The United States Environmental Protection Agency (EPA) began investigating the Site in 1997. Releases of hazardous substances occurred at the Site during the course of rail yard activities. Under EPA oversight, Union Pacific Railroad Company (UPRR), the current owner and operator of the railyard, completed a remedial investigation in September 2003 and a feasibility study in September 2004 for the Site. On September 30, 2004, EPA issued two Records of Decision for the Site. The Record of Decision (ROD) for Operable Unit One of the Site provides for capping of contaminated sediments in the 21st Street Pond, preventing further movement of waste into the pond through the construction of a cofferdam and collection drains, removing mobile dense non-aqueous phase liquids from the former Pinstch Gas Plant, monitoring the pond, and implementing institutiona1 controls to prevent use of ground water in the area and to protect the integrity of the cap (ROD for OU1). The Record of Decision for Operable Unit Four of the Site provides for removing the main trunk of the industrial sewer system and associated contaminated soils, flushing any remaining sludges from the branch lines of the industrial sewer system and for monitored natural attenuation to address ground water contamination for chlorinated volatile organic compounds.