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OCR for page 100
Groundwater Technical Element
The Groundwater Technical Element supports research on the
saturated zone at the Hanford Site, especially at its interfaces with the
vadose zone and Columbia River. The results of the work supported
under this technical element will be used by the Hanford Site's "core"
groundwater project, which is responsible for site-wide groundwater
monitoring and remediation (see Chapter 3), as well as the System
Assessment Capability (SAC; see Chapter 4~.
Groundwater occurs beneath the entire Hanford Site, and at
present, it provides the primary pathway for contaminant transport from
the site to potential receptors in the river and surrounding environment.
Many radionuclides of concern at the Hanford Site are highly mobile in
groundwater and are transported with little or no retardation (e.g., tritium,
technetium-99; see Figure 2.8a). Transport of other radionuclides by
groundwater tends to be slower, either because they are less soluble
(e.g., uranium, plutonium) or because they react strongly with minerals in
the vadose zone before they reach the groundwater (e.g., cesium-137~.
Chemical contaminants such as carbon tetrachloridc a dense,
nonaqueous phase liquid (DNAPL - are only slightly soluble in
groundwater. They tend to be partitioned between groundwater and a
pure phase, and their presence in the subsurface can actually modify
hydrologic properties (e.g., DNAPLs can partially fill pores, thereby
changing water-f~lled porosity and hydraulic conductivity). As discussed in
Chapter 2, DNAPL contamination is a serious problem in the 200 Area at
the site (see Figure 2.7~.
Rates of groundwater flow beneath the Hanford Site generally
range from a few to several hundred meters per year, depending on
hydraulic gradients and subsurface properties. At the faster rates,
contaminants can be transported across the site in a few decades, which
has in fact occurred for tritium (Figure 2.8a). Indeed, the groundwater
pathway of particular concern at the Hanford Site stretches from the 200
Area on the Central Plateau, where most of the waste inventory and
subsurface contamination exist today, to the Columbia River (see Figure
2.1), some 15-20 kilometers distant. As discussed in Chapter 2, chemical
processing operations in the 200 Area resulted in the discharge of billions
of gallons of water to ponds, cribs, and wells, which raised water table
elevations (see Figure 2.6~. These hydraulic mounds have generally
accelerated flow rates and, in some cases, have reversed flow directions
from natural conditions.
Groundwater tends to follow nearly horizontal flow paths in the
sediments underlying the Hanford Site. Because of this, groundwater flow
100
OCR for page 101
Groundwater Technical Element
101
is often modeled as two dimensional, with no vertical structure. In detail,
however, groundwater flow is three dimensional. Vertical components of
flow may be substantial where contaminants enter the groundwater from
disposal areas in the vadose zone. Vertical gradients influence the
distribution and transport of contaminants (Figure 7.1 ) and complicate the
task of monitoring contaminant movement in the subsurface. The
difficulties arising from the three-dimensional nature of contaminant
plumes in groundwater are reflected in the science and technology (S&T)
plan reviewed in this chapter.
10
E 20
-
Q
~ 30
a)
0 40
a)
m
rat
Q
8 so
60
70
. . 1
0 5000 10000 15000
Tc-99 Concentration (pCi/L)
Figure 7.1 Technetium-99 concentration gradient below the water table in
the 200 West Area. SOURCE: Data for well 299-W10-24,
sampled October 9-16, 1998, from Hartman et al., 2000, Table
2.8-3.
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102
Science and Technology for Environmental Cleanup
Groundwater represents the saturated end member of the vadose
zone, and several issues for understanding and characterizing the
unsaturated zone discussed in Chapter 6 also apply here, especially with
respect to hydrologic complexity and scaling relationships. However, the
"upscaling problem" described in Chapter 6 for the vadose zone is of less
a concern when describing physical transport mechanisms (i.e.,
advection, dispersion) in the saturated zone. In particular, established
procedures exist for determining large-scale hydrologic properties for
Groundwater transport from field tests (e.g., pump tests). Moreover,
hydrologic properties of the porous medium can usually be represented
by single values (or tensors). Corresponding properties in the vadose
zone must be represented by nonlinear functions of saturation that often
exhibit hysteresis, as discussed in Chapter 6. Scaling of geochemical
properties remains to be developecl, but in general, Groundwater transport
of contaminants is easier both to measure and to model than is vadose
zone transport.
SCOPE OF THE GROUNDWATER TECHNICAL ELEMENT
The main sources of information used in this assessment are the
Integration Project Roadmap (DOE, 2000a) and briefings received during
the committee's information-gathering meetings. The schedule and
budget for S&T work under the Groundwater Technical Element are
shown in Table 7.1.
The Groundwater Technical Element comprises six broad S&T
activities and, within these, 20 individual projects (Table 7.1~. To date,
only one of these projects has been funded, as discussed in more detail
below.
1. Groundwater-vadose zone infefface study. This activity
includes four projects (designated GW-1 through GW-4 in Table 4.1 in the
Integration Project Roadmap [DOE, 2000a]) designed to better document
the relationships between contaminant transport through the vadose zone
and the consequent formation and evolution of three-dimensional
contaminant plumes in groundwater. The four projects investigate three-
dimensional plume structure beneath soil sites for example, cribs and
tile drains (GW-1), dilute waste tanks (GW-2), concentrated waste tanks
(GW-3), and other waste sites (GWEN.
2. Biogeochemical reactive transport. This activity includes two
projects (GW-5, GW-6) to obtain an improved understanding of the effect
of redox and complexation reactions on radionuclide (mainly actinide
element) transport in Groundwater connected with two plutonium-bearing
waste streams and one project (GW-7) to obtain an improved
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Groundwafer Technical Element
understanding of multiphase reactive transport of DNAPLs, particularly
carbon tetrachloride.
103
3. Hydrogeological characterization study. This activity includes
five projects (GW-8 through GW-12) to evaluate the variability and scaling
of subsurface hydrological parameters that control contaminant transport.
One project (GW-8) will approach the problem using existing groundwater
data. Two projects (GW-9 and GW-10) will conduct otherwise unspecified
"multiple-scale studies" beneath clean and contaminated sites. The
remaining two projects (GW-1 1 and GW-12) will synthesize data and
construct three-dimensional visualizations of hydrogeological properties
under soil and tank sites.
4. Regional plume geometry. The activity includes one project
(GW-13) to develop a three-dimensional image of contaminant plumes
along a transect extending from the 200 West Area to the Columbia River.
5. Multiscale three dimensional model development. This
activity includes three projects (GW-14 through GW-16) to develop
approaches for implementing three-dimensional transport models that can
be run at multiple scales and three projects to develop methods for
incorporating heterogeneity and uncertainty in these models for
groundwater under a boiling waste tank (GW-17), a specific retention
basin (GW-18), and a dilute waste tank (GW-19~.
6. Groundwater discharge study. This activity includes one
project (GW-20) to quantify the three-dimensional plume dynamics at a
site along the Columbia River.
As shown in Table 7.1, work on these projects is planned to run
from fiscal year 2000 through fiscal year 2004. The total planned funding
for this technical element is about $16.3 million. Note, however that these
funding levels, which were identified in the roadmap, have been revised
by the Department of Energy (DOE) (see Table 3.1~.
EVALUATION OF WORK PLANNED UNDER THE GROUNDWATER
TECHNICAL ELEMENT
As of early 2001, only the "groundwater discharge" study (GW-20;
see Table 7.1), which is concerned with groundwater in the 100 Area, had
been initiated; it was supported by funding from Hanford's "core"
groundwater project (Chapter 3~. Consequently, there was little scientific
or technical output in the form of peer-reviewed reports or papers
available for the committee's evaluation. Accordingly, the committee
offers only general comments about the work planned under this technical
element, again focused on the five evaluation questions against which the
other S&T elements are compared. The lack of specificity in the
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Science and Technology for Environmental Cleanup
TABLE 7.1 Summary of S&T Activities and Planned S&T Projects Under the
Groundwater Technical Element
S&T Activity S&T Project Objectives Project Hanford EMSP
Projects Duration Fundinga Funding
Planned (fiscal (thousand (thousand
years) dollars) dollars)
Groundwater- 4 Obtain an improved 2001-2003 2,100 0
vadose zone understanding of the
interface relationships between
study contaminant transport
through the vadose
zone and plume
formation in
groundwater
Biogeochemical 3 Obtain an improved 2001-2004 7,800 0
reactive understanding of redox
transport conditions, the role of
complexants in
transport, and the
location and
characteristics of
DNAPL contamination
Hydrogeological 5 Develop an improved 2001-2003 3,000 0
charactenz- understanding and
ation study characterization of
subsurface
heterogeneity on
contaminant transport
Regional plume 1 Obtain an improved 2001 2,100 0
geometry understanding of the
three-dimensional
geometry of
contaminant plumes in
Groundwater
Multiscale three- 6 Obtain an improved 2001-2003 1,300 0
dimensional understanding of
model heterogeneity and
development uncertainty that can be
incorporated into
multiscale models
Groundwater 1 Obtain an improved In ob 0
discharge understanding of progress
study contaminant release
locations and fluxes to
the Columbia River
NOTE: EMSP = Environmental Management Science Program
The Integration Project intends to seek funding from national S&T programs (e.g., DOE Headquarters) for
some of this work.
blithe River Monitoring Project (see Chapter 3) is providing funding and leadership for this work.
SOURCE: DOE, 2000a, Figure 4-1, Table ~1.
OCR for page 105
Groundwater Technical Element
105
information available in the groundwater portion of the Integration Project
Roadmap precludes a more detailed assessment.
Can the objectives of the planned work be achieved?
The committee found it difficult to provide a definitive answer to
this question because of the lack of technical detail on the planned
projects in the Integration Project Roadmap (DOE, 2000a). The S&T
objectives may be achievable if the planned work is funded at adequate
levels and tied to site decisions. However, some fundamental issues must
be resolved to bring these tasks to completion.
In particular, the Integration Project may have unrealistic
expectations about the time that will be needed to complete some of
these studies. For example, task GW-11 (Synthesis and Visualization of
Hydrogeology Soil Site) has a 10-month time line. Task GW-12, which
has the same general objective for a high-level waste tank site, has a 24-
month time line. The expected outcomes of GW-1 1 and GW-12 include
providing estimates of small-scale hydrogeological property variability and
spatial correlation in a form amenable for use in numerical models,
investigating the scale dependence of hydraulic measurements, and
investigating important scales of physical and hydrogeological
heterogeneity characterization.
Issues of scaling that are raised within the scope of these projects
are an active focus of research efforts in many scientific disciplines (see
Sidebar 6.1 and an expanded discussion of scaling in Appendix C). It is
probably more realistic to anticipate that significant progress on scaling
issues will be measured on a time scale of 5 to 10 years, rather than the
1- to 2-year time frames allowed for these projects, even if funded at the
requested levels. The Integration Project should consider the implications
of slower-than-planned progress on these projects for other work at the
site (e.g., the SAC) and should adjust the schedules accordingly, if
appropriate.
Does the planned work represent new science?
Again, the lack of detailed information makes it impossible for the
committee to identify specific areas of new science. However,
opportunities appear to exist to develop new understanding and better
quantification of issues such as the three-dimensional nature of
contaminant plumes and hydrogeological characterization, both of which
are identified in Table 7.1. The research planned on each of these topics
is generalizable beyond Hanford. Underlying questions and anticipated
outcomes apply in a broad sense to many contaminated sites where
remediation and stewardship are planned or under way. It is critical,
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Science and Technology for Environmental Cleanup
however, that this research be conducted at Hanford, in light of the mix of
contaminants that have been released to the environment and with
respect to transport to and interactions with the Columbia River.
Can the planned work have an impact on cleanup decisions at the
Hanford Site?
Better characterization of groundwater pathways and contaminant
fate and transport in the saturated zone has obvious relevance to issues
of site remediation and long-term stewardship, especially in the 200 Area.
It is clear, however, that the understanding of groundwater flow and
transport is more mature than that for vadose zone flow and transport.
Consequently, uncertainties in groundwater models at the Hanford Site
are small relative to uncertainties in vadose zone and river models.
Therefore, S&T directed at refining the understanding of groundwater
transport may not be a good investment relative to S&T efforts that are
needed to improve the understanding of vadose zone and river transport
(see Chapters 6 and 8~.
Does the planned work address the important issues?
The broad tasks outlined in the Groundwater Technical Element
address the core issues that have to be resolved with respect to
contaminant fate and transport in groundwater at the Hanford Site. In the
course of these studies, sophisticated computational tools may be
developed that can aid in making sound site management decisions.
Valuable basic data on the hydrogeology of the saturated zone and
contaminant distribution in the groundwater system also may be obtained.
These data may be important for achieving progress in a number of other
site projects, such as the development of long-term monitoring plans for
the groundwater system at Hanford.
Are there other concerns, comments, or suggestions that should be
considered by the Integration Project in executing the planned work?
The committee has two concerns. First, as noted previously,
detailed project descriptions do not appear to exist in many cases, and
written descriptions of the projects in the Integration Project Roadmap
(DOE, 2000a) were too brief to determine how likely it is that the projects
will meet their objectives. Second, although the projects may provide
valuable contributions to science, it is not clear whether the S&T results
are needed for site decision making. Essentially all of the projects are
assigned to the priority ranking "Critical to the success of the Accelerated
Cleanup: Path to Closure" project in the Integration Project Roadmap
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Groundwater Technical Element
107
(DOE, 2000a). The discussion in Appendix B of DOE (2000a) of the
consequences of not filling a particular research need, although valid,
provides little substantive information to guide a prioritization effort.
Therefore, the committee recommends that a more selective system
of prioritization be developed for these projects and that each
project be referenced to this prioritization system before subsequent
funding cycles begin. A more detailed discussion of prioritization is
provided in Chapter 10.
DISCUSSION
The Integration Project has clearly assigned a lower priority to the
Groundwater Technical Element than to the Vadose Zone Technical
Element, as shown by the planned funding levels and schedules in Tables
3.1, 6.1, and 7.1. According to the Integration Project Roadmap (DOE,
2000a), there were plans to start 14 of the 20 Groundwater activities by
February 2001. As of March 2001, only one Groundwater activity (GW-20)
was under way.
Although the documentation of detailed research plans is sparse,
the planned S&T activities in the Groundwater Technical Element appear
to identify a set of projects and investigations that can add confidence to
the assessment of contaminant migration in Groundwater at Hanford.
Because Groundwater modeling has progressed to a greater degree than
many other S&T issues discussed in this report, the committee agrees
with the Integration Project's decision to assign a lower priority to the
Groundwater Technical Element relative to the other technical elements.
The committee notes, however, that the basis for this decision does not
appear to be documented and was therefore not reviewable.
Among the activities included with the Groundwater Technical
Element, assignment of the highest priority to the groundwater-river
interface study (GW-20) is clearly driven by the intensive restoration
efforts under way along the Columbia River (see Chapter 2~. This
research activity is likely to have a more immediate return in better
managing current cleanup activities along the river corridor than the other
projects planned under this technical element.
Representative terms from entire chapter:
groundwater technical
