Double-shell tank (DST) waste transfer activities are comprised of DST to DST transfers, DST waste recirculations and decant waste transfers.

  • DST to DST transfers pump the contents of one DST tank to another DST tank to make space or to stage waste in support of retrieval activities, 242-A Evaporator campaigns and waste feed delivery to the Waste Treatment Plant (WTP).
  • DST waste recirculations are conducted to provide for a homogenous solution prior to performing grab samples for chemistry control evaluations, for 242-A Evaporator waste feed candidacy requirements, or to ensure tank chemistry controls are maintained within the Operating Specification Documents (OSDs).
  • Decant waste transfer activities are needed to support the positioning of the DST system for waste feed delivery operations. Decants are performed to make space for receiving DSTs in support of waste retrieval activities.


This map is an example of an Industrial Hygiene monitoring strategy that has been developed, reviewed, and implemented during a 242-A Evaporator campaign. The work planning process includes subject matter experts, HAMTC representatives, and Operations staff.


Vapor Control Zones (VCZ)

An administrative control boundary established where farm COPCs have the potential to exceed a respective action limit (AL) utilizing an appropriate evaluative method (e.g., 95th percentile of sample distribution, maximum individual sample result, etc.). The VCZ boundary is to be identified using a physical barrier and signage.


Vapor Reduction Zones (VRZ)

An administrative notification boundary established to inform personnel of activities that may result in increased vapors or odors not expected to exceed a respective action limit (AL). The VRZ boundary is to be identified using signage.


Action Limit (AL)

The airborne exposure concentration of a chemical contaminant above which exposures will be controlled. If an action level is not established by regulation, an action level is established at 50% of the 8- hour Time Weighted Average (TWA) of the Occupational Exposure Limit.