Wisps of dust rose from the top of the South Avenue garage helix in Rochester, NY on Saturday morning as workers began chipping away at the huge concrete column.

The eight-story cylindrical core at the corner of Broad Street is all that remains of the garage's corkscrew exit ramp that partially collapsed in April 2006. No one was injured.

Demolition should be completed in mid-September. The process involves a track-mounted backhoe with an oversized mechanical arm that will alternate between a 6-inch diameter, pointed-steel pulsating ram to fracture the concrete, and large steel teeth to break it up.

The South Avenue garage opened in 1974. The Police Department's Mounted Patrol and its horses moved into the helix four years later and stayed through 2000.

After the collapse, city officials determined the ramp functioned well without the exterior exit ramp and debated about other uses for the helix, which remained structurally sound. An investigation into the collapse concluded that steel cables within one of the cantilevered ramp sections corroded and weakened.

Discussions continue on whether to build a multi use tower on the site, with levels for office or retail space, parking and residential units. The city is sure enough that a deal will come together with an unnamed private developer that the area will be left as a gravel lot.

"We feel it's close enough we're not going to make a park out of it that is then going to get destroyed," said city engineer Jim McIntosh.

Meanwhile, a garage renovation under way when the ramp collapsed is on schedule and within budget. Work should be done by November 2008. The $18 million price tag covers all post-collapse expenses, additional repairs, plus the original $6 million rehabilitation project. The costs are predominantly paid for with state funds.