RAND Review of UXO Risk Assessment

[Lenny Siegel <lsiegel@cpeo.org>]

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The RAND Corporation has recently published an independent, thoughtful,
and robust analysis of approaches to risk evaluation at sites known or
suspected to contain unexploded ordnance. UNEXPLODED ORDNANCE: A
CRITICAL REVIEW OF RISK ASSESSMENT METHODS, by Jacqueline MacDonald et
al, 2004, is a must read for anyone interested in setting priorities or
selecting remedies in the area of munitions response. 

For ordering information or an on-line version, see
http://www.rand.org/publications/MR/MR1674/.

The RAND team believes that existing methods provide a solid basis for
priority setting and assessing toxic risks, but they are more critical
of risk assessment methods used for explosive risk management. They
suggest that the Army develop a probabilistic risk assessment
methodology, based upon the work of other agencies that evaluate the
likelihood of catastrophic failure.

After the following key passages from the concluding chapter, I offer a
few thoughts of my own.

Lenny Siegel

***

Chapter Five
CONCLUSIONS AND RECOMMENDATIONS

None of the UXO risk assessment methods that we evaluated fully meets
the Army?s need for sound technical analysis to inform decision-making,
either for the purpose of setting priorities among UXO sites or for
detailed analysis of explosion and munitions constituents risks at
individual sites. Table 5.1 summarizes the methods? strengths and
limitations. As shown, each method falls short in one or more of the key
criteria necessary for an effective method: technical soundness of risk
calculations, effectiveness of implementation, or ease of communication.
Furthermore, stakeholders and regulators involved at the various sites
have not uniformly accepted these methods as credible elements of the
decision-making process, and continued reliance on them is likely to
delay the UXO response process further.

A fundamental reason why none of the modeling methods evaluated meets
the Army?s needs is that the UXO problem is not reducible to a single,
objective measure of risk. Risk methods must address the risk of
explosion of the munitions but also consider the risk of chemicals from
exploded munitions and UXO that leach into the soil and groundwater.
Further, the methods used for analyzing these two broad categories of
risk (explosion and munitions constituents), while different in
substance, both depend on subjective judgments about modeling
assumptions and data. For example, assessing the explosion risk
requires, among other types of information, estimates of the probability
that humans will come in contact with UXO. These estimates require
assumptions about human behavior and predictions of future population
and land use; the density and distribution of UXO items that cannot be
seen because they are buried; and the probability that the fuze of a UXO
item that may have been buried for decades is intact.

Despite these difficulties, credible UXO risk assessment methods are
needed to allow progress toward defining acceptable UXO cleanup
standards. Most would agree that zero risk at UXO sites would be the
ideal standard, but in reality that standard cannot be achieved with the
resources and technical capabilities available now or in the foreseeable
future. As explained in Chapter One, the only process that currently can
guarantee that all UXO has been removed involves

* burning or cutting all vegetation,

* excavating the entire site one foot at a time down to the maximum
possible penetration depth of the UXO (as much as 10 feet or more), and

* sifting all the excavated soil.

This process is too costly to be feasible for the DoD to implement as
the standard process for UXO response. Furthermore, it causes
irreparable damage to what are often uniquely preserved ecosystems and
in many cases will be unacceptable to regulators from natural resource
management agencies.

Because sifting is neither possible nor desirable in most cases, UXO
clearance relies on metal detectors to locate buried UXO items. Metal
detection technologies are imperfect: they do not find all buried UXO.
The Army and regulators alike need to publicly acknowledge this reality
and design risk-informed decision-making processes that can lead to
acceptable compromises.

This chapter suggests steps for the Army and DoD to take toward
developing risk assessment methods for prioritizing UXO sites and for
evaluating individual sites in detail. The goal is to develop methods
that are technically credible, acceptable to stakeholders, and practical
to implement. While challenging, evidence from the successful use of
risk assessment in other agencies (described in Chapter Four)
demonstrates that the task is not impossible.


...

SUMMARY OF RECOMMENDATIONS

In summary, UXO risk assessment requires two processes. The first
process would prioritize UXO sites for remediation (as Congress now
requires). The second process would provide for detailed evaluations of
appropriate responses to UXO at specific sites. The Army would benefit
from new technical methods for both applications because the existing
options are unsatisfactory for the Army?s current and future needs.

We recommend that a new UXO prioritization process (1) sort sites into
bins by explosion risk and (2) within these bins, sort sites by
munitions constituents risks.

The suggested prioritization process would preserve the information
about the two separate risk types: although sites would be grouped first
according to explosion risk, within these groups the sites would be
ordered by munitions constituents risk. Policy-makers then could decide
how much to allocate to sites with varying levels of explosion versus
munitions constituents risks.

We recommend developing a new process for sorting sites by explosion
risk (stage one of the prioritization process).

RAC could provide elements and a starting point for the new process, but
stakeholder concerns would need to be addressed.

We recommend using HRS or RRSE for sorting sites by munitions
constituents risks (stage two of the prioritization process). These
methods are well established and well accepted. There is no need for a
new approach for munitions constituents, since the behavior of these
contaminants and the risks they pose are similar to those of chemical
contaminants found at non-UXO hazardous waste sites.

We recommend producing two separate UXO site priority lists: one for
sites with known and documented future land use and another for sites
with uncertain future land use.

Having two lists would prevent manipulation of the process by choosing
the least restrictive land uses. Also, it would allow policy-makers to
decide how to trade off current and future risks when allocating funds.
The lists could be updated annually or as often as new information
became available.

We recommend using RAGS for site-specific assessment of munitions
constituents risks.

RAGS is well established for assessing risks of chemicals in water and
soil, and there is no need for the Army to develop a new method. We
recommend that the Army develop a new, probabilistic approach using the
PRA techniques developed by the NRC, NASA, and others for site-specific
assessment of explosion risks.

None of the available UXO explosion risk assessment methods by itself
satisfies our technical criteria for an effective risk assessment
method, and therefore a new approach is needed. Many other agencies use
PRA to assess risks of acute events analogous to UXO explosion.

Finally, we recommend that an independent technical review board and an
advisory committee of stakeholders oversee development of both the
prioritization system and scenario-based site-specific risk assessment processes.

The technical board would consist of independent experts in risk
assessment and explosive ordnance disposal. The advisory committee would
include representatives of the different groups of stakeholders (state
regulators, Native Americans, federal regulators, members of the public,
military personnel) involved at UXO sites.


***
(commentary by Lenny Siegel)

By clarifying the two major purposes of risk assessment, RAND has made a
valuable contribution to the science of munitions response. In
particular, I find novel and creative the suggestion that probabilistic
risk assessment (PRA) methods, such as event or fault trees, be used to
quantify explosive risk, but I'm not convinced. Though the primary goal
of munitions response is to prevent casualties, there is a secondary
goal: to prevent encounters. That is, I don't believe that people raking
leaves in their backyards, or even walking trails in a regional park,
should ever come into contact with unexploded ordnance. 

Perhaps the PRA approach could be modified to consider this problem, but
for now I think the solution lies in the establishment of clear risk
management principles. Not only should ordnance be removed from the
surface of land where there is public access, but further removal or
other responses should be taken to ensure that migration, erosion, or
excavation do not lead to contact.

The authors recognize the difficulty of incorporating potential land use
changes into risk-based prioritization process, but they say little
about anticipated land use in risk management (remedy selection). This
is emerging as one of the key issues in munitions response. For example,
if a developer want to build housing on privately owned property
containing unexploded ordnance deposited by the military, how much
remediation should be done to ensure that the future residents are safe?
And if the developer or regulators err on the side of safety, is the
Defense Department obligated to pay for additional cleanup?

-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org

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