the Army for clearing material that was suspected to be agent contaminated.4 What is measured by UMT is the agent in the atmosphere associated with the location being evaluated, which requires that that agent be present in the gas phase. UMT involves enclosing the room or object to be sampled with a plastic barrier that prevents diffusion and allows concentrations to build to the point where the agent can be readily detected by current near-real-time monitoring equipment. The method is designed to protect against airborne exposures to agent, but due to the vapor pressure of the agents and the sensitivity of the analyses, it is also used to infer the presence or absence of liquid agent. UMT, in sampling headspace, can be used for evaluating contamination in many different types of wastes and media. It does not require the time-consuming collection of solid samples and the extractive analyses thereof, which are also subject to uncertainties arising from nonuniform contamination distribution, a feature inherent to closure situations. UMT has been successfully applied in the closure of both the Aberdeen and the Newport facilities (Battelle Memorial Institute, 2010; Parsons, 2009).5,6

Chemical or physical phenomena that limit the volatilization of the agent are a potential limitation of the UMT approach, and occluded spaces are a particular concern in this regard. Any agent occupying occluded spaces (for example, agent trapped in small cracks or sorbed into porous materials) may not volatilize sufficiently for headspace measurements. Occluded spaces can prevent (a) contact of the agent with a decontamination solution; (b) volatilization of agent; and (c) subsequent detection using UMT.

In this chapter, the strengths and weaknesses of both conventional analyses and UMT for monitoring equipment and spaces undergoing closure are considered, with a primary focus on identifying approaches that maximize the utility and effectiveness of UMT during closure. Utilization of physical sampling followed by extractive analysis is also briefly discussed.

Properties of Agents Significant to Closure Situations

The chemical and physical properties of chemical agents affect their toxicity and their detectability. In the context of closure, agent volatility and hydrolysis behavior are the two most significant properties. While all three of the agents processed at the baseline chemical agent disposal facilities are considered semivolatile liquids, the nerve agent GB has a markedly higher vapor pressure (2.9 mm Hg at 25oC), consistent with faster rates of volatilization (Reutter, 1999). In addition, GB has the greatest ability to diffuse through porous or permeable materials, and hence it is less likely to survive for long periods of time on surfaces or in near-surface environments. Mustard is relatively nonvolatile, with a vapor pressure of 0.11 mm Hg at 25ºC. The nerve agent VX has an even lower vapor pressure (only 0.0007 mm Hg at 25ºC) (Reutter, 1999).7 In situations in which mustard or VX fills cracks or diffuses into permeable materials, volatilization may be inhibited, but subsequent disturbances of the system could expose intact agent. This could produce a potential for exposure from volatilization, or more likely from direct dermal contact. Migration or volatilization of mustard or VX from porous or permeable surfaces may not occur.

Chemical agent residues may also become depleted by chemical degradation processes that are principally hydrolysis reactions and that result in significant agent detoxification (with a salient exception of VX as described below). Since the majority of hydrolysis reactions produce degradation products having low toxicity, further discussion is not provided here; additional details can be found in Appendix C. However, VX hydrolysis via P-O bond cleavage is not in this category: this reaction produces S-(N,N-diisopropylaminoethyl) methylphosphonothioic acid (known as EA-2192 in the Army vernacular), which is a compound that retains much of the neurotoxicity of intact VX. Hence, the possible presence of this compound is an ongoing source of concern (Yang et al., 1990; Munro et al., 1999).8 However, concerns related to EA-2192 are reasonably mitigated by the following considerations:

tee by Raj Malhotra, Deputy, Risk Management Directorate, CMA, via email to Nancy Schulte, study director, May 3, 2010.

4

Headspace is the gaseous atmosphere associated with an object normally confined by an enclosure or container.

5

Brian O’Donnell, Chief, PMCSE Secondary Waste and Closure Team, CMA, “CMA Programmatic Closure,” presentation to the committee, January 27, 2010.

6

Jerry Spillane, Closure Engineer, NECDF, “NECDF Closure Lessons Learned,” presentation to the committee, October 20, 2009.

7

In the context of this report, bis-(2-chloroethyl) sulfide, or sulfur mustard, is referred to as H, HD (distilled mustard), or HT (distilled mustard mixed with bis-(2-(2-chloroethylthio)ethyl) ether).

8

The state of Utah requires measurement of EA-2192 to ensure detoxification to closure standards (see Chapter 5).



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement