One of the last two sites with chemical munitions and chemical materiel is the Pueblo Chemical Depot (PCD) in Pueblo, Colorado. The stockpile at PCD consists of about 800,000 projectiles and mortars, all of which are filled with the chemical agent mustard. Under the direction of the Assembled Chemical Weapons Alternatives (ACWA) program, the Army has constructed the Pueblo Chemical Agent Destruction Pilot Plant (PCAPP)1 to destroy these munitions. The primary technology to be used to destroy the mustard agent at PCAPP is hydrolysis, resulting in a secondary waste stream referred to as hydrolysate.
PCAPP features a process that will be used to treat the hydrolysate and the thiodiglycol (TDG)—a breakdown product of mustard—contained within. The process is a biotreatment technology that uses what are known as immobilized cell bioreactors (ICBs). After biodegradation, the effluent flows to a brine reduction system (BRS), producing a solidified filter cake that is intended to be sent offsite to a permitted hazardous waste disposal facility. Water recovered from the brine reduction system is intended to be recycled back through the plant, thereby reducing the amount of water that is withdrawn from groundwater. These processes will occur within the biotreatment area (BTA) of PCAPP. The entire process is detailed in Chapter 2.
While hydrolysis itself is a proven technology, as is biotreatment, never before have these technologies been combined. Considering the first-of-a-kind nature of the application of this combination of technologies for destruction of the mustard at PCAPP and TDG within the hydrolysate, ACWA program officials have been concerned that the operation may not function as designed, and have been particularly concerned with the back end of the process, biotreatment followed by brine reduction and water recovery. ACWA commissioned a National Research Council (NRC) study, completed in 2013, Review of Biotreatment, Water Recovery, and Brine Reduction Systems for the Pueblo Chemical Agent Destruction Pilot Plant. The authoring committee identified a number of concerns in this report, but, overall, it had no overarching concerns that the process would not work on mustard hydrolysate.
The ACWA program managers and the PCAPP facility, including its contractor design, construction, and operations staffs, believe that the facility will perform successfully. The NRC committee writing this report believes that there is a high probability that the PCAPP facility should be able to perform successfully. However, there is still a possibility that the biotreatment, water recovery, and/or brine reduction processes may not perform satisfactorily.
In the event that one or more of these systems is shut down, even for a short period of time, destruction of the primary stockpile at PCD may need to be halted unless there is sufficient storage capacity for hydrolysate while agent hydrolysis continues, or there is an alternative means for treatment of the hydrolysate. The committee believes that destruction of the stockpile at PCD must continue, because it is destruction of the munitions and the agent that will reduce the primary risk to the local community. Hence, even though the PCAPP facility is expected to be operated successfully, it is prudent, even necessary, to establish a backup plan. Installing additional hydrolysate storage capacity is an option but would require additional regulatory permitting, and there may be a limit to how much or how long hydrolysate can be stored.
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.
1 PCAPP is named a pilot plant because some of the processes used for destroying the agent and munition bodies have not been used, or used in combination with each other, before.
An alternative to onsite hydrolysate treatment that may be quickly implementable would be to ship the hydrolysate offsite to an existing prequalified, permitted treatment, storage, and disposal facility (TSDF). To study this alternative, the ACWA program asked the 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 (referred to in this report as “the committee”), to assess the PCAPP process and the potential for offsite transport of the hydrolysate. The committee’s statement of task can be found in Appendix A.
Key in the offsite decision process is to consider the concerns of the local community. As explained in Chapter 3, the local citizenry in the Pueblo area are represented by a Citizens’ Advisory Commission (CAC), formed in 2003, that is composed of nine members appointed by the state governor. The CAC has been and continues to be the focal point for public discussion of PCAPP issues.
The committee held its first meeting with ACWA and PCAPP representatives in Pueblo in July 2014 to facilitate local attendance. It had purposely scheduled the meeting during a period when the CAC had scheduled one of its public meetings. In this manner, NRC committee members were able to attend the CAC meeting, introduce committee members, provide a brief overview of the study, respond to questions, and emphasize the importance of community input. Equally important, CAC members were invited to join the meetings with ACWA and PCAPP, where they could listen in on the presentations and participate in open discussion. Two members of the CAC, including the chair, attended the 2-day open meetings.
From these interactions, it has become clear to the committee that the CAC and PCAPP staff have developed a sound working relationship. The committee believes that this working relationship will serve as a strong foundation for a credible consultation process should issues arise with operation of the PCAPP and the BTA.
The committee also learned during these interactions that the CAC continues to maintain its long-standing opposition to offsite shipment of hydrolysate. The committee recognizes the concern of the CAC, especially members’ skepticism concerning the need for offsite shipment of hydrolysate, but it also believes that the PCAPP facility and the ACWA community are firmly behind the commitment to make the hydrolysis, biotreatment, and brine reduction processes work. Nevertheless, the committee also believes that a backup plan is needed.
At the same time, it is prudent and even necessary for PCAPP officials and ACWA to maintain discussions with the CAC and put in place an institutional mechanism that would aim to ensure regular, open communication throughout operations and help to avoid the potential for misinterpretation of motives and decisions, thereby enhancing the probability of achieving common program goals, despite different priorities. Such a mechanism would be supplementary to, yet part of, the CAC and would build on the sound relationships that PCAPP and the CAC have worked so hard to develop.
Recommendation 3-1. In consultation with the CAC, ACWA should institutionalize an explicit consultation process that focuses on the potential for offsite shipment. This process should be established immediately and give stakeholders a clearly defined and meaningful role. The consultation process should (1) be supplementary to the more general role of the CAC; (2) provide to the CAC regular updates on the status of operations as they bear on the possible need for offsite shipments; and (3) be explicitly designed to ensure there are no surprises on the part of stakeholders if they are called on to consider offsite shipments.
As discussed in Chapter 4, regulatory requirements for offsite hydrolysate shipment and treatment are complex. Requirements stem from the Resource Conservation and Recovery Act (RCRA), as administered by the Colorado Department of Public Health and Environment (CDPHE), the National Environmental Policy Act (NEPA), and the Pueblo County Board of County Commissioners Certificate of Designation. In addition, the Organisation for the Prohibition of Chemical Weapons (OPCW) has requirements applicable to the treatment of the hydrolysate, whether onsite or offsite.
Should the offsite shipment of hydrolysate become necessary, it is clear that PCAPP’s RCRA permit would need to be modified. Approval of a permit modification might take 3 to 6 months or more. Further, additional NEPA documentation might be needed to support the offsite option, as this option was never fully evaluated in the PCD/PCAPP environmental impact analyses performed earlier in support of the PCAPP technologies. The NEPA documentation process, if necessary, is also time-consuming and may take months, depending on the level of controversy.
Recommendation 4-2. PCAPP should process a permit modification for the RCRA Research and Development and Demonstration (RD&D) permit that would allow for the offsite transport of hydrolysate as a backup plan. The modification application should contemplate a temporary authorization for site preparation, preconstruction, and similar activities while PCAPP is operating under the RD&D permit.
RCRA permit modifications and NEPA documentation that support the backup plan of offsite shipment must be in place as soon as practical, and all regulatory requirements must be identified and prebriefed with the CDPHE, the CAC, ACWA, and Pueblo County, so that should the decision be
made that there is no other option, implementation can be rapid, with no delay for the destruction mission.
One of the primary concerns regarding potential offsite transportation of hydrolysate is the risk of a transportation accident. Chapter 5 summarizes previous offsite shipments of hydrolysate from other chemical demilitarization facilities (Aberdeen Proving Ground, Maryland, and Newport Chemical Depot, Indiana), and offsite shipments of similar agent-associated fluids such as waste liquids from operation of the explosive destruction system. This summary demonstrates that hydrolysate and similar fluids have been shipped offsite without incident many times in the past.
That is not to say that a transportation accident could not occur, however. But it is important to understand that the hazard here is not from the presence of mustard within the hydrolysate; during the hydrolysis process, mustard is reduced to levels that are below the detection limit of sophisticated analytical instruments. And, although the presence of TDG is a concern, the primary hazard during transportation of hydrolysate comes from the caustic nature of the hydrolysate.
PCAPP hydrolysate may or may not be considered a Class 8 (corrosive) material, but for purposes of risk identification, Class 8 is assumed.2 Examples of Class 8 materials are hydrochloric acid, nitric acid, sulfuric acid at a concentration of >51 percent, and solid sodium hydroxide.
The hazards due to hydrolysate exposure are modest compared to exposure to materials such as concentrated sodium hydroxide, a typical Class 8 material, which may be considered a greater hazard. While the hydrolysate risks may be considered moderate, the committee concurs with a previous committee, NRC (2008), which recommended that ACWA perform a quantitative transportation risk assessment for hydrolysate, including a quantitative assessment of the human health consequences of hydrolysate. It should also prepare a prototypical emergency response plan for hydrolysate shipment (NRC, 2008). These documents will help facilitate discussions with the public and regulators about the possible alternative of shipping hydrolysate offsite. As with regulatory documentation, the transportation assessment and emergency response plan should be prepared as a backup plan and be ready to go should it be determined that offsite transport of hydrolysate is needed (NRC, 2008).
CRITERIA FOR SUCCESS FOR PCAPP
Success for PCAPP operations is defined in Chapter 6. The primary criteria for successful treatment of hydrolysate are meeting RCRA permit requirements and ACWA requirements for treatment of the hydrolysate. This includes the production of a filter cake that meets regulatory requirements that the cake contain no free liquids and the production of process water from the BRS that is of good enough quality that it can be recycled to the plant. In addition, the overall schedule for destruction of the munitions at PCAPP must be met.
Chapter 6 sets up a decision process for evaluating treatment alternatives. It includes a number of criteria for evaluating these alternatives, including the offsite option for hydrolysate treatment. A graded evaluation of system risk allows stakeholders to qualitatively rate the potential for overall program success at any point in the project. This type of graded evaluation will facilitate communication between stakeholders and allow them to track and document PCAPP progress in a transparent and consistent way throughout the course of the project. Table S-1 exemplifies a graded scale for success that could be used for the PCAPP project.
Finding 6-4. In its recent white paper on risk reduction and mitigation, PCAPP has done a thorough job of identifying potential failure risks and providing targeted strategies to mitigate these risks in the BTA (PCAPP, 2014). Employing the decision-making framework outlined previously, the overall systemization plan, and the BTA risk reduction
|0||Success is practically certain (very low possibility of project failure): Operations are proceeding as expected. No PCAPP actions needed.|
|1||High likelihood of success (low possibility of project failure): Actions should be taken by PCAPP to prepare ahead of time for implementation of contingencies in the event of failures. For example, PCAPP might begin to prepare permit modifications and planning documents, including building plans for piping and shipping.|
|2||Success is uncertain (moderate possibility of project failure): Actions should be taken to prepare for implementation of contingency operations. For example, PCAPP might begin processing environmental documentation and finalizing contingency plans, purchasing needed materials, and implementing changes to the infrastructure.|
|3||Success is unlikely with current operations (high possibility of failure of the project): Actions are taken to accelerate the implementation of contingency operations. For example, construction of needed facilities is completed as quickly as possible, and environmental approvals are expedited if they have not already been obtained.|
NOTE: WRS, water recovery system.
2 Class 8 hazmat is defined in 49 CFR 173.136 as a liquid or solid that causes (1) full thickness destruction of human skin within a specified period of time or (2) a specified corrosion rate of steel or aluminum.
and mitigation plan provides targeted strategies for PCAPP to mitigate any operational problems that become apparent during surrogate testing and systemization.
FAILURE RISKS AND CONTINGENCY OPTIONS
In Chapter 7, the committee begins with the graded scale for success that it introduced in Chapter 6 and discusses a number of potential failure risks within the BTA at the PCAPP facility. PCAPP itself identified several such sources of possible failure in the BTA along with contingency options in its aforementioned white paper on risk reduction and mitigation. PCAPP’s plan is to troubleshoot the majority of these risks during facility systemization.
The hydrolysate generated by agent neutralization is a unique and complex mixture. While ICBs have been used successfully in the past to treat complex hazardous organic wastes, they have not been used to treat mustard hydrolysate, aside from bench-scale testing by ACWA. Hence, there are a number of technical factors that could lead to incomplete hydrolysate treatment. These include hydrolysate toxicity to microbial biomass, the need for careful pH and temperature control, nutrient and oxygen limitations, biomass buildup and sloughing, start-up and acclimation issues, and release of odorous compounds. The committee believes that to address these factors, which could inhibit efficient ICB operations, PCAPP should develop risk mitigation plans. These plans need to be in place prior to system start-up so that agent neutralization operations are not delayed.
Another potential issue with the BTA is the complexity of the hydrolysate feed. Biodegradation of the hydrolysate has been carried out in a laboratory setting, but it has never been done with ICBs under full-scale operating conditions. To address this, PCAPP plans to test a number of key process variables, identify potential failure points, and determine optimal ways to operate the downstream processes at PCAPP. The culmination of these measures is testing with actual TDG in a surrogate hydrolysate. This testing will be conducted under full-scale conditions, which the committee believes should allow for rapid start-up and steady-state operation of the ICBs when munitions processing begins. Nevertheless, PCAPP should have contingency plans in place prior to start-up, ready to be implemented immediately should ICB operation be suboptimal during the risk reduction and mitigation testing with the surrogate hydrolysate.
Recommendation 7-1. PCAPP should develop contingency plans to mitigate risk in the event that one or more of the above factors inhibits efficient ICB operations. Such plans should be in place prior to system start-up so that agent neutralization operations are not unduly delayed.
The committee believes that some operational strategies could be implemented in the unlikely event of insufficient biotreatment or if operational problems arise. The technical factors leading to insufficient treatment in the ICBs along with the contingency options are summarized in Table S-2. Each factor is also evaluated against the performance criteria described in Chapter 6 and assigned to a performance category based on the overall risk to PCAPP operations.
Similar to the ICBs, there are also failure risks with operation of the WRS and the BRS, and there are also contingency options that may be taken to address these risks. As explained in Chapter 7, downstream from the ICBs, the WRS and BRS will enable PCAPP to recover and recycle most of the process water into munitions processing. The WRS primarily serves as a holding tank where effluent from the ICBs and other processes are collected, mixed, and stored before being transferred to the BRS. Aside from addition of acid and stripping of carbon dioxide, no treatment or processing takes place in the WRS. As a result, failure risks and contingency options are identified only for the BRS.
Technical factors that may lead to insufficient treatment of the ICB effluent include liquid droplet carryover in the evaporator and crystallizer; failure or excessive replacement frequency of the granular activated carbon (GAC) adsorbers; high chloride content leading to corrosion; excessive biomass or organic compounds leading to fouling, foaming, or odors; and excess liquid in the filter cake. PCAPP should develop risk mitigation plans in the event that one or more of the above factors inhibits efficient BRS operations. As with the ICBs, these plans need to be in place prior to system start-up.
Recommendation 7-3. PCAPP should develop contingency plans to mitigate risk in the event that one or more of the above factors inhibit efficient BRS operations. Such plans should be in place prior to system start-up so that agent neutralization operations are not unduly delayed.
If the BRS does not perform as designed, recycling the water within the plant at PCAPP may be problematic. This failure will place much greater strain on the aquifer from which PCAPP withdraws water. Moreover, the effluent from the ICBs will also need to be shipped offsite for treatment and disposal. Because the hydrolysate is diluted eightfold prior to entering the ICBs, the liquid volume leaving the ICBs is much larger than the original hydrolysate volume. Therefore, in the event of BRS failure, the committee believes that it would be prudent to consider shipping undiluted hydrolysate offsite for treatment and disposal rather than continuing to operate the ICBs on-site. This action would minimize the total volume of material that needs to be shipped offsite and it would minimize the fresh water intake by the plant.
The BRS is expected to operate as planned, but there may be some issues that, while serious, could be mitigated and would not result in total BRS failure. The technical factors leading to incomplete treatment in the ICBs, their impacts, and contingency options are summarized in Table S-3. Each factor is also evaluated against the performance criteria
|Technical Factor||Grade||Rationale for Assigned Grade||Contingency Option|
|TDG toxicity||0 to 1||TDG will be diluted; respirometry will identify toxicity limits. Systemization with TDG will verify treatability.||Reduce TDG loading and/or reduce flow rate to the ICBs.|
|Inability to control pH||1 to 2||Hydrolysate pH will be neutralized with H2SO4; acid generated within ICBs will be neutralized with NaOH. Systemization with TDG will verify pH control capability.||Buffer with sodium carbonate as an alternative.|
|Inability to control temperature||0 to 1||Steam injection ports exist for heating reactors during cold weather. No contingency as yet for cooling during hot weather, if needed.||Reduce hydrolysate throughput to accommodate slower kinetics of biodegradation during high summer temperatures.|
|Start-up difficulty/acclimation||1 to 2||Systemization with TDG should facilitate smooth transition to hydrolysate treatment.||Halt start-up to address problems with hydrolysate feed.|
|Nutrient limitations||0 to 1||Urea will be added as a source of N; DAP will be added as a source of P. Precipitation of FePO4 may limit P availability; systemization with TDG will verify P availability.||DAP may be added directly to the process water recirculation line, or higher amounts of DAP may be added to the feed tank.|
|Oxygen limitations||0 to 1||Air will be supplied by coarse bubble diffusers to all ICB chambers to meet oxygen demand of TDG biodegradation. Systemization with TDG will verify need to redistribute influent TDG load or oxygen supply.||If oxygen demand of TDG in first chamber exceeds oxygen supply, the TDG influent can be distributed uniformly across all ICB chambers. The urea and DAP as sources of nutrients both exert an oxygen demand. Switching to nitrate and phosphate salts will eliminate this oxygen demand.|
|Loss/sloughing of biomass solids||1 to 2||Biomass is immobilized in ICBs, so continuous loss of biosolids should be limited; systemization with TDG surrogate will verify biomass retention and potential losses.||Increase retention time in ICBs to ensure sufficient TDG biodegradation.|
|Buildup of biomass solids||1 to 2||Biomass sloughing should occur naturally; systemization with TDG will help verify that solids do not build up to undesirable levels.||Increase retention time in ICBs to reduce the TDG loading rate, which will reduce the amount of biomass accumulation and sloughing.|
|Limited hydrolysate storage capacity||2 to 3||30-day capacity available to store hydrolysate from agent neutralization. If kinetics of biotreatment are inhibited, rate of agent neutralization can be slowed. This is not expected to be a regular occurrence but may happen intermittently.||Reduce rate of agent neutralization as needed. Construct more hydraulic buffer (storage) capacity.|
|Release of malodorous compounds||1 to 2||GAC adsorbers are in place to remove volatile compounds.||Install additional GAC capacity.|
NOTE: DAP, diammonium phosphate.
described in Chapter 6 and assigned to a performance category based on the overall risk to PCAPP operations.
The committee believes that PCAPP has adequately researched potential issues with BTA operations and believes that the risk reduction and mitigation measures to be conducted during systemization will help identify these issues. And while it believes that, overall, PCAPP is well positioned for successful operations, the contingency measures identified above would help to resolve any issues quickly.
OFFSITE SHIPMENT AS A CONTINGENCY OPTION
The committee acknowledges that there are many uncertainties surrounding the start-up and performance of each separate component within the BTA and that one or more contingency options may have to be implemented. Each decision may have to consider a continuum of options, from quick operational tweaks to improve performance (e.g., changing chemicals to maintain pH levels), to more long-term operational changes (e.g., longer retention times) and
|Technical Factor||Grade||Rationale for Assigned Grade||Contingency Options|
|BRS product water quality is acceptable for reuse but does not meet permit requirements.||2 to 3||Product water may not consistently meet RCRA permit requirements.||Initiate obtaining permit modification to adjust the BRS water treatment requirements.|
|Liquid droplet carryover through the entrainment separators.||1 to 2||Liquid droplets in the evaporator could damage compressor. In the crystallizer, they could reduce recycle water quality.||Upgrade de-entrainment devices.|
|Poor performance of GAC adsorbers.||0 to 1||High TOC, suspended solids, or microbial growth on GAC lead to need for backwash due to the large pressure drop across adsorbers or frequent replacement of GAC.||Install additional GAC capacity, standby GAC adsorbers.|
|Corrosion, especially on heat transfer surfaces.||1 to 2||High chloride content and high temperatures could lead to corrosion in crevices and under deposits.||Aggressive corrosion monitoring and deposit removal are required to avoid unexpected failures.|
|Foaming and fouling, especially on heat exchangers.||1 to 2||Biomass carryover from ICB can lead to acid hydrolysis of biomass and solubilization of organic matter; currently unknown how much biomass will be carried over.||Install clarifier after ICBs to remove biomass and other TSS; monitor antiscalant effectiveness and fouling tendencies; add antifoaming agents; increase cleaning frequency.|
|Filter cake with biological activity and organic material.||0 to 1||Biological activity may lead to unacceptable odors.||Include additives (e.g., fly ash or lime) in filter cake to inhibit biological activity.|
|Liquid content of filter cake is too high.||0 to1||Treatment in BRS does not yield a solid product owing to high organic content; drying agents used as additives are insufficient to dry the cake.||Find an alternate TSDF that will accept waste.|
|pH control.||0 to 1||Low pH is required for CO2 stripping in the WRS, and a neutral pH is required for the BRS to minimize the corrosion potential.||Control pH in the WRS with sulfuric acid and control pH in the BRS with NaOH.|
NOTE: TSDF, treatment, storage, and disposal facility; TOC, total organic content; TSS, total suspended solids.
infrastructure changes (e.g., installing a clarifier) to accommodate performance issues, to interim actions while other contingency options are being implemented (e.g., constructing and employing additional hydrolysate storage capacity), to, finally, instituting offsite shipment of hydrolysate.
The committee believes that the optimum outcome is that the existing BTA operates without the need to implement the offsite option. It considers offsite shipment of hydrolysate to be the last resort, the final option on the continuum. However, if offsite shipment of hydrolysate is implemented, one very crucial decision that will need to be made is whether the offsite shipment is temporary or permanent. The committee acknowledges the possibility that once the decision to implement offsite hydrolysate shipment is made, it may be necessary to make that process permanent due to cost, the need for stability, or other considerations. The committee also acknowledges that the fix or set of fixes needed for the BTA might take only a few days, or weeks, or even a month or two, and that it might be possible, after some delay, to start the process again and continue with onsite hydrolysate treatment.
Implementing offsite transport of hydrolysate will affect plant, paper, and people, as discussed in Chapter 7, and the effort to implement offsite transport will be considerable. If offsite transport is implemented as a temporary fix, with the intent of restarting the BTA processes, the effort to switch back to the BTA would also be considerable. Depending on the length of the delay and whether staff furloughs or layoffs have occurred, original staff may no longer be available. Besides, if the BTA processes are restarted, there is no guarantee that the fix will even work, and PCAPP may need to restart offsite shipment again. Still, the committee believes that there may be circumstances under which restarting the BTA processes, after some delay, may be feasible. The committee discussed at length whether a change to offsite shipment could be temporary, or whether this change should be permanent. However, the committee acknowledges that at this time it is impossible to predict the exact circumstances of a failure once the plant enters systemization or actual operations. It therefore concluded that it would make no specific recommendation concerning the exact nature, extent, or permanence of any option,
including implementation of permanent, offsite shipment of hydrolysate.
Recommendation 7-7. To preserve the ability to ship hydrolysate offsite for treatment in the event that offsite shipment is found to be the only viable option, steps should be taken as soon as possible. Examples of such steps include initiating permit modifications; drafting alternative standard operating procedures; preparing transportation risk documentation; designing process safety controls, spill containment, and fall protection for hydrolysate loading facilities; and communicating with stakeholders about if and when this option would be utilized, including how the stakeholders would be involved in the decision process.
NRC (National Research Council). 2008. Review of Secondary Waste Disposal Planning for the Blue Grass and Pueblo Chemical Agent Destruction Plants. Washington, D.C.: The National Academies Press.
PCAPP (Pueblo Chemical Agent Destruction Pilot Plant). 2014. White Paper Bio-Treatment Area Risk Reduction and Mitigation. 24852-30H-BTA-V0001. Rev. 000. April.