Chicago covers alleys with special concrete that cleans polluted rain runoff . They cleanse the water of pollutants from cars and lawns . Microbes in concrete eat materials such as fertilizer and oil . This avoids having to clean Chicago 's massive sewer system . Unique concrete also helps to keep Chicago cooler on sunny days .
Chicago covers alleys with special concrete that cleans polluted rain runoff . Microbes in concrete eat materials such as fertilizer and oil . This avoids having to clean Chicago 's massive sewer system . Unique concrete also helps to keep Chicago cooler on sunny days .