The river is where the Interstate 35W bridge came to rest, and the river is helping take it away.

Some of it's not going very far. The twist of green metal, and many others like it, are being floated not even a half-mile downstream to a swath of land called Bohemian Flats, just north of the Washington Avenue bridge. Parkland until just a few weeks ago, the flats have become a temporary resting place for the bulky remnants of the 40-year-old bridge.

The former green space is now a place of barges, high chain-link fences, piles of rebar and a lot of mud. It's where the bridge parts that the National Transportation Safety Board wants to study more closely are being stored.

The pieces won't be reassembled, said Terry Williams of the NTSB, and segments that require extensive analysis are being shipped to Washington D.C. He declined to give more specifics about the investigation into the Aug. 1 collapse, which killed 13 people.

Fast, slow, not at all

With the recovery of bodies completed and plans for the replacement bridge being fast-tracked, demolition has accelerated, with different things happening to different portions of the bridge.

The southernmost section, which sits over land, is coming down in more of a hurry -- it didn't collapse, so investigators aren't as interested in it. It's being noisily dismantled and will be trucked away for recycling. The concrete will be ground into aggregate, the steel turned into scrap.

The northern half of the bridge, by contrast, is silent. Much of it gave way, but it isn't believed to be where the collapse started, so investigators are leaving it be. It's lying where it fell, awkwardly draped over the five remaining railroad cars stuck at the scene.

The middle of the bridge is where the dissection is taking place. On Friday, a few dozen workers in fluorescent vests and red life jackets were moving around on boats, barges and a cherry picker as pieces of steel were hauled out and sections of pavement removed. Truck drivers were pouring gravel to build a causeway that will extend most of the way across the river to give heavy equipment easier access.

The center section of the bridge deck, with its orange barrels and spray-paint numbers, has always looked like it's resting on the water, making it easy to forget that there are tons upon tons of steel still in the river.

Crews are hoping to get all the girders out of the barge channel by Sept. 6 so it can be reopened, but they're only moving what the NTSB tells them to, said Donna Lindberg, a spokeswoman for the Minnesota Department of Transportation. She said 80 to 100 workers are at the two sites, with demolition going on from 7 a.m. to 7 p.m., six days a week. A seventh day could be added, she said, depending on progress in the investigation and the construction timetable for the new bridge.

The floodlights that had shone down on the wreckage from the 10th Avenue Bridge were part of the recovery operation and have been removed, she said. She also said MnDOT has been working with other agencies to monitor pollution at the site and has been using booms to contain floating debris.

Workers have also been spraying water to keep the concrete dust down -- no small effort with a nearly 2,000-foot bridge.

Jim Foti • 612-673-4491

Jim Foti • jfoti@startribune.com