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9
Monitoring, Remediation, and
Risk Technical Elements
As noted in Chapter 3, detailed science and technology (S&T)
plans for the Remediation, Monitoring, and Risk Technical Elements were
being developed during the committee's information gathering for this
report. S&T plans for the Remediation and Monitoring Technical Elements
will not be issued until fiscal years 2002 and 2003,4 respectively, and the
S&T plan for the Risk Technical Element exists only in draft form (DOE,
2000d).2 Consequently, the committee was unable to obtain detailed
descriptions of the projects under these technical elements, and it is
therefore able to provide only a general overview and assessment of the
planned work.
The main sources of information used in this assessment are the
Integration Project Roadmap (DOE, 2000a) for the Remediation and
Monitoring Technical Elements and that roadmap and subsequently
issued risk S&T plan (DOE, 2000cl) for the Risk Technical Element. A
summary of the S&T activities and projected budgets are given in Table
9.1 .
MONITORING AND REMEDIATION TECHNICAL ELEMENTS
The Monitoring Technical Element and the Remediation
Technical Element have only one planned S&T activity each, and they are
scheduled for completion in 2003. The S&T activity for the Remediation
Technical Element, identification, development, and deployment of
improved groundwater Remediation strategies, includes two projects to
develop an improved technical basis for remediation of contaminant
plumes at the Hanford Site. In the first project (Rem-13), the distribution of
carbon tetrachloride plumes in the 200 West Area (see Chapter 2) will be
investigated, and the results will be used to assist in the development of a
strategy for corrective actions. The planned work is to include
geophysical, geochemical, and modeling studies to assist with the
selection and deployment of remediation technologies.
These plans were originally scheduled to be issued in fiscal years 2001 and
2002, respectively, but were delayed because of funding cutbacks.
The committee received a copy of this draft in October 2000.
3As noted in previous chapters, the projects under each of the six activities
are given these identification numbers in DOE (2000a, Table 4-1~.
125
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Science and Technology for Environmental Cleanup
TABLE 9.1 Summary of S&T Activities and Planned S&T Projects Under the Monitoring
Remediation, and Risk Technical Elements
S&T Activity S&T Project Objectives Project Hanford EMSP
Projects duration Funding Funding
Planned (fiscal (thousand (thousand
years) dollars) dollars)
Monitoring
Identification,
development,
and
deployment of
improved
environmental
monitoring
Remediation
Idenfflcation,
development,
and
deployment of
improved
groundwater
remediabon
strategies
Risk
1
2
Investigate and
develop strategies and
technologies for
environmental
monitoring of multiple
media
Investigate the
distribution of DNAPLs
in the 200 Area and
contaminant plumes in
the 100 Area, and
assist in the
development of
corrective strategies
2001-2003 0
2,600
2001-2003 0 5,300
2001 150 0
General risk 1 Develop methods to
assessment identify, involve, and
build consensus
among stakeholders
on desired foci for the
risk technical element
Ecological risk 11 Develop methods to 2001-2003 9,900a 0
assessment predict the impacts of
exposures to
contaminants from the
Hanford Site on
selected species
Economic risk 5 Develop methods and 2001-2003 3,300& 0
assessment data for predicting how
human populations
and economies will
respond from potential
exposures of
environmental
contamination at the
Hanford Site
Human health 9 Develop methods to 2001-2003 8,900a 0
risk predict the impacts on
assessment humans of exposures
to contaminants from
the Hanford Site
Sociocultural 1 Develop a risk 2002 600a 0
risk assessment perception model for
groups affected by
Hanford Site
contaminants
NOTE: DNAPL = dense nonaqueous phase liquid; EMSP = Environmental Management Science Program
'The Integration Project intends to seek funding from national S&T programs (e.g., from DOE Headquarters)
for some of this work.
SOURCE: DOE, 2000a, Figure 4-1, Table ~1.
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Monitoring, Remediation, and Risk Technical Elements
In the second project (Rem-2), contaminant plumes (particularly
chromium, strontium, and tritium plumes) in the 100 Area will be
investigated, and the results will assist in the development of a strategy
for corrective actions. The planned work will include geophysical and
geochemical studies to help select and deploy remediation technologies.
The S&T activity for the Monitoring Technical Element,
identification, development, and deployment of improved environmental
monitoring, involves one project (M-1 ) to develop technologies and
strategies to monitor air, vadose zone, groundwater, river, and selected
biota, especially after the active phase of site cleanup is completed.
Evaluation of Work Planned Under the
Monitoring and Remediation Technical Elements
127
The monitoring and remediation projects were begun before S&T
plans were developed, so it is difficult for the committee to judge the
appropriateness or effectiveness of current work. The total planned
funding for these technical elements is $2.6 million and $5.3 million,
respectively (last column of Table 9.1), all of which is being provided to
principal investigators through the Environmental Management Science
Program (EMSP, see Chapter 3~. The Integration Project has no plans at
present to provide Hanford Site funding to these efforts.
Detailed S&T plans for these technical elements are still not
complete, and detailed objectives and S&T projects are not yet defined. If
the planned projects are executed appropriately, however, the broad
objectives defined for the Remediation Technical Element may be
attainable. Knowledge of the distribution of contaminant plumes obtained
from the planned S&T work will feed other Department of Energy (DOE)
programs in the Office of Science and Technology that deal with
remediation technology selection and deployment.
There is a clear opportunity to develop and evaluate new
geophysical and geochemical methods for plume detection and treatment
under these technical elements. The current field testing of in situ
treatment of chromium in 100 Area groundwater is noteworthy in this
regard.4 Additionally, there exists much prior knowledge on remediating
4The In Situ Redox Manipulation Treatability Test is occurring near the 100-D
Area. It involves the installation of a line of injection wells into the groundwater to
intercept a plume of chromium(\/l) just east of the Columbia River. A solution of
sodium bichromate is being injected into the groundwater through these wells to
form a chromium barrier. The solution reduces irontl11) in the sediments to irontil),
which in turn undergoes a redox reaction with chromium(VI) and reduces it to
insoluble chromium~l11) that precipitates onto the sediment grains. The test was
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128
Science and Technology for Environmental Cleanup
carbon tetrachloride and other dense nonaqueous phase liquids
(DNAPLs) at other sites that should be applicable to Hanford.
New treatment methods and better technologies for locating and
defining plumes should have broad application throughout the site (see
Figure 2.8, for example) and to other DOE sites as well. Knowledge of the
quantities and distributions of contaminants in the subsurface is essential
so that decisions can be made to contain, actively treat, or rely on natural
attenuation processes.
Not only will monitoring methods have to be developed to meet
site needs for unprecedented time periods after the active phase of
cleanup is completed, but monitoring results will be critical in decisions
resulting in transitions from "watchful waiting" (surveillance) to active
containment or remediation. However, there is insufficient information
provided in the Integration Project Roadmap (DOE, 2000a) to determine
whether the S&T work planned under the Monitoring Technical Element
addresses Hanford's most critical needs in this area.
Discussion
In the committee's view, there is disproportionately small
emphasis in the S&T program on remediation~nly two projects are
planned (Table 9.1), and both focus on determination of contaminant
distributions in groundwater plumes. Little is being done within the S&T
program on remediation technologies per se and their potential
applications to waste pits, cribs, and other disposal areas. Further, there
is no Integration Project S&T work planned on barriers to isolate, contain,
and treat contaminants that will remain in the subsurface after the active
cleanup program is completed.
The committee views the development of effective long-term
barriers as one of the most important S&T needs at the Hanford Site, and
an earlier National Research Committee (NRC) also identified this need
as significant for DOE's national cleanup program (DOE, 2000a). In fact,
S&T to develop and deploy effective barriers at Hanford has been under
way for the better part of the last decade.
Field research on surface barriers in the 200 Area was initiated in
the early 1 990s with construction of the Field Lysimeter Test Facility
(Fayer et al., 1999), followed by construction of the Hanford Surface
Barrier over an actual waste site in 1994 (DOE, 1 999d). These two
initiated in 1997 with the installation of a 50-meter-long segment of wells, and
initial tests look promising. Recently, however, some breakthrough of
chromium(VI) has been detected, likely due to oxygenation of groundwater near
the test wells. The cause of this oxygenation is under investigation.
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Monitoring, Remediation, and Risk Technical Elements 129
facilities are unique, with the Iysimeter providing site-specific information
on fluid infiltration rates and amounts through different surface soil and
vegetative covers and the surface barrier providing site-specific data on
the effectiveness of a specially designed cover system (the Hanford
Surface Barrier) in preventing fluid infiltration into a waste crib (Figure
9.1~.
In 1996, a feasibility study (BHI, 1996) examined possible
designs for capillary-evapotranspiration barriers. These included (1 ) the
Hanford Surface Barrier, a thick, multilayer, long-term barrier intended for
use on the most contaminated sites (e.g., cribs and trenches; see Figure
9.1 ); (2) a standard Resource Conservation and Recovery Act (RCRA) C
(hazardous waste) barrier; (3) a modified RCRA C barrier, to be used for
,~ ~
-
~ ~ ~ ~ ~ .. ~ .. ~.~ ~ .. ~ ~ ~
~..~:~ -
Figure 9.1 Cross-sectional view of the Hanford Barrier. SOURCE: DOE,
1998d, Figures 1.2,1.3, 1.4.
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130
Science and Technology for Environmental Cleanup
low-level and mixed (radioactive and chemical) waste sites; and (4) a
modified RCRA D (municipal waste) barrier for municipal and low-level
waste sites without hazardous chemicals.
Some additional work on surface barriers is planned by DOE and
Hanford, as noted below:5
.
The Office of Science and Technology is initiating a three-
year project in fiscal year 2001 on the Hanford Surface Barrier to (1 )
compare geophysical techniques, including ground-penetrating radar, for
monitoring seasonal changes in moisture storage in the top two meters at
scales larger than can be detected using neutron probe methods;6 (2)
determine the as-built water storage capacity of the barrier; and (3)
validate the performance of the asphalt layer at the base of the barrier
using chemical tracers.
A study of the RCRA C barrier is also planned to begin in
fiscal year 2001, with identification of local soil materials for use in its
construction, followed by construction of a prototype barrier in the 200
Area in 2002 and performance monitoring thereafter. One of the Hanford
Site's core projects, the 200 Area Remedial Action Project (see Chapter
3), is carrying out this work. Funding for the construction and monitoring
phases is to be provided by Hanford and possibly by the Office of Science
and Technology.
Detailed monitoring of properly constructed RCRA C (hazardous-
toxic waste) and RCRA D (municipal waste) barriers has shown cover
and liner systems to be very effective in preventing infiltration of water
and escape of leachate. Some areas of the Hanford Site will remain too
contaminated for any use other than waste disposal and containment for
a very long time for example, the 200 Area tank farms and disposal
facilities like the Environmental Restoration Disposal Facility (see Chapter
2~. Concentration and containment of waste using barriers with careful
monitoring over time are environmentally defensible strategies.
Continued infiltration of wastes into the vadose zone in the 200
Area from tanks, cribs, waste ditches, and ponds may exacerbate the site
remediation problems, as may the continued migration of contaminants
away from these locations. Characterization data on the vadose zone
(Chapter 5), combined with a fully functioning System Assessment
5This information was provided in a teleconference call with Integration
Project and Pacific Northwest National Laboratory staff on October 3, 2000.
6Horizontal tubes were built into the Hanford Surface Barrier so that neutron
probes could be inserted to measure moisture storage in the barrier materials
(see Figure 9.1~. Such methods provide only near-field moisture values that is,
values in the vicinity of the probe tubes.
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Monitoring, Remediation, and Risk Technical Elements
Capability (SAC; see Chapter 4), can be used to illustrate how barriers
over some or all of the source areas could reduce contaminant migration
and plume development. Furthermore, use of surface and in-ground
barrier systems can serve the additional purpose of containment, both
temporary and long term. As new waste treatment technologies become
available in the future, they could be used to treat and mitigate the
hazards from wastes contained within them.
Interim barriers could find wide application across the site, for
131
example, as barriers to reduce water infiltration in and around tank farms
that have leaked waste,7 or as subsurface barriers to reduce contaminant
leakage into the vadose zone during single-shell tank waste retrieval
operations. Access restrictions to and additional loading on the 200 Area
tank farms have been cited to the committee as reasons for not placing
interim barriers over them to reduce infiltration. However, there are
options to avoid these problems; for example, tent-type structures that
could easily be constructed over the tank farms, with grading to intercept
surface runoff. S&T can play an important role in investigating and testing
the feasibility of such strategies.
Perhaps the past and planned studies cited above account for the
lack of a major S&T program on barriers as part of the Integration Project.
Nonetheless, the committee believes that more research is needed on the
development, deployment, and evaluation of interim, long-term, and
reactive barrier systems. Recent research on new technologies for site
remediation using chemically reactive barriers shows great promise. The
development of reactive barrier systems for the unique site and waste
conditions at Hanford could be an especially fruitful area of research.
The committee makes the following recommendations with
respect to barrier S&T:
· S&T research on the feasibility, effectiveness, and long-
term performance of surface barriers should be expanded to include
other barrier types and materials for prevention of surface water
infiltration into tank farms and other regions containing high
concentrations of buried and spilled waste.
· S&T should be undertaken to assess the potential for
using vertical and inclined cutoff barriers and reactive barriers as
part of "interim" waste containment systems, which can provide
containment for one to a few decades, as well as "permanent" waste
7At the request of DOE, a TechCon Forum was held in Richland, Washington,
on May 4-6, 1999 to discuss approaches for reducing water infiltration around the
Hanford tanks. The forum concluded that many technologies were already
available or could be developed and deployed at the site (TechCon,
1 999a, 1 999b).
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Science and Technology for Environmenta/ Cleanup
containment systems that are designed to last for much longer
periods.
· S&T should also be undertaken to develop reactive
barriers that can be used to treat or immobilize radionuclide and
chemical contaminants of concern in Hanford Site groundwater.
Since the development of new and improved barriers would likely
find wide application across the DOE complex, much of the needed S&T
work might be done in cooperation with other DOE programs. The focus
of S&T at Hanford might be to adapt technologies developed elsewhere to
the needs and environmental conditions at the site and perform pilot
demonstrations.
The need for more and better methods for site characterization
and monitoring has been cited throughout this report (see especially
Chapters 5, 6, and 8~. Monitoring is now being used at the site to detect
contaminant transport in the environment, especially the groundwater and
river (PNNL, 1999), and monitoring will no doubt find widespread use to
assess the efficacy of future containment and cleanup actions. Monitoring
utilizes many of the same strategies and tools as characterization and, in
fact, is often piggybacked on,8 or iterated with, characterization efforts.
Thus, as characterization capabilities are improved through
Integration Project S&T efforts (see Chapter 5), there will be parallel
opportunities to improve monitoring capabilities, especially through the
use of minimally invasive or noninvasive approaches based on new
detection, data collection (including improved statistical strategies for
sampling), data transmission, data processing, and information display
technologies. Such improvements are especially needed for monitoring
the vadose zone, which will contain most of the waste and contamination
to be left in place at the site when DOE's cleanup program is completed,
and where contamination is especially difficult to detect because of
subsurface heterogeneity and transient hydrologic conditions.
The development of new and improved monitoring strategies and
capabilities is a difficult technical challenge, and it will likely take many
years of effort to make useful progress. Consequently, S&T on monitoring
strategies and tools must begin now so that useful results will be available
before the initiation of large-scale remediation and containment activities
at the site. Therefore, the committee recommends that Integration
Project S&T on new and improved strategies and technologies for
monitoring the vadose zone be expanded. As part of this work, the
Integration Project should assess what monitoring capabilities will
be needed in the future at the site, based on cleanup decisions to be
For example, boreholes drilled to obtain data on subsurface characteristics
may subsequently be used for groundwater monitoring.
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Monifonng, Remediation, and Risk Technical Elements
made and likely end-state scenarios, so that the SOT work can be
properly planned and prioritized.
Since the development of new and improved monitoring
capabilities would likely find wide application across the DOE complex,
much of the needed S&T work might be done in cooperation with other
DOE programs. The focus of S&T at Hanford might be to adapt
technologies developed elsewhere to the needs and environmental
conditions at the site and perform pilot demonstrations.
RISK TECHNICAL ELEMENT
133
The Risk Technical Element has one general S&T activity on
stakeholder involvement and four S&T activities focused on ecological,
human health, economic, and sociocultural issues (Table 9.1~. In general,
the objective of the planned S&T work is to reduce uncertainties
associated with risk assessments so that less conservative assumptions
and models can be used. The approach taken is described in Appendix B
and Table 4-1 in the Integration Project Roadmap (DOE, 2000a) and also
in DOE (2000d).
1. General risk assessment This activity includes one project
(R-1) to develop methods to identify, develop, and build consensus
among Hanford stakeholclers on areas of focus for the Risk Technical
Element.
2. Ecological risk assessment. This activity includes 11 projects
(R-2 through R-12) to address technical gaps in ecological risk issues
relevant to the Hanford Site. One project, described as contributing to
better understanding of problem formulations, is designed to explore the
relationship between impacts on individual entities and effects considered
on a community level. Three exposure-related projects are described;
these include the effects of multiple exposure pathways on uptake, uptake
factors for plants and benthic species, and bioavailability. Six projects are
defined that address ecological effects. These include a study of
continuous (in contrast to acute) toxicological response, extrapolations
across end points (such as population-level and individual-level
responses) and taxa, toxicity by mode of action, and adaptive response.
Finally, a risk characterization project is proposed in which a "weight-of-
evidence" approach, as used for human health risk assessment, would be
applied to the integration of data on ecological effects.
3. Economic ask assessment. This activity includes five projects
(R-13 through R-17) to assess recreational use patterns for the Columbia
River that can be used to define human exposure scenarios, assessment
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Science and Technology for Environmental Cleanup
of how people might respond to risk information of various types,
preferences regarding ecological scenarios, and study of population
mobility and benefits transfer.
4. Human health risk assessment. This activity includes nine
projects (R-18 through R-26) that address bioavailability, food-chain
transfer factors, biomarkers, exposure pathways-factors, variability in
exposures, toxicokinetics, treatment of uncertainties in cancer slope
factors, and characterization of multiple health end points. Several of
these projects (food-chain transfer factors and exposure pathways) would
address risk assessment issues relevant to more accurate
characterization of exposures of Native Americans.
5. Sociocultural risk assessment. This activity consists of one
project (R-27) to model risk knowledge, in which cultural experts would
attempt to convert information on concentrations of contaminants in
environmental media into impacts on cultural values.
Evaluation of Work Planned Under the
Risk Technical Element
As shown in Table 9.1, work on some of these projects is under
way and will be completed in fiscal year 2003. The total planned funding
for this technical element is about $22.8 million (second-to-last column of
Table 9.1~. These budget estimates are taken from the Integration Project
Roadmap (DOE, 2000a), which was published before the more detailed
draft Risk Assessment Science and Technology Plan (DOE, 2000d) was
issued. DOE (2000d) does not include budget information, so it is not
clear to the committee whether the budget has evolved along with the
technical project plans.
In comparison to DOE (2000a), the project descriptions in DOE
(2000d) indicate that substantial progress has been made in defining risk-
related projects concerning issues at the Hanford Site. A majority of the
projects in the human health risk area apply to generic (rather than site-
specific) risk assessment issues (e.g., R1 8-R20, R22, Ram. These
generic risk assessment issues have been recognized as important by
many organizations and agencies, and technical advances in these areas
would lead to reductions of uncertainty in risk estimates. However, these
technical issues can have a strong influence on how environmental health
risks are regulated and, for this reason, are of active interest to the
Environmental Protection Agency (EPA) and other agencies. Additional
comments on this point are offered later in this analysis.
Despite improvements in the planned risk project descriptions in
DOE (2000d), many are still general and vague, such that detailed review
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Monitoring, Remediation, and Risk Technical Elements
135
comments cannot be provided. For example, the description of the
biomarkers-of-exposure project does not identify specific chemicals or
technical approaches, nor does it provide any comparison with the current
capabilities (e.g., sensitivity of measures of chromosome aberrations to
ionizing radiation) relative to exposures of interest at the Hanford Site.
Can the objectives of this work be achieved?
The human health risk projects that involve factors specific to the
Hanford Site are achievable. These projects (bioavailability, food-chain
transfer factors, exposure pathways, and spatiotemporal variation in
exposure) involve measurements and analyses that have been performed
successfully in other contexts.
Other aspects of the risk element are more ambitious and seem
unlikely to be achieved except over extended periods of time. The
determination of health and ecosystem risks from complex mixtures is an
example of such an issue; this has been studied by various government
and research agencies for many years. Some of the scientific issues
listed for the human health risk component are issues in which there is
substantial regulatory involvement (determination of cancer slope factors,
for example).
In general, regulators require the use of published guidance such
as that found in EPA's Integrated Risk Information System (IRIS) for
cancer slope factors. Although EPA periodically updates the IRIS values
and will consider submitted information when it does so, this is not an
area in which the Integration Project should expect large changes from
the status quo. The only exception may be for rarely encountered
substances for which the toxicological information base is poor. The
ecosystem risk analysis is similarly hampered by a dependence on
exposure-concentration-effect concentration pairs that are unknown or
poorly defined for multiple stressors.
In the committee's judgment, these more ambitious proposed
health science and ecosystem impact analysis activities would make
more sense as components of long-term research supported by DOE
Headquarters or other agencies such as EPA than as S&T under the
Hanford Integration Project. To be useful at Hanford, any scientific
advances in human health risk assessment would first have to be
accepted by national and international scientific bodies, and then adopted
by EPA. The committee notes that although a number of these ambitious
projects appear in the S&T plan (DOE, 2000a, Table 4-1 ), they have not
yet been funded under the Integration Project.
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Science and Technology for Environmental Cleanup
Does the planned work represent new science?
The achievable aspects of the work, such as a refined
characterization of Native American diets and other exposure factors,
would improve the quality and applicability of site risk assessments. Some
of the more ambitious human health and ecosystem studies would
represent new science if successful, but as noted above, the committee's
view is that such work would be a better fit elsewhere in DOE or other
agencies. The planned ecosystem risk analysis approach does not
represent new science, and the planned studies to begin defining dose-
response relationships for Columbia River flora and fauna are necessary,
but studies of this type are standard toxicological testing elements of risk
assessment.
Can the planned work have an impact on cleanup decisions at the
Hanford site?
To the extent that Hanford cleanup decisions will be based on
avoiding unacceptable risks to human health and the environment, the
committee judges that this work can be helpful in several respects. The
ecological work to refine the understanding of food webs could allow for
more robust assessments of the effect of contaminant seepage into the
Columbia River, and there is a critical need to build ecosystem risk
foundations based on a comprehensive understanding of ecosystem
structure and function in the Columbia River. However, the committee's
view is that, taken as a whole, the Risk Technical Element is less likely to
impact site decisions than is S&T to better characterize the locations
concentration, and speciation of existing contaminants (see Chapter 5~.
Does the planned work address important issues?
The committee believes that the planned work does address
important issues. The primary objective of most Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA)
activities is the protection of human health and the environment in the
future. The CERCLA process also identifies community concerns as
important to site decisions. The risk element directly addresses these
Issues.
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Monitoring, Remediation, and Risk Technical Elements
Are there other concerns, comments, or suggestions that should be
considered by the Integration Project in executing the planned work?
137
The committee's main concern with the planned work, as noted in
the previous discussion, is that it addresses issues that have been
studied by various government and research agencies for many years
and have substantial regulatory involvement. The work planned under the
auspices of the Integration Project's S&T program is modest in
comparison to the scope and magnitude of work on these issues by other
agencies and is therefore unlikely to make major contributions to
resolving these issues. Consequently, these issues are more appropriate
targets for long-term research programs funded by DOE Headquarters
and other federal agencies. The Integration Project's main focus should
be to maintain awareness of this work and to use new results as they
become available. Most of these projects of questionable value have not
yet been funded by the Integration Project and probably should not be
funded in the future for the reasons given above.
Discussion
The Risk Technical Element includes some potentially important
work to identify ecological impacts that may result from contaminant
seepage into the Columbia River. In particular, the identification of
locations where contaminant concentration and characteristics of
exposure can have substantial effects on Columbia River flora and fauna
is likely to be very useful in future versions of the SAC.
The committee's review of the Risk Technical Element revealed
two important issues that are not being addressed by the S&T program at
present: (1 ) the impacts of extreme events on the risk assessment and (2)
the appropriateness of the time period selected for risk assessment. The
committee comments on these in the following paragraphs.
Rare but high-magnitude (also known as "extreme") events such
as fires, floods, and earthquakes are considered routinely in risk
assessments. A large range fire, such as occurred at the Hanford Site in
the summer of 2000, could have a substantial effect on contaminant
releases by removing protective ground cover, which could lead to
increased infiltration and surface runoff and erosion (see Figure 9.2~.
Other episodic events also could affect the movement of subsurface
contaminants, such as climate changes that result in drought or increased
precipitation. Floods have been an important erosional agent at the
Hanford Site, as evidenced by the geological record of extreme flooding
during the past 100,000 years (Sidebar 9.1~.
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?38 Sconce and ~chno~ far amend bags
....
ague 9.2 July 12, 2000, SPOT image of we Hangs Site showing the
extent of the June 2000 range fee. Dark regions on the photo ar
burned areas. Copyright CNES~000.
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Monitoring, Remediafion, and Risk Technical Elements
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OCR for page 140
140
Science and Technology for Environmental Cleanup
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Documents and presentations to the committee indicate that risk
assessments to be made using the SAC are to be carried out for of 1,000
years following site closure, from 2050 to 3050 (see Chapter 4~. The
committee has two recommendations with respect to this period of
analysis. First, the committee recommends that the results of such
calculations be reviewed to ensure that the analytical period
includes the time of peak dose or risk. Such a review could be
undertaken under the auspices of the Risk Technical Element. For some
toxic materials, the rate of transport through the subsurface may be so
slow that peak concentrations at locations of concern, especially the
Columbia River, could occur more than 1,000 years in the future. If peak
risks occur beyond 1,000 years, then other assumptions in the SAC may
also need to be reexamined, particularly the assumption of no climate
change (see Table 4.1~.
The second recommendation concerns the "status quo"
assumption made in the SAC with respect to the continuing existence of
dams along the Columbia River. As discussed in Chapter 4 (see
especially Table 4.1), the SAC contains the assumption that Columbia
River dams will continue to operate for 1,000 years following the assumed
closure of the Hanford Site in 2050. No justification for this assumption is
given in any of the documents that the committee has reviewed, and it
seems on its face to be unrealistic. The committee recommends that an
evaluation be made of the sensitivity of SAC risk assessments to the
assumed continuing existence of these dams. Again, such a review
could be undertaken under the auspices of the Risk Technical Element.
The committee is not recommending that analyses be made of a broad
array of alternative future states with respect to the dams, only that the
potential effect on analytical results of changes to the dams be
considered.
Representative terms from entire chapter:
technical element
