PM STRAUSS & ASSOCIATES
Energy and Environmental Consulting
TO:
FROM:
DATE:
SUBJ:
MEMORANDUM
Lenny Siegel
Peter Strauss
June 22, 2012
Review of the Draft Groundwater Feasibility Study and Draft Plume
Clean-up Timeline Evaluation
Background
The EPA has required the MEW Responsible Parties, the Navy and NASA to prepare a
Focused Feasibility Study (FFS) for Groundwater. In part, purpose the of this study is to
take a hard look at the groundwater remedy that was developed pursuant to the 1989
Record of Decision, and adapt the remedy so that it would be more protective, and could
take advantage of new technologies and methods that would hasten the clean-up effort.
In addition, as a result of the 2010 Vapor Intrusion ROD Amendment, a new remedial
action objective (RAO) was established for the groundwater remedy. This new RAO
states:
“Accelerate the reduction of the source of vapor intrusion (i.e., Site contaminants in
shallow groundwater and soil gas) to levels that are protective of current and future
building occupants, such that the need for a vapor intrusion remedy would be minimized
or no longer be necessary.”
An earlier memo from CPEO was addressed to EPA in 2011 recommending the criteria
to be used in this FS. The memo states:
“The community, represented by the Community Advisory Board and Center for Public
Environmental Oversight believes that new Feasibility Study and remedy selection
should focus on the following:

In areas with high mass

In areas that continue to act as a source

In areas that reduce the need for long-term Vapor Intrusion mitigation

Where the detectable plume encroaches on residential areas, schools
and other sensitive uses

In areas that enable reasonable future use of the property.’
Two weeks ago, we received a Preliminary Draft Supplemental Site-wide Groundwater
Feasibility Study and a Draft Plume Cleanup Time Evaluation for the Middlefield-EllisWhisman Superfund Study Area. This memo is a review and analysis of these
documents, followed by some suggestions and questions concerning the reports’ contents.
1
Two Tables with background information concerning the current Groundwater Extraction
and Treatment Systems at MEW and Moffett are appended at the end of this memo. In
addition, Figures provided in the Annual Report Memo, can be of help in understanding
this memo and draft Feasibility Study.
Groundwater Feasibility Study
A Feasibility Study (FS) is intended to define the options for cleaning up contamination.
In the case of this Focused Feasibility Study (FFS), it is intended to supplement the FS
that was prepared in the late 1980s to incorporate new techniques and technologies that
could be more effective than had previously been considered. In addition, two additional
factors were incorporated into this FFS. The first was that an additional Remedial Action
Objective that was established in conjunction with the 2010 Vapor Intrusion ROD, which
states:
Accelerate the reduction of the source of vapor intrusion (i.e., Site contaminants
in shallow groundwater and soil gas) to levels that are protective of current and
future building occupants, such that the need for a vapor intrusion remedy would
be minimized or no longer be necessary.
The second has been the addition of 1,4-dioxane to the list of Chemicals of Concern
(COC), as well as deleting several COCs that are no longer a concern because of
infrequent low detections. 1,4-dioxane was commonly used as a stabilizer for another
industrial solvent, 1,1,1-TCA. It has been detected above the NPDES permit
requirements (3 μg/L). There is no MCL for 1,4-dioxane and 1 μg/L was selected as the
cleanup goal for the site.
1,4-dioxane, which is more mobile than TCE, is present in groundwater throughout the
plume at relatively low concentrations. The maximum concentration of 1,4-dioxane
detected in on-site monitoring wells between 2002 and 2009 is 24 μg/L in a sample
located within the slurry wall at the former Raytheon site. A monitoring well with a
concentration of 20 g/L has also been found North of 101. 1,4-dioxane does not present
a potential vapor intrusion risk due to its low potential to volatilize from groundwater.
The primary pathway of concern for 1,4-dioxane is ingestion.
Given the need to address the vapor intrusion RAO by accelerating groundwater cleanup,
EPA developed an overall strategy for cleanup of the plume. This strategy involves
aggressively targeting certain areas of the plume based on the concentration of the
CVOCs within the shallow A/A1 Zone. EPA has defined these targeted areas to include
former source areas and high concentration areas (i.e., greater than 1,000 μg/L). As
additional information is collected during implementation of the vapor intrusion remedy
and additional data is obtained during further site characterization, EPA may revise the
definition of the areas requiring targeted cleanup.
Four broad categories of technologies were considered in the FS. Only those that were
included are summarized below.
In-situ oxidation and reduction (redox) treatment. These include three in-situ
technologies, which are briefly described below. Each of the technologies has been pilot
tested at various facility-specific source areas at the Site as described below.
2

ISCO is generally applied in high concentration areas where conditions are
aerobic or only mildly reducing and there is little chemical oxidant demand from
reduced species. ISCO does not generally form any undesirable intermediate
degradation products such as vinyl chloride but can mobilize naturally occurring
metals present in subsurface soil. It must come into contact with the contaminant
to be effective. This is difficult in less permeable zones.

Enhanced reductive dechlorination (ERD) is a form of in situ bioremediation in
which a carbon source such as lactate, molasses, or vegetable oil is injected into
the subsurface to “feed” the microbial populations that metabolize chlorinated
compounds. In some cases, the native microorganisms are unable to metabolize
cis-1, 2-DCE and/or vinyl chloride, leading to potential accumulation of these
compounds. In such cases, the carbon substrate can be augmented with
microorganisms capable of completing the reductive dechlorination sequence
through ethene. The distribution of carbon substrate within the subsurface can be
enhanced by hydrofracturing or pumping and recirculation. ERD does not require
direct contact between the carbon substrate and the contaminant.

In-situ abiotic dechlorination using ZVI (zero-valent iron) entails the reduction of
chlorinated compounds that occur as ZVI placed into the subsurface is oxidized.
Intermediate degradation products such as DCE and vinyl chloride do not
generally persist with ZVI treatment. However, ZVI must be in direct contact
with the target contaminants as is the case with ISCO. Treatability studies using a
combination of a carbon substrate and ZVI (EHC®), have been conducted at the
Navy Sites 26 and 28. The pilot test results indicate that injection of ZVI can be
significantly more difficult to control than injection of carbon substrates (ERD),
but where ZVI injection is successful, appropriate reducing conditions may be
maintained for a longer period.
Extraction, removal, treatment and disposal. This includes the current system and the
optimized groundwater extraction system. Most of the treated water is discharged into
Stevens Creek. If discharge is significantly reduced, there may be ecological effects in
Stevens Creek, but I expect that the system will find equilibrium after some time.
Subsurface barriers. Permeable Reactive Barriers (PRBs) are installed downgradient
from or in the flow path of a contaminant plume. Contaminants in the plume react with
the media inside the barrier to either break the compound down into harmless products or
immobilize contaminants. This technology is a passive system that requires no pumping.
The most common of the permeable barrier walls is the Iron Treatment Wall, using ZVI.
PRB-like treatment zones also can be installed to depths as great as 100 ft or more.
Monitored natural attenuation (MNA). Several lines of evidence suggest that natural
attenuation processes are occurring in certain portions of plume. MNA is a system that
monitors these processes to ensure that they are proceeding as expected. MNA was
retained as a viable technology to be used in conjunction with other technologies. MNA
would not be implemented in residential or commercial areas if there is an existing risk or
potential increase in risk for vapor intrusion. When evaluating a transition from an active
remedy to MNA, the following general process would be followed:

Identify potentially applicable area for MNA transition
3








Complete MNA analysis based on lines of evidence criteria
Prepare a plan for MNA implementation and demonstration
Obtain EPA concurrence on the approach
Implement MNA
Document VOC loss
Document indirect (geochemistry) or direct (biological) evidence supporting
natural biodegradation processes
Estimate time to achieve RAOs under MNA
Document that vertical and downgradient containment is in place during MNA
demonstration
Five alternatives using these technologies were developed in order to provide
comparisons among the alternatives. It should be noted that the alternatives are best on
conceptual designs. The configuration of the alternative components such as the location
and number of extraction wells, the area for in-situ redox treatment, and location of PRBs
will likely be modified during the remedial design of the selected remedy. The five
alternatives are listed below:
Alternative 1: Existing Groundwater Treatment System
Alternative 2: Optimized Groundwater Treatment System
Alternative 3: Optimized Groundwater Treatment System and MNA
Alternative 4: Targeted In Situ Redox Treatment, Optimized Groundwater
Treatment System, and MNA
Alternative 5: Targeted In Situ Redox Treatment, PRBs, Optimized Groundwater
Treatment System, and MNA
These are summarized below, with the exception of alternative 1.
Alternative 2 – Optimized Groundwater Extraction and Treatment System (GWET)
The GWET systems would be optimized to improve mass recovery by installing
additional wells and modifying pumping rates. Wells would also be installed in areas
specified for targeted cleanup and medium concentrations areas of the plume, where
additional extraction would likely improve mass recovery. The optimization goal for
improved mass recovery is an approximate doubling of the extracted contaminant mass in
targeted areas, compared with the 2009/2010 mass recovery rates. It is estimated that this
alternative will reduce the high concentrations in the targeted areas approximately 30%
more in the first decade as compared to the current remedy (alternative 1).
Alternative 3 – Optimized GWET and MNA
This alternative includes a transition to MNA from the optimized GWET if it is
demonstrated that MNA is capable of achieving the RAOs in specific areas of the plume.
Specifically, the alternative would consist of the following:

GWET systems would be optimized to improve mass recovery in high and
medium concentration areas and to achieve complete hydraulic containment of the
regional plume, except where MNA is demonstrated.

The target for improved mass recovery is the same as alternative 2.

Some portions of the plume are assumed to already have sufficient lines of
4
evidence to warrant entering a MNA demonstration phase, reducing the number
of extraction wells. Optimized GWET systems would operate until groundwater
COCs are reduced to a concentration where sufficient evidence demonstrates that
subsequent passive treatment using MNA would be capable of meeting the RAOs
within a reasonable timeframe and it is determined that there is no risk from vapor
intrusion into overlying buildings.
Alternative 4 – Targeted In Situ Redox Treatment, Optimized GWET, and MNA
In this alternative, all high-concentration areas in the A/A1 Zone (concentrations
exceeding 1,000 μg/L) and facility-specific source areas (low to medium concentration
areas) would be treated with any of the three in situ redox technologies (ISCO, ERD,
ZVI), except where it is demonstrated that those technologies are infeasible. In those
situations, optimized GWET will be utilized. It is estimated that this alternative will
reduce the high concentrations in the targeted area approximately 50% more in the first
decade as compared to the current remedy (alternative 1).
In the lower aquifer zones, where high-concentration areas are more extensive and the
concern about vapor intrusion does not apply, in-situ redox technologies would be
targeted only at facility-specific source areas with high residual concentrations. The
extent of these treatment areas would be determined during the remedial design. For
purposes of this FS, it is assumed that approximately 15 percent of the facility-specific
source areas shown on the conceptual design figures would ultimately require treatment
by in-situ redox technologies.
Groundwater within the remaining regional plume (all aquifer zones) would be
hydraulically contained and treated using optimized GWET. Active treatment and
hydraulic containment may be transitioned to MNA when and if sufficient evidence
demonstrates, and ongoing monitoring confirms, that natural attenuation processes are
capable of meeting the RAOs within a reasonable timeframe.
Alternative 5 – Targeted In Situ Redox Treatment, PRBs, Optimized GWET, and MNA
For Alternative 5, one facility-specific PRB and three regional PRBs would be installed.
The facility-specific PRB would be installed in the A/A1 Zone only at the former Vishay
facility, to treat residual contamination following in situ treatment. The regional PRBs
would be installed in both the A/A1 Zone and the B1/A2 Zone in the following areas: (1)
on the north side of Highway 101 (mid-plume PRB); (2) on Moffett Field along Wescoat
Road (Wescoat PRB); and (3) on Moffett Field along King Road (downgradient PRB).
Costs Estimates
Costs estimates are based on a 50-year time period. The current system (without sunk
costs being accounted for) is estimated to cost $131 million. Alternative 2 (optimized
system) is estimated to cost $162 million. Alternative 3 (optimized system with MNA) is
estimated to cost $89 million. Alternative 4 (in-situ redox, optimized system, MNA) is
estimated to cost $141 million. Alternative 5 (in-situ redox, PRBs, optimized system,
MNA) is estimated to cost $171 million.
The following table provides some insight into the assumptions about cost, and I assume,
the model development. It provides the number of extraction wells that would be required
under each alternative. Of note is that in alternative 5, 80 extraction wells are assumed to
5
be shut down within the first 10 years. There is not much difference between alternatives
3 and 4 – they both have a marked decrease in the number of operating wells after 10 and
20 years. I assume that these assumptions are carried through in developing the model to
evaluate plume cleanup time.
Alternative
1
2
3
4
5
Number of Extraction Wells Assumed by Alternative
Time period Time period Time period Time period
0 - 10
11 - 20
21 - 30
31 - 40
100
99
92
89
112
111
103
100
98
42
30
29
88
32
23
22
20
20
18
18
Time period
41 - 50
88
N/A
29
22
18
Plume Cleanup Time Evaluation
A plume model was constructed to evaluate both cleanup times and mass removal rates
for each of the alternative. The results did not indicate a clear advantage of one
alternative over others with respect to the time required for the plume to meet MCLs,
which is projected to be centuries under all alternatives. This is primarily because the
model simulates the lasting effects of matrix diffusion (the process by which
contaminants are desorbed slowly from low transmissive zones to high transmissive
zones). Matrix diffusion becomes the dominant driver of lengthy cleanup times even
with aggressive treatments in high concentration areas. However, there are positive
results in mass removal rates for some alternatives.
In developing the model, the authors were careful not to overstate the accuracy of these
models. The report states that when “making relative comparisons of cleanup times
between the alternatives considered, the clean-up time estimates should not be expected
to be reliable much beyond one significant figure (e.g. a clean-up time estimates of 20 or
24 years should be viewed as effectively the same, and clean-up time estimates of 200
and 240 years should likewise be viewed as effectively the same). “ The authors also
observe that there is not a proven model that fits the regional plume, in part because of
the heterogeneity of the subsurface. They also note that simulations of each alternative
reflect the estimated cleanup time assuming that each technology is successful at
achieving its intended performance goals.
The authors attempt to model the plume by breaking parts of the subsurface into cells or
boxes, and modeling what is understood about the subsurface. The boxes were placed
within each aquifer zone into one or more longitudinal “strips” running parallel to the
groundwater flow direction. For example, in the A-aquifer zone, there are 21 boxes
transecting the entire plume midway from south to north, and 5 boxes on the eastern
edge. However, there are no boxes on the western portion of the plume with high
concentrations. For B1-aquifer zone, the boxes seem to intersect highest concentration
areas. For the B2-aquifer zone, boxes intersect the western and eastern portions of the
plume, and south of 101. The same boxes were used to evaluate cleanup times for each of
the alternatives.
6
I will not spend too much time analyzing the assumptions in the model, except to say that
many are questionable. The model assumes that all alternatives are implemented at once,
which is not realistic. I assume, although it was not specifically stated in the text of the
model report, that the number of wells in the cost estimate was carried through to the
model. Because only certain portions of the plume are modeled, and the results are
generalized for the entire plume, the model provides only a “best guess”, and should not
be relied upon except to provide a broad framework in which to analyze the alternatives.
Analysis
This is a very general set of alternatives. In practice, each strategy, if selected, would be
implemented over a period of years, and the actual end-result may look quite different
than any of the alternatives chosen. There would likely be multiple pilot tests and
treatability studies for alternatives 3, 4 and 5 over a number of years, which are not
reflected in the model.
It is important to note that the model described in the Draft Plume Cleanup Time
Evaluation indicated significant short-term reductions in high concentrations areas in the
A/A1-aquifer zone. This zone is most relevant for vapor intrusion. The model, no matter
how imperfect, indicates a clear advantage for using in-situ redox (alternative 4) than
with other techniques. For example, TCE concentrations in high concentration zones are
predicted to be reduced by 53% in 10 years. By comparison, alternatives 2 and 3 reduce
TCE concentrations from by 32% in the first 10 years. Alternative 4 also results in more
TCE concentration reductions compared to Alternatives 2, 3 and 5 for the 50-year and
100-year timeframes. However, I found it difficult to determine how performance goals
were established and much they were influenced by modeling results, or conversely, if
the performance goals were established and the model plugged them in.
For alternative 3, 4, and 5, there is no clear concentration level at which point the
optimized extraction system is transitioned to passive treatment using MNA. It is worth
noting that Site 26 at Moffett (a site not within the regional groundwater study area),
concentrations of VOCs are lower than 100 g/L and the remedial process us continuing.
Also, note that MNA will be applied only in cases where there is no risk from vapor
intrusion into overlying buildings.
The model results for alternative 5 are somewhat counter-intuitive: TCE concentrations
are predicted to increase during the first 10-year period. This is because the model
assumes that contaminants desorbed from the matrix would migrate with groundwater
flow until treatment by the permeable reactive barriers. That assumes that the PRBs
would be constructed at one time and 80% of the extraction wells would be turned off in
the first 10 years. Additionally, the locations of the four PRBs, 3 of which transect the
plume from east to west, do not have a basis that is explained in the FS.
A slurry wall/PRB was not retained for further review. The reasoning was that repairing
a damaged wall if this did not work would be too expensive. I think that this is a mistake:
the upstream side of at least one of the existing slurry walls could be retrofitted without a
requirement that it be retrofitted. The downstream side of the slurry wall would remain
intact. Although this is an unproven configuration, I do not believe that it presents too
much of a risk. The slurry walls are over 30 years old, and they are showing signs of age:
that is they are not fully containing the plume within the walls. Therefore, the optimized
7
system had to add additional capture wells downstream from the walls downstream
portions of the walls. On the other hand, it is difficult for the community to recommend a
solution, which in the view of the proponents, carries a significant financial risk.
Recommendations
I have the following recommendations:

The Groundwater FS should be integrated with the vapor intrusion remedy. There
is no integration of these reports with the vapor intrusion sampling data or the
proposed vapor intrusion remedies. Eventually, as there is a set of complete
indoor samples for the site, we would like to see this data integrated into the
remedy selection decision.

All Community Criteria should be addressed in the FS. Several of the Community
Criteria are not considered in the remedies. These criteria were listed at the
beginning of this memo and will not be repeated. Criteria concerning high mass
reduction and source areas are addressed. However, residential areas, facilities
housing sensitive populations and areas where there is likely to be future
development are not addressed. These areas may entail additional monitoring in
low-concentration areas near residential areas, and additional extraction wells
near low concentration areas and areas with sensitive receptors, such as schools.
The conceptual design for the optimized system may need adjustment to address
these areas.

No final decisions should be based on the model without other supporting
documentation. The Draft Plume Time Evaluation Report should only be used to
develop a comparative framework to evaluate the efficacy of the various
alternatives. It should not be determinative.

The model assumes that the remedies would be implemented overnight, and this
should be modified with professional judgment. Professional judgment would
give us a more realistic cleanup time evaluation.

The community should support alternative 4 (in-situ redox plus optimized system
and MNA). Alternative 4 is clearly preferable in terms of removing mass more
quickly than other alternatives.

The use of a slurry wall combined with a PRB should be reconsidered. As
described above, I don’t believe that this carries a high risk ($) of failure if done
prudently. If this is successful, other applications could greatly enhance the
effectiveness of the remedy, and may result in a decrease in long-term costs.

MNA should not be considered until concentrations reach 50 μg/L. The transition
from active remediation to MNA must be more definitive than is described in the
document. Because the Navy is required to continue to treat concentrations below
100 μg/L and more often below 50 μg/L, setting a higher level will cause
inequity. If this recommendation is adopted, both the Feasibility Study and the
Model must be re-evaluated to make sure that the conceptual design is within
keeping of this recommendation.
Questions and Suggestions
8
1.
Please add a figure with conceptual layout for each alternative within an aquifer
zone on one page for comparison.
2.
Please add a figure in the FS of plume time series (10 – 20 - 30 yrs. Etc) for each
alternative. Note that this is already presented in the Time Evaluation.
3.
Please explain the logic behind the placement of the PRBs in text. See Figure 413 for reference.
4.
Please add a figure for the A-aquifer zone plume and overlying buildings and
proposed projects of concern. This should include recent VI sampling results.
5.
Please provide an explanation of why was 1,000 μg/L selected as the target
concentration. Is it due to attenuation factors or some other reason?
6.
Please explain if, in the description of Alternative 4, where it is stated that: ”It is
estimated that this alternative will reduce the high concentrations in the targeted
area approximately 50% more in the first decade...” is driven by the model
simulation or was arrived at independently?
7.
The distribution of 1,4-dioxane in groundwater at the Site is shown on Figure 2-1.
It would be helpful to have an additional figure depicting contour lines of this
plume, using the most recent data available.
8.
Although mentioned as a new chemical of concern, treatment of 1,4-dioxane is
not addressed in any of the alternatives. Please confirm that it is EPA’s intent to
allow this contaminant to go untreated.
9.
Please explain why the TCE cleanup goal of 0.8 μg/L for deep wells has been
removed from Table 2-3 in the FS?
10.
We would like some additional explanation of the conclusion that multi-phase
extraction was not retained. Soil cleanup standards were established at 3 orders of
magnitude greater than groundwater standards. We have been unable to find the
source of these standards, and the vapor intrusion pathway has been identified
after soil standards were established. For this reason, these standards were
questionable. We have seen very good results with multiphase extraction at other
sites.
11.
We suggest using environmental molecular diagnostic tools, such as compoundspecific isotope analysis and qPCR to learn about rates of attenuation, what
factors are contributing and the application of both biotic and abiotic
enhancements, and the transition to MNA. (See ITRC EMD publications).
12.
There is no analysis of potential ecological effects of the various alternatives. For
example, if groundwater extraction and treatment systems significantly reduce
capacity, would there be any ecological effects along Stevens Creek? Is there a
need for a biological assessment when a remedy is chosen?
13.
Do the in-situ redox alternatives include hydrofracturing or pumping and
recirculation to enhance the distribution of carbon substrate within the
subsurface?
9
14.
How is the no action alternative defined in the Plume Time Evaluation Report?
Table 1 does not coincide with the Alternatives at the beginning of the report. All
figures in this report may need to be changed or clarified.
15.
Please explain how performance goals for each alternative were established. Did
modeling results influence them, or was there other information that was used? If
other information, please explain.
16.
Table 6 in the Draft Plume Time is mislabeled – it has two sub tables labeled the
same, latter should be B2 zone.
Appended Tables
Groundwater Extraction and Treatment System Summary
Extraction
Wells
9
10
15
8
N/A
3
2
8
Pounds of
VOCs
Removed in
2010
351
234
274
581
N/A
3.4
1.5
149
MEW Regional
Program S101
MEW Regional
Program N101
Navy WATS
10
458
15
544
9
306
NASA Ames
TOTAL
3
3.4
2,624
Facility
Fairchild (System 1)
Fairchild (System 3)
Fairchild (System 19)
Raytheon
Intel*
SMI
NEC/ Renesas
Vishay/SUMCO
Treatment
GAC
GAC
GAC
Oxidation/GAC
Bioremediation
GAC
None
UV/Oxidation/airstripper
GAC
Air-stripper/vaporphase GAC
Oxidation/GAC
GAC
Discharge
Location
Stevens Crk
Stevens Crk
Stevens Crk
Stevens Crk
N/A
Stevens Crk
Sanitary Sewer
Stevens Crk
Stevens Crk
Stevens Crk
Moffett storm
drain
Stevens Crk
Depth Intervals
Zone
A or A1 or Upper A
B1 or A2 or Lower A
B2
B3
C
Deep Aquifers
Approximate Depth Interval Below Ground
Surface
0 to 45 feet
50 to 75 feet
75 to 110 feet
120 to 160 feet
200 to 240 feet
> 240 feet
10