This Corrective Action Investigation Plan for Corrective Action Unit (CAU) 552, Area 12 Muckpile and Ponds, Nevada Test Site, Nevada, has been developed in accordance with the Federal Facility Agreement and Consent Order that was agreed to by the State of Nevada, the U.S. Department of Energy, and the U.S. Department of Defense. The general purpose of the investigation is to ensure that adequate data are collected to provide sufficient and reliable information to identify, evaluate, and select technically viable corrective actions. Corrective Action Unit 552 is comprised of the following corrective action site (CAS) in Area 12 of the Nevada Test Site: -12-23-05, Ponds Corrective Action Site 12-23-05 consists of dry ponds adjacent to the G-Tunnel muckpile. One additional CAS, 12-06-04, Muckpile (G-Tunnel Muckpile), was removed from this CAU when it was determined that the muckpile is an active site.