(CBS) — Lollapalooza is underway in Grant Park, and the president of the Grant Park Conservancy says the evolution of the 3-day event has reached the point where the park needs the event as much as the event needs the park.

Lollapalooza, says onetime skeptic Bob O’Neill, has become one the of the best rock concert public-private partnerships in the world.

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For about two decades, O’Neill has worked to improve Grant Park, known as Chicago’s front yard.  Ten years ago, he says, when the event came to Chicago, he could not have envisioned what the event has done for Grant Park and other parks.

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The event’s organizers not only pay to repair what gets damaged, but also finance new gardens and trees and other projects in Grant Park and other neighborhood parks, he says.

Grant Park looks as good as it does today because of Lollapalooza. And the infusion of cash into neighborhood parks — $2 million this year — has meant all kinds of improvements that could not have been made without the festival.

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O’Neill says economic impact to the city is about $100 million a year. That’s $1 billion over the 10 years Lollapalooza has been in Chicago.