As part of a plan to utilize the city's rainwater and recycle it back to lake Michigan, Chicago has been renovating its 13,00 alleys to become permeable surfaces, where rainwater can soak back into the ground. 40 alleys have been redone so far.
"Chicago's 13,000 alleys, which allow rear access to buildings, date back to the 1800s. The 1,900 miles of back alleys ease access for garbage collection, loading and parking."
"They also make up about 3,500 acres of impermeable surface, which has created a big problem."
"Many of the alleys were built without connections to storm sewers. Rainwater puddles on the pavement and can run into buildings, sometimes flooding basements."
"The extreme alley makeover started with the pavement. The alleys are being resurfaced with concrete, asphalt or paving stones that are permeable -- that is, water runs through them like a sieve to the dirt beneath."
"Microbes that thrive on stuff like fertilizer and oil are seeded into the pavement or migrate there naturally. They cleanse the water of pollutants from cars and lawns. The cleaner water makes its way into the groundwater, called an aquifer, and then flows into Lake Michigan."