limit and 1,602 had high amounts of solids (heels).1 At the time this report was prepared, the committee had no definitive information on the mercury content in mustard agent munitions.

Fewer samples have been taken of the heels than of the liquid-phase agent. In general, despite significant scatter in the data, high concentrations of mercury in liquid-phase agent suggest even higher mercury concentrations in the accompanying heel. When the amount of the mercury in the heels of 96 ton containers was measured, 18 of them averaged mercury levels of 2,440 mg/kg (2,440 parts per million (ppmw)), while the average concentration of mercury in liquid-phase agent was 22 ppmw. CMA believes that many munitions and ton containers contain some heel (UDEQ, 2008). Based on historical documentation, the mercury contamination in ton containers at UMCDF should be similar to that at TOCDF. Information on the mercury content of munitions at UMCDF as well as HD/HT stockpiles at ANCDF and PBCDF was not available when this report was being prepared.

Destruction of the heel portion of HD/HT requires special processing because it is generally too viscous to be extracted from the containers or munitions by simply pumping or draining. Also, early test burns of containers with large heels revealed that boiling over of the contents was a problem.2 TOCDF is permitted to destroy ton containers holding up to 632 lb heel in the MPF, but it has set a more conservative upper limit of 550 lb per container.3 Also, it has developed a special procedure for handling ton containers with heels exceeding this limit—namely, it mobilizes and dissolves the heel by flushing with jets of hot water. Then the rinsate is transferred to empty ton containers, which are treated in the MPF. This flushing process completely dissolves the heel. UMCDF is adopting the same processes to identify and flush ton containers having a high content of heel and to transfer the resultant rinsate into transfer ton containers.

FATE OF MERCURY WITHIN THERMAL DESTRUCTION PROCESSES AT CHEMICAL AGENT DISPOSAL FACILITIES

Given the diverse uses of activated carbon at chemical agent disposal facilities and the focus of this report on disposal options for activated carbon from these facilities, it is important to understand that the adsorption of mercury and the adsorption of agent onto activated carbons occur in physically different carbon filter units in separate locations during HD/HT thermal destruction. There is virtually no opportunity for both mercury and agent to be adsorbed onto the same carbon bed during normal operations at chemical agent disposal facilities.

As shown in Table 2-1, activated carbon is expected to be exposed to agent when the latter volatilizes into the ambient air during disassembly and preprocessing of munitions and ton containers in Level A areas. This contaminated air flows through the heating, ventilation, and air conditioning (HVAC) systems of the munitions demilitarization building (MDB) to the HVAC filter units, where the agent is captured.

However, no mercury is expected in the MDB HVAC air. Although the ton containers will be opened to the atmosphere in the MDB rooms, the volatilization of elemental mercury will be negligible. The tendency of a liquid to evaporate at a specified temperature depends on its vapor pressure at that temperature. The vapor pressure of elemental mercury is 2.47 × 104 kPa at 27°C. Any mercury salts would be insoluble or ionized in solution. Thus, the low vapor pressure of elemental mercury and the nonvolatility of ionic mercury salts in solution virtually eliminate the possibility that the MDB HVAC air would contain mercury in concentrations of any significance with respect to human health and safety, nor would the activated carbon in the MDB HVAC system filters be exposed to mercury over the duration of the mustard agent disposal campaign to an extent that would be of regulatory concern with respect to mercury.

No agent is expected to be found on the PFS carbons because in normal operation, the two-stage design of the LIC, MPF, and DFS provides a more than sufficient time-temperature history for the constituent elements of mustard agent—hydrogen, carbon, sulfur, and chlorine—to be fully converted to common gaseous combustion products such as HCl, SOx, NOx, H2O, and CO2. Because HCl and SO2 are soluble in aqueous solu-

1

 Personal communication between Gary McCloskey, TOCDF General Manager, URS Corporation, EG&G Division, and Robert Beaudet, committee chair, March 4, 2009.

2

 Information gathered from committee site visit to TOCDF, September 4, 2008.

3

 Information gathered from committee site visit to TOCDF, September 4, 2008.



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