Chikaskia River Sediments is a superfund site located at Tonkawa Tribal Headquarters And Pow Wow Grounds. 1 Rush Buffalo Road, Tonkawa, OK 74653. The Environmental Protection Agency (EPA) identifies sites such as Chikaskia River Sediments because they pose or had once posed a potential risk to human health and/or the environment due to contamination by one or more hazardous wastes. Chikaskia River Sediments is currently registered as an Active superfund site by the EPA. However, it is not on the NPL (National Priorities List), which means the EPA does not consider it one of the nation's most hazardous waste sites.