Any individual or company that may have contributed to contamination at a Superfund site. Under CERCLA, PRPs are expected to conduct or pay for site cleanup. In the case of mining-related Superfund sites in western Montana, there are numerous PRPs due to the complexity and geographic spread of the pollution. The largest single PRP in the case of Butte is BP-ARCO, which purchased the Anaconda Company’s mining operations in the 1970s. Another major PRP at the Berkeley Pit site, a part of what the EPA has designated as the greater Butte Mine Flooding Operable Unit (BMFOU), is Montana Resources, Inc., which currently operates the active Continental Pit mine and associated concentrating facilities on the northeast side of Butte.