We've known for a few months that a new running track is being built there, but there's a lot more going in as well, including a multi-use sports field, an ADA-compliant sidewalk, bleacher seating, and new trees.
Ald. Cappleman's website says:
"If you have been by this area near the lakefront trail, you have noticed some construction in this area. The Chicago Park District is adding a new artificial turf field that will host football, soccer, lacrosse and will be surrounded by an 8 lane running track. They will be also adding some shade trees and fencing for this area."
Click on the image for a larger version that shows all the details.