The Arsenic Trioxide site is located in Richland and Sargent counties in southeastern North Dakota. It covers 26 townships (about 568 square miles) of sparsely populated farmland with a few small towns, including Lidgerwood, Wyndmere, Milnor and Hankinson. Historical use of arsenic-based grasshopper bait and naturally occurring sources contaminated groundwater in the shallow aquifer with arsenic. Following cleanup, EPA took the site off the Superfund program�s National Priorities List (NPL) in July 1996.