^In the
Plan of Chicago, Burnham noted that the city was annually disposing of one million cubic feet of "clean" fill by carrying it far out into the lake for dumping, and suggested that it could be used to create many acres of new parkland. Most of it was the spoil removed for new basements and ashes from the coal furnaces of the day, but some of it (particularly for Grant & Burnham Parks) came from the freight tunnels and I think some came from construction of the Sanitary & Ship Canal as well. The last chunk, from Foster to Hollywood, came from excavation for the Congress Superhighway. After the fill was generally in place, they would sluice sand and silt from the lake bottom to fill in the interstices. Being wet, it also helped pack down the landfill. Here's work about the same time on Burnham Park: