Sawyer and four others formed A & E Salvage and began a project of recovering salvage materials from the site of the former Liberty Fibers rayon plant. The site consisted of 300 acres, multiple buildings, and extensive ground piping. As A & E removed the salvage materials, it discovered that many of the pipes and buildings contained RACM, a toxic substance. In the removal process, RACM was not treated or removed properly according to statutory requirements. The federal government stepped in and cleaned up the RACM from the property and sought reimbursement from liable parties. Who is liable for the clean-up costs?