Facts: Program Executive Office, Assembled Chemical Weapons Alternatives Closure Terminology

The Program Executive Office, Assembled Chemical Weapons Alternatives, or PEO ACWA, was responsible for the safe and environmentally compliant destruction of the remaining U.S. chemical weapons stockpile stored at the U.S. Army Pueblo Chemical Depot in Colorado and the Blue Grass Army Depot in Kentucky, and is now responsible for the closure of the destruction facilities.

The Pueblo Chemical Agent-Destruction Pilot Plant, or PCAPP, destroyed the stockpile in Colorado and the Blue Grass Chemical Agent-Destruction Pilot Plant, or BGCAPP, destroyed the stockpile in Kentucky, completing stockpile destruction operations by the Chemical Weapons Convention treaty commitment of Sept. 30, 2023.

PEO ACWA will continue to prioritize the safety of the workforce, community and environment throughout the closure process. As PEO ACWA focuses on closure, specific terms and acronyms being used are described below.


Administrative Close-Out: The final step of the closure process, during which any remaining property is dispositioned, contracts and agreements are closed, and real property (land and any remaining infrastructure and buildings) are vacated and are returned to the land owner (U.S. Army).

Airborne Exposure Limit (AEL): Allowable concentration in the air for workplace and general population exposures. AELs include:

  • General Population Limit (GPL): A criterion that is set to protect the general public, including all ages and medical conditions. GPL is the maximum concentration to which members of the general population may be continually exposed to for the following duration and agent:
    • Three continuous years for mustard agents H/HD/HT
    • 24 hours per day for seven days a week for nerve agent GB
    • 24 hours per day for three days a week for nerve agent VX
  • Worker Population Limit (WPL): A time-weighted average for a conventional eight-hour workday and a 40-hour week.
  • Short-Term Exposure Limit (STEL): A 15-minute time-weighted average exposure that should not be exceeded during the workday, even if the 8-hour WPL is not exceeded. Exposures up to STEL should not occur more than once per day for H/HD/HT and VX, and not more than four times per day for GB with at least 60 minutes in between events.
  • Immediately Dangerous to Life or Health (IDLH) value: An atmosphere that poses an immediate threat to life, causes irreversible adverse health effects, or impairs an individual’s ability to escape from a dangerous atmosphere. IDLH values are used to select appropriate personnel protective equipment (PPE) for personnel entering toxic environments and as criteria used to ensure workers can safely escape from a toxic environment in the event of failure of PPE.

Clean for Unrestricted Use: Items, equipment or facility areas that have never been exposed to or contaminated with chemical agent, may have potentially been exposed to chemical agent vapor for short durations, but meet certain monitoring and risk criteria, or have been decontaminated to less than the GPL (see definition above).

Closure: The final phase of a PEO ACWA chemical weapons demilitarization project. It includes workforce draw-down, destruction or disposal of remaining secondary waste, decommissioning of facilities and equipment, decontamination of equipment and facilities, property dispositioning and the close-out of permits and contracts.

Clean Closure: Decontamination or removal of all equipment, systems and areas containing, or contaminated with, hazardous waste (including chemical agent) or hazardous constituents in a manner that is protective of human health and the environment and such that no post-closure care or monitoring is required.

Contaminated: Items, equipment or facility rooms that have been exposed to chemical-agent liquid, vapor or hazardous constituents and have not undergone sufficient decontamination.

Decommissioning: Withdrawal of a facility or equipment from service, followed by decontamination (as applicable) and transition to required end-state configuration to ensure readiness for disposition, demolition or return to the landowner (real property).

Decontamination: The process of making safe any object or area by absorbing, destroying, neutralizing, making harmless or removing the hazardous substance (e.g., chemical agent or other hazardous material) from the object or area.

Demolition: Dismantling, destruction or razing of facilities or equipment for scrap recovery followed by off-site disposition or disposal.

Dismantling: Breaking down equipment or systems into multiple pieces for removal.

Disposition: Process of disposal of government property.

  • Personal Property: Any end item, material, spares or repair parts. Static Detonation Chamber (SDC) units are included in this category
  • Real Property: Land, buildings, utility systems and other infrastructure delineated on the land owner’s real property inventory

End State Memorandum of Understanding: The agreement between PEO ACWA and the U.S. Army installations housing PEO ACWA chemical weapons destruction facilities and offices regarding the end state of real property used by PEO ACWA on each installation and detailing the final configuration of real property returned to the installations after completion of facility and PEO ACWA closure.

Facility Closure Plan: The overarching document guiding the closure process for the chemical weapons destruction facilities including main plant and SDC facilities.

General Population Limits: See Airborne Exposure Limits entry, above.

Hazardous Waste Management Unit: A contiguous area of land in which hazardous waste was placed or managed. This could include a waste pile, waste storage area, incinerator or tank system and associated piping.

Headspace Monitoring: The process of measuring contained off-gassing vapors after a required hold time and temperature conditions from an item in an enclosed, or shrouded, unventilated space.

Immediately Dangerous to Life or Health values: See Airborne Exposure Limits entry, above.

Lay-up: Non-contaminated or contaminated equipment or facilities placed into a holding state for potential later use or disposition.

Monitoring: The continuous or periodic act of taking air samples to determine whether a chemical agent is present and at what concentration.

Occluded Space: Cavity or other space that can potentially trap liquid agent, prevent contact with a decontamination solution, or prevent agent vapors from trapped liquid agent from being detected during monitoring.

Scabbling: A technique used to roughen up surfaces or reduce concrete sections by breaking up and then removing a layer from the top. Scabbling is one of the methods that may be used to eradicate occluded spaces in concrete in contaminated areas of destruction facilities.

Short-Term Exposure Limits: See Airborne Exposure Limits entry, above.

Shrouding/Tenting: Enclosure of an area or equipment to prevent air exchange outside of the enclosed volume. Used for headspace monitoring.

Surety: Standards and programs for the security of the chemical weapons and for the safety and reliability of the personnel working with them. The chemical weapons destruction facilities will remain subject to surety standards until all recoverable liquid agent has been destroyed. At the BGCAPP main plant, all liquid agent drained from munitions and from agent processing equipment (e.g., pumps, piping and vessels) has been destroyed and agent processing equipment has been flushed and the flush destroyed. Destruction of all recoverable agent at BGCAPP will be deemed complete when the last containerized, drained rocket warhead is destroyed in the SDC units and verification activities are complete. At PCAPP, destruction of all recoverable agent was considered complete when all munitions were processed, all agent in agent collection and neutralization tanks was destroyed, agent tanks/lines were flushed and verification activities were complete.

Uncontaminated: Equipment or areas never exposed to liquid or aerosol chemical agent or vapor concentrations exceeding the STEL concentration.

Unrestricted Release: Decontamination condition that allows release to the general public without restriction.

Unventilated Monitoring Test (UMT): A collection of representative air samples captured from a prescribed space in an unventilated condition which is achieved when an enclosed space, such as a room, is isolated from exchanges of exterior sources of air. The test determines if the room has been decontaminated sufficiently to meet decontamination criteria prescribed in the chemical weapons destruction facility’s Resource Conservation and Recovery Act (RCRA) permit. The UMT is sometimes referred to as the milestone when all rooms in the Main Plant or SDC units have achieved the decontamination criteria prescribed in the RCRA permit (there will be a UMT milestone for each of the plants and SDC units).

Vapor Screening Level (VSL): The agent concentration level to which an item is monitored under unventilated conditions to determine the level of cleanliness. The VSLs for chemical agents H, HD, HT, GB, and VX are the results of a single near-real-time monitoring cycle and are based on the STEL concentration independent of exposure duration for each agent.

Worker Population Limits: See Airborne Exposure Limits entry, above.


AEL – Airborne Exposure Limits
BRAC – Base Realignment and Closure
CAA – Clean Air Act
CAC – Citizens’ Advisory Commission (Colorado and Kentucky)
CDCAB – Chemical Destruction Community Advisory Board (Kentucky)
CWC – Chemical Weapons Convention
CWG – Closure Working Group
DLA – Defense Logistics Agency
EPA – U.S. Environmental Protection Agency
GPL – General Population Limit
GSA – General Services Administration
HWMU – Hazardous Waste Management Unit
IDLH – Immediately Dangerous to Life or Health
ISSA – Intra Service Support Agreement
MOA – Memorandum of Agreement
MOU – Memorandum of Understanding
OPCW – Organisation for the Prohibition of Chemical Weapons
RCRA – Resource Conservation and Recovery Act
STEL – Short-Term Exposure Limit
TSCA – Toxic Substances Control Act
UMT – Unventilated Monitoring Test
VSL – Vapor Screening Level
WPL – Worker Protection Limit

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