The St. Regis Paper Company (St. Regis) Superfund site occupies 125 acres within the exterior boundaries of the Leech Lake Band of Ojibwe (LLBO) Indian Reservation in the city of Cass Lake in Cass County, Minnesota. The St. Regis site is located north of the Chippewa National Forest and west of Pike Bay and Cass Lake.

The St. Regis Paper Company began wood treatment activities at the site in the 1950s while leasing the land from the Great Northern Railroad (now the Burlington Northern Santa Fe (BNSF) Railway Company). Lumber was pressure-treated with creosote, pentachlorophenol (PCP), and copper chromium arsenate. Wastewater from these processes was discharged into a number of disposal ponds located at the site. Between 1957 and 1960, wastewater and sludges were hauled to a pit within the former Cass Lake city dump and burned. The disposal from the ponds occurred almost daily at an estimated rate of 500 gallons per day for a total of 547,500 gallons over the three-year period. From 1960 to 1975, unknown quantities of sludge were hauled to the city dump pit. The pit, containing the ash and unburned residuals, was eventually covered.

EPA placed the St. Regis site on the Superfund National Priorities List in 1984. Groundwater, soil, and sediment on and in the vicinity of the St. Regis site have been contaminated with polycyclic aromatic hydrocarbons (PAHs), heavy metals, and pentachlorophenol (PCP). Dioxins and furans, impurities in PCP, are also chemicals of concern.