Evaluation of Potential Impacts of Microbial Activity on Drift Chemistry Rev 01, ICN 00

ANL-EBS-MD-000038 

November 2004

1. PURPOSE 
1.1 PURPOSE OF THE SCIENTIFIC ANALYSIS 
Evaluation of Potential Impacts of Microbial Activity on Drift Chemistry focuses on the potential 
for microbial communities that could be active in repository emplacement drifts to influence the 
in-drift bulk chemical environment. This report feeds analyses to support the inclusion or 
exclusion of features, events, and processes (FEPs) in the total system performance assessment 
(TSPA) for the license application (LA), but this work is not expected to generate direct feeds to 
the TSPA-LA. The purpose was specified by, and the evaluation was performed and is 
documented in accordance with, Technical Work Plan For: Near-Field Environment and 
Transport In-Drift Geochemistry Analyses (BSC 2004 [DIRS 172402], Section 2.1). This report 
addresses all of the FEPs assigned by the technical work plan (TWP), including the development 
of exclusion arguments for FEPs that are not carried forward to the TSPA-LA. Except for an 
editorial correction noted in Section 6.2, there were no other deviations from the TWP. 
This report documents the completion of all assigned tasks, as follows (BSC 2004 
[DIRS 172402], Section 1.2.1): 
 
Perform analyses to evaluate the potential for microbial activity in the waste 
emplacement drift under the constraints of anticipated physical and chemical conditions. 
 
Evaluate uncertainties associated with these analyses. 
 
Determine whether the potential for microbes warrants a feed to TSPA-LA to account 
for predicted effects on repository performance. 
 
Provide information to address the Yucca Mountain Review Plan, Final Report 
(NUREG-1804) (NRC 2003 [DIRS 163274]) and Key Technical Issues and agreements, 
as appropriate. 
 
Develop information for inclusion or exclusion of FEPs. 
The planned scientific approach specified the inclusion of the following activities (BSC 2004 
[DIRS 172402], Section 2.2): 
 
Review of repository-related microbiological and biogeochemical studies, to establish a 
defensible technical framework for the evaluation of the impacts of microbial activity on 
long-term repository performance 
 
Review of Yucca Mountain site characterization data for microbial population 
distributions, and identification of potential limiting factors for the growth of Yucca 
Mountain bacteria 
 
Description of the physical and chemical repository environment, as documented in 
other Project documents 

 
Systematic evaluation of the environmental constraints on microbial activity in actual 
repository environments 
 
Systematic evaluation of the impacts of microbial activity on waste drift chemistry. 
1.2 LIMITATIONS OF THE EVALUATION 
As provided by the TWP, the boundary conditions for this work are established in related process 
model documents, such as Multiscale Thermohydrologic Model (BSC 2004 [DIRS 169565]) and 
Engineered Barrier System: Physical and Chemical Environment (BSC 2004 [DIRS 169860]), 
and in applicable information exchange drawings (IEDs). This evaluation is limited to the drift 
environment established by those boundary conditions. 
The general chemical environments within the repository and its adjacent regions will remain 
oxic (containing oxygen) over the regulatory period of 10,000 years. As discussed in Section 
6.4, the oxygen concentration in the waste drift could be depleted during a thermal event, when 
the air mass is pushed away from the drift by water vapor, but this depletion is transitional and 
will not affect microbial reaction pathways in the repository. Also, oxygen will be consumed by 
metal corrosion within the drift. This consumption is ignored in this evaluation. 
1.3 SCOPE OF THIS DOCUMENT 
AP-SIII.9Q, Scientific Analyses, establishes the responsibilities and the process for performing 
and documenting this scientific analysis. In accordance with the outline specified by that 
procedure, the first three sections of this report place the work in the context of the plans and 
requirements established by the U.S. Department of Energy Office of Civilian Radioactive Waste 
Management and by the Yucca Mountain Project (YMP). In particular, Sections 2 and 3 of this 
report identify the applicability of the quality assurance (QA) program to this analysis, including 
software QA. 
Sections 4 and 5 present the essential information required for development of the conclusions 
found in Section 6 and summarized in Section 7. Section 4 documents the key inputs to the 
evaluation, including: 
 
Sources of information or data used to develop the conclusions (direct inputs) 
 
The acceptance and completion criteria, including the applicable criteria from 
NUREG-1804 
 
The required documentation level of accuracy 
 
The applicable codes, standards, and regulations. 
This report does not address any key technical issues. 
Section 6 evaluates the potential of microbial activity in the waste emplacement drift under the 
constraints of anticipated physical and chemical conditions, beginning with three sections that 
provide background. 

Section 6.1 reviews repository-related microbiological and biogeochemical studies to establish 
the framework for the evaluation of the impacts of microbial activity on long-term repository 
performance. 
Section 6.2 lists the included and excluded FEPs addressed in this analysis. 
Section 6.3 reviews Yucca Mountain site characterization data for microbial population 
distributions, and identifies potential limiting factors for the growth of bacteria in the repository. 
Section 6.4 describes the physical and chemical repository environment as documented in other 
YMP documents, and systematically evaluates the environmental constraints on microbial 
activity, leading to the conclusion that the high early temperatures, the oxic environment, the 
high-radiation field, and a scarcity of water and organic carbon will combine to limit microbial 
activity in the repository drifts. 
Section 6.5 systematically evaluates the potential impacts on repository chemistry, given limited 
microbial activity. 
Section 6.6 points out that the qualitative arguments and bounding calculations used in the 
evaluation fully capture uncertainties associated with the inputs. 
Section 7 summarizes the evaluation, and consists of conclusions, the recommendation regarding 
a feed to TSPA-LA, and satisfaction of the criteria listed in Section 4. 

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2. QUALITY ASSURANCE 
As stated in the TWP (BSC 2004 [DIRS 172402], Section 8.1), this report is subject to Quality 
Assurance Requirements and Description (DOE 2004 [DIRS 171539]). This analysis evaluates 
the effects of microbial activity on the environment in the engineered barrier system (EBS), 
which carries the Safety Category (SC) classification, as documented in Q-List (BSC 2004 
[DIRS 168361], Table A-2). 
Approved quality assurance procedures identified in the TWP (BSC 2004 [DIRS 172402], 
Section 4) have been used to conduct and document the activities described in this report. 
Specifically, this report has been prepared in accordance with AP-SIII.9Q, Scientific Analyses, 
and reviewed in accordance with AP-2.14Q, Document Review. All input data are identified and 
tracked in accordance with AP-3.15Q, Managing Technical Product Inputs. 
As required by the TWP (BSC 2004 [DIRS 172402], Section 8.4), electronic data were managed 
and controlled in accordance with AP-SV.1Q, Control of the Electronic Management of 
Information. To ensure accuracy and completeness of the information generated by the activities 
described in the TWP, access to information on the computer workstations used by all staff was 
controlled with password protection. Access privileges were set to prevent unauthorized changes 
to files housed on network servers. In addition, the servers were periodically backed up and the 
backups labeled and stored. All electronic files used in this activity were stored and backed up 
on network servers. There were no variances from these methods for controlling the electronic 
management of data. 

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3. USE OF SOFTWARE 
This report did not use any software described as controlled and baselined in LP-S1.11Q-BSC, 
Software Management. No solutions were obtained through the use of a commercial 
off-the-shelf software program. 

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4. INPUTS 
4.1 DIRECT INPUTS 
This section documents and substantiates the direct inputs used in this report (i.e., those data and 
other information items that were used to develop the results or conclusions). Because the 
conclusions are based on environmental factors that can severely limit microbial activity in the 
repository, only the inputs related to the limiting environmental factors are direct inputs. 
4.1.1 Direct Inputs from Project Sources 
Table 4.1-1 lists direct inputs from the following Project sources: 
 
Project data identified by data tracking number (DTN) 
 
IEDs 
 Analysis and model reports that support the TSPA-LA. 
None of the Project sources is a product output from a canceled/superseded document. 
Table 4.1-1. Direct Inputs from Project Sources 
Parameter(s) or Information Value(s) Source 
In-drift thermal history See Figure 6.4-1 BSC 2004 [DIRS 169856], Figure 6.5-3 
Evolution of air mass fractions in drift See Figure 6.4-2 BSC 2004 [DIRS 169856], Figure 6.5-8 
Growth rates of Yucca Mountain See Figure 6.4-4 DTN: LL040801512251.115 [DIRS 171476] 
aerobic bacteria in unconcentrated 
groundwater 
Range of relative humidity on all See Figure 6.4-5 BSC 2004 [DIRS 169565], Figure. 6.3-68 
waste packages 
Liquid saturations in fractures at 
three drift-wall locations 
See Figure 6.4-6 BSC 2004 [DIRS 169856], Figure 6.5-6 
Growth rates of Yucca Mountain See Figure 6.4-7 DTN: LL040801512251.115 [DIRS 171476] 
culturable aerobic bacteria as a 
function of macronutrient 
concentration 
Largest concentration of organic 1.1 mg/L DTN: GS011108312322.006 [DIRS 162911], 
carbon in qualified analyses of table name: S 01174_003, col. J 
groundwater from locations in the 
vicinity of Yucca Mountain 
CO2 flux See Figure 6.5-1 DTN: SN0407T0510102.017 [DIRS 170667], 
file: gas_flux.xls, worksheet: Moles per m chart 
Emplacement drift committed BSC 2004 [DIRS 170058] 
materials have no organic  
components 
A large quantity of Fe(III) may be BSC 2004 [DIRS 169868], Section 5.6 and 
accumulated from oxic steel  Table 6.3-4 
corrosion 

Table 4.1-1. Direct Inputs from Project Sources (Continued) 
Parameter(s) or Information Value(s) Source 
Under oxidizing conditions, Pu will BSC 2004 [DIRS 169425], Figure 6.5-5 
be dominated by Pu(V) and Pu(VI)  
instead of Pu(IV) 
Brine solutions ionic strength 10M BSC 2004 [DIRS 169860], Section 6.1.3 
4.1.2 Direct Inputs from Outside Sources 
Table 4.1-2 lists the direct inputs (from outside sources) that were obtained from investigation 
activities such as measurement, testing, and analysis. Of these outside sources, the National 
Institute of Standards and Technology (NIST) maintains the database of reaction constants that is 
accepted by the scientific and engineering communities as established fact, and therefore the 
constants do not need to be qualified in accordance with YMP procedures. Data from the other 
two external sources listed in Table 4.1-2 and Table 4.1-3 are not established fact and are 
therefore demonstrated to be qualified for their intended use in Table 4.1-4 in accordance with 
Section 5.2.1.1 of AP-SIII.9Q. 
Table 4.1-2. Numeric Data from Outside Sources Used as Direct Inputs 
Parameter(s) or Information Value(s) Source 
Upper temperature limit for microbial growth 110C Pedersen and Karlsson 1995 
[DIRS 100810] 
Concentration of O2 for aquatic sediments 
above which anaerobic microbial reactions 
are completely inhibited 
1 to 30 M (approximately 0.4 to 
10% atmospheric oxygen) 
Wang and Van Cappellen 1996 
[DIRS 171057], Table 3 
Water activity levels at which bacteria can 0.75 to 1.00 Pedersen & Karlsson 1995 
grow [DIRS 100810] 
Complexation constants See Table 6.5-2 NIST 2003 [DIRS 171201] 
Growth of Yucca Mountain bacteria See Table 6.3-1 Horn et al. 2004 [DIRS 171058] 
Table 4.1-3. Information from Outside Sources, Other Than Data, Used as Direct Inputs 
Information Source 
Water is essential for microbial growth. Horn et al. 2004 [DIRS 171058] 
There is negligible long-distance biocolloid transport in porous DeFlaun et al. 1997 [DIRS 171060] 
geologic media that are not significantly fractured. 
Table 6.1-1  Nutritional Requirements of Microorganisms Pedersen and Karlsson 1995 [DIRS 100810] 

Table 4.1-4. Qualification of Data for Its Intended Use (as Direct Input) for This Analysis 
Factors Description 
Pedersen and Karlsson 1995 [DIRS 100810] 
Description of use The study by Pedersen and Karlsson (1995 [DIRS 100810]) is used in Section 6.4.1 as 
a direct input for the maximum temperature at which known microorganisms can exist 
in an active state. This source is also used in Section 6.4.3 as a direct input for the 
level of water activity at which bacteria grow well. 
Extent to which the data 
demonstrate the 
properties of interest 
The study by Pedersen and Karlsson (1995 [DIRS 100810]) is a comprehensive 
literature survey on the ranges of temperature and water activity that are conducive to 
microbial activities. 
Qualifications of personnel 
or organizations 
generating the data 
Professor Karsten Pedersen is director of the Deep Biosphere Laboratory at Gteborg 
University, in Sweden. He has published more than 50 papers, reviews, and book 
chapters in the peer-reviewed international scientific press, and he has written many 
reports for international research agencies. He was engaged as an author and expert 
in microbiology for the Swedish National Encyclopaedia between 1990 and 2000, and 
wrote more than 150 entries. He is serving on four international scientific journals. He 
is on the editorial board of the Microbial Ecology and Geobiology journals, and is editor 
for Europe for the scientific Geomicrobiology Journal. Professor Pedersen is also an 
ad hoc reviewer for many different international scientific journals, including Nature 
and Science, and for research agencies such as the U.S. National Science 
Foundation. He was chairman of the European Science Foundations scientific 
program on groundwater pollution, GPoll, from 1998 to 2001. 
Reliability of data source Geochimica et Cosmochimica Acta is a professional scientific research journal of 
geochemistry and cosmochemistry. Articles are usually evaluated by three reviewers. 
Availability of 
corroborating data 
The maximum temperature is corroborated by Horn and Mike (1995 [DIRS 100765]). 
Wang and Van Cappellen 1996 [DIRS 171057] 
Description of use The study by Wang and Van Cappellen (1996 [DIRS 171057]) is used in Section 6.4.2 
as a direct input for a typical limiting O2 concentration, above which anaerobic 
microbial reactions are inhibited. 
Extent to which the data 
demonstrate the 
properties of interest 
These data, combined with the predicted O2 concentrations, demonstrate that 
anaerobic microbial reactions are unlikely. 
Qualifications of personnel 
or organizations 
generating the data 
Dr. Yifeng Wang, a geochemist at Sandia National Laboratories, is the originator of 
this scientific analysis document. Philippe Van Cappellen is Professor of 
Geochemistry at Utricht University, Holland. The work was performed at the School of 
Earth and Atmospheric Sciences, Georgia Institute of Technology. 
Reliability of data source Geochimica et Cosmochimica Acta is a professional scientific research journal of 
geochemistry and cosmochemistry. Articles are usually evaluated by three reviewers 
Horn et al. 2004 [DIRS 171058] 
Extent to which the input 
demonstrates the 
properties of interest 
This input is a premise antecedent to a limitation on microbial growth. 
Description of use The study by Horn et al. (2004 [DIRS 171058]) is used in Section 6.3, Table 6.3-1, and 
Figure 6.4-4 as a direct input to demonstrate that water is essential for microbial 
growth and for the growth rates of bacteria at Yucca Mountain. 
Extent to which the data 
demonstrate the 
properties of interest 
Demonstrated growth rates and total number of bacteria present in Yucca Mountain 
samples from the ESF. 
Qualifications of personnel 
or organizations 
generating the data 
Dr. Joanne Horn is a microbiologist at Lawrence Livermore National Laboratories, and 
is the originator of this scientific analysis document. 

Table 4.1-4. Qualification of Data for Its Intended Use (as Direct Input) for This Analysis (Continued) 
Factors Description 
Horn et al. 2004 [DIRS 171058] (Continued) 
Reliability of data source Geomicrobiology Journal is a professional scientific research journal of 
geomicrobiology. Articles are reviewed and evaluated by peers in the field of 
geomicrobiology. 
Availability of corroborating 
input 
This input is corroborated by Amy (1997 [DIRS 100696]), Amy and Haldeman (1997 
[DIRS 100697]), and Madigan et al. (2003 [DIRS 171083]). 
DeFlaun et al. 1997 [DIRS 171060] 
Extent to which the input 
demonstrates the 
properties of interest 
This input is direct support of a conclusion of this evaluation. 
Description of use The study by DeFlaun et al. (1997 [DIRS 171060]) is used in Section 6.5.4 as a direct 
input to demonstrate that there is negligible long-distance biocolloid transport in 
porous geologic media that is not significantly fractured. 
Extent to which the data 
demonstrate the properties 
of interest 
Microbial transport testing conducted in a sandy aquifer on the coastal plain of Virginia 
demonstrated that bacteria traveled the length of the flowfield, but was mostly retained 
between the injection point and 0.5-m sample area. 
Reliability of data source FEMS Microbiology Reviews is a professional scientific research journal of 
microbiology. The journal articles are peer reviewed and independently edited by 
acknowledged experts in their field of microbology. 
Availability of corroborating 
input 
This input is corroborated by Delany (1995 [DIRS 100134]) and Means (1982 
[DIRS 171136]). 
4.2 CRITERIA 
The TWP (BSC 2004 [DIRS 172402], Section 3) provides the applicable criteria from Yucca 
Mountain Review Plan, Final Report (NRC 2003 [DIRS 163274]), the required documentation 
of level of accuracy, and the source of completion criteria. Each criterion is detailed in Section 
4.2.1. 
4.2.1 Yucca Mountain Review Plan Criteria 
The TWP (BSC 2004 [DIRS 172402], Section 3.2) applies to this evaluation with the acceptance 
criteria for the model abstraction, Quantity and Chemistry of Water Contacting Engineered 
Barriers and Waste Forms. Yucca Mountain Review Plan, Final Report (NRC 2003 
[DIRS 163274]) lists the following acceptance criteria for that model abstraction (NRC 2003 
[DIRS 163274], Section 2.2.1.3.3.3): 
 
Acceptance Criterion 1  System Description and Model Integration Are Adequate. 
(1) 
Total system performance assessment adequately incorporates important design 
features, physical phenomena, and couplings, and uses consistent and appropriate 
assumptions throughout the quantity and chemistry of water contacting engineered 
barriers and waste forms abstraction process; 
(2) 
The abstraction of the quantity and chemistry of water contacting engineered 
barriers and waste forms uses assumptions, technical bases, data, and models, that 
are appropriate and consistent with other related U.S. Department of Energy 

abstractions. For example, the assumptions used for the quantity and chemistry of 
water contacting engineered barriers and waste forms are consistent with the 
abstractions of Degradation of Engineered Barriers (Section 2.2.1.3.1); 
Mechanical Disruption of Engineered Barriers (Section 2.2.1.3.2); Radionuclide 
Release Rates and Solubility Limits (Section 2.2.1.3.4); Climate and Infiltration 
(Section 2.2.1.3.5); and Flow Paths in the Unsaturated Zone (Section 2.2.1.3.6). 
The descriptions and technical bases provide transparent and traceable support for 
the abstraction of quantity and chemistry of water contacting engineered barriers 
and waste forms; 
(3) 
Important design features, such as waste package design and material selection, 
backfill, drip shield, ground support, thermal loading strategy, and degradation 
processes, are adequate to determine the initial and boundary conditions for 
calculations of the quantity and chemistry of water contacting engineered barriers 
and waste forms; 
(4) 
Spatial and temporal abstractions appropriately address physical couplings 
(thermal-hydrologic-mechanical-chemical). For example, the U.S. Department of 
Energy evaluates the potential for focusing of water flow into drifts, caused by 
coupled thermal-hydrologic-mechanical-chemical processes; 
(5) 
Sufficient technical bases and justification are provided for total system 
performance assessment assumptions and approximations for modeling coupled 
thermal-hydrologic and mechanical-chemical effects on seepage and flow, the 
waste package chemical environment, and the chemical environment for 
radionuclide release. The effects of distribution of flow on the amount of water 
contacting the engineered barriers and waste forms are consistently addressed, in all 
relevant abstractions; 
(6) 
The expected ranges of environmental conditions within the waste package 
emplacement drifts, inside of breached waste packages, and contacting the waste 
forms and their evolution with time are identified. These ranges may be developed 
to include: 
(i) 
the effects of the drip shield and backfill on the quantity and chemistry of 
water (e.g., the potential for condensate formation and dripping from the 
underside of the shield); 
(ii) 
conditions that promote corrosion of engineered barriers and degradation of 
waste forms; 
(iii) irregular wet and dry cycles; 
(iv) 
gamma-radiolysis; and 
(v) 
size and distribution of penetrations of engineered barriers; 

(7) 
The model abstraction for quantity and chemistry of water contacting engineered 
barriers and waste forms is consistent with the detailed information on engineered 
barrier design and other engineered features. For example, consistency is 
demonstrated for: 
(i) 
dimensionality of the abstractions; 
(ii) 
various design features and site characteristics; and 
(iii) alternative conceptual approaches. Analyses are adequate to demonstrate 
that no deleterious effects are caused by design or site features that the 
U.S. Department of Energy does not take into account in this abstraction; 
(8) 
Adequate technical bases are provided, including activities such as independent 
modeling, laboratory or field data, or sensitivity studies, for inclusion of any 
thermal-hydrologic-mechanical-chemical couplings and features, events, and 
processes; and 
(9) 
Performance-affecting processes that have been observed in thermal-hydrologic 
tests and experiments are included into the performance assessment. For example, 
the U.S. Department of Energy either demonstrates that liquid water will not reflux 
into the underground facility or incorporates refluxing water into the performance 
assessment calculation, and bounds the potential adverse effects of alteration of the 
hydraulic pathway that result from refluxing water. 
(10) 
Likely modes for container corrosion are identified and considered in determining 
the quantity and chemistry of water entering the engineered barriers and contacting 
waste forms. For example, the model abstractions consistently address the role of 
parameters, such as pH, carbonate concentration, and the effect of corrosion on the 
quantity and chemistry of water contacting engineered barriers and waste forms; 
(11) 
The abstraction of in-package criticality or external-to-package criticality, within 
the emplacement drift, provides an adequate technical basis for screening these 
events; 
(12) 
Guidance in NUREG-1297 [DIRS 103597] and NUREG-1298 [DIRS 103750] or 
other acceptable approaches, is followed. 
 
Acceptance Criterion 2  Data Are Sufficient for Model Justification. 
(1) 
Geological, hydrological, and geochemical values used in the license application 
are adequately justified. Adequate description of how the data were used, 
interpreted, and appropriately synthesized into the parameters is provided; 
(2) 
Sufficient data were collected on the characteristics of the natural system and 
engineered materials to establish initial and boundary conditions for conceptual 
models of thermal-hydrologic-mechanical-chemical coupled processes, that affect 
seepage and flow and the engineered barrier chemical environment. 

(3) 
Thermo-hydrologic tests were designed and conducted with the explicit objectives 
of observing thermal-hydrologic processes for the temperature ranges expected for 
repository conditions and making measurements for mathematical models. Data 
are sufficient to verify that thermal-hydrologic conceptual models address 
important thermal-hydrologic phenomena; 
(4) 
Sufficient information to formulate the conceptual approach(es) for analyzing water 
contact with the drip shield, engineered barriers, and waste forms is provided; and 
(5) 
Sufficient data are provided to complete a nutrient- and energy-inventory 
calculation, if it has been used to justify the inclusion of the potential for microbial 
activity affecting the engineered barrier chemical environment and the chemical 
environment for radionuclide release. As necessary, data are adequate to support 
determination of the probability for microbially influenced corrosion (MIC) and 
microbial effects, such as production of organic byproducts and microbially 
enhanced dissolution of the high-level radioactive waste glass form. 
 
Acceptance Criterion 3  Data Uncertainty Is Characterized and Propagated Through 
the Model Abstraction. 
(1) 
Models use parameter values, assumed ranges, probability distributions, and 
bounding assumptions that are technically defensible, reasonably account for 
uncertainties and variabilities, and do not result in an under-representation of the 
risk estimate; 
(2) 
Parameter values, assumed ranges, probability distributions, and bounding 
assumptions used in the total system performance assessment calculations of 
quantity and chemistry of water contacting engineered barriers and waste forms are 
technically defensible and reasonable, based on data from the Yucca Mountain 
region (e.g., results from large block and drift-scale heater and niche tests), and a 
combination of techniques that may include laboratory experiments, field 
measurements, natural analog research, and process-level modeling studies; 
(3) 
Input values used in the total system performance assessment calculations of 
quantity and chemistry of water contacting engineered barriers (e.g., drip shield and 
waste package) are consistent with the initial and boundary conditions and the 
assumptions of the conceptual models and design concepts for the Yucca Mountain 
site. Correlations between input values are appropriately established in the 
U.S. Department of Energy total system performance assessment. Parameters used 
to define initial conditions, boundary conditions, and computational domain in 
sensitivity analyses involving coupled thermal-hydrologic-mechanical-chemical 
effects on seepage and flow, the waste package chemical environment, and the 
chemical environment for radionuclide release, are consistent with available data. 
Reasonable or conservative ranges of parameters or functional relations are 
established; 

(4) 
Adequate representation of uncertainties in the characteristics of the natural system 
and engineered materials is provided in parameter development for conceptual 
models, process-level models, and alternative conceptual models. The 
U.S. Department of Energy may constrain these uncertainties using sensitivity 
analyses or conservative limits. For example, the U.S. Department of Energy 
demonstrates how parameters used to describe flow through the engineered barrier 
system bound the effects of backfill and excavation-induced changes; 
(5) 
If criticality is included in the total system performance assessment, the U.S. 
Department of Energy uses an appropriate range of input parameters for calculating 
the effective neutron multiplication factor; and 
(6) 
Where sufficient data do not exist, the definition of parameter values and 
conceptual models is based on other appropriate sources, such as expert elicitation 
conducted in accordance with NUREG-1563 [DIRS 100909]. 
 
Acceptance Criterion 4  Model Uncertainty Is Characterized and Propagated Through 
the Model Abstraction. 
(1) 
Alternative modeling approaches of features, events, and processes are considered 
and are consistent with available data and current scientific understanding, and the 
results and limitations are appropriately considered in the abstraction; 
(2) 
Alternative modeling approaches are considered and the selected modeling 
approach is consistent with available data and current scientific understanding. A 
description that includes a discussion of alternative modeling approaches not 
considered in the final analysis and the limitations and uncertainties of the chosen 
model is provided; 
(3) 
Consideration of conceptual model uncertainty is consistent with available site 
characterization data, laboratory experiments, field measurements, natural analog 
information and process-level modeling studies; and the treatment of conceptual 
model uncertainty does not result in an under-representation of the risk estimate; 
(4) 
Adequate consideration is given to effects of thermal-hydrologic-mechanical-
chemical coupled processes in the assessment of alternative conceptual models. 
These effects may include: 
(i) 
thermal-hydrologic effects on gas, water, and mineral chemistry; 
(ii) 
effects of microbial processes on the engineered barrier chemical 
environment and the chemical environment for radionuclide release; 
(iii) changes in water chemistry that may result from the release of corrosion 
products from the engineered barriers and interactions between engineered 
materials and ground water; and 

(iv) changes in boundary conditions (e.g., drift shape and size) and hydrologic 
properties, relating to the response of the geomechanical system to thermal 
loading; and 
(5) 
If the U.S. Department of Energy uses an equivalent continuum model for the total 
system performance assessment abstraction, the models produce conservative 
estimates of the effects of coupled thermal-hydrologic-mechanical-chemical 
processes on calculated compliance with the postclosure public health and 
environmental standards. 
 
Acceptance Criterion 5  Model Abstraction Output Is Supported by Objective 
Comparisons. 
(1) 
The models implemented in this total system performance assessment abstraction 
provide results consistent with output from detailed process-level models and/or 
empirical observations (laboratory and field tests and/or natural analogs); 
(2) 
Abstracted models for coupled thermal-hydrologic-mechanical-chemical effects on 
seepage and flow and the engineered barrier chemical environment, as well as on 
the chemical environment for radionuclide release, are based on the same 
assumptions and approximations demonstrated to be appropriate for process-level 
models or closely analogous natural or experimental systems. For example, 
abstractions of processes, such as thermally induced changes in hydrological 
properties, or estimated diversion of percolation away from the drifts, are 
adequately justified by comparison to results of process-level modeling, that are 
consistent with direct observations and field studies; and 
(3) 
Accepted and well-documented procedures are used to construct and test the 
numerical models that simulate coupled thermal-hydrologic-mechanical-chemical 
effects on seepage and flow, engineered barrier chemical environment, and the 
chemical environment for radionuclide release. Analytical and numerical models 
are appropriately supported. Abstracted model results are compared with different 
mathematical models, to judge robustness of results. 
4.2.2 Required Documentation of Level of Accuracy 
The TWP (BSC 2004 [DIRS 172402], Section 3.3) requires this report to state the level of 
accuracy, precision, and representativeness of the results of the analyses, and to state how each 
of these were determined. 
4.2.3 Completion Criteria 
The TWP (BSC 2004 [DIRS 172402], Section 3.4) requires the work that is done to be consistent 
with the activities performed as part of Technical Work Plan: Regulatory Integration Evaluation 
of Analysis and Model Reports Supporting the TSPA-LA (BSC 2004 [DIRS 169653]), and that it 
fulfill the portion of the Phase 2 work identified in that plan. That is, the work should address 
the prioritized list of actions selected in Phase 1 for disposition in Phase 2 (BSC 2004 
[DIRS 169653], Section 1.3). 

4.3 CODES, STANDARDS, AND REGULATIONS 
This report was prepared in accordance with 10 CFR Part 63 [DIRS 156605]. Relevant 
requirements for performance assessment from Section 114 of that document are: 
Any performance assessment used to demonstrate compliance with Sec. 113(b) 
shall: 
(a) 
Include data related to the geology, hydrology, and geochemistryused to define 
parameters and conceptual models used in the assessment. 
(b) 
Account for uncertainties and variabilities in parameter values and provide the 
technical basis for parameter ranges, probability distributions, or bounding values 
used in the performance assessment. 
(g) 
Provide the technical basis for models used in the performance assessment such as 
comparisons made with outputs of detailed process-level models. 
The source of complexation constants used in this evaluation is the NIST database of reaction 
constants. No other codes, standards, or regulations were used in the scientific analysis 
documented in this report. 

5. ASSUMPTIONS 
The analyses in this report use the following assumptions: 
 
Organic substances such as diesel fuel, diesel exhaust, lubricants, rock drill oil, coolants, 
and cleaning solvents may be introduced into the repository during construction and 
operations. The quantities and types of such substances will be controlled, with analysis 
of the potential impacts to waste isolation (BSC 2004 [DIRS 169885], Section 6.12.3); 
LP-SA-001Q-BSC, Determination of Importance and Site Performance Protection 
Evaluations). It is assumed that these control and analysis practices will continue during 
repository construction and operation, and that construction and operation activities will 
not contribute committed materials that cause microbial activity to significantly affect 
the in-drift chemical environment. 
 
The concentrations of organic carbon in groundwater at Yucca Mountain will remain at 
a current level (< 1.1 mg/L) over the whole regulatory time period. Most groundwaters 
that are not affected by pollution have dissolved organic carbon concentrations below 
2 mg/L (Drever 1997 [DIRS 140067], p. 118). Thus, even if future climatic changes 
may take place at Yucca Mountian site, the organic carbon concentrations in 
groundwaters are expected to be still less than 2 mg/L. Such small changes will not 
affect the conclusion about nutrient limitations in this document. 

INTENTIONALLY LEFT BLANK 

6. SCIENTIFIC ANALYSIS AND DISCUSSION 
This section evaluates the potential of microbial activity in the drift, under the constraints of 
anticipated physical and chemical conditions. The first three sections provide background. 
Section 6.1 reviews microbiological and biogeochemical studies for repositories, including 
Yucca Mountain. Section 6.2 lists the FEPs addressed in the analyses. Section 6.3 reviews 
Yucca Mountain site characterization data for microbial population distributions, and identifies 
potential limiting factors for the growth of Yucca Mountain bacteria. 
The conclusions of the evaluation are based on Section 6.4 and Section 6.5. Section 6.4 
describes the physical and chemical repository environment as documented in other YMP 
products and systematically evaluates the environmental constraints on microbial activities. 
Section 6.5 systematically evaluates the potential impacts on repository chemistry, given the 
limitations of microbial activity. Section 6.5.1 concludes that the effects on water chemistry are 
negligible. Although microorganisms may release chemicals that complex with radionuclides, 
Section 6.5.2 concludes that either the concentrations of complexing agents are low, or their 
binding sites will be dominated by iron ions, or both. Section 6.5.3 concludes that potential 
effects on radionuclide solubility can be conservatively ignored. Section 6.5.4 examines the 
potential for biocolloid-facilitated transport; it concludes that the concentration of suspended 
microbial cells is low compared to that of groundwater colloid particles and a separate 
consideration of biocolloid-facilitated transport is not necessary. Section 6.6 notes that 
uncertainties in the input parameters are fully captured by qualitative arguments and bounding 
calculations. 
6.1 SYSTEMATICS OF REPOSITORY BIOGEOCHEMISTRY 
Microbes are ubiquitous in the subsurface environment, and play a major role in the 
biogeochemical cycling of various elements. Of particular concern is the microbial impact on 
radioactive wastes disposed of within deep geological formations. Under appropriate conditions, 
various microbial processes can operate, and will potentially affect the mobility of radionuclides 
and the integrity of the engineered barrier system (EBS) of the repository. In this section, the 
general concepts of subsurface biogeochemistry related to nuclear waste disposal in a deep 
geologic formation are reviewed, and the relevant processes are identified. 
6.1.1 Heterotrophs Versus Autotrophs 
Depending on the availability of nutrients, electron donors, and electron acceptors, as well as 
other environmental factors, various microbial processes with diverse metabolic activity can be 
stimulated (Chapelle 2001 [DIRS 171162], Chapter 4). The environmental factors that can 
potentially affect microbial growth and activity include moisture, temperature, pH, Eh, 
availability of organic and inorganic nutrients, and radiation. Microbes are exceedingly 
adaptable, and they are successful in colonizing a new environment. In fact, the environment 
provides the conditions necessary for the selection and adaptation of the organisms. The 
metabolic pathway that a given microorganism will use depends on the energy source (light or 
chemical); thus, a microorganism is described as either a phototroph or chemotroph, 
respectively. In a deep geologic repository, the activity of phototrophs can be excluded because 

of the lack of a light source after closure. On the basis of the environmental conditions and 
nutrient availability, the types of organisms that can exist in the Yucca Mountain repository 
environment should primarily follow the chemotrophic metabolic pathway. 
If a chemotroph uses organic carbon as its source of carbon, it is referred to as a heterotroph; if it 
derives energy from the oxidation of inorganic compounds and derives cell carbon from CO2, it 
is called an autotroph. Table 6.1-1 shows the nutritional requirements of microorganisms. 
Because of their different nutritional requirements, the activities of these two groups of 
microorganisms in a deep geologic repository are limited in different ways, depending on the 
ambient chemical environment and the type of wastes to be emplaced in the repository. 
Table 6.1-1. Nutritional Requirements of Microorganisms 
Type Carbon Source Electron Source or Sink Example of Organisms 
Autotrophic CO2 H2, NH4 
+, NO2 
-, Mn2+ , 
Fe2+, H2S, S 
Ammonium, nitrite, manganese 
iron, sulfur, and hydrogen-
oxidizing bacteria; methanogenic 
bacteria 
Heterotrophic Organic 
compounds 
O2, NO3 
-, MnO2, Fe(OH)3, 
SO4 
2-, organic compounds 
Most bacteria 
Source: Pedersen and Karlsson 1995 [DIRS 100810]. 
Autotrophs obtain their energy by the oxidation of inorganic compounds or ions, and acquire 
from CO2 the carbon necessary for cell synthesis. A typical pathway of autotrophic metabolism 
is the H2-based methanogenesis, which can be described by the following overall reaction: 
4H 2 +CO2 . CH 4 + 2O H (Eq. 6-1) 
2 
An autotrophic reaction is generally limited by the availability of inorganic electron donors such 
as H2 in Equation 6-1. To support cellular growth, autotrophs fix CO2 through a Calvin cycle 
(Chapelle 2001 [DIRS 171162], p. 111). The Calvin cycle begins with the reaction of CO2 with 
ribulose 1,5-diphosphate (RuDP) to form a six-carbon compound, which is then split into two 
molecules of 3-phosphoglycerate (PGA). Both PGA molecules are then reduced by 
nicotinamide adenine dinucleotide phosphate (NADPH). Next, a molecule of RuDP is 
regenerated, and the cycle repeats. Three turns of the cycles are necessary for the production of 
one molecule of glyceraldehydes-3-phosphate. A total of 12 NADPH and 18 ATP (adenosine 
triphosphate) are required to synthesize 1 hexose molecule. Therefore, the autotrophic fixation 
of CO2 requires a considerable investment of energy (Chapelle 2001 [DIRS 171162], p. 111). As 
a result, the direct utilization of CO2 by autotrophs in subsurface systems is probably slow. In 
contrast, heterotrophs show a great range of flexibility with respect to carbon sources. Some 
bacteria will degrade almost any reduced carbon source, whereas others will only catabolize a 
few carbon compounds. Heterotrophic metabolism dominates over autotrophic metabolism in 
many subsurface environments, even in some pristine environments where the organic carbon 
supply is relatively limited, since it is observed that carbonate species, which are the end 
products of heterotrophic metabolism, are accumulated in these natural systems (Chapelle 2001 
[DIRS 171162]). 

6.1.2 Microbially Mediated Redox Processes 
Microbial groups are known to use many redox pairs to derive their energy. If such chemical 
kinetic constraints exist that the rate of a given chemical reaction is sufficiently slow, bacteria 
can compete; thus, almost any redox pair that yields energy could be exploited. Microorganisms 
tend to accumulate at redox interfaces, where both metabolic electron donors and electron 
acceptors are available. Numerous studies have shown that microbial metabolism couples the 
inorganic redox chemistry of groundwaters to the oxidation of organic carbon (e.g., Lovley and 
Phillips 1988 [DIRS 171171]). As discussed in Section 6.1.1, heterotrophs derive their energy 
from the oxidative breakdown of external organic substrates; hence, microbial ecologies are 
frequently classified in terms of dominant pathways. The principal pathways are aerobic 
respiration, denitrification, manganese reduction, iron reduction, sulfate reduction, fermentation, 
and methanogenesis. From a biochemical point of view, the energy-yielding metabolic processes 
involve complex electron transfer chains. From a geochemical perspective, the significant 
reaction is the final electron transfer to an external electron acceptor. The common electron 
acceptors in subsurface environments are O2, NO3 
-, MnO2, Fe(OH)3, SO42-, and CO2. 
Fermentation does not rely on an external electron acceptor; instead, it partially oxidizes and 
reduces an organic substrate. The final fermentation products include CO2, H2, alcohols, and 
organic acids (Table 6.1-2). 
The primary pathways of organic carbon oxidation tend to occur in a predictable sequence 
(Table 6.1-2). The most energetically favorable is aerobic respiration, followed, in order of 
decreasing free energy yield, by denitrification, Mn(IV) reduction, Fe(III) reduction, sulfate 
reduction, and methanogenesis. The differences in the energy yields of these reactions, plus the 
availability of electron acceptors, lead to physical (spatial or temporal) separation of redox zones 
in which each pathway dominates. Because aerobic respiration is the most energetically 
favorable reaction, aerobic bacteria have a competitive advantage over anaerobic 
microorganisms when a certain level of O2 is present. This redox sequence is well established 
for natural systems including aquatic sediments (Wang and Van Cappellen 1996 
[DIRS 171057]), groundwater systems (e.g., Chapelle 2001 [DIRS 171162]), and landfills (e.g., 
Baedecker et al. 1993 [DIRS 171125]). This sequence imposes an important constraint on 
metabolic processes that can occur in a specific repository environment. 
The distribution of dissimilative pathways depends not only on their relative energy yields but 
also on the availability of organic carbon and electron acceptors. Hence, not all pathways 
necessarily occur within a given system. Most pristine subsurface systems, especially the UZs 
(such as those in Yucca Mountain), are oligotrophic (organic-poor) and, thus, generally remain 
aerobic. Within systems that have significant inputs of organic materials, O2 may become 
depleted, thereby allowing the emergence of anaerobic metabolic pathways. 
Anaerobic degradation of organic compounds generates a variety of reduced species (e.g., H2, 
NH4+, NO2 
-, Mn2+, Fe2+, H2S, and S) as metabolic products. Autotrophic bacteria can use these 
reduced species as their energy source. Thus, the anaerobic oxidation of organic compounds, 
coupled with the reduction of electron acceptors, could be the primary source of reduced 
inorganic substrates that are used for autotrophic metabolism. In such systems, both 
heterotrophic and autotrophic microbial activities are limited by the supply of organic carbon in 
the subsurface systems. Reduced inorganic species also can be derived from ferrous minerals in 

ambient rocks or from anoxic corrosion of waste package materials in a repository; the latter 
generates H2. 
Table 6.1-2. Representative Heterotrophic Metabolic Pathways 
Primary Pathways 
Aerobic respiration: CH2O + O2 = CO2 + H2O 
Denitrification: CH2O + 4/5NO3 
- + 4/5H+ = 2/5N2 + CO2 + 7/5 H2O 
Manganese reduction: CH2O + 2MnO2 + 4H+ = 2Mn2+ + CO2 + 3H2O 
Iron reduction: CH2O + 4FeOOH + 8H+ = 4Fe2+ + CO2 + 7H2O 
Sulfate reduction: CH2O + 1/2SO4 
2- + H+ = 1/2H2S + CO2 + H2O 
Fermentation: 6CH2O = CH3COOH + CH3CH2COOH + CO2 + H2 
Methanogenesis: CH2O = 1/2CH4 + 1/2CO2 
Source: Van Cappellen and Wang 1996 [DIRS 171128]. 
6.1.3 Relevant Biogeochemical Processes 
The relative importance of various microbial processes in a specific repository greatly depends 
on the ambient environment of the repository, and the materials to be emplaced (Figure 6.1-1). 
A repository in unsaturated igneous rock formations (such as volcanic tuff rocks at Yucca 
Mountain) is generally expected to be oxidizing in its chemical environment; a repository in a 
hydrologically saturated zone, particularly in sedimentary rocks, could be reducing. Sedimentary 
rocks contain a certain amount of organic matter, which may stimulate significant microbial 
activities and, thus, maintain the repository and its surrounding areas in a reducing condition. 
Both low-level and intermediate-level radioactive wastes contain a large portion of organic 
materials (e.g., cellulosics) and a significant amount of inorganic nutrients (e.g., NO3 
-). 
Microbial degradation of these materials has been a major concern for long-term repository 
performance assessment. An example is the Waste Isolation Pilot Plant (WIPP), which is located 
within a salt bed in Southern New Mexico and was designed for disposal of defense-related 
transuranic wastes. Microbial degradation of organic carbon-rich materials in the WIPP 
repository has been studied for its impact on repository pressurization and water chemistry 
(Francis et al. 1997 [DIRS 171062]; Wang et al. 1997 [DIRS 171122]). Unlike low-level and 
intermediate-level wastes, high-level radioactive wastes generally contain no organic materials, 
and are not conducive to microbial activity. In addition to the ambient rocks and the introduced 
materials, groundwater and gas flow may also provide inputs of organic compounds, electron 
acceptors (e.g., O2 and NO3 
-), and electron donors (e.g., H2), in addition to micronutrients. 
As discussed in Section 6.1.1, based on the nutritional requirements, microorganisms in a 
repository can be classified into two groups: heterotrophs and autotrophs. The interplay of the 
two groups of microbes is shown in Figure 6.1-1. The overall activity of heterotrophs is limited 
by the supply of organic carbon; the relative importance of individual reaction pathways depends 
on the availability of electron acceptors. Similarly, autotrophs are limited by the supply of 
electron donors and inorganic carbon. Since carbon dioxide is present in most systems, the 
availability of reduced inorganic species (e.g., H2) is expected to be a major limiting factor for 
autotrophs. 

MW = Molecular weight; RN = Radionuclides. 
Figure 6.1-1. Systematics of Repository Biogeochemistry 
ANL-EBS-MD-000038 REV 01 6-5 November 2004 

In a nuclear-waste repository, the electron donors are derived from three sources: 
 
The anaerobic oxidation of organic compounds by heterotrophic bacteria can serve as the 
primary source of both the reduced inorganic substrates and the inorganic carbon for 
autotrophic metabolisms. For instance, fermentation produces H2 and CO2, both of 
which are needed by autotrophic methanogens for synthesizing methane. 
 
A large fraction of metals or metal alloys is always present in repositories, either as waste 
package materials or as other engineered components. Anoxic corrosion of these metals 
generates hydrogen gas: 
Fe + 2H2O = Fe(OH)2 + H2 (Eq. 6-2) 
 
Reduced inorganic species may be brought in by groundwater or gas flows from the 
surrounding areas. 
Sustainable autotrophic microbial activity requires the accumulation of a certain amount of 
reduced inorganic species in the repository, implying that a reducing environment is a 
prerequisite to possible autotrophic microbial activity within a geologic repository. As discussed 
further in subsequent sections, this requirement is not satisfied for the Yucca Mountain 
repository. Figure 6.1-1 illustrates the possibility that, through biomass recycling, a biomass 
synthesized by autotrophic bacteria can be used by heterotrophs. 
The impacts of microbial activity on repository performance are several-fold (Wang and 
Papenguth 2001 [DIRS 171123]). The following impacts may affect radionuclide mobility in a 
specific repository environment: 
 
Microbes may be directly involved in redox reactions of multivalent radionuclides such 
as uranium and plutonium (Francis et al. 1991 [DIRS 171134]), whose solubilities highly 
depend on oxidation states. 
 
Microbial reactions may play an important role in regulating water chemistry (e.g., pH, 
Eh, and SCO2) as well as secondary mineral distributions (i.e., radionuclide sorption 
sites). 
 
Microorganisms release low molecular weight (MW) organic acids including acetate, 
lactate, and formate, which are able to complex with radionuclides. On the other hand, 
biodegradation may eliminate organic ligands and reduce the mobility of radionuclides. 
 
Microbial cells may act as colloidal particles and thus facilitate radionuclide transport. 
Additionally, microbial reactions may impact metal corrosion and therefore the integrity of the 
engineered barrier system (EBS). The combination of radionuclide mobility and EBS integrity 
ultimately controls total radionuclide release from a repository. 

Figure 6.1-2. Microbial Transformations of Radionuclides and Metals in Wastes 
Source: Francis 1990 [DIRS 171093]. 
Mobilization or immobilization of radionuclides by the activities of autotrophs (in the case of 
inorganic compounds) and by heterotrophs (in mixed wastes containing organics) could be 
significant (Francis 1990 [DIRS 171093], Figure 6.1-2): 
 
Autotrophic activity. The iron and sulfur oxidizing bacteria play a significant role in the 
solubilization of uranium from ores and mill tailings. The biogeochemistry of uranium 
has been extensively studied in light of the recovery of U from ores. Microbial leaching 
of pyretic uranium ore is primarily indirect, and confined to the generation of the 
oxidizing agent, ferric sulfate, and the solvent sulfuric acid. The indirect involvement of 
Fe2+/Fe3+ in the process of cyclically mediating the oxidation of the insoluble uranium 
oxide has been documented: UO2 + Fe3+ .UO22+ + 2Fe2+. T. ferroxoxidans can also 
directly oxidize reduced compounds of uranium (uranous sulfate and UO2) to their 
hexavalent form without the involvement of extraneous Fe3+/Fe2+ complex as the 
chemical electron carrier. Iron- and sulfur-oxidizing bacteria (T. ferrooxidans and 
T. thiooxidans) were isolated from several uranium ores. 
 
Heterotrophic activity. An increase in heterotrophic microbial activity due to 
biodegradation of organic compounds can affect the solubility of radionuclides and 
metals. Heterotrophic bacteria and fungi are able to release metals from various 

materials, including copper-nickel concentrates, low-grade copper ore, uranium and 
manganese ore. Several mechanisms for heterotrophic aerobic microbial solubilization of 
insoluble metal have been proposed. These include organic acid production, formation of 
chelating agents, and metabolism of metal-associated anion. Leaching by heterotrophic 
organisms is entirely due to chemical reaction of excreted microbial metabolites and 
decomposition products. 
Figures 6.1-1 and 6.1-2 provide a theoretical framework for the evaluation of the microbial 
activity within the repository. Note that (in addition to the processes described in Figure 6.1-1 
and Figure 6.1-2) temperature, water availability, and radiation will play an important role in the 
regulation of microbial activities within the repository during relevant periods. 
6.1.4 Status of Repository-Related Microbiological Studies 
In the past two decades, numerous studies have been conducted on microbial population 
distributions related to nuclear waste disposal. The results are summarized in Tables 6.1-3 
through 6.1-6. For example, a survey of microbial population distributions in water and subsoil 
samples (from deep mines designated for disposal of high-level radioactive waste in Europe) was 
conducted by West et al. (1985 [DIRS 110047]; 1986 [DIRS 171088]). They reported finding a 
variety of organisms representing autotrophic and heterotrophic groups that include native 
organisms and organisms introduced from mining operations. The presence of active microbial 
populations in deep subsurface environments clearly suggests that, under certain conditions, 
these microbes could play a significant role in the transformation and transport of radionuclides 
in the subsurface environments. Furthermore, microbial effects on low-level radioactive wastes 
disposed of in shallow-land burial grounds, and their potential effects in deep geological 
formations, are of considerable interest for assessing the performance of waste repositories, and 
from the standpoint of environmental remediation of contaminated sites. Microorganisms have 
been detected in backfill materials, natural analogue sites, plutonium-contaminated soils, 
low-level radioactive wastes, and waste-repository sites slated for high-level radioactive wastes. 
It can be seen from Tables 6.1-3 to 6.1-6 that microbial population varies greatly between 
locations within a specific site and between different sites. Microbial populations at the 
surveyed sites are generally lower than 107 cells per gram, with the exception of populations 
found within some bentonite materials, in which the population can be higher than 1011 cells per 
gram. Generally, it is difficult to correlate the presence of specific organisms with site 
conditions. The presence of a specific set of bacteria does not guarantee that they will be active; 
some of them may be dormant if conditions are not conducive to their active state. This implies 
that data on microbial population alone are not able to provide sufficient information on the 
geochemical impact of microbial activities. 
Efforts also have been made to model the microbial processes within repositories. McKinley 
et al. (1997 [DIRS 100796]) proposed an approach to calculating the upper limit of microbial 
population, based on energy and mass balance. In this approach, all possible redox reactions are 
first identified, and the total energy released from these reactions is calculated from the change in 
Gibbs free energy of formation across each reaction. The calculated energy is then converted to 
the number of microbial cells. The maximum microbial population can also be estimated from a 
mass balance calculation of nutrients. Another modeling approach has been developed based on 
the determination of individual metabolic pathways and their relative contributions. For 

instance, Humphreys et al. (1997 [DIRS 171127]) developed a biogeochemical source term 
model for low-level radioactive waste disposal. In this model, both microbial degradation and 
metal corrosion were considered. Monod kinetics were used to describe microbial processes. A 
similar, but simpler, approach was used to describe microbial gas generation in the WIPP 
repository (Wang et al. 1997 [DIRS 171122]). 
The first approach, which is primarily focused on the upper bounds of biomass production, is not 
sufficient for addressing the overall impacts of microbial activity on repository chemistry. 
Therefore, this approach, though previously adopted by the YMP (CRWMS M&O 2000 
[DIRS 151561]), is no longer intended for use in this report. Importantly, in the current 
repository design, organic components that could contribute to microbial growth have been 
eliminated from the list of committed materials (BSC 2004 [DIRS 170058]). This design change 
allows us to evaluate microbial activity in the Yucca Mountain repository using simple bounding 
calculations with relevant environmental constraints. 
Table 6.1-3. Abundance of Microorganisms in Plutonium-Contaminated Soils and Radioactive Wastes 
Sample Source Plutonium 
Concentration 
Microorganisms Detected Reference 
SOIL N/A Bacteria Au and Leavitt 1982 
Nevada Test Site 2.9  0.3 to 8.0  0.7  106/g [DIRS 171090] 
Area 13 Fungi 
(Soil pH 8.4  9.2) 3.1  0.7 to 24.6  2  103/g 
Los Alamos National Labs N/A Bacteria Barnhart et al. 1979 
TRU waste shallow burial 
site TA-54, 
aerobes: 2.3  106/g 
anaerobes: 3.3  106/g 
[DIRS 171092] 
Area C Actinomyctetes 
detected with depth, not 
counted 
Fungi 
4.9  104/g 
SEDIMENT/WATER: Johnson et al. 1974 
Rocky Flats Plant: Pond [DIRS 171153] 
B1 
Sediment 
(Total Pu 81.5 mCi) 1000 dpm/g Bacteria 
aerobes: 3 - 300  106/mL 
anaerobes: 0.2 - 2.0  106/mL 
Water N/A aerobes: 1.1 - 340  103/mL 
anaerobes: 2 - 7.8  102/mL 

Table 6.1-3. Abundance of Microorganisms in Plutonium-Contaminated Soils and Radioactive Wastes 
(Continued) 
Sample Source Plutonium 
Concentration 
Microorganisms Detected Reference 
WASTE  SOLIDS: 
239Pu contaminated waste 
from a steel burial drum 
N/A 
Bacteria 
aerobes: 33 - 9500/sample 
Fungi: 46 CFU/sample 
Barnhart et al. 1979 
[DIRS 171092] 
Waste leachates: Francis 1990 
Maxey Flats, KY [DIRS 171093] 
Trench 19S: 
238Pu 170 000 pCi/L Bacteria 
239,240Pu 210 000 pCi/L aerobes: 2.2  102 CFU/mL 
anaerobes: 3.2  102 CFU/mL 
N/A = not available. 
Table 6.1-4. Bacteria Detected in Radioactive Waste Repository Environments 
Site Bacteria Detected Reference 
Waste Isolation Pilot Plant (WIPP), 
New Mexico, USA 5M NaCl brine 
(pH 7) 
Repository Groundwater 
Far-field: 1.02  0.49  105 cells/mL 
Near-field: 1.24  0.13  105 cells/mL 
(denitrifiers, fermenters, sulfate reducers, 
methanogens 
Francis et al. 1998 
[DIRS 171078] 
Nevada Test Site, USA Study Site Groundwater 
102 viable cells/mL (Pseudomonas, 
Acinetobacter) 
Amy et al. 1992 
[DIRS 116973] 
sp Hard Rock Lab, Sweden granite 
fracture zone (pH 7.5) 
0.44  9.3  105 cells/mL (methanogens and 
homoacetogens) 
Pedersen et al. 1996 
[DIRS 171101] 
Grimsel Test Site, Switzerland granite 
shear zone (pH 10) 
3.97  0.37  103 cells/mL (fermenters and 
homoacetogens) 
Gillow et al. 2000 
[DIRS 171096] 
Yucca Mountain tuff, Nevada, USA 0.32  2.0  105 cells/g Kieft et al. 1997 
[DIRS 100767] 
Table 6.1-5. Number of Bacteria at Natural Analogue Sites 
Analogue Site Bacteria Detected Reference 
Cigar Lake uranium ore deposit, 
Saskatchewan, Canada  
sandstone w/ clay-hosted U ore 
Groundwater: 4.7  102  4.4  104 cells/mL 
(denitrifiers, fermenters, sulfate reducers, 
methanogens) 
Ore: 1.4  0.9  105 cfu/g viable cells 
(denitrifiers) 
Francis et al. 1994 
[DIRS 110014] 
Pocos de Caldos, Brazil Yes West et al. 1992 
[DIRS 171109] 
Oklo, Gabon, Africa Yes Pedersen et al. 1996 
[DIRS 171103] 
Yucca Mountain tuff, Nevada, USA 0.32  2.0  105 cells/g Kieft et al. 1997 
[DIRS 100767] 

Table 6.1-6. Microbial Population in Backfill Materials Proposed for Use at the Radioactive Waste 
Repositories 
Backfill Bacteria Detected Reference 
Wyoming bentonite 5.32  0.34  1011 cells/g; 
<1.07  3.54  102 cfu/g viable cells 
Haveman et al. 1995 
[DIRS 171097] 
Avonlea bentonite 6.29  0.75  1011 cells/g; 
3.48  0.56  104 cfu/g viable cells 
Haveman et al. 1995 
[DIRS 171097] 
Canadian sand and 
bentonite buffer material 
101 to 106 viable cells/g 
(Acinetobacter, Pseudomonas) 
Stroes-Gascoyne et 
al. 1997 
[DIRS 171108] 
6.2 FEATURES, EVENTS, AND PROCESSES ADDRESSED BY THIS ANALYSIS 
Tables 6.2-1 and 6.2-2 list the FEPs that are addressed in this report in accordance 
with the technical work plan (TWP) (BSC 2004 [DIRS 172402], Section 2.5), and 
DTN: MO0407SEPFEPLA.000 [DIRS 170760]. The tables provide specific references to 
sections within this document. The FEP numbers and names from the TWP have been corrected 
to match the DTN. 
Table 6.2-1. FEPs Included in the TSPA-LA and Addressed by This Document 
FEP No. FEP Name 
Section of Document 
Where FEP Is 
Addressed 
2.1.09.01.0A Chemical characteristics of water in drifts 6.5 
2.1.09.02.0A Chemical interaction with corrosion products 6.5 
2.1.09.06.0B Reduction-oxidation potential in drifts 6.4.2 
2.1.11.08.0A Thermal effects on chemistry and microbial activity in the EBS 6.4.1 
Table 6.2-2. FEPs Excluded in the TSPA-LA and Addressed by This Document 
FEP No. FEP Name 
Section of Document 
Where FEP Is 
Addressed 
1.1.02.00.0A Chemical effects of excavation/construction in EBS 6.4.5 
2.1.06.01.0A Chemical effects of rock reinforcement and cementitious 
materials in EBS 
6.4.5 
2.1.10.01.0A Microbial activity in EBS 6.4 
2.1.12.01.0A Gas generation (repository pressurization) 6.5.1 

6.3 CHARACTERIZATION OF THE MICROBIAL POPULATION AT YMP 
The repository is located in an unsaturated zone of welded volcanic tuff. Thus, the geochemical 
impact of microbial activity within the repository should be considered in the context of 
physical, chemical, and hydrologic conditions in vadose zones. Characterization of microbial 
communities has principally focused on correlating the types, numbers, and activities of present 
microorganisms to extant geological features, and with water and carbon availability (Colwell 
1989 [DIRS 171111]; Haldeman and Amy 1993 [DIRS 145228]; Kieft et al. 1997 
[DIRS 100767], 1998 [DIRS 171098]; Brockman et al. 1992 [DIRS 171110]; Russell et al. 1994 
[DIRS 119578]). These studies, along with those examining the activities of subsurface isolates 
in pure cultures, have shown bacteria are present in all vadose zones examined thus far. The 
contributions of microorganisms to chemical reactions that affect geological processes and mass 
transfer have been affirmed. 
The quantity of intact phospholipid fatty acids (PLFA) is a direct indicator of viable or 
potentially viable cells in an environmental sample. Thus, PLFA analysis permits the direct 
quantification of microbial biomass in environmental samples without the need for culturing 
microorganisms (Tunlid and White 1992 [DIRS 120501]). Quantitative analysis of the total 
number of bacteria present in a Yucca Mountain rock sample aseptically collected from the 
Exploratory Studies Facility (ESF) was undertaken using this technique (Horn et al. 2004 
[DIRS 171058]). A single rock core was collected and cut into two pieces: one piece consists of 
the region facing the tunnel (proximal to the drift), and the other piece is the area reaching into 
the tunnel wall (distal to the drift). Using this method, it was deduced that the proximal sample 
contained 6  104 cells per gram of dry rock (3 pmole (pM) of PLFA/g dry rock); the 
deeper-dwelling distal sample had 4  104 cells per gram of dry rock (2 pM of PLFA/g dry rock), 
using a conversion factor of 2  104 cells/pM PLFA. No diglycerides, an indicator of dead 
bacteria, were detected. The PLFA analysis showed a preponderance of gram-negative 
organisms. 
Subsurface environments have demonstrated high proportions of heterotrophic bacteria (Balkwill 
1989 [DIRS 171091]), especially in studies of oxygenated volcanic tuff at the Nevada Test Site 
(Amy et al. 1992 [DIRS 116973]; Haldeman and Amy 1993 [DIRS 145228]). Microbial 
analyses conducted in the ESF have determined the existence of aerobic heterotrophs and 
autotrophs (Ringelberg et al. 1997 [DIRS 100824]), including iron oxidizing, sulfur oxidizing 
and nitrifying organisms. Cell counts for autotrophs range between 10 and 500 cells per gram 
dry weight and, for the heterotrophs, between 3.2  104 to 2  105 cells per gram of tuff. The 
relatively small population of autotrophs reflects the oxidizing environment at Yucca Mountain, 
which is not conducive to sustaining autotrophic bacteria. Microbial growth in various tuffs has 
been investigated (Horn et al. 2003 [DIRS 167221]). After a one-year incubation in microcosms 
fed with 10xJ13 Synthetic groundwater, microorganisms were collected from the microcosm 
efflux and plated on R2A agar (Horn et al. 2003 [DIRS 167221]). An effort was made to 
single-colony purify as many individual morphotypes as could be discerned; these were 
subjected to Biolog analysis to eliminate duplicate strains, and then identified using 16S rDNA 
sequence determination and analysis (Lane et al. 1985 [DIRS 171119]). Six different organisms 
were identified after growth in 10xJ13 Synthetic medium by determination of their closest 
relatives extant within the examined databases: Ralstonia pickettii, Burkholderia cepacia, 
Sphingomonas paucimobilis, Blastobacter natatorius, Caulobacter subvibroidies, and 

Methylobacterium mesophilicum. All of these isolates, with the exception of the 
M. mesophilicum, demonstrated a 3-percent or less rDNA sequence divergence from reference 
organisms in the existing GenBank and Microseq databases, thereby showing close phylogenetic 
relationships to reference organisms (Benson et al. 2000 [DIRS 171117]; Stackebrandt and 
Goebel 1994 [DIRS 171105]; Patel et al. 2000 [DIRS 171100]). 
Stationary phase cultures grown in 1xJ13 Synthetic medium both with or without added glucose 
were also subjected to single-colony purification, Biolog analysis, and 16S rDNA analysis 
(Horn et al. 2003 [DIRS 167221]). These generally showed greater rDNA sequence divergence 
from database reference strains than did isolates derived after growth in 10xJ13 Synthetic 
medium, thereby demonstrating a 3.45-percent median divergence (3.88 percent average) from 
reference strains in the MicroSeq and Genbank databases (Table 6.3-1). Although formally they 
cannot be considered identical species since sequence divergence is greater than 3 percent 
(Stackebrandt and Goebel 1994 [DIRS 171105]), for ease of reference, these organisms are 
referred to here by the name of their closest relatives. 
Virtually all of the organisms isolated from 1xJ13 Synthetic-grown cultures were not found in 
10xJ13 Synthetic medium cultures, although Ralstonia-like bacteria were found in all cultures, 
and Sphingomonads were present in 10xJ13 Synthetic-grown cultures and in 1xJ13 
Synthetic-grown cultures without glucose (Horn et al. 2003 [DIRS 167221]). Similarly, most of 
the organisms grown in 1xJ13 Synthetic with glucose differed from those isolated from 1xJ13 
Synthetic without glucose; the single exception was a Microbacterium keratanolyticum-like 
bacteria (Table 6.3-1). 
Even though identical organisms were not isolated from all cultures, most of the isolates cultured 
from 1xJ13 Synthetic without glucose correlated to phylogenetically related isolates in either 
1xJ13 Synthetic with glucose or 10xJ13 Synthetic. Pseudomonas stutzeri-like organisms were 
found in 1xJ13 cultures; its close relative, B. cepacia, was identified from 10xJ13 
Synthetic-grown cultures. 
Two of the isolates that were grown from rock when using 1xJ13 Synthetic with glucose as a 
growth medium were identical or related to isolates obtained from other studies that examined 
diversity within alternative systems (Horn et al. 2003 [DIRS 167221]). Arthrobacter SMCC 
G964 was isolated from a saturated zone in fine-grained lacustrine sediments, at a depth of 
approximately 173 m, in Hanford, Washington (Van Waasbergen et al. 2000 [DIRS 171075]); it 
is completely homologous to a strain isolated from Yucca Mountain tuff. Bacterium oxSCC was 
identified from a 16S rDNA analysis of the oxic zone of flooded paddy soils collected in 
Vercelli, Italy (Ldemann et al. 2000 [DIRS 171074]); it is the nearest sequenced relative of an 
isolate identified here. That these homologues were found in very different environments and in 
widely disparate locales attests to their adaptability and their ability to compete in alternative 
types of strata, and is evidence of their widespread distribution. 

Table 6.3-1. Organisms Isolated After Growth in Various Yucca Mountain Simulated Groundwaters and 
16S rDNA Sequence Divergence from Reference Organisms 
Organisma 
Growth Medium from Which Organism Isolated 
1xJ13 Synthetic with Glucose 1xJ13 Synthetic without Glucose 
% Divergence from Database 
Ralstonia pickettii   
Ralstonia eutrophus 4.5/MS 6.9/MS 
Burkholderia cepacia   
Blastobacter natatorius   
Sphingomonas paucimobilis  2.0/GB 
Methylobacterium mesophilicum   
Caulobacter subvibroidies   
Uncultured bacterium oxSCC-6b 
Pseudomonas (Janth) mephitica 
4.0/GB 
6.06/MS 
 
Microbacterium barkeri 4.5/MS  
Microbacterium keratanolyticum 4.15/MS 4.15/MS 
Microbacterium chocolatum 5.16/MS  
Arthrobacter sp. SMCC G964c 0.0/GB  
Pseudomonas stutzeri 3.93/MS 1.0/GB 
Afipia genosp.  4.0/GBMS 
Source: Horn et al. 2004 [DIRS 171058]. 
MS = MicroSeq database; GB = GenBank database; RDP = Ribosomal Database project. 
a 
bClosest relative in 16S rDNA sequence comparisons to three separate databases (i.e., MS, GB, and RDP). 
Ludemann et a
l. 2000 [DIRS 171074]. Spatial changes in the bacterial community structure along a vertical 
oxygen gradient in flooded paddy soil cores. 
Van Waasbergen et al. 2000 [DIRS 171075]. Genetic diversity among Arthrobacter species collected across a 
heterogeneous series of terrestrial deep-subsurface sediments, as determined on the basis of 16S rRNA and 
recA sequences. 
It has been commonly acknowledged that only a small fraction of organisms (extant in any given 
environmental sample) grow and can be isolated on a single type of growth medium. Therefore, 
methods that use direct DNA extraction from environmental samples, with subsequent 
characterization of the 16S rDNA genes in the obtained DNA, have been developed to better 
assess community compositions without the need to grow and isolate organisms. 
Characterization of DNA extracted directly from Yucca Mountain rock was therefore undertaken 
to generate a more complete roster of the organisms contained within the Yucca Mountain 
community (Horn et al. 2003 [DIRS 167221]). Four hundred grams of Yucca Mountain rock 
were subjected to extraction. The resulting DNA was purified and subjected to a series of 
biochemical and genetic manipulations that included amplification of microbial 16S rDNA genes 
and cloning amplified genes. Two hundred rDNA clones were screened to obtain those that were 
unique based on restriction fragment length polymorphisms. 
Note that collected rocks may contain both native organisms and organisms introduced by 
construction. No effort has been made to distinguish between them, because both may affect 
repository environments. Statistical analysis that involved the screening of 200 clones confirmed 
that those organisms representing more than 3.5 percent of the community have a 0.1 percent 
probability of not being detected. Conversely, those organisms that represent less than 

0.5 percent of the Yucca Mountain community have a 37-percent probability of not being 
detected. Therefore, although screening 200 clones may not detect all organisms extant at the 
site, the vast majority of organisms were detected, and only those that represented a very small 
percentage of the total microbial community would not have been detected and identified. 
Source: Horn et al. 2003 [DIRS 167221]. 
NOTE: After amplification and cloning of 16S rDNA genes, 200 clones were screened; the frequency of 
occurrence of unique clone types is depicted as the percentage of the total number of clones screened. 
Figure 6.3-1. Frequency of Unique Clone Types in Yucca Mountain Rock (of 200 Screened) 
After screening 200 rDNA clones, 65 unique clonal types, representing 65 separate types of 
organisms, were distinguished (Horn et al. 2003 [DIRS 167221]). The frequency of occurrence 
during screening may indicate the relative abundance of these organisms in the Yucca Mountain 
rock samples (Figure 6.3-1). 
After sequencing, an evolutionary (or phylogenetic) tree of all unique cloned sequences was 
generated, together with related reference organisms from the rDNA database (Horn et al. 2003 
[DIRS 167221], Figure 6.3-2). These trees show the relatedness between the organisms that 
were identified, and known extant organisms; nodes denote common evolutionary ancestors; the 
length of branches connote evolutionary time since divergence from a common ancestor. 
Identified Yucca Mountain organisms span a wide phylogenetic range, and include groups of 
organisms known to reside in dry environments (e.g., the High Guanine (G) + Cytosine (C) 
Gram Positives), in addition to those that sporulate into resistant forms that can survive 
desiccation and elevated temperatures (e.g., the Bacilli and Clostridia). When collecting rock 
samples for extraction, no effort was made to isolate purely endogenous Yucca Mountain 
organisms; both those from tunnel walls (which may be introduced during construction) and 
those within the rock were collected. Clearly, at least two identified Yucca Mountain organisms 
were introduced into the repository; these were related to photosynthetic cyanobacteria, which 

may be able to survive due to the artificial light or could be plant pollens that were introduced by 
ventilation of the ESF. 
In summary, the site characterization studies have demonstrated both the variability in 
population and the diversity in genetic types for microorganisms present at the Yucca Mountain 
site. These microorganisms are highly adaptable and sufficiently diverse for carrying out any 
specific metabolic reaction that the environment permits. In other words, the extent of each 
individual microbial reaction will be limited by environmental constraints, not by the types of 
microbes present. Similarly, a specific group of microbes will thrive only to the extent that the 
environment allows. If conditions, however, are not conducive to activity, some microbial cells 
may be in a dormant state and therefore will not contribute to the overall biogeochemical 
process. This may be the reason for the difficulty in correlating microbial population 
distributions with geochemical environments. This argument is consistent with the modeling 
approach that has been used successfully over the years for modeling biogeochemical processes 
in aquatic sediments (e.g., Van Cappellen and Wang 1996 [DIRS 171128]; Wang and Van 
Cappellen 1996 [DIRS 171057]). In this approach, microbial population is not explicitly 
included. A theoretical basis for this has been provided by Wang and Papenguth (2000 
[DIRS 171123]). 

Evaluation of Potential Impacts of Microbial Activity on Drift Chemistry 
Source: DTN: LL021007312251.020 [DIRS 171179]. 
NOTE: Phylogenetic tree of Yucca Mountain microbial community as identified by 16S rDNA analysis of DNA extracted from Yucca Mountain rock. Named 
species are those extant in the RDP database to serve as reference benchmarks; YMRB- designated strains are those identified from Yucca Mountain 
rock. Lengths of horizontal branches denote relative time since divergence from common ancestors (nodes). Large phylogenetic groupings are 
provided to the right of the tree. 
Figure 6.3-2. Phylogenetic Tree of Yucca Mountain Microbial Community 
ANL-EBS-MD-000038 REV 01 6-17 November 2004 

Evaluation of Potential Impacts of Microbial Activity on Drift Chemistry 
INTENTIONALLY LEFT BLANK 
ANL-EBS-MD-000038 REV 01 6-18 November 2004 

6.4 ENVIRONMENTAL CONSTRAINTS ON MICROBIAL ACTIVITY AT YMP 
This section on microbial activity in the repository addresses those impacts of FEP 2.1.10.0A 
(microbial activity in EBS) that do not involve the waste. This section considers various 
environmental constraints. The environmental factors considered include: temperature, pressure, 
oxic and anoxic conditions, relative humidity, water availability, pH, salinity, nutrient 
availability, biofilm formation, and radiation effect. The evaluation shows that the high early 
temperatures, the otherwise oxic environment, and a relative scarcity of water and organic 
carbon will combine to limit microbial activity in the emplacement drifts. 
6.4.1 Temperature and Pressure Constraints 
This section addresses the aspects of FEP 2.11.08.0A (thermal effects on chemistry and 
microbial activity in the EBS) that involve microbial activity. 
The temperature of the subsurface environment will affect or limit the type of bacteria that are 
present, based on the optimum growth temperatures of the organisms that are present. The 
maximum temperature at which known microorganisms can exist in an active state is 110C 
(Table 4.1-2). Based on the growth of bacteria they are classified psychrophiles, facultative 
psychrophiles, mesophiles, thermophiles, and hyperthermophiles. Table 6.4-1 shows the ranges 
of temperatures supporting the growth of bacteria. 
Table 6.4-1. Temperature Range for Microbial Growth 
Minima 
Temperature Class Maxima Optimum Range 
Psychrophiles * 0C to 15C 
20C 
Facultative Psychrophiles 0C 20C to 30C 
35C 
Mesophiles 15C 20C to 45C 
45C 
Thermophiles 45C 55C to 65C 
70C 
Hyperthermophiles 60C 80C to 100C 
120C 
Source: Pedersen and Karlsson 1995 [DIRS 100810]. 
* No lower bound reported. 
Only a few of the identified isolates are known to withstand elevated temperatures (P. stutzeri, 
R. pickettii, B. natatorius). Only one isolate, M. mesophilicum, is capable of forming cysts that 
are desiccation resistant; M. mesophilicum has also been found to be dominant in soils 
surrounding the Chernobyl Atomic Power Station (Overbeck 1997 [DIRS 171182]). Other 
bacteria, if they survive, will remain in a dormant state, without any contribution to the 
geochemical processes of interest. Sulfate-reducing bacteria isolated from a mine in Britain and 
Thiobacillus ferrooxidans found in several sites in Europe have been subjected to repository 
conditions in order to establish their ability to survive under these conditions (West et al. 1986 
[DIRS 171088]). These experiments have included establishing growth curves, temperature 

tolerance tests, combined high pressure and temperature tolerance, and gamma-irradiation. The 
experimental data suggest that sulfate-reducing bacteria are more tolerant to extreme 
environmental conditions than the sulfur-oxidizing Thiobacillus ferroxidans (West et al. 1986 
[DIRS 171088]). Sulfate-reducing bacteria, strict anaerobes, are not expected to be active in the 
oxidizing Yucca Mountain environment (Section 6.4.2). 
Drift Scale Coupled Processes (DST and THC) Seepage Models (BSC 2004 [DIRS 169856], 
Figure 6.5-3) provides the in-drift thermal history predicted by a thermal-hydrologic model that 
accounts for heat conduction from the drift wall, into the rock matrix, resulting in vaporization 
and boiling, with vapor migration out of matrix blocks into fractures. The vapor moves away 
from the drift through the permeable fracture network by buoyancy, by the increased vapor 
pressure caused by heating and boiling, and through local convection. In cooler regions, the 
vapor condenses on fracture walls, where it drains through the fracture network either down 
toward the heat source from above, or away from the drift into the zone underlying the heat 
source. Slow imbibition of water from fractures into the matrix gradually leads to increases in 
the liquid saturation in the rock matrix. Under conditions of continuous heat loading due to 
radiation, a dryout zone may develop closest to the heat source separated from the condensation 
zone by a nearly isothermal zone maintained at about the boiling temperature. The predicted 
in-drift thermal history is shown in Figure 6.4-1. 
During the period of thermal perturbation resulting from waste package emplacement, the 
temperature in the repository drifts could exceed 120C (the upper temperature limit for the 
presence of microorganisms) and, for a waste package surface, could be as high as 170C 
(Figure 6.4-1). Therefore, microbes initially present in the drift will be severely limited in 
growth, if not totally eliminated, by heating for a few hundred years at the early stage of the 
repository. As discussed in Section 6.4.3, during this heating period, relative humidity and water 
availability will also diminish; this will add another detrimental environmental factor to the 
survival of microorganisms. 
Bacteria may migrate into the repository with infiltrating fracture flow, once temperatures 
decrease. Infiltrating organisms that survived the heating period may be presumed to colonize if 
conditions are favorable for growth. It is shown in Figure 6.4-1 that, even after the peak 
temperature, the in-drift temperature will remain above 50C for the duration of the 10,000-year 
regulatory period. Therefore, the microbial population will be dominated by thermophiles and 
hyperthermophiles. 
Bacteria are able to withstand and flourish at the highest hydrostatic pressures on the planet 
(Madigan et al. 2003 [DIRS 171083]). Ordinary bacteria that have not been challenged by high 
hydrostatic pressure during their evolution are, nevertheless, remarkably tolerant to such 
pressure. At a high temperature, a high hydrostatic pressure may even help microbes to survive 
by preventing water loss from boiling and thus maintaining sufficient liquid water for microbes 
to carry out necessary metabolic reactions. Because the repository is located in an unsaturated 
zone, the in-drift gas pressure is close to atmospheric pressure. A significant microbial activity in 
the repository is possible only after the first 1,000 years, when the drift temperature drops below 
the boiling point (approximately 96C) (Figure 6.4-1). During the thermal event, the relative 
humidity is low enough to inhibit microbial growth (Section 6.4.3). 

Figure 6.4-1. TH Simulation (Tptpll): Time Profiles of Modeled Temperatures in Fractures (Similar in 
Matrix) at Three Drift-Wall Locations and in the Waste Package 
Source: BSC 2004 [DIRS 169856], Figure 6.5-3. 
6.4.2 Redox Conditions 
This section addresses the microbial aspects of FEP 2.1.09.06.0B (reduction-oxidation potential 
in drifts). 
Bacteria that are able to grow in the presence of molecular oxygen, either in gaseous or dissolved 
form, are termed aerobes; those that can grow without oxygen are anaerobes. Table 6.4-2 shows 
the terms used to describe the O2 relations of bacteria. Thus, different microbes can thrive at 
various redox conditions, including both the oxygenated environments that are at high redox 
potential, and the reducing environments in which the oxygen abundance is minimal. Wang and 
Van Cappellen (1996 [DIRS 171057]) have shown that a typical limiting concentration of O2 for 
aquatic sediments is 1 to 30 M (approximately 0.4 to 10 percent atmospheric oxygen), above 
which anaerobic microbial reactions are completely inhibited. 
Table 6.4-2. Oxygen Relationship and Growth of Bacteria 
Type O2 Relation 
Aerobes 
Obligate O2 is required 
Facultative O2 is not required, but growth is better with O2 
Microaerophilic O2 is required, but at lower-than-atmospheric levels 
Anaerobes 
Aerotolerant O2 is not required, and growth is not better with O2 
Obligate (strict) O2 is harmful or lethal 
Source: Madigan et al. 2003 [DIRS 171083]. 

During the thermal pulse, water vapor will drive air mass away from the waste drift, thus 
resulting in depletion in oxygen concentration, which is proportional to the fraction of remaining 
air mass in the gas phase. The evolution of air mass in the drift has been calculated by the 
thermal-hydrologic model, and is shown in Figure 6.4-2. As shown in Figure 6.4-2, the air mass 
fraction will decrease to less than 10 percent during the thermal pulse, and will then quickly 
recover (back to 100 percent) after the thermal pulse, as does the oxygen concentration. 
However, the depletion in oxygen concentration is not expected to have an impact on microbial 
reaction pathways, because microbial activity will be severely limited, if not completely 
eliminated, due to both the heating and the desiccating effects, during the thermal pulse, as 
discussed in Section 6.4.1. Therefore, within the time window permissive for microbial activity 
(i.e., with temperature less than 100C), the oxygen concentration in the repository will be 
maintained above its limiting concentration (i.e., greater than 10 percent of atmospheric value). 
The overall chemical environment in the repository will therefore be oxic, and a significant 
anaerobic microbial activity will be unlikely. Some local anaerobic environments may exist in 
the rock matrix, but they will not affect repository chemical conditions, because such an effect, if 
there is one, is already accounted for by water chemistry measured at Yucca Mountain. 
The assertion of an overall oxic environment in the repository is consistent with field 
observations (BSC 2004 [DIRS 169734], Section 5.2). Iron and manganese 
oxides/oxyhydroxides are the most common mineral phases found in the fractures in both 
saturated zones and UZs. The redox state of UZ waters is probably dominated by the presence of 
oxygen in the UZ gas phase. At the two locations where such measurements have been made, 
the UZ gas phase has atmospheric levels of oxygen. The measured Eh values are typically high 
(400 to 600 mV). In addition to the oxic background environment, radiolysis of water inside the 
waste drift will generate hydrogen peroxide, thus adding another oxidizing agent to the water. 
Nitrate (NO3 
-) is an inhibitor for metal corrosion as opposed to chloride (Cl-), as summarized in 
General Corrosion and Localized Corrosion of the Waste Package Outer Barrier (BSC 2004 
[DIRS 169984], Section 1.2). The ratio of NO3 
-/Cl- is an important parameter in the control of 
the longevity of the waste package and drip shield as engineered barriers. In principle, 
microorganisms could consume nitrate through denitrification, either heterotrophically or 
autotrophically, under anaerobic conditions (Korom 1992 [DIRS 172324], pp. 1657 to 1668). 
This, however, will be unlikely in the repository because the overall environment will be oxic, 
which, together with low organic-carbon concentrations, will prevent significant anaerobic 
microbial reactions, including denitrification, as shown by the field observation that a significant 
amount of NO3 
- is currently present in groundwaters. Even if some anaerobic 
microenvironments may exist in rock matrix, their impact on nitrate concentration has already 
been captured by the current water analysis. 

Figure 6.4-2. Temporal Evolution of Air Mass Fractions in the Gas Phase in Fractures and Matrix at 
Three Drift-Wall Locations 
Source: BSC 2004 [DIRS 169856], Figure 6.5-8. 
NOTE: Oxygen concentrations are proportional to air mass fractions. 
Furthermore, the oxidizing environment will also prevent the generation or accumulation of 
reduced inorganic species (e.g., H2, NH4+, NO2 
-, Mn2+, Fe2+, H2S, and S), which are a 
prerequisite substrate for autotrophic microbial processes (Table 6.1-1). Chemical analyses of 
groundwaters from Nye County Early Warning Detection Program wells show that the waters 
contain only trace amounts of dissolved iron (less than 2.34 ppm) and manganese (less than 
Fe
2+
0.58 ppm) (not necessarily all in and Mn2+), and NH4+ (less than 1 ppm) 

(DTN: GS011108312322.006 [DIRS 162911]). These waters were obtained from the saturated 
zone and thus provide an upper bound on the water in the unsaturated zone in terms of reduced 
inorganic species concentrations. Given the limited quantity of organic inputs (see Section 6.4.5), 
metals or metal alloys are the only major reducing components in the repository. Under 
oxidizing conditions, metal corrosion will not extensively generate reduced inorganic species, for 
instance, for iron corrosion: 
Feo + 3/4O2 = 1/2Fe2O3 (Eq. 6-3) 
Fe2+ ions may be present as an intermediate product of the above reaction, but they are transient 
in time and localized in space to the corrosion front. Long-term corrosion tests have been 
conducted to evaluate waste package material coupons in various solutions under anticipated 
repository conditions (Horn et al. 2003 [DIRS 167221]). Although deionized water was used in 
the composition of tank solutions, microorganisms were not purposefully excluded, and the tanks 
were not fully sealed from the surrounding laboratory environment. Therefore, these test tanks 
pose a somewhat analogous environment to the evolving repository. A differential staining and 
epifluorescence microscopic analysis indicated that microorganisms were present in testing tanks 
that contained acidic water, and in dilute and concentrated waters at 60C. With direct DNA 
extraction and characterization, three different microbial inhabitants were identified in simulated 
groundwater increased to 10-fold ionic concentration and incubated at 60C (Figure 6.4-3). 
Interestingly, even in this oligiotrophic and metallic alloy-dominated environment, the microbial 
population was dominated by hetrotrophic bacteria. Bacilli, known as heterotrophs, were 
observed to be the most numerous, representing 84 percent of the screened clones (Figure 6.4-3). 
This indicates that metal corrosion under Yucca Mountain-relevant conditions will not support 
any significant autotrophic microbial growth. This may be partly because abiotic Fe2+ oxidation 
is kinetically favored over microbial oxidation. 
Source: Horn et al. 2003 [DIRS 167221]. 
NOTE: After amplification and cloning of 16S rDNA genes, 100 clones were screened; the frequency of 
occurrence of unique clone types is depicted as the percentage of the total number of screened clones. 
Figure 6.4-3. Frequency of Unique Clone Types in a Long-Term Corrosion Tests Tank Containing 
Simulated 10X Groundwater at 60C 

6.4.3 Relative Humidity and Water Availability 
Water is essential for microbial growth (Table 4.1-4). The microbes found in unsaturated 
environments seem to be desiccation resistant (Kieft et al. 1993 [DIRS 100766]). Work done in 
several vadose zones at arid and semiarid sites indicates that the total numbers of microbes that 
are considered ambient range from 104 to 107 cells per gram dry weight (Kieft et al. 1993 
[DIRS 100766]). It was also stated that, in the various vadose systems, there were many 
populations that were growth limited; most were growth limited by water or by organic carbon, 
but some systems were growth limited by nitrogen or by phosphorous (Kieft et al. 1993 
[DIRS 100766]). 
Figure 6.4-4. Growth Rates of Yucca Mountain Aerobic Bacteria in Unconcentrated Groundwater 
(1xJ13 Synthetic Medium) with and without Glucose Added 
Source: DTN: LL040801512251.115 [DIRS 171476]. 
NOTE: Growth rates of Yucca Mountain aerobic bacteria in unconcentrated groundwater (1xJ13 Synthetic medium) 
with or without 0.1 percent glucose amendment, incubated under agitated batch conditions. 
Observations of bacterial growth in unconcentrated groundwater provide evidence that 
sustainable population growth of microbial species requires significant quantities of liquid. 
Results of experiments conducted using a four to one ratio of simulated Yucca Mountain 
groundwater (1xJ13 Synthetic medium) to crushed rock sampled from relevant repository 
stratigraphic unit(s) are depicted in Figure 6.4-4, taken from Horn et al. (2004 [DIRS 171058], 
p. 280, Figure 4). J13 well water (DTN: MO0006J13WTRCM.000 [DIRS 151029]) has been 
extensively used as a representative groundwater for various modeling activities on Yucca 
Mountain (e.g., BSC 2004 [DIRS 169425]). 1xJ13 Synthetic medium used in the microbial 

growth experiments mimics the composition of inorganic compounds in actual J13 water. Three 
experimental conditions were tested: 1xJ13 with an added carbon source (glucose), without an 
added carbon source, and a sterile control sample. Both cultures using Yucca Mountain 
simulated groundwater attained stationary phase in three to four days of incubation (Horn et al. 
2004 [DIRS 171058]. Between cultures that contained glucose and cultures that did not, 
stationary phase cell densities differed by approximately one order of magnitude. Without 
glucose amendment, maximal planktonic cell densities were approximately 4  106 cells/mL to 
8  106 cells/mL; with added glucose, cell densities were approximately 2  107 cells/mL to 
7  107 cells/mL. Only planktonic cell density, the number of cells suspended in water per mL 
of solution, was determined. Kieft et al. (1997 [DIRS 100767]) made a similar observation for 
microbes cultured from tuff collected in the ESF. The source of cellular carbon for growth of 
detected heterotrophs remains speculative; 1xJ13 Synthetic medium initially contained no 
organic carbon. The detected heterotrophs could be growing on dead and lysed cellular 
materials, or on volatile organic compounds (Horn et al. 2004 [DIRS 171058]). Also, in the 
experiment, only planktonic cell density, the number of cells suspended in water per mL of 
solution, was determined. The observed increase in planktonic cell density could be due to 
detachment of cells from crushed rock to liquids. 
Water activity is ordinarily defined by the ratio of the solution vapor pressure to the vapor 
pressure of pure water at a given temperature. In order for microorganisms to grow, water 
activity needs to be 0.75 to 1.00 (Pedersen and Karlsson 1995 [DIRS 100810]; Brown 1976 
[DIRS 118921]). Many bacteria perish, sporulate, or become dormant when water activity falls 
below approximately 0.90 (Brown 1976 [DIRS 118921]; Atlas and Bartha, 1981 [DIRS 118890], 
p. 154). Some fungi and yeast can be active at lower water activity levels (on the order of 0.7 to 
0.85; see Pedersen and Karlsson 1995 [DIRS 100810]). However, these microorganisms have 
very small populations as compared to bacteria (Table 6.1-3) and are solely dependent on the 
availability of organic carbon, which is currently limited in the Yucca Mountain repository 
(<1.1 ppm). 
In a full-scale test conducted at Atomic Energy Canada Ltd. (AECL), a simulated waste 
container (maximum heat output 85C) was buried for 2.5 years, surrounded by compacted 
buffer materials. Extensive microbial analysis of this test has shown that most viable organisms 
in the buffer material disappear around a moisture content of 15 percent (corresponding to RH 95 
to 96 percent) (Stroes-Gascoyne 1996 [DIRS 171851]). 
The activity and availability of water for microbial growth in the UZ at Yucca Mountain will be 
dependent upon thermal-hydrologic conditions. The range of relative humidity (defined as water 
activity multiplied by 100) on all waste packages is shown in Figure 6.4-5. During the thermal 
pulse, relative humidity on the waste package surface can be lower than 10 percent. In some 
realizations, relative humidity recovers (back to 100 percent) after approximately 1,000 years. In 
many other realizations, relative humidity remains below 90 percent, and even below 70 percent 
in some cases, throughout the regulatory period, thus limiting microbial growth and activity. In 
addition, low water activity generally corresponds to low liquid-water availability (Figure 6.4-6). 
Low saturation of liquid water fractures on the drift wall will limit the transport growth 
substrates to microbial cells and, therefore, the activity of the cells. 

Figure 6.4-5. Range of Relative Humidity Histories for All Waste Packages, Accounting for Uncertainty of 
Host-Rock Thermal Conductivity and Percolation Flux 
Source: BSC 2004 [DIRS 169565], Figure 6.3-68. 

Figure 6.4-6. TH Simulation (Tptpll): Time Profiles of Modeled Liquid Saturations in Fractures at Three 
Drift-Wall Locations 
Source: BSC 2004 [DIRS 169856], Figure 6.5-6. 

6.4.4 pH and Salinity 
Bacteria grow over wide ranges of pH, but there are limits to their tolerance (Amy and Haldeman 
1997 [DIRS 100697]; Banfield and Nealson 1997 [DIRS 100703]; Pedersen and Karlsson 1995 
[DIRS 100810]). Bacteria frequently change the pH of their own habitat by producing acidic or 
basic metabolic waste products. Most bacteria create their own habitats by forming biofilms. 
Each species of microbe has a pH growth range and growth optimum. Table 6.4-3 shows the 
types of microbes and their pH relationships. One natural analogue to alkaline groundwater 
comes from the natural springs in the Maqarin area in northwest Jordan, where the groundwaters 
have pH values as high as 12.9. These springs contain diverse microbial populations; therefore, 
the high alkalinity of the cementitious material and water in equilibrium with it will not preclude 
the growth of microorganisms (Pedersen 1999 [DIRS 110036]). The types of microorganisms 
residing in this environment would be alkalophiles and extreme alkalophiles. Where biofilms 
have been known to form on concretes, even the extreme alkaline pH environments will not 
preclude microbial colonization. Since cementitious materials are not used in ground support in 
the emplacement drifts, an extremely alkaline environment is not expected. 
Table 6.4-3. Microbial Growth at Different pH 
pH pH Range 
Acidophiles 1.0 to 5.5 
Neutrophiles 5.5 to 8.5 
Alkalophiles 8.5 to 11.5 
Extreme Alkalophiles >10.5 
Source: Pedersen and Karlsson 1995 [DIRS 100810]. 
Bacteria can be affected by changes in the osmotic concentration of their surroundings (Madigan 
et al. 2003 [DIRS 171083]). However, some bacteria have adapted to extremely saline 
conditions, and can grow where there are high levels (2.8 to 6.8 M) of sodium chloride (Francis 
et al. 1997 [DIRS 171062]). Many bacteria are osmotolerant, and thrive in saline solutions that 
have concentrations of up to 3 M. Evaporation of seepage waters, or deliquescence of water on 
dust, in a low relative-humidity environment during the thermal pulse may result in concentrated 
brine solutions that have ionic strengths higher than 10 M (BSC 2004 [DIRS 169860], Figure 
6.13-33), in which only a few halophilic bacteria can survive. Still, the activity of these bacteria 
will be limited after the thermal pulse, when a low ionic strength environment (close to the 
current environment) is reestablished. The current ionic strength of Yucca Mountain pore water 
is typically much less than 1 M (DTN: GS011108312322.006 [DIRS 162911]). 
6.4.5 Inputs of Nutrients 
This section addresses the impacts of microbial activity on two FEPs: 
1. 
FEP 1.1.02.00.0A (chemical effects of excavation/construction in EBS) 
2. 
FEP 2.1.06.01.0A (chemical effects of rock reinforcement and cementitious 
materials). 

In addition to the presence of water, the other major necessity for microbial life is the 
environmental presence of a few major nutritional elements: carbon, nitrogen, sulfur, and 
phosphorous). These elements, the chief building blocks of a microbe, can derive from four 
sources: ambient rock, groundwater flow, gas flow, and introduced materials. 
Experiments have been performed to define conducive and inhibitory environmental conditions 
that pertain to growth of Yucca Mountain microbial communities in modified Yucca Mountain 
groundwater. Specifically, these experiments were designed to determine whether individual 
macronutrient (i.e., nitrogen, sulfate, phosphate, and carbon) concentrations extant in Yucca 
Mountain groundwater would support microbial growth in Yucca Mountain, and to determine 
growth rates and stationary phase microbial densities under aerobic, saturated conditions. 
Experimental data (Figure 6.4-7) show that nitrogen and sulfate sources are apparently sufficient 
to support microbial growth, even in unconcentrated Yucca Mountain groundwater. Nitrogen is 
often incorporated into cellular metabolism by reducing nitrate to ammonia that can then be 
utilized by various biosynthetic pathways. Limited numbers of bacterial species are able to 
reduce and assimilate atmospheric nitrogen. Most bacterial species use sulfate as a source of 
sulfur, and reduce it by assimilatory reduction. Sulfate is available in groundwater; it is not 
usually a limiting nutrient. 
Next in importance after water availability, according to the relative effect on increasing cell 
density, is phosphate availability, which increased cell densities approximately 1.5 orders of 
magnitude (Figure 6.4-7). The addition of a carbon source, glucose, had the least effect on 
increasing maximal cell densities; it only resulted in increases of one order of magnitude in 
unconcentrated simulated groundwater medium (1xJ13 Synthetic) (Figure 6.4-4). Yucca 
Mountain groundwater has extremely low levels of organic carbon and phosphate 
(DTN: GS011108312322.006 [DIRS 162911]). Except when it was added exogenously, the 
only source of phosphorous available to the Yucca Mountain organisms growing from crushed 
rock in these studies was the Yucca Mountain tuff, which reportedly contains from 0.01 to 0.02 
weight percent (100 to 200 ppm) of phosphorous (DTN: LL981209705924.059 [DIRS 110317]). 
Phosphate was also introduced into the ESF by construction activities. Microorganisms are well 
known to solubilize phosphate through the production of acids and a variety of other 
well-characterized mechanisms (Ehrlich 1996 [DIRS 119001]). Therefore, mineralogical or 
introduced phosphate in Yucca Mountain tuff will be the major source of phosphate to support 
cellular growth. 
Only trace concentrations of organic carbon (up to 1.1 mg/L) have been reported in qualified 
measurements of Yucca Mountain groundwater (DTN: GS011108312322.006 [DIRS 162911]). 
Even without the addition of glucose to experimental growth media, however, significant 
heterotrophic microbial growth was observed (Figure 6.4-4), and few isolates that were 
enumerated and identified from unconcentrated simulated groundwater without glucose had 
autotrophic capabilities (Table 6.3-1); the source of cellular carbon for growth of detected 
heterotrophs is, therefore, unknown. 

Source: Horn 2004 [DIRS 171476]. 
NOTES: Growth rates of Yucca Mountain culturable aerobic bacteria as a function of macronutrient concentrations 
found in 10xJ13 Synthetic and derivative media which had increased levels of individual macronutrients. 
10xJ13 Synthetic medium is a concentrated (by a factor of 10) synthetic J13 water, which contains 5.55 
mM glucose and 0 mM phosphate. 
Panel A: Continuously fed microcosm reactors. Panel B: Unreplenished, agitated batch systems. 
Filled arrow designates the time at which 10 mM sodium phosphate was added to 10xJ13 Synthetic 
culture. Unfilled arrow designates the time at which sodium phosphate was added to all other culture 
media. Results shown are those of a single, representative trial. 
Legend:  = 10xJ13 Synthetic 
. = 10xJ13 Synthetic + SO4
{ = 10xJ13 Synthetic + NO3
 = 10xJ13 Synthetic + SO4+ NO3 
z = Sterilized rock and 10xJ13 Synthetic + SO4+ NO3 
Figure 6.4-7. Growth of Yucca Mountain Culturable Aerobic Bacteria as a Function of Macronutrient 
Concentration in Yucca Mountain 
Organic carbon concentrations in Yucca Mountain groundwater are low. Most groundwaters 
that are not affected by pollution have dissolved organic carbon concentrations of zero to 2 mg/L 
(Drever 1997 [DIRS 140067], p. 118). The dissolved organic carbon of shallow groundwaters 
generally comes from surface organic matter composed of soil and plant humic matter; in deeper 
groundwaters (100 m and deeper), the source of dissolved organic carbon is the microbial 
degradation of kerogen, the fossilized organic matter that is present in the geological material of 
the aquifer. Means (1982 [DIRS 171136]) analyzed deep aquifer samples (collected from Sterno 
and Stripa mines in Sweden, and from Hanford, Washington, USA) for organic compounds. 
Several phenols, organic acids, low-MW fulvic acids, hydrocarbons, aldehydes, and alcohols 
have been identified. 

The materials introduced into emplacement drifts will not contain any organic carbon (BSC 2004 
[DIRS 170058]), except for a trace amount of reduced carbon in metal or metal alloys. These 
carbons, like graphite, are expected to be refractory and thus will not be biodegradable. 
Therefore, the reduced carbon in the introduced materials is not expected to be available for 
microbial reactions. 
In summary, organic carbon is an important limiting factor for Yucca Mountain microbial 
growth. The extremely low organic-carbon supply in the repository will limit heterotrophic 
microbial activity. 
6.4.6 Biofilm Formation 
After attachment to surfaces, microbes initiate production of slimy adhesive substances, 
generally exopolysaccharides. These extracellular polymers, which frequently extend from the 
cell to form a tangled matrix of fibers, provide structure to the microbial assemblage. This 
structure is normally termed a biofilm. Microorganisms within biofilms are capable of 
maintaining unique environments at biofilm/surface interfaces (both liquid-solid and gas-liquid 
interfaces) that are radically different from the bulk in terms of pH, dissolved oxygen, and other 
organic and inorganic species (Little et al. 1997 [DIRS 100774]). Microorganisms that carry out 
MIC can occur in, and are facilitated by, biofilms. 
Else et al. (2003 [DIRS 168172]) studied the effects of relative humidity and temperature on the 
attachment of microbial cells to metal surfaces. Mined Yucca Mountain tuff was collected near 
the North Portal entrance. Flame-sterilized tools were used to remove the surface layer of the 
tunnel wall, and the newly exposed rock was put into sterile plastic bags and placed on ice. 
Flame-sterilized mortars and pestles were used to aseptically crush the rock into fine grains. 
One-centimeter-square coupons were constructed from the following metals: C22 nickel alloy 
(Alloy 22), N-316 stainless steel, and titanium. Aseptically crushed rock was transferred to 
sterile glass petri plates, metal coupons were placed within the crushed rock, and microcosms 
were placed in chambers held to specific relative humidity and temperature values. Microcosms 
were equilibrated for 1 week prior to the addition of metal coupons. At designated time points, 
adherent materials were scraped off coupons and homogenized by vortexing in 1.0 mL of R2 
broth. Homogenized materials (100 l) were plated onto R2A agar, and were incubated at room 
temperature (25C) for 2 weeks. Colony-forming units (CFUs) were counted. Note that only 
heterotrophs would be detected on R2A. 
From day 0 to day 1, at 100-percent relative humidity and 30C, the heterotrophic plate count 
(HPC) values from the three metal types increased from less than 1  102 to a range of 2  104 to 
4  104 CFU per coupon (Else et al. 2003 [DIRS 168172]). All three metal types supported 
increased HPC values by 5 months (4  104 to 7  104 CFU per coupon); however, after 
18 months of incubation fewer microbes were cultured (5  102 to 8  102 CFU per coupon). 
After day 0, HPC values at 84-percent relative humidity were lower than at 100-percent relative 
humidity for all three metal types. Although there was attachment of microorganisms 
(approximately 2  102 CFU per coupon at day 1 for all three-coupon types), it was followed by 
stable to decreasing values until 18 months of incubation, after which HPC values nearly equaled 
the 18-month value at 100-percent relative humidity. At 70.5-percent relative humidity, HPC 
values consistently decreased, from slightly less than 102 CFU per coupon at day 0, for the 

remainder of the test. At 32-percent relative humidity, N-316 coupons demonstrated microbial 
attachment, 102 CFU per coupon at day 0, which gradually increased and then remained stable 
during the remainder of the experiment. Titanium coupons showed microbial attachment, less 
than 102 CFU per coupon at day 0, with an increase in CFU values to almost 103 CFU per 
coupon after 5 months of incubation; however, by 12 to 18 months of incubation, CFU values 
decreased by 10-fold, to near their original level. For C22 nickel alloy, the HPC values 
increased from day 0, with a peak at 5 months, followed by a decrease in cell number to 102 CFU 
per coupon. The data indicate the complexity of the dependence of microbial attachment on 
relative humidity. When viewed by SEM, the attached cells, including heterotrophs and 
autotrophs, only formed small clusters, and there was no continuous-biofilm formation. 
At 60C and 70C, HPC values decreased, for all three coupon types, from less than 102 CFU per 
coupon to undetectable levels at day 1, and then remained undetectable for the duration of the 
test, with the exception of detectable values at 1 and 5 months of incubation in each case. The 
difference in HPC values at 60C and 70C is significant in comparison to those at 30C. 
Microbial attachment was negligible compared to that at 30C, as evidenced by scanning 
electron microscope (SEM) on all three coupon types. Cell attachment might have been limited 
not only by elevated temperature, but by individual microbial ability to produce extracellular 
polymeric substances (EPS). Temperature may have had an effect on the production of EPS, 
which is known to enhance the adherence capability of microbial cells. SEM studies have shown 
that Listeria monocytogenes cells produced an EPS matrix at 21C, but not at 10C or 35C 
(Norwood and Gilmour 2001 [DIRS 171133]). EPS is critical not only for initial adhesion, but 
for the firm anchorage of bacteria to solid surfaces (Norwood and Gilmour 2001 
[DIRS 171133]), and to the ability of biofilm microorganisms to deal with environmental 
stresses, such as nutrient limitations, solar radiation, and variations in temperature (Perrot et al. 
1998 [DIRS 171124]). 
In summary, increased temperature (to 60C or 70C) or decreased relative humidity (values 
below 100 percent) impeded biofilm formation on N-316 stainless steel, C22 nickel alloy, and 
titanium coupon surfaces. In the repository, where temperatures will be maintained above 50C 
(Figure 6.4-1), and the supply of water and nutrients will be limited, the formation of biofilm 
will be limited. This is consistent with a report that under unsaturated conditions of soil and 
vadose rock, extensive biofilm development has not been observed (Auerbach et al. 2000 
[DIRS 171116]). This is also consistent with a full-scale test conducted by AECL, in which a 
simulated waste container was buried for 2.5 years surrounded by a compacted buffer material. 
The test showed that, together, decreased relative humidity (95 to 96 percent), elevated 
temperature (60C to 90C), high radiation doses, and limited nutrient supplies prevented biofilm 
formation (Stroes-Gascoyne 1996 [DIRS 171851]). 
6.4.7 Radiation Effect 
Microorganisms, in general, are tolerant or resistant to ionizing radiation. Much of the 
information on the radiation resistance of microorganisms comes from the food industry, because 
ionizing radiation is used in many countries as a means of preserving foods. Exposing foods to 
low doses of ionizing radiation (less than 1 Mrad) substantially reduces the number of those 
microorganisms responsible for food spoilage, thereby extending the shelf life of the food. 
Gamma radiation has also been used to disinfect and treat wastewater effluents. 

Many radioresistant strains of bacteria have been isolated from soil, and studies of soil 
microflora irradiated with long-term .-radiation (in an open-air facility at 15, 150, 800, and 
1500 krad over 18 months) showed that radiation resistance increased at all doses (Table 6.4-4) 
when compared with the radiation resistance of soil microflora from soil shielded from 
irradiation with lead bricks (Eriksen and Emborg 1978 [DIRS 171113]). Barnhart et al. (1980 
[DIRS 171112]) found that approximately 68 percent of the microbial isolates from radioactive 
shallow land burial site soil exhibited greater resistance to .- and -radioactivity than did the 
common soil bacterium Bacillus subtilis to ionizing radiation. Approximately 25 percent of the 
isolates from nonradioactive soil were more resistant than B. subtilis, but all these microbial 
isolates were less radioresistant than Deinococcus radiodurans, which is resistant to .-radiation 
(105 rad). However, radio-resistant bacteria are constantly being enriched in an environment 
containing nanocurie levels of .- and -radioactivity (Barnhart et al. 1980 [DIRS 171112]). In 
the later study, the radio-resistance of 10 isolates of bacteria from a soil core (of a 40-cm to 
50-cm depth, and containing 20 nCi to 30 nCi of radioactivity), taken from a shallow land burial 
site at Los Alamos National Laboratory, was studied. Several of the isolates were resistant to 
5  104 rad .-radiation. At 7.5  104 rad, none of the isolates survived. Radiation resistance of 
bacteria, with reference to the studies dealing with radioactive waste, is shown in Table 6.4-5. 
These data are in good agreement with the values reported from sewage, food, and sterilization 
processes in the literature. 
Table 6.4-4. Radioresistance of Soil Microorganisms Previously Exposed to Long-Term .-Irradiation 
(Expressed as a Percentage of Tubes with Visible Growth) 
Soil Sample Previously 
Exposed to .-Radiation 
(krad/18 months) 
Irradiation dose (Mrad) 
2 3 4 5 
0 (Control) 100 47 0 0 
15 100 93 3 0 
150 100 100 100 0 
800 100 100 40 7 
1500 100 100 100 4 
Source: Erikson and Emborg 1978 [DIRS 171113]. 
Table 6.4-5. Gamma Radiation Resistance of Bacteria Isolated from Various Sources 
Organism/Source Radiation dose (rad) Reference 
Deinoccocus radiodurans (ATCC 13939) 
(wet) 
105 Barnhart et al. 1980 [DIRS 171112] 
Deinoccocus radiodurans (ATCC 13939) 
(dry) 
2.4  106 Barnhart et al. 1980 [DIRS 171112] 
Bacillus subtilis (ATCC 6051) < 2.5  105 Barnhart et al. 1980 [DIRS 171112] 
Microbial isolate QB2 from BNL reactor spent 
resin (wet) 
104 Francis and Quinby 1981 [DIRS 171114] 
Strain K.3.24 and K.3.25 from control soil 
(dry) 
1.5  106; 2.25  106 Erikson and Emborg 1978 [DIRS 171113] 
Strain 30.5.11 and 30.5.16 from irradiated soil 
(dry) 
5  106; 8  106 Erikson and Emborg 1978 [DIRS 171113] 
Several isolated from radioactive waste 
disposal sites 
5  106; 8  106 Erikson and Emborg 1978 [DIRS 171113] 

A time-course experiment was conducted to evaluate the effects of .-radiation on the indigenous 
microbiota present in rock obtained from Yucca Mountain and the Nevada Test Site (Pitonzo et 
al. 1999 [DIRS 150442]). Microcosms were constructed by placing pulverized Yucca Mountain 
rock in polystyrene cylinders. Continuous exposure (96 h) at a dose rate of 1.63 Gray (Gy)/min 
was used to mimic the near-field environment surrounding waste canisters. The microbial 
communities were characterized after receiving cumulative doses of 0 kGy, 0.098 kGy, 
0.58 
kGy, 2.33 kGy, 4.67 kGy, 7.01 kGy, and 9.34 kGy. Radiation-resistant microorganisms in 
the pulverized rock became viable but nonculturable (VBNC) after a cumulative dose of 
2.33 
kGy. VBNC microorganisms lose the ability to grow (on media on which they have 
routinely been cultured) in response to the environmental stress imposed (i.e., radiation), but can 
be detected throughout the time course by means of direct fluorescence microscopy techniques. 
Two representative exopolysaccharide-producing isolates from Yucca Mountain were exposed to 
the same radiation regimen in sand microcosms. One isolate was much more radiation-resistant 
than the other, but based on culturable counts both had greater resistance than the general 
microbial community. However, when respiring cell counts (using only VBNC) were compared 
after irradiation, the results would indicate much more radiation resistance of the individual 
isolates and the microbial community in general. These results have significant implications for 
underground storage of nuclear waste, because they indicate that indigenous microorganisms are 
capable of surviving .-irradiation in a VBNC state. 
To further investigate the VBNC bacteria, portions of irradiated rock were placed at 4C for 
2 months, in an attempt to resuscitate the microbes to a culturable state (Pitonzo et al. 1999 
[DIRS 150442]). Culturable heterotrophs were enumerated, and BIOLOG plates were used to 
determine the metabolic capability of the microbial community. Culturable bacteria that had 
previously been nonculturable were found at all doses. The number of colony types decreased 
from 26 in the nonirradiated control rock to between 9 and 10 in rock irradiated at doses ranging 
from 2.34 kGy to 9.34 kGy. BIOLOG plates indicated partial recovery of metabolic capacity in 
all tested samples. Using the MIDI system (Microbial ID, Inc.), fatty acid methyl ester analysis 
of the recovered isolates yielded three distinct groups of related bacteria. All resuscitated 
isolates clustered with the original nonirradiated isolates at the genus level, and 92 percent of 
them clustered at the species level. These results indicated that microbes were probably 
resuscitated from a VBNC state. 
Based on the current repository loading design, the expected maximum surface dose rate from 
one unbreached canister designed to contain spent nuclear fuels is: 
0.06 Gy/min (= 31.5 kGy/yr = 3.15 Mrad/yr) (conversion: 1 kGy = 0.1 Mrad) 
(Pitonzo et al. 1999 [DIRS 150442]). 
By comparison with the radiation dose resistance values listed in Table 6.4-7 and Table 6.4-8, it 
is expected that radiation may inhibit microbial growth in the repository. This assessment is 
consistent with an AECL test that used a simulated waste container with a maximum heat output 
of 85C). The test has shown that the surface of a nuclear fuel waste container is sterilized 9 to 
33 days after emplacement (Stroes-Gascoyne 1996 [DIRS 171851]). 

6.5 POTENTIAL IMPACTS ON REPOSITORY CHEMISTRY 
Together, the subsections of Section 6.5 address the impacts of microbial activity on two FEPs: 
1. 
FEP 2.1.09.01.0A (chemical characteristics of water in drifts) 
2. 
FEP 2.1.09.02.0A (chemical interaction with corrosion products). 
Section 6.5.1 also addresses the impact of microbial activity on FEP 2.1.12.01.0A (gas 
generation [repository pressurization]). 
Microbial growth and activity at Yucca Mountain are limited by multiple factors: elevated 
temperatures, oxic environments, low relative humidity, high water salinity, limited nutrient 
supplies, and high radiation fields (see Section 6.4). Given these environmental constraints, the 
upper bound of microbial cell density in the repository can be constrained as follows: 
 
Cell density in the surrounding rocks: Because the perturbation of waste emplacement 
in the drift (e.g., elevated temperatures, low relative humidity, and high radiation field) 
will lead to a near-field environment less conducive to microbial growth, and because 
metal corrosion under the anticipated repository conditions will not be able support any 
significant autotrophic microbial growth (Section 6.4.2), the upper limit of microbial 
population in the surrounding rocks can be set to 5  105 cells/g dry rock throughout the 
regulatory time period. This value bounds all reported values (Section 6.3). 
 
Suspended cell density in water: No field measurements are available for suspended cell 
density in Yucca Mountain underground water. The upper limits of this cell density can 
be constrained from Yucca Mountain-related microbial incubation experiments. The 
results of the most relevant experiments are shown in Figure 6.4-4. In these 
experiments, tuff rocks were incubated with simulated J13 water amended with or 
without glucose. As shown in the figure, a significant microbial growth was stimulated 
by the addition of an organic source. Because the concentration of glucose in the growth 
solution was as high as 5.55 mM, which was about 55 times higher than the maximum 
organic carbon concentration (1.1 mg/L = 0.1 mM) in Yucca Mountain groundwaters, 
the planktonic cell density (7  107 cells/mL) measured in the organic-carbon-amended 
experiment thus provides a reasonable upper bound on the suspended cell density in the 
in-drift water throughout the regulatory period. 
6.5.1. Water Chemistry (pH, SCO2) 
Heterotrophic degradation of organic carbon will release CO2 as a metabolic product. For 
example, in an aerobic environment: 
CH2O + O2 = CO2 + H2O (Eq. 6-4) 
The release of carbon dioxide could potentially perturb the carbonate equilibrium and therefore 
the pH in water entering the repository. The extent of this perturbation solely depends on the 
availability of organic carbon, which can derive from two sources: groundwater and introduced 
materials. 

According to the current repository design, the committed construction materials will contain no 
biodegradable organic carbon (see Table 4.1-1). Yucca Mountain groundwater contains only a 
trace concentration of organic carbon (1.1 mg/L) (Table 4.1-1), which is much lower than the 
total carbonate concentration (41 to 430 mg/L) in the solution (DTN: GS011108312322.006 
[DIRS 162911]). Therefore, even if all the dissolved organic carbon is converted to carbon 
dioxide, the perturbation to the water chemistry is still negligible: 
...
/
1.1 mL C mg 

41 e bicarbonat mg / mL
...
=
%14
<
//
12 molC C g 61 C mol carbonate g 
.
.
Additional organic substances (e.g., diesel fuel, diesel exhaust, lubricants, rock drill oil, coolants 
and cleaning solvents) may be introduced into the repository during construction and operations. 
The quantities and types of such substances are currently controlled, with analysis of the 
potential impacts to waste isolation (BSC 2004 [DIRS 169885], Section 6.12.3); 
LP-SA-001Q-BSC). Thus, the total quantity of such substances committed in the repository will 
be limited (see Section 5, Assumptions). 
These substances will tend to be removed with the waste rock during construction, or dispersed 
by construction water into the host rock. Elevated temperature and ventilation during preclosure 
operations will also disperse volatile organic compounds. Furthermore, degradation of residual 
organic material in the drift will have limited effect on the bulk chemical environment, which is 
demonstrated by a simple example. As shown in Figure 6.5-1, carbon dioxide in the drift will be 
continuously circulated by gas flow after repository closure, due to thermal-hydrologic-chemical 
processes in the host rock, with a flux greater than 0.1 mole CO2 per year per meter of drift. This 
gas flux is sufficient to dissipate the CO2 generated from complete conversion of at least 
1.4 grams of diesel fuel (= 0.1/8*(8*12 + 18)g) using C8H18 as a representative formula) over 
one meter drift within a year, without significantly changing the CO2 abundance in the 
emplacement drifts. Therefore, small quantities of organic substances will have an insignificant 
effect on the bulk chemical environment in the drifts. Potential microbial effects on radionuclide 
transport (e.g., associated with microbial degradation of organic carbon in the invert) are 
discussed in Section 6.5.4. 

Figure 6.5-1. CO2 Flux Calculated from a Cumulative Gas Flux Predicted by the THC Model 
Source: DTN: SN0407T0510102.017 [DIRS 170667], file: gas_flux.xls, worksheet: moles per m chart. 
6.5.2 Low Molecular-Weight Organic Ligands 
Microorganisms also perturb the geochemical speciation of radionuclides by releasing (into the 
surrounding extracellular environment) organic chemicals as by-products of metabolism (Stone 
1997 [DIRS 110045]). These chemicals contain a variety of functional groups that may complex 
with radionuclides. Two groups of microbial compounds are considered complexing agents: 
 
By-products of microbial metabolism and degradation 
 
Microbial exudates. 
The first group consists of simple organic compounds such as low-MW organic acids. The 
second group includes microbial exudates induced by metals ions. Iron-binding siderophores are 
produced in response to low iron concentrations. 

Table 6.5-1. Microbial Production of Low-MW Organic Acids Detected in the WIPP Microbial 
Gas-Generation Experiments 
Experimental Condition Formate (M) Acetate (M) Lactate (M) 
Cellulose + cells + no nutrients 9.99 10-04 2.01 10-03 8.88 10-05 
Cellulose + cells + nutrients 2.90 10-03 4.45 10-03 6.88 10-04 
Cellulose + cells + nutrients + extra nitrate 3.92 10-03 4.43 10-03 1.57 10-03 
Source: Francis et al. 1997 [DIRS 171062]. 
NOTE: The measurements were performed at 1,228 days after inoculation with cellulose materials. 
Depending on the types of organic materials introduced into the repository and the 
environmental conditions, there could be variable abundances of the small MW complexing 
agents. These low-molecular organic acids, released as intermediate metabolites, are also 
subjected to additional microbial degradation. Thus, the concentrations of these organic 
compounds are limited in natural systems. For example, in the Middendorf aquifer of South 
Carolina, the concentration of acetate was in the range of 0.5 to 3 M; the concentration of 
formate was in the range of 0 M to 15 M (Chapelle 2001 [DIRS 171162], p. 179). It was also 
observed that the concentration of formate increased in the iron-rich zone of the aquifer. In a 
system extremely rich in organic carbon and nutrients, the concentrations of these organic acids 
can be higher. In experiments incubating cellulose materials with the WIPP-related bacteria, the 
concentrations of formate, acetate, and lactate could be up to a few mM, especially in those 
amended with extra nitrate (Table 6.5-1) (Francis et al. 1997 [DIRS 171062]). 
The repository is an extremely oligotrophic environment, in which microbial activity is limited. 
The concentration of the microbially generated organic acids, if there are any, should be low. 
Concentration for any organic ligands present should be lower than the values reported for the 
Middendorf aquifer (0 to 15 M for each ligand present), which is located in organic-carbon-rich 
sedimentary rocks. To evaluate the capability of these organic acids for metal complexation, a 
conservative upper bounding concentration of 50 M for each ligand is chosen. The fraction of a 
radionuclide complexed by an organic acid can be calculated by considering formation constants 
of metal complexes as described by Dean (1992 [DIRS 100722], Section 8.2.2). For a reaction 
stoichiometry written as: 
R +C =RC 
where R is a metal (or radionuclide) and C is the complexant, the formation constant is defined 
by Dean as: 
[RC]
K =
[][C]
R 
where the [ ]s indicate concentrations. The fraction of R complexed is written as: 
[RC]
Fraction = 
[]+[RC]
R 

Now use [RC]=K[R][C] and substitute in the above to obtain: 
[ [
R K ][C] C K ]
Fraction = = 
[]+R K []
R [][C] 1 +C K 
This is equivalent to: 
[
11 +C K ]-1 C K ]
Fraction - == =
1
[] 1 +C K 
[
[] (Eq. 6-5) 
1 +C K [] 1 +C K 
The calculation result for Am(III) is shown in Table 6.5-2. It can be seen that even at such a 
high ligand concentration, the complexed americium is less than 2 percent of the total americium 
in the solution and is therefore negligible compared to free americium ions. 
Table 6.5-2. Complexation of Am3+ with Intermediate Metabolites 
Organic acid Metal Log K Am Complexed 
Formic Am 1.2 0.08% 
Acetic Am 1.99 0.49% 
Lactic Am 2.43 1.33% 
Source: NIST 2003 [DIRS 171201]. 
NOTE: Percentages of americium complexed are calculated by assuming the 
concentrations of intermediate metabolites to be 50 M. 
As mentioned above, another group of organic acids are microbial exudates, among which 
siderophores are of particular concern. Microbes require iron for DNA synthesis, electron 
transfer proteins, and nitrogen fixation. However, iron suffers from extreme insolubility in 
aerobic environments at physiological pH. Aerobic and facultatively anaerobic microorganisms 
have developed a system to acquire Fe(III). This is accomplished by siderophore generation. 
Siderophores are low molecular mass, ferric-specific ligands that are induced at low iron 
concentration for the purpose of biological assimilation of Fe(III). The most common 
siderophores contain the hydroxamic acid functional group -R-CO-N(OH)-R', which forms a 
five-membered chelate ring with Fe3+ (Hersman 1997 [DIRS 100763]). Because Fe(III) and 
Pu(IV) are similar in their charge/ionic radius ratio, Pu(IV) might serve as an analogue to Fe(III) 
(Hersman et al. 1993 [DIRS 100762]). However, in the repository, a large quantity of Fe(III) 
will be accumulated from oxic steel corrosion (Table 4.1-1), which will overwhelm Pu(IV) in 
complexation with siderophores. In addition, under oxidizing conditions anticipated in the 
repository, plutonium will be dominated by Pu(V) and Pu(VI), instead of Pu(IV) (Table 4.1-1). 
Therefore, the effect of siderophores for plutonium dissolution will be insignificant. 
6.5.3 Biotransformation and Biosorption of Radionuclides 
Microorganisms are known to accumulate radionuclides both extracellularly and intracellularly. 
In this section, possible processes of biotransformation and bioaccumulation of radionuclides by 
microorganisms are summarized based on open literature search. The relevance of these 
processes to the repository is then evaluated in the context of anticipated repository conditions. 

Studies on the association of uranium with bacteria by nuclear magnetic resonance spectroscopy, 
by time-resolved laser fluorescence spectroscopy, and by extended X-ray absorption fine 
structure (EXAFS) analysis have shown the involvement of phosphate and carboxylate groups in 
uranium binding (Andres et al. 1994 [DIRS 171126]; Henning et al. 2001 [DIRS 171121]; Kelly 
et al. 2002 [DIRS 171135]). 
Francis et al. (2004 [DIRS 171467]) determined the association of uranium with bacteria isolated 
from WIPP (Carlsbad, New Mexico), and compared this association with known strains of 
halophilic and nonhalophilic bacteria and archaea. Examination of the cultures by transmission 
electron microscopy and energy dispersive X-ray spectroscopy showed uranium accumulation 
extracellularly and/or intracellularly to varying degrees. 
In Pseudomonas fluorescens and Bacillus subtilis, uranium was associated at the cell surface, 
and in the latter it was present as irregularly shaped mineral grains. In Halobacterium halobium, 
an archaea, uranium was present as dense deposits; in Haloanaerobium praevalens, uranium was 
present as spikey deposits. Halomonas sp. isolated from the WIPP site accumulated uranium 
both extracellularly (on the cell surface) and intracellularly (as electron-dense discrete granules). 
EXAFS analysis of uranium with the halophilic and nonhalophilic bacteria and archaea at 
physiological pH (5 to 6.8) showed that the uranium present in whole cells was bonded to an 
average of 2.4  0.7 U-P phosphoryl groups at a distance of 3.65  0.03 . However, analysis of 
the cell wall fragments of lysed Halomonas sp. showed that uranium formed a bidentate complex 
with a carboxylate group on the cell wall at 2.91  0.03 , and a U-U interaction at 3.71  0.03 
, indicating a precipitated hydroxide phase was also present; no U-P interaction was observed. 
Addition of uranium to the cell lysate of Halomonas sp. resulted in the precipitation of uranium 
due to the inorganic phosphate released from the cells. These results show that the microbial 
polyphosphates and phosphates released from mineralization bind a significant amount of 
uranium. However, the microbially immobilized uranium mineral phase was readily solubilized 
by bicarbonate with concurrent release of phosphate into solution. 
Spectroscopic techniques have been used to elucidate the functional groups involved in the 
bonding of uranium with microbial cells. In general, the microbial cell surfaces contain 
carboxyl, phosphoryl, amino, and hydroxyl functional groups, which are known to form 
complexes with uranium (Fowle et al. 2000 [DIRS 155808]). 31P-NMR studies showed that 
uranium was bound to the phosphate groups of the phospholipid fraction isolated from 
Mycobacterium smegmatis, and that the phosphate groups and carboxylate groups of the 
peptidoglycan (Pg) also are involved in its binding (Andres et al. 1994 [DIRS 171126]). 
Time-resolved laser fluorescence spectroscopy studies of Thiobacillus ferrooxidans and 
Thiomonas cuprina and several Bacillus species (Bacillus cereus, B. sphaericus, and B. 
megaterium) formed inner-sphere complexes of uranium with organophosphate groups on the 
cell surface, and that the polysaccharides and teichoic acids of cell walls or the phospholipid 
layers of membranes were responsible for uranium binding (Panak et al. 1999 [DIRS 171085]). 
EXAFS analysis of uranium complexes with B. cereus, B. sphaericus, and B. megaterium have 
shown that uranium U(VI) is bound to phosphate group (Henning et al. 2001 [DIRS 171121]; 
Panak et al. 1999 [DIRS 171085]), whereas studies with B. subtilis (Kelly et al. 2002 
[DIRS 171135]) show that, at extremely low pH (pH 1.67), U(VI) binds exclusively to 
phosphoryl functional groups on the cell wall and, with increasing pH (3.22 and 4.80), U(VI) 

binds increasingly to microbial surface carboxyl functional groups. In a related study, Panak et 
al. (2002 [DIRS 171120]) showed that, in B. sphaericus, Pu(VI) was primarily bound to 
phosphate groups on the cell surface, and no carboxylate complexation was detected. However, 
the bond lengths between Pu(VI) and the equatorial oxygens, as well as the phosphorus atoms, 
are longer in the microbial phosphate complex than in the Pu(VI) dihydrogen phosphate 
precipitate with an overall decrease in the number of phosphorus atoms. This led them to 
conclude that Pu(VI) is bound to organophosphate groups at the cell surface (Panak et al. 2002 
[DIRS 171120]); in addition, EXAFS analysis of several examined microbial species showed the 
formation to be an inner-sphere complex of uranium with phosphoryl and the carboxyl groups of 
the microbial cells. 
The EXAFS analysis of the whole cells of halophiles, nonhalophiles, and archaea indicates the 
complexation of uranium predominantly with cellular inorganic phosphate. Although it is 
difficult to distinguish monophosphate bonding from polyphosphate bonding by EXAFS, the 
detection of four phosphate bonds to uranium is a good indication of polyphosphate formation. 
In Halomonas sp., uranium was bound as a diphosphate group with the whole cells, whereas, 
with the cell walls, it was bound to the carboxylate group as bidentate complex with indications 
that uranyl hydroxide is present. The complexation of uranium as bidentate complex at 
physiological pH has been reported (Fein et al. 1997 [DIRS 100744]). 
Polyphosphates are widely distributed throughout the microbial cell. Numerous and varied 
biological functions are performed by polyphosphate including: phosphate storage in the cell; a 
reservoir of energy for cellular functions; a chelator of metals (e.g., Mn2+ and Ca2+); a pH buffer; 
a capsule for bacteria; and in physiological adjustments to growth, development, stress, and 
deprivation (Kornberg 1995 [DIRS 171079]). The amount of polyphosphate that is stored by 
cells varies between microbial species, and is determined, in part, by the rate at which it can be 
degraded (for example, in response to the presence of metals), and the amount of inorganic 
phosphate secreted into the medium. Inasmuch as all of the uranium exposure studies reported 
were conducted with cells in the stationary phase, the cells are responding to heavy metal stress 
by releasing phosphate from the mineralization of cellular polyphosphate. In some experiments 
reported in the literature, the cells were in fact incubated with uranium, from several hours to 
days. Under these conditions, the cells undergo lysis and release inorganic phosphate (H2PO4 
-) 
with the precipitation of uranium as uranyl phosphate [UO2(H2PO4)2]. These results show that 
an increase in the concentration of inorganic phosphate released from mineralization of cellular 
phosphates during starvation or under stress binds significant amounts of uranium. 
The possible biotransformation of actinide, and its relevance to the repository, are summarized in 
Table 6.5-3. Because an oxidizing environment will be maintained in the repository, and 
because the supply of organic carbon will be limited, reduction of actinides from higher to lower 
valence states will be unlikely. Even if it occurs, it can be conservatively ignored because it 
would lead to a lower solubility. For the same reason, microbial activity will not reductively 
dissolve Fe(III) oxides generated from oxic metal corrosion and therefore will not change the 
availability of sorption sites for radionuclides in the repository. Other biotransformation 
processes may occur, but their impacts on radionuclide mobility will be insignificant 
(Table 6.5-3). 

Table 6.5-3. Summary of Biotransformation of Actinides and Its Relevance to the YMP 
Process Th U Np Pu Am Relevance to YMP 
Biosorption ? ++++ + ++ + Possible, but limited by low microbial activity. It 
can be conservatively ignored, because most 
microbial cells are associated with solid matrix. 
Reductiona  ++++ ? ?  Minimal due to oxidizing environment. It can be 
conservatively ignored, because it leads to a low 
solubility. 
Dissolutionb + ++ ? + ? Microbially mediated oxidation. Limited by low 
microbial activity. No impact on repository 
performance, since the solubility model assumes 
high oxidation states for all radionuclides (BSC 
2004 [DIRS 169425]). 
Biocolloidc + + + + + Possible, but limited by low microbial activity and 
mobility. Negligible compared to groundwater 
colloids. 
a 
b 
Precipitation due to reduction from higher to lower valence states. 
Due to metabo
lic products including siderophores; oxidation from lower to higher valence states. 
c 
Association of radionuclides with suspended microbial cells. 
Legend: 
? = Not known. 
 
= Not possible. 
+ = Possible.
++ = Likely. 
++++ = Very likely.
6.5.4 Colloid-Facilitated Transport 
Groundwater is expected to be the principal medium for the potential movement of radionuclides 
from a repository. Colloidal transport of radionuclides is recognized as a potential mechanism of 
migration, and includes mineral fragments, humic substances, intrinsic colloids, and 
microorganisms. Microbes fall at the upper end of, and above, the colloidal size range of 1 nm 
to 1 m. Growing bacteria are several micrometers long, with volumes of several cubic microns; 
nongrowing bacteria under oligotrophic conditions may be as small as 0.2 m to 0.3 m. 
Significant numbers of bacteria exist in subterranean environments including extreme 
environments, such as deep-sea hydrothermal vents, hot springs, and deep aquifers; they are 
present in the groundwaters of all repository environments investigated. Therefore, there has 
been a concern with a potential radionuclide transport facilitated by suspended microbial cells, 
often referred to as biocolloids. However, such a mechanism has not been confirmed by 
experimental data. To the contrary, these data have shown that biocolloids can only travel over a 
short distance in a porous medium lacking fractures (such as the invert materials in the 
repository), and the presence of microbial cells and their by-products may even help 
immobilization of radionuclides. 
Francis et al. (1998 [DIRS 171078]) evaluated the interactions of dissolved 239Pu (as 
plutonium-nitrate, perchlorate and EDTA complex) under anaerobic conditions with a pure 
culture and a mixed culture of halophilic bacteria isolated from the WIPP repository 
environments to evaluate the potential transport as biocolloids from the waste site. 

The sizes of the microbial cells ranged from 0.54  0.48 m to 7.7  0.67 m. The association 
of plutonium with suspended microbial cells (106 to 109 cells/mL) at various growth phases in a 
medium containing NaCl or MgCl2 brine was determined by sequential microfiltration. The 
amount of plutonium associated with the suspended cell fraction (calculated as mol/cell) is low 
(Pu 10-18 to Pu 10-21), and it varies with the particular microbial culture. In addition, most cells 
tend to attach to solid surfaces (Johnson et al. 1974 [DIRS 171153]). These results support other 
studies that assessed the influence of bacteria on the migration of radionuclides from a deep 
spent-fuel repository, based on total number of bacteria present; these studies concluded that 
negligible amounts of the released radionuclides would be bound to unattached bacteria 
(Pedersen 1996 [DIRS 171086]). 
In the presence of microorganisms, colloidal movement through a rock matrix could be reduced 
because of an overall increase in the size of colloidal particle agglomerates (Hersman 1995 
[DIRS 100750]). There are several general interactions between microorganisms and solid 
surfaces (including colloidal particles) and the effects of microbial adhesion on colloids. These 
interactions include attraction processes such as adhesion, adsorption, and flocculation. Solid 
surfaces are potential sites for concentrating nutrients and for the promotion of microbial 
activity. In addition to movement of water across a solid surface, there are many 
physico-chemical and biological attraction mechanisms at solid surfaces. These attraction 
mechanisms include chemotaxis, Brownian motion, electrostatic attraction, van der Waals 
interaction, electrical double layer effects, and cell surface hydrophobicity (for a more detailed 
discussion of these processes, refer to Hersman 1995 [DIRS 100750], p. 2-4). Depending on the 
nature of the particulate matter, fabric organization, clay type, etc., the availability of the 
substrate may be either enhanced or reduced by the presence of particulates. 
If substrates were concentrated on the surface of clay minerals, this would enhance the 
colonization of microbes on those surfaces. These interactions can lead to the formation of 
multiple microbial-colloidal particle agglomerates (Hersman 1997 [DIRS 100763]). In addition, 
Hersman (1995 [DIRS 100750]) indicates that clay colloids can be adsorbed onto the surfaces of 
microbes. Hersman (1995 [DIRS 100750]; 1997 [DIRS 100763]) discusses the processes that 
have been patented for the flocculation of clays. They include microbial polysaccharides and 
nucleoproteins. These processes have the potential to inhibit colloidal transport by increasing 
particle size. 
Adhesion of microorganisms is involved in fouling of man-made surfaces, in microbial 
influenced corrosion, and in syntrophic and other community interactions between 
microorganisms in natural habitats. Unlike inorganic colloidal particles, bacteria appear to 
adhere to surfaces by means of surface polymers, including cellular lipopolysaccharides, 
extracellular polymers and capsules, pili, fimbriae, and flagella. The composition and quantity 
of microbial surface polymers vary considerably, and are influenced by growth and 
environmental conditions (Hersman 1997 [DIRS 100763]). Because of their large sizes, and 
because of this adhesion effect, microorganisms are expected to be much less liable to be 
transported in a subsurface system than inorganic colloid particles. 
Jewett et al. (1999 [DIRS 154325]) used porous medium column experiments to investigate 
Pseudomonas fluorescens strain P17 transport as a function of water content and the influences 
of the solid-liquid and gas-liquid interfaces. The experiments were conducted for sub-rounded 

quartz sand at the water-saturation degrees of 100, 84, and 46 percent. The mean grain diameter 
of the sand was 158 m, with a range of 50 m to 250 m. The sand was washed with HCl/heat 
treatment to remove oxide and organic coating from the particle surface. The porosity of the 
compacted sand was 0.36. Bacteria used in the experiment had a cell size of 0.86 m to 
0.90 m, and the bacteria were injected into the top of the sand column at a flow velocity of 
0.48 cm/s to 4.78 cm/s, and at a concentration of 1.0 cells/mL to 1.66  106 cells/mL. The 
column length is 12.5 cm. The experimental results showed that maximum cell retention 
occurred in the top centimeter of porous media at all three water contents, and decreased with 
depth in the column. The total fraction of cells retained was inversely proportional to water 
content, with nearly twice the cell retention at 46-percent saturation than at 100-percent 
saturation. 50 percent of cells were retained within the column under the fully saturated 
condition; 95 percent of the cells were retained at a 46-percent water saturation. 
Cattaneo et al. (1997 [DIRS 171059]) studied the transport of Burkholdera cepacia in the 
unsaturated soil column. The soil used in the experiments was collected from the upper 6 inches 
of a forest soil. It was sieved (2 mm) without air drying, and the content and density of the 
organic matter were measured as 15.5 percent and 2.39 g/mL. The number of cells was reduced 
by 90 percent over a 2-cm percolation distance. 
Microbial transport testing was also conducted in a sandy aquifer on the coastal plain of Virginia 
(DeFlaun et al. 1997 [DIRS 171060]). The 30-m-long flow cell consisted of groundwater 
production and injection wells, a tracer injection well, and 10 multilevel samplers screened every 
half meter from 4.0 m to 10.5 m below ground surface. The bacteria used in this test were 
selected for low adhesion to site sediments, so that they might be readily transported through the 
aquifer. The selected bacteria were then labeled by 13C for detection. The results from this field 
test indicate that bacteria traveled the length of the flow field (4 m), but the majority of the 
injected biomass was retained in the sediments between the injection well and the first multilevel 
sampler at 0.5 m. 
Furthermore, field measurements indicate that most microbial cells are associated with solid 
matrix. For example, in the Rocky Flats Plant Pond B-1, the cell density in the sediments ranges 
from 3 to 300  106 cells/mL for aerobes and from 0.2 to 2  106 cells/mL for anaerobes; the 
waters have only 1.1 to 340  103/mL for aerobes and 2 to 7.8  102/mL for anaerobes (Johnson 
et al. 1974 [DIRS 171153]). In this case, less than 1 percent of cells are in suspension. 
Therefore, if biosorption and bioaccumulation occur, microbes tend to immobilize radionuclides 
in subsurface systems. 
Based on the above discussion, given that the invert material is composed of crushed tuff rocks, 
which can be considered a nonfractured porous medium, biocolloids generated in the Yucca 
Mountain drift will be, at least partly, filtered out within the invert. 

The transport of microbes through fractures must exist. Otherwise, there are no microbes that 
can be detected in the rock, because volcanic ash precluded inclusion of microbes de novo. 
However, transport and the facilitated radionuclide migration are expected to be limited due to: 
 
Low liquid-water saturation (Section 6.4.3) 
 
High-ionic strength, which tends to destabilize colloidal suspension (BSC 2004 
[DIRS 170025], Section 6.3.2) 
 
Low microbial activity, as discussed in Section 6.4. 
Even if microbial cells can transport through rock fractures in unsaturated and saturated zones, 
their impact on radionuclide transport is still negligible. The concentration of microbial cells in 
the in-drift water (< 7  107 cells/mL, see Section 6.5) is much lower than the concentration of 
groundwater colloids (106  1011 particles/mL) (BSC 2004 [DIRS 170025], Figure 6-11). 
6.6 UNCERTAINTIES 
The evaluation of the impacts of microbial activity on the Yucca Mountain in-drift chemistry, as 
summarized above, is based on bounding analyses. Therefore, uncertainties associated with 
input parameters used in this report are fully captured. Variations in the input parameter values 
within reasonably expected ranges will not change the conclusions drawn in this report. 

7. CONCLUSIONS 
7.1 EVALUATION CONCLUSIONS 
This evaluation addresses eight FEPs, as listed in Tables 6.2-1 and 6.2-2. Table 6.2-1 identifies 
the section(s) in this report that develop information for inclusion of a FEP in the TSPA-LA. 
Table 6.2-2 identifies the section(s) that develop information for exclusion of a FEP from the 
TSPA-LA. 
Based on different nutritional requirements, microorganisms are categorized into one of two 
groups: 
 
Heterotrophs, which use organic carbon compounds as their carbon and energy source 
 
Autotrophs, which derive their energy from the oxidation of inorganic compounds and 
derive cell carbon from CO2. 
Section 6.1 of this report describes the systematics of repository biochemistry. In the repository, 
heterotrophic microbial activity is limited by the lack of a significant organic carbon supply; 
autotrophic microbial activity is limited by the lack of available inorganic electron donors in an 
oxic environment. Microbial analyses conducted in the ESF have determined the existence of 
aerobic heterotrophs and autotrophs. The organisms present include iron oxidizing, sulfur 
oxidizing and nitrifying organisms. Cell counts range from 10 to 500 cells per gram of tuff for 
autotrophs, and from 3.2  104 to 2  105 cells per gram for heterotrophs. The total microbial 
population at Yucca Mountain is relatively low in comparison to other subsurface environments. 
The direct DNA extraction and 16S rDNA analysis have demonstrated that microorganisms at 
the Yucca Mountain site are highly adaptive and sufficiently diverse to carry out any specific 
metabolic reaction that the environment permits. 
The following environmental factors severely limit microbial activity in the repository: 
 
The in-drift temperatures during the thermal pulse will exceed the temperature tolerance 
of all known microbes for a significant portion of the repository time, thus exerting a 
sterilization effect on microorganisms. 
 
An oxic environment will prevail in the repository over the growth-permissive period 
and therefore prevent the generation and accumulation of reduced inorganic species that 
are the prerequisite for autotrophic metabolism. 
 
Microbial incubation experiments have demonstrated that water availability is the 
primary limiting factor for Yucca Mountain microbial growth. The relative humidity 
and the liquid-water saturation in the repository are predicted to be low for a significant 
duration, thus further limiting microbial activity. 
 
Evaporation of seepage waters in the low relative humidity environment due to radiation 
heat will result in brine solutions with ionic strengths higher than 10 M, which is an 
environment in which only a few halophiles may be able to survive. The activity of 

these microbes should be limited after the thermal pulse, when low ionic strength 
environments are reestablished. 
 
Organic carbon is an important limiting factor for Yucca Mountain microbial growth. 
The extremely low organic carbon supply in the repository will limit heterotrophic 
microbial activity. 
 
Elevated temperatures, radiation fields, low humidity, and low nutrient supplies, will 
severely limit the formation of biofilm in the repository. 
Due to the aforementioned environmental constraints, the microbial activity in the repository is 
expected to be low, and its impacts on drift chemistry can be negligible: 
 
Yucca Mountain groundwater only contains a trace concentration of organic carbon, 
which is negligible compared to the total carbonate concentration in the solution. 
Furthermore, an autotrophic microbial reaction, if it occurs, will not generate CO2, 
because it is a CO2-fixation process, and the accumulated biomass will probably be 
recycled back to CO2, resulting in zero CO2 accumulation or depletion. Even if all the 
organic carbon were converted to carbon dioxide, the perturbation to the water chemistry 
is negligible. Therefore, the impact of microbial activity on water chemistry (pH and 
SCO2) will be negligible. 
 
In an oligotrophic environment such as the repository, microbial activity is limited, and 
the concentrations of the microbially generated low-MW organic acids are expected to 
be very low (< 50 M). Bounding calculations show that the complexation effect of 
these organic acids on radionuclide dissolution is negligible. 
 
Because an oxic environment will prevail in the repository, actinide precipitation due to 
reduction from higher to lower valence states will be limited and can be ignored. For the 
same reason, microbial activity will not reductively dissolve Fe(III) oxides generated 
from oxic metal corrosion and therefore will not change the availability of sorption sites 
for radionuclides in the repository. Other biotransformation processes (such as 
dissolution due to oxidation reactions, production of sequestering agents, and 
biosorption) may occur, but their impacts on radionuclide mobility will be insignificant. 
 
Because of the oxic environment, denitrification is inhibited. Significant microbial 
consumption of nitrate will not occur. 
 
The concentration of suspended microbial cells is low compared to that of groundwater 
colloid particles, and a separated consideration of biocolloid-facilitated transport is not 
necessary in the Yucca Mountain environment. Field measurements indicate that a 
majority of microbial cells are attached to solid matrix. Through biosorption and 
bioaccumulation, microbes actually tend to immobilize radionuclides in subsurface 
systems. 
MIC could be a potential concern for the integrity of the waste package. Although this report is 
not intended to address MIC specifically, it does provide boundary conditions for evaluating the 

potential effect of microbial activity on waste package corrosion in relevant Yucca Mountain 
environments. As summarized in this section, microbial activity in the Yucca Mountain 
repository is expected to be minimal due to the environmental limitations. Specifically, the 
following factors will limit, if not completely prevent, microbially influenced corrosion: 
 
Oxic environments will prevail in the repository over the regulatory time period. 
Therefore, sulfate reduction (an anaerobic reaction pathway generally considered to be 
responsible for MIC) is unlikely to occur. Microbial oxidation of sulfide will be 
unlikely, due to a lack of reduced sulfur species in the repository. 
 
The repository transient conditions of decreased relative humidity, elevated 
temperature, and high radiation doses, together with limited nutrient supplies, will 
prevent the formation of biofilms, which are required for MIC. 
As discussed in Section 6.4.3, although microbes can be active at a relative humidity as low as 
75 percent, most microbes can thrive only when relative humidity is above 90 percent. For the 
purpose of TSPA calculations, it is recommended to choose 90 percent relative humidity as a 
threshold for MIC. This choice likely leads to an overestimate of the MIC effect, because other 
factors (such as elevated temperature, high radiation dose, and limited nutrient supplies) will also 
limit microbial activity; microbes will require even higher relative humidity to maintain their 
active metabolism. Microbial activity, including MIC, is expected to be minimal in the Yucca 
Mountain repository. 
The qualitative analyses and bounding calculations in this evaluation fully capture the ranges of 
uncertainty in the inputs. Therefore, the potential impact of microbial activity on drift chemistry 
does not warrant a direct feed to the TSPA-LA. That is, the above conclusions support 
arguments in Engineered Barrier System Features, Events, and Processes (BSC 2004 
[DIRS 169898]) and therefore each FEP addressed in this report will either: 
 
Exclude the FEP from the TSPA-LA on the basis of low consequence, or 
 
Have a TSPA-LA disposition of the FEP in which the contribution from microbial 
activity can be neglected. 
7.2 YUCCA MOUNTAIN REVIEW PLAN CRITERIA ASSESSMENT 
This model predicts results that directly pertain to the abstraction of the quantity and chemistry 
of water contacting engineered barriers and waste forms. This section summarizes the contents 
of this report as they apply to NRC criteria for a detailed review of that abstraction. These are 
the relevant criteria from Yucca Mountain Review Plan, Final Report (NRC 2003 
[DIRS 163274], Section 2.2.1.3.3.3), which is from 10 CFR 63.114(a)  (c) and (e)  (g) 
[DIRS 156605]. 
 Acceptance Criterion 1  System Description and Model Integration Are Adequate. 
(1) Total system performance assessment adequately incorporates important design 
features, physical phenomena, and couplings, and uses consistent and appropriate 

assumptions throughout the quantity and chemistry of water contacting 
engineered barriers and waste forms abstraction process. 
This evaluation incorporates current design features and latest analyses of physical phenomena 
and couplings by taking inputs directly from current IEDs and current analyses and model 
reports, as listed in Table 4.1-1. The use of these sources also ensures that appropriate 
assumptions have been consistently used throughout the abstraction process. 
(2) The abstraction of the quantity and chemistry of water contacting engineered 
barriers and waste forms uses assumptions, technical bases, data, and models, that 
are appropriate and consistent with other related U.S. Department of Energy 
abstractions. For example, the assumptions used for the quantity and chemistry of 
water contacting engineered barriers and waste forms are consistent with the 
abstractions of Degradation of Engineered Barriers (Section 2.2.1.3.1); 
Mechanical Disruption of Engineered Barriers (Section 2.2.1.3.2); Radionuclide 
Release Rates and Solubility Limits (Section 2.2.1.3.4); Climate and 
Infiltration (Section 2.2.1.3.5); and Flow Paths in the Unsaturated Zone 
(Section 2.2.1.3.6). The descriptions and technical bases provide transparent and 
traceable support for the abstraction of quantity and chemistry of water contacting 
engineered barriers and waste forms. 
The assumptions and models used in this evaluation are the same as those incorporated in the 
analyses that establish the technical bases for this evaluation and the technical bases for related 
abstractions. Other data (Table 4.1-2) are widely accepted constraints on microbial activity that 
are justified in Table 4.1-3. These data are appropriate and consistent with other related 
abstractions. 
(3) Important design features, such as waste package design and material selection, 
backfill, drip shield, ground support, thermal loading strategy, and degradation 
processes, are adequate to determine the initial and boundary conditions for 
calculations of the quantity and chemistry of water contacting engineered barriers 
and waste forms. 
The sources for the boundary conditions for this evaluation, which are listed in Table 4.1-1, 
address that the important design features are adequate to determine those boundary conditions. 
(4) Spatial and temporal abstractions appropriately address physical couplings 
(thermal-hydrologic-mechanical-chemical). For example, the U.S. Department of 
Energy evaluates the potential for focusing of water flow into drifts, caused by 
coupled thermal-hydrologic-mechanical-chemical processes. 
This evaluation appropriately addresses physical couplings by taking its boundary conditions 
from sources (Table 4.1-1) that appropriately have addressed those couplings. 
(5) Sufficient technical bases and justification are provided for total system 
performance assessment assumptions and approximations for modeling coupled 
thermal-hydrologic-mechanical-chemical effects on seepage and flow, the waste 
package chemical environment, and the chemical environment for radionuclide 

release. The effects of distribution of flow on the amount of water contacting the 
engineered barriers and waste forms are consistently addressed, in all relevant 
abstractions. 
Technical bases and justification for modeling coupled effects on seepage and flow are addressed 
in the sources (Table 4.1-1) for the boundary conditions used in this evaluation. These sources 
also address the technical bases and justification for modeling the chemical environments in the 
absence of microbial activity. This evaluation does not make use of any additional assumptions 
or approximations. 
(6) The expected ranges of environmental conditions within the waste package 
emplacement drifts, inside of breached waste packages, and contacting the waste 
forms and their evolution with time are identified. These ranges may be 
developed to include: 
(i) 
the effects of the drip shield and backfill on the quantity and chemistry of 
water (e.g., the potential for condensate formation and dripping from the 
underside of the shield); 
(ii) 
conditions that promote corrosion of engineered barriers and degradation 
of waste forms; 
(iii) irregular wet and dry cycles; 
(iv) 
gamma-radiolysis; and 
(v) 
size and distribution of penetrations of engineered barriers. 
This evaluation is based on qualitative analyses and bounding arguments that capture the entire 
expected ranges of environmental conditions as they evolve over time. Figure 6.4-5 provides an 
example of an input that includes the expected ranges. 
(7) The model abstraction for quantity and chemistry of water contacting engineered 
barriers and waste forms is consistent with the detailed information on engineered 
barrier design and other engineered features. For example, consistency is 
demonstrated for: 
(i) 
dimensionality of the abstractions; 
(ii) 
various design features and site characteristics; and 
(iii) alternative conceptual approaches. 
Analyses are adequate to demonstrate that no deleterious effects are caused by 
design or site features that the U.S. Department of Energy does not take into 
account in this abstraction. 

Detailed information on EBS design provides the basis for the analyses that provide boundary 
conditions for the evaluation. Multiscale Thermohydrological Model (BSC 2004 
[DIRS 169565]) includes an especially detailed model of the EBS, and provides input to this 
evaluation. Therefore, this evaluation is consistent with the detailed design information. 
(8) Adequate technical bases are provided, including activities such as independent 
modeling, laboratory or field data, or sensitivity studies, for inclusion of any 
thermal-hydrologic-mechanical-chemical couplings and features, events, and 
processes; and 
The sources of boundary conditions for this evaluation (Table 4.1-1) address that the technical 
basis for inclusion of thermal-hydrologic-mechanical-chemical couplings is adequate. 
Section 6.2 lists the FEPs addressed by this evaluation, and the location where each FEP is 
addressed. These sections provide the technical bases for exclusion or disposition of these FEPs 
in the TSPA-LA. 
(9) Performance-affecting processes that have been observed in thermal-hydrologic 
tests and experiments are included into the performance assessment. For 
example, the U.S. Department of Energy either demonstrates that liquid water will 
not reflux into the underground facility or incorporates refluxing water into the 
performance assessment calculation, and bounds the potential adverse effects of 
alteration of the hydraulic pathway that result from refluxing water. 
This sub-criterion is not applicable to the evaluation of microbial impacts because observations 
in thermal-hydrologic tests and experiments have been consistent with thermal-hydrologic 
predictions that neglected microbial impacts. 
(10) Likely modes for container corrosion are identified and considered in determining 
the quantity and chemistry of water entering the engineered barriers and 
contacting waste forms. For example, the model abstractions consistently address 
the role of parameters, such as pH, carbonate concentration, and the effect of 
corrosion on the quantity and chemistry of water contacting engineered barriers 
and waste forms. 
Section 6.5.1 includes a bounding analysis that demonstrates that the container-corrosion effects 
on water chemistry do not significantly alter the environmental factors that limit microbial 
activity. Other effects of container corrosion on the chemistry of water are identified and 
considered in Engineered Barrier System: Physical and Chemical Environment (BSC 2004 
[DIRS 169860]). 
(11) The abstraction of in-package criticality or external-to-package criticality, within 
the emplacement drift, provides an adequate technical basis for screening these 
events. 
This evaluation does not address criticality. 
(12) Guidance in NUREG-1297 and NUREG-1298 or other acceptable approaches, is 
followed. 

Inputs were selected and documented, and documentation was developed, checked, and reviewed 
in accordance with applicable BSC and Office of Civilian Radioactive Waste Management 
procedures, which comply with NUREG-1297 [DIRS 103597] and NUREG-1298 
[DIRS 103750] (see Section 2). 
 Acceptance Criterion 2  Data Are Sufficient for Model Justification. 
(1) Geological, hydrological, and geochemical values used in the license application 
are adequately justified. Adequate description of how the data were used, 
interpreted, and appropriately synthesized into the parameters is provided. 
This evaluation uses geological, hydrologic, or geochemical values indirectly from the sources 
that provided environmental boundary conditions, which are adequately justified (Table 4.1-1). 
The development of the parameters from the data is addressed in the referenced sources. 
(2) Sufficient data were collected on the characteristics of the natural system and 
engineered materials to establish initial and boundary conditions for conceptual 
models of thermal-hydrologic-mechanical-chemical coupled processes, that affect 
seepage and flow and the engineered barrier chemical environment. 
This evaluation uses boundary values from data collected on the abundance of organic carbon 
and orthophosphate in groundwater near the repository site (Table 4.1-1). This evaluation uses 
other data on the characteristics of the natural system, indirectly from the sources that provided 
environmental boundary conditions (Table 4.1-1). The information on engineered materials 
required to conclude that microbial activity is limited is the recognition that emplacement drift 
committed materials have no organic components (Table 4.1 1). 
(3) Thermo-hydrologic tests were designed and conducted with the explicit objectives 
of observing thermal-hydrologic processes for the temperature ranges expected 
for repository conditions and making measurements for mathematical models. 
Data are sufficient to verify that thermal-hydrologic conceptual models address 
important thermal-hydrologic phenomena. 
This sub-criterion is not applicable to the evaluation of microbial impacts because the relevant 
thermal-hydrologic tests are addressed in the sources that provide the boundary conditions 
(Table 4.1-1) for this evaluation. 
(4) Sufficient information to formulate the conceptual approach(es) for analyzing 
water contact with the drip shield, engineered barriers, and waste forms is 
provided. 
This sub-criterion is not applicable to the evaluation of microbial impacts because this evaluation 
does not address the contact of water with the drip shield, engineered barriers, or waste forms. 
(5) Sufficient data are provided to complete a nutrient- and energy-inventory 
calculation, if it has been used to justify the inclusion of the potential for 
microbial activity affecting the engineered barrier chemical environment and the 
chemical environment for radionuclide release. As necessary, data are adequate 

to support determination of the probability for MIC and microbial effects, such as 
production of organic byproducts and microbially enhanced dissolution of the 
high-level radioactive waste glass form. 
Section 6.4 provides bounding analyses and qualitative assessments of environmental 
constraints, including nutrient availability. These constraints support the exclusion of the 
impacts of microbial activity on the engineered barrier chemical environment and on the 
chemical environment for radionuclide release. Section 6.5.1 includes a boundary analysis 
demonstrating that corrosion does not significantly affect the bulk chemical environment. 
Therefore, the impact of microbial activity on the bulk chemical environment does not affect the 
probability for MIC and microbially enhanced dissolution of the high-level radioactive waste 
glass form. 
 Acceptance Criterion 3  Data Uncertainty Is Characterized and Propagated Through 
the Model Abstraction. 
(1) Models use parameter values, assumed ranges, probability distributions, and 
bounding assumptions that are technically defensible, reasonably account for 
uncertainties and variabilities, and do not result in an under-representation of the 
risk estimate. 
In this evaluation, bounding calculations and qualitative analyses are from sources (Table 4.1-1) 
that provide ranges of boundary conditions. These ranges include results for the full range of 
expected inputs, and capture the associated uncertainties (i.e., see Figure 6.4-5). Data from 
outside sources (Table 4.1-2) are widely accepted by the scientific community, and are justified 
in Table 4.1-3. Other inputs (Table 4.1-4) are generally accepted qualitative statements. 
Therefore, models that neglect the impact of microbial activity on drift chemistry reasonably 
account for uncertainties and variabilities in these impacts and do not result in an 
under-representation of the risk estimate. 
(2) Parameter values, assumed ranges, probability distributions, and bounding 
assumptions used in the total system performance assessment calculations of 
quantity and chemistry of water contacting engineered barriers and waste forms 
are technically defensible and reasonable, based on data from the Yucca Mountain 
region (e.g., results from large block and drift-scale heater and niche tests), and a 
combination of techniques that may include laboratory experiments, field 
measurements, natural analog research, and process-level modeling studies. 
This document supports the exclusion of the impacts of microbial activity on drift chemistry 
from the TSPA-LA. As a result, this evaluation does not provide any parameter values, assumed 
ranges, probability distributions, or bounding assumptions for use in the TSPA-LA. 
(3) Input values used in the total system performance assessment calculations of 
quantity and chemistry of water contacting engineered barriers (e.g., drip shield 
and waste package) are consistent with the initial and boundary conditions and the 
assumptions of the conceptual models and design concepts for the Yucca 
Mountain site. Correlations between input values are appropriately established in 

the U.S. Department of Energy total system performance assessment. Parameters 
used to define initial conditions, boundary conditions, and computational domain 
in sensitivity analyses involving coupled thermal-hydrologic-mechanical-
chemical effects on seepage and flow, the waste package chemical environment, 
and the chemical environment for radionuclide release, are consistent with 
available data. Reasonable or conservative ranges of parameters or functional 
relations are established. 
This document supports the exclusion of the impact of microbial activity on drift chemistry from 
the TSPA-LA. Therefore, this evaluation does not provide any input values to the TSPA-LA. 
(4) Adequate representation of uncertainties in the characteristics of the natural 
system and engineered materials is provided in parameter development for 
conceptual models, process-level models, and alternative conceptual models. The 
U.S. Department of Energy may constrain these uncertainties using sensitivity 
analyses or conservative limits. For example, the U.S. Department of Energy 
demonstrates how parameters used to describe flow through the engineered 
barrier system bound the effects of backfill and excavation-induced changes. 
This sub-criterion is not applicable to the evaluation of microbial impacts on drift chemistry 
because the evaluation does not make use of conceptual models or process-level models, and 
therefore no alternative conceptual models. 
(5) If criticality is included in the total system performance assessment, the U.S. 
Department of Energy uses an appropriate range of input parameters for 
calculating the effective neutron multiplication factor. 
This sub-criterion is not applicable because this evaluation does not address criticality. 
(6) Where sufficient data do not exist, the definition of parameter values and 
conceptual models is based on other appropriate sources, such as expert elicitation 
conducted in accordance with NUREG-1563 [DIRS 100909]. 
In this evaluation, sufficient data exist for the definition of parameter values. The evaluation 
does not make use of conceptual models. 
 Acceptance Criterion 4  Model Uncertainty Is Characterized and Propagated Through 
the Model Abstraction. 
This criterion is not applicable to this evaluation of microbial impacts on drift chemistry because 
the evaluation does not use any models. 
 Acceptance Criterion 5  Model Abstraction Output Is Supported by Objective 
Comparisons. 
This document supports the exclusion of the impacts of microbial activity on drift chemistry 
from the TSPA-LA. As a result, this evaluation does not provide input to the model abstraction, 
and this criterion is not applicable. 

7.3 REQUIRED DOCUMENTATION OF LEVEL OF ACCURACY 
This evaluation is based on bounding calculations and qualitative analyses that capture the full 
range of expected emplacement drift environments, including uncertainty (Section 6.6). 
Therefore, the conclusion of insignificant impacts on bulk chemistry (Section 7.1) is 
representative of expected environments, and level of accuracy and precision are not relevant. 
7.4 COMPLETION CRITERIA 
This evaluation is consistent with the activities performed as part of Technical Work Plan: 
Regulatory Integration Evaluation of Analysis and Model Reports Supporting the TSPA-LA 
(BSC 2004 [DIRS 169653]), and fulfills a portion of the Phase 2 work identified in that plan. 
That is, the work addresses the prioritized list of actions selected in Phase 1 for disposition in 
Phase 2 (BSC 2004 [DIRS 169653], Section 1.3). 

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Interactions Between Microbes and Minerals. Banfield, J.F. and Nealson, K.H., eds. 
Reviews in Mineralogy Volume 35. Washington, D.C.: Mineralogical Society of 
America. TIC: 236757. 
Lovley D.R. and Phillips, E.J.P. 1988. Manganese Inhibition of Microbial Iron 171171 
Reduction in Anaerobic Sediments. Geomicrobiology Journal, 6, 145-155. 
London, England: Taylor & Francis. TIC: 256429. 
Ldemann, H.; Arth, I.; and Liesack, W. 2000. Spatial Changes in the Bacterial 171074 
Community Structure along a Vertical Oxygen Gradient in Flooded Paddy Soil 
Cores. Applied and Environmental Microbiology, 66, (2), 754-762. Washington, 
D.C.: America Society for Microbiology. TIC: 256374. 
Madigan, M.T.; Martinko, J.M.; and Parker, J. 2003. Brock Biology of 171083 
Microorganisms. 10th Edition. Upper Saddle River, New Jersey: Prentice Hall. 
TIC: 256412. 
McKinley, I.G.; Hagenlocher, I.; Alexander, W.R.; and Schwyn, B. 1997. 100796 
Microbiology in Nuclear Waste Disposal: Interfaces and Reaction Fronts. FEMS 
Microbiology Reviews, 20, (3-4), 545-556. Amsterdam, The Netherlands: Elsevier. 
TIC: 235823. 
Means, J.L. 1982. The Organic Geochemistry of Deep Ground Waters. ONWI-268. 171136 
Columbus, Ohio: Battelle Columbus Laboratories, Office of Nuclear Waste 
Isolation. ACC: MOL.20041025.0182. 
NIST 2003. NIST Critically Selected Stability Constants of Metal Complexes 171201 
Database. NIST Standard Reference Database 46 Version 7.0. Gaithersburg, MD: 
NIST- U.S. Department of Commerce Technology Administration. On Order 
Norwood, D.E. and Gilmour, A. 2001. The Differential Adherence Capabilities of 171133 
Two Listeria Monocytogenes Strains in Monoculture and Multispecies Biofilms as a 
Function of Temperature. Letters in Applied Microbiology, 33, 320-324. Oxford, 
England: Blackwell Publishing. TIC: 256415. 
NRC (U.S. Nuclear Regulatory Commission) 2003. Yucca Mountain Review Plan, 163274 
Final Report. NUREG-1804, Rev. 2. Washington, D.C.: U.S. Nuclear Regulatory 
Commission, Office of Nuclear Material Safety and Safeguards. TIC: 254568. 
Overbeck, J.; Dijkhuizen, L.; and Romanovskaya, V. 1997. Investigation of the 171182 
Effect of Prolonged Nuclear Radiation on the Aboriginal Bacterial Populations in 
the Zone of the Chernobyl Atomic Power Station Castastrophe. INTAS-94-2825. 
Belgium, Brussels: INTAS. Accessed August 10, 2004. TIC: 256400. 
http://www.intas.be/catalog/94-2825.htm

Panak, P.; Selenska-Pobell, S.; Kutschke, S.; Geipel, G.; Bernhard, G.; and Nitsche, 171085 
H. 1999. Complexation of U(VI) with Cells of Thiobacillus Ferrooxidans and 
Thiomonas Cuprina of Different Geological Origin. Radiochimica Acta, 84, 
183-190. Mnchen, Germany: Oldenbourg Wissenchaftsverlag. TIC: 256430. 
Panak, P.J.; Booth, C.H.; Caulder, D.L.; Bucher, J.J.; Shuh, D.K.; and Nitsche, H. 171120 
2002. X-Ray Absorption Fine Structure Spectroscopy of Plutonium Complexes 
with Bacillus Sphaericus. Radiochimica Acta, 90, 315-321. Mnchen, Germany: 
Oldenbourg Verlage. TIC: 256432. 
Patel, J.B.; Leonard, D.G.B.; Pan, X.; Musser, J.M.; Berman, R.E.; and Nachamkin, 171100 
I. 2000. Sequence-Based Identification of Mycobacterium Species Using the 
MicroSeq 500 16S rDNA Bacterial Identification System. Journal of Clinical 
Microbiology, 38, (1), 246-251. Washington, D.C.: American Society for 
Microbiology. TIC: 256375. 
Pedersen, K. 1996. Investigations of Subterranean Bacteria in Deep Crystalline 171086 
Bedrock and their Importance for the Disposal of Nuclear Waste. Canadian 
Journal of Microbiology, 42, 382-391. Ottawa, Ontario, Canada: National Research 
Council of Canada. TIC: 256424. 
Pedersen, K. 1999. Subterranean Microorganisms and Radioactive Waste Disposal 110036 
in Sweden. Engineering Geology, 52, 163-176. New York, New York: Elsevier. 
TIC: 244755. 
Pedersen, K. and Karlsson, F. 1995. Investigations of Subterranean 100810 
Microorganisms: Their Importance for Performance Assessment of Radioactive 
Waste Disposal. SKB 95-10. Stockholm, Sweden: Swedish Nuclear Fuel and 
Waste Management Company. TIC: 221443. 
Pedersen, K.; Arlinger, J.; Ekendahl, S.; and Hallbeck, L. 1996. 16S rRNA Gene 171101 
Diversity of Attached and Unattached Bacteria in Boreholes along the Access 
Tunnel to the Asp Hard Rock Laboratory, Sweden. FEMS Microbiology Ecology,
19, 249-262. New York, New York: Elsevier. TIC: 256414. 
Pedersen, K.; Arlinger, J.; Hallbeck, L.; and Pettersson, C. 1996. Diversity and 171103 
Distribution of Subterranean Bacteria on Ground Water at Oklo in Gabon, Africa, as 
Determined by 16S-rRNA Gene Sequencing. Molecular Ecology, 5, 427-436. 
Oxford, England: Blackwell Science. TIC: 256418. 
Perrot, F.; Jouenne, T.; Feuilloley, M.; Vaudry, H.; and Junter, G.A 1998. Gel 171124 
Immobilization Improves Survival of Eschericia Coli Under Temperature Stree in 
Nutrient-Poor Natural Water. Pergamon, 32, (12), 3521-3526. New York, New 
York: Pergamon. TIC: 256376. 

Pitonzo, B.J.; Amy, P.S.; and Rudin, M. 1999. Effect of Gamma Radiation on 150442 
Native Endolithic Microorganisms from a Radioactive Waste Deposit Site. 
Radiation Research, 152, 64-70. New York, New York: Radiation Research 
Society. TIC: 248156. 
Ringelberg, D.B.; Amy, P.S.; Clarkson, W.W.; Haldeman, D.L.; Khalil, M.K.; Kieft, 100824 
T.L.; Krumholtz, L.R.; Stair, J.O.; Suflita, J.M.; White, D.C.; and Hersman, L.E.H. 
1997. Microbial Community Composition in a Volcanic Tuff, Yucca Mountain, 
Nevada. Rough draft. Vicksburg, Mississippi: U.S. Army Corps of Engineers 
Waterways Experiment Station. TIC: 234025. 
Russell, C.; Jacobsen, R.; Haldeman, D. L.; and Amy, P. S. 1994. Heterogeneity of 119578 
Deep Subsurface Microorganisms and Correlations to Hydrogeological and 
Geochemical Parameters. Geomicrobiology Journal, 12, 37-51. London, England: 
Taylor & Francis. TIC: 246865. 
Stackebrandt, E. and Goebel, B.M. 1994. Taxonomic Note: A Place for 171105 
DNA-DNA Reassociation and 16S rRNA Sequence Analysis in the Present Species 
Definition in Bacteriology. International Journal of Systematic Bacteriology, 44, 
(4), 846-849. Washington, D.C.: American Society for Microbiology. 
TIC: 256427. 
Stone, A.T. 1997. Reactions of Extracellular Organic Ligands with Dissolved 110045 
Metal Ions and Mineral Surfaces. Chapter 9 of Geomicrobiology: Interactions 
Between Microbes and Minerals. Banfield, J.F. and Nealson, K.H., eds. Reviews in 
Mineralogy Volume 35. Washington, D.C.: Mineralogical Society of America. 
TIC: 236757. 
Stroes-Gascoyne S. 1996. Microbial Studies in the Canadian Nuclear Fuel Waste 171851 
Management Program. High Level Radioactive Waste Management, Proceedings 
of the Seventh Annual International Conference, Las Vegas, Nevada, April 29-May 
3, 1996. Pages 4-6. La Grange Park, Illinois: American Nuclear Society. 
TIC: 226494. 
Stroes-Gascoyne, S.; Pedersen, K.; Haveman, S.A.; Dekeyser, K.; Arlinger, J.; 171108 
Daumas, S.; Ekendahl, S.; Hallbeck, L.; Hamon, C.J.; Jahromi, N.; and Delaney, 
T-L. 1997. Occurrence and Identification of Microorganisms in Compacted 
Clay-Based Buffer Material Designed for Use in a Nuclear Fuel Waste Disposal 
Vault. Canadian Journal of Microbiology, 43, 1133-1146. Ottawa, Ontario, 
Canada: National Research Council of Canada. TIC: 256425. 
Tunlid, A. and White, D.C. 1992. Biochemical Analysis of Biomass, Community 120501 
Structure, Nutritional Status, and Metabolic Activity of Microbial Communities in 
Soil. Soil Biochemistry, 7, 229-262. New York, New York: Marcel Dekker. 
TIC: 246536. 

Van Cappellen, P. and Wang, Y. 1996. Cycling of Iron and Manganese in Surface 171128 
Sediments: A General Theory for the Coupled Transport and Reaction of Carbon, 
Oxygen, Nitrogen, Sulfur, Iron, and Manganese. American Journal of Science,
296, 197-243. New Haven, Connecticut: Yale University, Kline Geology 
Laboratory. TIC: 256367. 
van Waasbergen, L.G.; Balkwill, D.L.; Crocker, F.H.; Bjornstad, B.N.; and Miller, 171075 
R.V. 2000. Genetic Diversity among Arthrobacter Species Collected Across a 
Heterogeneous Series of Terrestrial Deep-Surface Sediments as Determined on the 
Basis of 16S rRNA and recA Gene Sequences. Applied and Environmental 
Microbiology, 66, (8), 3454-3463. Washington, D.C.: American Society for 
Microbiology. TIC: 256377. 
Wang, Y. and Papenguth, H.W. 2001. Kinetic Modeling of Microbially-Driven 171123 
Redox Chemistry of Radionuclides in Subsurface Environments; Coupling 
Transport, Microbial Metabolism and Geochemistry. Journal of Contaminant 
Hydrology, 47, 297-309. New York, New York: Elsevier. TIC: 256378. 
Wang, Y. and Van Cappellen, P. 1996. A Multicomponent Reactive Transport 171057 
Model of Early Diagenesis: Application to Redox Cycling in Coastal Marine 
Sediments. Geochemica et Cosmochimica Acta, 60, (16), 2993-3014. New York, 
New York: Pergamon. TIC: 256357. 
Wang, Y.; Brush, L.H.; and Bynum, R.V. 1997. Use of MgO to Mitigate the Effect 171122 
of Microbial CO2 Production in the Waste Isolation Pilot Plant. WM'97 
Proceedings, March 2-6, 1997, Tucson, Arizona, HLW, LLW, Mixed Wastes and 
Environmental Restoration - Working Towards a Cleaner Environment. La Grange 
Park, Illinois: American Nuclear Society. TIC: 256402. 
West, J.M.; Christofi, N.; and Arme, S.C. 1986. The Influence of Groundwater and 171088 
Extreme Environments on Microbial Activity and Radionuclide Transport. The 
Effects of Natural Organic Compounds and Microorganisms on Radionuclide 
Transport, Proceedings of an NEA Workshop held in Paris on 12th June, 1985. 
Pages 19-38. Paris, France: Organisation for Economic Co-operation and 
Development. TIC: 256686. Copyright Requested 
West, J.M.; Christofi, N.; and McKinley, I.G. 1985. An Overview of Recent 110047 
Microbiological Research Relevant to the Geological Disposal of Nuclear Waste. 
Radioactive Waste Management and the Nuclear Fuel Cycle, 6, (1), 79-95. New 
York, New York: Harwood Academic Publishers. TIC: 244498. 
West, J.M.; McKinley, I.G.; and Vialta, A. 1992. Microbiological Analysis at the 171109 
Poos de Caldas Natural Analogue Study Sites. Journal of Geochemical 
Exploration, 45, 439-449. Amsterdam, The Netherlands: Elsevier. TIC: 256413. 

8.2 CODES, STANDARDS, REGULATIONS, AND PROCEDURES 
10 CFR 63. Energy: Disposal of High-Level Radioactive Wastes in a Geologic 156605 
Repository at Yucca Mountain, Nevada. Readily available. 
AP-2.14Q, Rev. 3, ICN 0. Document Review. Washington, D.C.: U.S. Department 
of Energy, Office of Civilian Radioactive Waste Management. 
ACC: DOC.20030827.0018. 
AP-3.15Q, Rev. 4, ICN 5. Managing Technical Product Inputs. Washington, D.C.: 
U.S. Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: DOC.20040812.0004. 
AP-SIII.9Q, Rev. 1, ICN 7. Scientific Analyses. Washington, D.C.: U.S. 
Department of Energy, Office of Civilian Radioactive Waste Management. 
ACC: DOC.20040920.0001. 
AP-SV.1Q, Rev. 1, ICN 1. Control of the Electronic Management of Information. 
Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive 
Waste Management. ACC: DOC.20040308.0001. 
LP-SA-001Q-BSC, Rev. 0. Determination of Importance and Site Performance 
Protection Evaluations. Washington, D.C.: U.S. Department of Energy, Office of 
Civilian Radioactive Waste Management. ACC: MOL.20020510.0386. 
8.3 SOURCE DATA, LISTED BY DATA TRACKING NUMBER 
GS011108312322.006. Field and Chemical Data Collected between 1/20/00 and 162911 
4/24/01 and Isotopic Data Collected between 12/11/98 and 11/6/00 from Wells in 
the Yucca Mountain Area, Nye County, Nevada. Submittal date: 11/20/2001. 
LL021007312251.020. Yucca Mountain Rock Bacterial Community 171179 
Characterization Data. Submittal date: 12/11/2002. 
LL040801512251.115. Bacterial Growth Dynamics, Limiting Factors, and 171476 
Community Diversity in a Proposed Geological Nuclear Waste Repository 
Environment. Submittal date: 08/18/2004. 
LL981209705924.059. Biochemical Contributions to Corrosion of Carbon Steel and 110317 
Alloy 22 in a Continual Flow System. Submittal date: 12/15/1998. 
MO0006J13WTRCM.000. Recommended Mean Values of Major Constituents in 151029 
J-13 Well Water. Submittal date: 06/07/2000. 
MO0407SEPFEPLA.000. LA FEP List. Submittal date: 07/20/2004. 170760 

SN0407T0510102.017. In-Drift Gas Flux and Oxygen Demand. Submittal date: 170667 
07/16/2004. 

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