The U.S. effort to destroy its chemical weapons and materiel was already well under way when, in 1993, it signed the Chemical Weapons Convention (CWC),1 an international treaty outlawing the production, stockpiling, and use of chemical weapons. The weapons and chemical materiel at five of the nine U.S. storage sites have now been destroyed by robotically opening the munitions, then removing, collecting, and incinerating the chemical agent, and at two other storage sites by hydrolyzing the agent with hot water or caustic. The remaining two sites with chemical munitions and chemical materiel are the Pueblo Chemical Depot (PCD) in Pueblo, Colorado, and the Blue Grass Army Depot (BGAD) in Richmond, Kentucky.
In 1996, in response to local opposition to the use of incineration, the U.S. Congress passed Public Laws 104-201 and 104-208. These laws froze funds for construction of chemical agent destruction facilities at PCD and BGAD and directed the Army to demonstrate at least two alternatives to incineration for the destruction of the agent. Thus, in 1996, a program then called the Assembled Chemical Weapons Assessment (ACWA) program was established to evaluate other means of destroying the chemical agent.
The ACWA program manager asserted early on that stakeholders would have their voice considered in the decision-making process. During the initial phases of the ACWA program, a panel called the Dialogue Group was established to give stakeholders a voice in all decision making. The Dialogue Group included representatives of local citizens, federal, state, and local regulators, the Army, and the National Research Council (NRC). After the technologies had been selected, the Dialogue Group was disbanded in favor of Citizens’ Advisory Commissions (CACs), which were based in Colorado and Kentucky. Both CACs include former members of the Dialogue Group. The ACWA program has resulted in the selection of alternatives to incineration at the two sites and has since June 2003 been referred to by the same acronym, ACWA, but with a slightly different wording: the Assembled Chemical Weapons Alternatives program.
The stockpile at PCD consists of about 800,000 projectiles and mortars, all of which are filled with the chemical agent mustard. The munitions consist of 105-mm and 155-mm artillery shells and 4.2-in. mortars. The total amount of chemical agent is approximately 2,600 tons. Two forms of mustard are included: HD, distilled mustard, with the chemical formula Cl-CH2-CH2-S-CH2-CH2-Cl, and HT, an ether form of HD, (Cl-CH2-CH2-S-CH2-CH2)2O. All the projectiles and three-quarters of the mortars contain HD; the rest of the mortars contain HT. All the munitions and their quantities are listed in Table 1-1.
The facility to destroy the munitions at PCD is called the Pueblo Chemical Agent Destruction Pilot Plant (PCAPP). At the writing of this report, the plant has been constructed and is now completing systemization. Risk reduction and mitigation studies are being conducted concurrent with systemization. Processing of the mustard munitions through the plant is scheduled to begin in September 2015.2 It is expected that it will require between 4 and 5 years to completely destroy the PCD stockpile. The PCAPP process involves hydrolysis of the mustard, followed by biotreatment of the residual, known as hydrolysate, in immobilized cell bioreactors (ICBs), and treatment of the ICB effluent in a brine reduction system (BRS). While destruction of the mustard itself is conducted under the auspices of the CWC, because the hydrolysate contains thiodiglycol (TDG), a Schedule 2 compound3 under
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1 Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction. The treaty entered into force in 1997.
2 The committee learned after report writing had been substantially completed that the operations start date for PCAPP had been reset to before the end of the calendar year 2015.
3 Under the Chemical Weapons Convention, Annex on Chemicals, Schedule 1 chemicals are those that were developed, produced, and stockpiled or used as a chemical weapon, or are chemicals that would pose a high risk to the object and purpose of the Convention by virtue of their high potential for use as a chemical weapon. Schedule 2 chemicals pose a significant risk to the object and purpose of the Convention because they possess lethal or incapacitating toxicity as well as other properties that could enable them
TABLE 1-1 Inventory of Assembled Chemical Weapons at Pueblo Chemical Depot
| Type of Munition | Size of Munition | Agent | Total No. of Munitions | Total Weight of Agent (lb) |
| M104 projectiles | 155 mm | HD | 33,062 | 386,820 |
| M110 projectiles | 155 mm | HD | 266,492 | 3,117,960 |
| M60 cartridges | 105 mm | HD | 383,418 | 1,138,760 |
| M2 mortars | 4.2 in. | HT | 20,384 | 118,220 |
| M2A1 mortars | 4.2 in. | HD | 76,722 | 460,340 |
| Total | 780,078 | 5,222,100 | ||
NOTE: HD, distilled mustard agent; HT, distilled mustard mixed with bis(2-chloroethylthioethyl) ether.
the CWC, the biodegradation process is also subject to CWC oversight. The TDG will be biodegraded within the ICBs.
The PCAPP process is described in Chapter 2 of this report. A subsequent report will address destruction of the stockpile at the BGAD facility, known as the Blue Grass Chemical Agent Destruction Pilot Plant (BGCAPP).
Treatment of the hydrolysate at PCAPP involves biotreatment followed by brine reduction and water recovery. The biotreatment system, including the BRS and a water recovery system (WRS), was extensively reviewed by an NRC committee in 2013 (NRC, 2013). Relevant findings and recommendations from that study are repeated in this report as necessary.
NEED FOR THE PRESENT NRC STUDY
Although biotreatment of toxic chemicals, brine reduction, and water recovery are established technologies, never before have these technologies been combined to treat mustard hydrolysate. And while extensive testing of these systems has been conducted by ACWA in a laboratory setting, the process has never been operated at full scale. The ACWA program managers and the PCAPP facility, including its contractor design, construction, and operations staffs, have every reason to believe that the facility will perform successfully. The NRC committee writing this report has reviewed extensive documentation on the PCAPP process and received two days of briefings from PCAPP staff and also from Colorado regulators, and it agrees that the PCAPP facility should be able to perform successfully. However, because it is a first-of-a-kind application of a combination of technologies to a unique matrix—mustard hydrolysate—there is still a possibility that the biotreatment, brine reduction, or water recovery processes may not perform satisfactorily.
Finding 1-1. The ACWA program managers and the PCAPP facility, including its contractor design, construction, and operations staffs, have every reason to believe that the facility will perform successfully.
Finding 1-2. The NRC committee writing this report agrees that the PCAPP facility should be able to perform successfully. However, because the facility entails a first-of-a-kind application of a combination of technologies to a unique matrix—mustard hydrolysate—the committee also believes that there still exists a possibility that the biotreatment, brine reduction, or water recovery processes may not perform satisfactorily.
For example, the throughput of the ICBs may not match the throughput of the hydrolysate production. As another example, corrosion could lead to frequent repairs that shut down subsequent hydrolysate treatment. If these types of problems occur, then the hydrolysate may have to be collected and stored, and the actual munitions disassembly and mustard hydrolysate production may have to be interrupted until the downstream processes are able to catch up. Occurrences like these could also lead to other issues, such as storage of the hydrolysate for unanticipated long periods of time and idle periods for PCAPP workers.
Chemical weapons have been stored at the PCD for over 60 years, representing a steady-state or even increasing (due, for example, to the potential for the munitions to spring leaks) risk profile for the community; final destruction of these munitions at PCAPP will eliminate the primary risk posed by the munitions. Delays in the destruction process will halt this risk reduction and protract the risk that the community faces. Decisions that might delay PCAPP operations should consider potential impacts to the community, which in addition to protracting the risk associated with storing aging chemical weapons for longer periods of time, might include employee reassignment, furloughs, or even layoffs. Risk-based decision making should balance the new risks against the risk that has long been posed by the stockpile.
In the event that one or more of the hydrolysate treatment systems are shut down, even for a short time, destruction of the primary stockpile at PCD may need to be halted unless
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to be used as a chemical weapon or as a precursor in one of the chemical reactions at the final stage of formation or in the production of a Schedule 1 chemical or another Schedule 2 chemical.
there is an alternative means for treating the hydrolysate. The committee firmly believes that destruction of the stockpile at PCD must continue, because it is destruction of the munitions and the agent that will eliminate the primary risk to the community. Hence, even though the PCAPP facility is expected to perform successfully, it is prudent, even necessary, to establish a backup plan—an alternative to the onsite treatment processes intended for the hydrolysate.
Finding 1-3. Destruction of the munitions and the agent will eliminate the primary risk to the local community. Hence, even though the PCAPP facility is expected to perform successfully, it will be prudent, even necessary, to establish a backup plan—an alternative to the onsite treatment processes intended for the hydrolysate.
One alternative for treatment of the hydrolysate that might be quickly implementable would be to ship the hydrolysate offsite to an existing, prequalified, and fully permitted treatment, storage, and disposal facility (TSDF). The offsite shipment would close the downstream portions of the plant that were constructed to treat the hydrolysate after its formation. Workers associated with these processes might need to be placed on furlough or laid off, which could cause them to seek alternative employment and PCAPP to lose trained staff. This is not the desire of ACWA program staff, the PCAPP contractors, or the local stakeholders.
To study this situation, the ACWA program requested the National Research Council (NRC) to form an ad hoc committee, the Committee on Review Criteria for Successful Treatment of Hydrolysate at the Pueblo and Blue Grass Chemical Agent Destruction Pilot Plants, to assess the process and the potential for offsite transport of the hydrolysate.
Chapter 2 provides information on the composition of the hydrolysate and describes the PCAPP processes for treating it in more detail. Chapter 3 discusses stakeholder concerns. Chapter 4 reviews regulatory considerations at the federal, state, and local levels and addresses requirements of the CWC. Chapter 5 discusses Department of Transportation regulations and identifies risks associated with the offsite shipment of hydrolysate. Chapter 6 establishes criteria for successfully treating the hydrolysate and identifies systemization data that should factor into the criteria and decision process for offsite transport and disposal of the hydrolysate. Chapter 7 discusses failure risks and contingency options as well as the downstream impacts of a decision to ship hydrolysate offsite.
There are also four appendixes. Appendix A contains the statement of task for the committee, Appendix B contains public interest and input documents received by the committee from the Colorado CAC, Appendix C provides biographical sketches of committee members, and Appendix D identifies the committee meetings and locations.
NRC (National Research Council). 2013. Review of Biotreatment, Water Recovery, and Brine Reduction Systems for the Pueblo Chemical Agent Destruction Pilot Plant. Washington, D.C.: The National Academies Press.
