Despite the bitter wind, Kim Wasserman showed me around La Villita Park. Occupying 21 acres in the middle of this city’s largest Mexican-American neighborhood, called Little Village, the park used to be a brownfield and illegal dump. Back then, the site leached toxins into hundreds of nearby basements. Sickened residents protested for years. The federal cleanup, finally completed in 2012, became the largest urban Superfund project in America.