There was no wastewater treatment facility in Mankato, Minn., in the 1870s, when Laura Ingalls Wilder, who later would write the Little House on the Prairie memoirs, lived in nearby Walnut Grove. But the staff at the Mankato Wastewater Treatment Plant retains the heartland values of pride of place and making do with materials at hand that those books celebrate.A plant upgrade to tertiary treatment in 2000 left mounds of stone rubble just inside the plant entrance. Instead of paying to remove it, the plant staff got creative and built a scenic pond with it. Using an existing tree as
