In conjunction with the GEM project, the agencies reviewed historic disposal records, probe data and geophysical studies to prioritize areas for larger-scale retrieval.

The Agencies selected Pit 9 for waste retrieval activities in the early 1990s because of its location on the corner of the SDA and a general knowledge of its contents. After better mapping of waste locations based on historic records, the Agencies determined that Pit 4 was likely to contain a greater concentration of plutonium and mobile chemicals so retrieval efforts shifted to this location.

Excavation of a ½-acre plot in Pit 4 began in 2005 under the Accelerated Retrieval Project (ARP). Excavation of a second ½-acre location straddling Pits 4 and 6 began in 2007 and is referred to as ARP II. The ARP I and ARP II projects focus on retrieval of certain waste types likely to contain higher concentrations of transuranic radionuclides, uranium and volatile organic chemicals. These waste types include certain sludges, graphite waste and filters. This approach allows faster retrieval of higher-concentration waste, but leaves less hazardous, less radioactive waste in the Pit.

Waste in Pit 4 is now being removed through a pilot project called "Accelerated Retrieval Project," or "ARP."