Document ID: EPA-HQ-OAR-2019-0534-0043
Agency: epa
Document Type: Rule
Title: Criteria for Certification and Recertification of Waste Isolation Pilot Plant's Compliance with Disposal Regulations: Recertification Decision
Posted Date: 2022-05-03T04:00Z

[Federal Register Volume 87, Number 85 (Tuesday, May 3, 2022)]
[Rules and Regulations]
[Pages 26126-26136]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-09209]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 194

[EPA-HQ-OAR-2019-0534; FRL-9737-01-OAR]

Criteria for the Certification and Recertification of the Waste 
Isolation Pilot Plant's Compliance With the Disposal Regulations: 
Recertification Decision

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notification of recertification decision.

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SUMMARY: The Environmental Protection Agency (EPA or the Agency) 
recertifies that the U.S. Department of Energy's (DOE or the 
Department) Waste Isolation Pilot Plant (WIPP) continues to comply with 
the final disposal regulations, known as the ``Environmental Standards 
for the Management and Disposal of Spent Nuclear Fuel, High-Level and 
Transuranic Radioactive Waste.'' This is the fourth periodic evaluation 
of the WIPP's continued compliance with the disposal regulations and 
WIPP Compliance Criteria. The WIPP Compliance Criteria implement and 
interpret the disposal regulations specifically for the WIPP. This 
recertification process is required every five years. This 
recertification decision is based on a thorough review of information 
submitted by DOE, independent technical analyses and public comments. 
The Agency has determined that DOE continues to meet all applicable 
requirements of the final disposal regulations and the WIPP Compliance 
Criteria and recertifies the WIPP facility. EPA has also identified 
areas in which the DOE's technical analyses and justifications could be 
improved for the next recertification application.

DATES: May 3, 2022.

FOR FURTHER INFORMATION CONTACT: Ray Lee, Radiation Protection 
Division, Mail Code 6608T, U.S. Environmental Protection Agency, 1200 
Pennsylvania Avenue, Washington, DC, 20460; telephone number: 202-343-
9463; email address: [email protected]. Copies of the Compliance 
Application Review Documents (CARDs) supporting this action and all 
other recertification-related documentation can be found in the 
Agency's electronic docket found at https://www.regulations.gov (Docket 
ID No. EPA-HQ-OAR-2019-0534).

SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information
II. What is the WIPP?
III. Compliance Certification History
    A. 1998 Certification Decision
    B. Previous Recertification Decisions
IV. WIPP Compliance With Radioactive Waste Disposal Regulations and 
the WIPP Compliance Criteria
    A. How does EPA ensure ongoing compliance with the WIPP 
compliance criteria?
    B. Compliance Certification Conditions
    1. Panel Closure System
    2. Quality Assurance
    3. Waste Characterization
    4. Passive Institutional Controls
V. The 2019 CRA
    A. DOE's 2019 CRA
    B. EPA Evaluation of the 2019 CRA
    C. EPA's 2019 Recertification Decision
VI. EPA's Technical Review
    A. Performance Assessment and EPA Standards
    B. Status of EPA Identified Areas for Improvement From the 2017 
Recertification Decision
    1. Plutonium Oxidation States
    2. Geochemistry Database
    3. Microbial Colloids
    4. Creep Closure of Open Areas
    C. Changes to the Disposal System Identified by DOE for CRA-2019
    1. Abandonment of Panel Closures and Waste Panel 9
    2. Updated Plugging Patterns and Borehole Drilling Rates
    3. Radionuclide Solubilities
    4. Revised Colloid Parameters
    5. Inclusion of Brine Radiolysis in the Gas Generation Model
    D. Other Issues Identified by EPA During Review
    1. Geochemistry Database
    2. Initial Assumptions for Solubility Calculations
    3. Actinide Solubility Uncertainty
    E. EPA Sensitivity Studies
    1. Sensitivity to Creep Closure of Empty Rooms (CRA19_COMP 
Analysis)
    2. Sensitivity to Borehole Plugging Frequency (PLG_PROB 
Analysis)
    3. Sensitivity to Actinide Solubility (GCHM_S0 Analysis)
    4. Sensitivity to Actinide Solubility and Colloid Parameters 
(GCHM_S2 Analysis)
    5. Sensitivity to Actinide Solubility, Colloid Parameters, and 
Actinide Oxidation State (GCHM_S3 Analysis)
    6. Sensitivity to Combined Geotechnical and Geochemical 
Parameter Changes (CRA19_COMB Analysis)
    F. Waste Characterization
    G. Peer Review
    H. Individual and Groundwater Protection Requirements
VII. What is EPA's role in future WIPP activities?

Abbreviations

Am Americium
APCS Abandonment of Panel Closures in the South
CARD Compliance Application Review Document
CCA Compliance Certification Application
CFR Code of Federal Regulations
CRA Compliance Recertification Application
DOE U.S. Department of Energy
EPA U.S. Environmental Protection Agency
FR Federal Register
KPLA Known Potash Leasing Area
LWA Land Withdrawal Act
OAR Office of Air and Radiation
Pa Pascal
PA Performance Assessment
Pu Plutonium
TRU Transuranic
TSD Technical Support Document
WIPP Waste Isolation Pilot Plant

I. General Information

How can I get copies of this document and other related information?

    EPA has established a docket for this action under Docket ID No. 
EPA-HQ-OAR-2019-0534. Publicly available docket materials are available 
either electronically at https://www.regulations.gov or in hard copy at 
the Air and Radiation Docket in the EPA Docket Center, (EPA/DC) EPA 
West,

[[Page 26127]]

Room B102, 1301 Constitution Ave. NW, Washington, DC. Due to public 
health concerns related to COVID-19, the EPA Docket Center and Reading 
Room are open to the public by appointment only, and walk-ins are not 
allowed. Visitors to the Reading Room must complete docket material 
requests in advance and then make an appointment to retrieve the 
material. Please contact the EPA Reading Room staff at (202) 566-1744 
or via email at [email protected] to arrange material 
requests and appointments. Hand deliveries and couriers may be received 
by scheduled appointment only. For further information on EPA Docket 
Center services and status, please visit us online at https://www.epa.gov/dockets.
    EPA inspection or audit reports are routinely published on the 
Agency's WIPP website https://www.epa.gov/radiation/epas-role-waste-isolation-pilot-plant-wipp and WIPP-NEWS email listserv.

II. What is the WIPP?

    The WIPP is a disposal system developed specifically, and 
exclusively, for defense-related transuranic (TRU) radioactive waste, 
operated by the U.S. Department of Energy (DOE) and located near 
Carlsbad in southeastern New Mexico. TRU waste is material containing 
alpha emitting radioisotopes, with half-lives greater than twenty 
years, in concentrations greater than 100 nanocuries per gram (nCi/g). 
WIPP Land Withdrawal Act (LWA), Public Law 102-579 (October 30, 1992), 
section 2(18). This waste primarily consists of clothing, tools, rags, 
residues, research material, sludges, debris, soil and other items 
contaminated with small amounts of plutonium (Pu) and other man-made 
radioactive elements. At the WIPP, DOE disposes of radioactive waste 
approximately 655 meters (2,150 feet) underground in an ancient salt 
layer which will eventually creep, encapsulate, and isolate the waste. 
Under LWA section 7(a)(3), the WIPP has a total statutory capacity of 
175,570 cubic meters (6.2 million cubic feet) of TRU waste.
    The LWA provides EPA the authority to oversee and regulate the 
WIPP. Pursuant, in part, to such authority, EPA promulgated or revised 
the Environmental Radiation Protection Standards for Management and 
Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive 
Wastes, 40 CFR part 191,\1\ and the ``Criteria for the Certification 
and Re-Certification of the Waste Isolation Pilot Plant's Compliance 
With the 40 CFR part 191 Disposal Regulations'' and 40 CFR part 194 
(the WIPP Compliance Criteria).\2\ The LWA directs DOE every five years 
to demonstrate continued compliance with the disposal regulations, and, 
after receipt of the submission from DOE, EPA determines whether the 
WIPP continues to be in compliance.\3\ The WIPP Compliance Criteria 
make further provisions relating to the periodic (every five years) 
recertification of the WIPP.\4\ EPA's determination published in this 
document is for DOE's fourth periodic recertification.
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    \1\ See 50 FR 38066 (September 19, 1985) and 58 FR 66398 
(December 20, 1993).
    \2\ See 61 FR 5224 (February 9, 1996).
    \3\ LWA, section 8(f).
    \4\ Since EPA's initial certification, the operation of the WIPP 
proceeded without substantial interruption until 2014. However, two 
events took place at the WIPP in February 2014 that led DOE to 
suspend the emplacement of additional waste in the facility for 
nearly three years. Refer to the prior recertification document (82 
FR 33106, July 19, 2017) for more information.
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III. Compliance Certification History

A. 1998 Certification Decision

    LWA section 8(d) required EPA to conduct an initial compliance 
evaluation of the WIPP and to certify whether the WIPP facility will 
comply with the final disposal regulations. On May 18, 1998, EPA 
conditionally certified that the WIPP will comply with the disposal 
regulations. See 63 FR 27354. The complete record and basis for the 
EPA's 1998 certification decision can be found in Air Docket A-93-02.

B. Previous Recertification Decisions

    Subsequent to EPA's 1998 initial compliance certification of the 
WIPP, DOE periodically (every five years) has submitted, as required by 
the LWA, documentation of continued compliance, and EPA previously 
recertified the WIPP on three separate occasions. EPA's first WIPP 
recertification decision was announced on April 10, 2006 (see 71 FR 
18010); the second on November 18, 2010 (see 75 FR 70584); and the 
third on July 19, 2017 (see 82 FR 33106).

IV. WIPP Compliance With Radioactive Waste Disposal Regulations and the 
WIPP Compliance Criteria

    The WIPP must comply with EPA's radioactive waste disposal 
regulations, located at subparts B and C of 40 CFR part 191 (referred 
to as the ``final disposal regulations'' in LWA sections 8(d) and (f)). 
These regulations limit the amount of radioactive material which may 
escape from a disposal facility to protect individuals and groundwater 
resources from dangerous levels of radioactive contamination.
    DOE submits a Compliance Recertification Application (CRA) every 
five years to demonstrate compliance with 40 CFR parts 191 and 194 per 
LWA section 8(f). Compliance applications must demonstrate compliance 
with the requirements contained within each section of 40 CFR part 194 
\5\ and provide a comprehensive, technically justified assessment of 
repository performance demonstrating compliance with 40 CFR part 191, 
subparts B and C (through a process known as ``performance 
assessment''). Upon receiving the CRA from DOE, EPA first makes a 
completeness determination by performing an in-depth review to ensure 
DOE's submission is sufficiently detailed to support EPA's technical 
evaluation with respect to all compliance criteria. EPA finishes its 
technical evaluation after DOE responds to EPA's completeness comments 
and EPA considers the CRA complete (40 CFR 194.11).
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    \5\ To some extent, the discussion in this Federal Register 
document describing EPA's evaluation of CRA-2019 tracks the various 
requirements or sections of 40 CFR part 194. So, for example, 
Section IV.B of this document relates to certain conditions 
associated with EPA's basic certification of compliance for the 
WIPP, as set out in part 194, App. A.; Section VI.C of this document 
substantially relates to requirements associated with Sec. Sec.  
194.14, 194.15, 194.23, and 194.31 through 194.34. This 
organization, though, is not strict and there is some overlap and 
intersection among the subparagraphs of Section VI.C of this 
document and the various requirements of part 194 (and part 191). In 
addition, the provisions of some sections of part 194 require 
little, if any, discussion. So, for example, DOE did not conduct any 
activities during the period covered by this CRA related to future 
states assumptions (Sec.  194.25), expert judgment (Sec.  194.26), 
or assurance requirements (Sec. Sec.  194.41 through 194.46). See 
the corresponding CARDs for more discussion.
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    DOE's WIPP compliance applications must include, at a minimum, 
basic information about the WIPP site and disposal system design, 
including information about the following topics: The geology, 
hydrology, hydrogeology and geochemistry of the WIPP disposal system 
and the WIPP vicinity; the WIPP materials of construction; standards 
applied to design and construction; background radiation in air, soil 
and water; and past and current climatological and meteorological 
conditions (40 CFR 194.14). Section 194.15 states that DOE's 
recertification applications shall update this information to provide 
sufficient information for EPA to determine whether the WIPP facility 
continues to be in compliance with the disposal regulations.
    In addition, the WIPP must comply with the WIPP Compliance Criteria 
at 40

[[Page 26128]]

CFR part 194. The WIPP Compliance Criteria implement and interpret the 
general disposal regulations specifically for the WIPP and clarify the 
basis and process by which EPA makes certification and recertification 
decisions.\6\
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    \6\ In addition to EPA's radioactive waste disposal regulations 
and the WIPP Compliance Criteria, the WIPP must also comply with a 
number of other Federal laws and regulations pertaining to public 
health and safety or the environment. See, for example, LWA section 
9. In a separate process, distinct from this periodic (every five 
years) compliance recertification process, DOE also must 
periodically (every two years) submit documentation of continued 
compliance with such other laws and EPA (or the State of New Mexico, 
as appropriate) must, in response, determine whether the WIPP is in 
compliance with such laws. The most recent Biennial Environmental 
Compliance Report (BECR) determination for the WIPP, dated 04/13/
2021, may be found at Docket ID No. EPA-HQ-OAR-2001-0012-0701.
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A. How does EPA ensure ongoing compliance with the WIPP compliance 
criteria?

    In addition to the periodic recertification process, EPA, on an on-
going basis, monitors and ensures continuing compliance with EPA 
regulations through a variety of activities, including the following: 
Review and evaluation of DOE's annual change reports, monitoring the 
conditions of compliance, addressing planned change requests, 
information requests concerning the WIPP, inspections of the WIPP site, 
and inspections of waste characterization operations. The Agency has 
conducted periodic inspections to verify the adequacy of information 
relevant to certification applications. EPA conducts inspections at the 
WIPP site to review and ensure that the monitoring program meets the 
requirements of Sec.  194.42. EPA has also inspected the emplacement 
and tracking of waste in the repository. The Agency's inspection 
reports can be found in Air Docket A-98-49, Categories II-A1 and II-A4, 
as well as online at https://www.regulations.gov, Docket ID No. EPA-HQ-
OAR-2001-0012.
    DOE must report any planned or unplanned changes in activities or 
conditions pertaining to the disposal system that differ significantly 
from the most recent compliance application and, at least annually, 
report any other changes in disposal system conditions or activities. 
40 CFR 194.4(b)(3), (4). DOE must also report any releases of 
radioactive material from the disposal system. 40 CFR 194.4(b)(3)(iii). 
DOE's annual change reports reflect the progress of quality assurance 
and waste characterization inspections, minor changes to DOE documents, 
information on monitoring activities, and any additional EPA approvals 
for changes in activities. In addition, EPA may request additional 
information from DOE (see, for example, 40 CFR 194.4(b)(2)). These 
requirements assist EPA with monitoring the performance of the disposal 
system and evaluating whether the certification should be modified, 
suspended or revoked. All correspondence and approvals regarding the 
annual change reports can be found in hard copy in the Air Docket A-98-
49, Categories II-B2 and II-B3, and also in Docket ID No. EPA-HQ-OAR-
2001-0012 at https://www.regulations.gov.

B. Compliance Certification Conditions

    In connection with the compliance criteria, there also are four 
conditions of compliance described in 40 CFR part 194, appendix A, that 
must be met. Below are brief descriptions of each condition and any 
changes made by DOE since the last CRA to meet those conditions.
1. Panel Closure System
    Certification Condition 1 states that DOE shall close filled waste 
panels in a manner that has been specifically approved by EPA. The WIPP 
waste panel closure system design changed between the 2014 
recertification application and this 2019 recertification following the 
February 2014 radiological release that contaminated the south end of 
the repository.\7\ The run-of-mine salt closures planned for panels 3-6 
could not be emplaced and panel 9 was abandoned due to safety concerns. 
Because access to panels 3-6 was through panel 9, DOE installed run-of-
mine salt closures and steel bulkheads in the access drifts to panel 9 
to block personnel access to the south end waste panels, which the 
Agency verified in an May/August 2019 inspection (Docket ID No. EPA-HQ-
OAR-2001-0012-04700). The closure system design for panels 1, 2, 7, 8 
and 10 consisting of run-of-mine salt closures and steel bulkheads were 
not changed by the accidental release.
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    \7\ For a discussion of the 2014 incidents at the WIPP, see 
EPA's prior recertification determination. 82 FR 33106, 33107 (July 
19, 2017).
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2. Quality Assurance
    Certification Condition 2 requires waste generator sites to 
establish and execute a quality assurance program for waste 
characterization activities. Section 194.22 establishes quality 
assurance requirements for the WIPP. DOE must adhere to a quality 
assurance program that implements the requirements of ASME NQA-1-1989 
edition, ASME NQA-2a-1990 addenda, part 2.7, to ASME NQA-2-1989 
edition, and ASME NQA-3-1989 edition (excluding Section 2.1 (b) and 
(c), and Section 17.1). EPA determined that the CRA-2019 provides 
adequate information to verify the establishment and implementation of 
a quality assurance program in accordance with ASME NQA-1-1989 through 
periodic audits conducted in accordance with Sec.  194.22(e). EPA's 
determination of compliance with 40 CFR 194.22 can be found in Table 1 
of CARD 22. Between March 2014 and March 2019, EPA conducted several 
quality assurance audits and found the site-specific quality assurance 
programs to be adequate. Records of EPA's quality assurance 
correspondences and waste characterization approvals can be found in 
Air Docket A-98-49, Categories II-A1 and II-A4, respectively, as well 
as online in Docket ID No. EPA-HQ-OAR-2001-0012 on https://www.regulations.gov.
3. Waste Characterization
    Certification Condition 3 requires waste generator sites to have 
waste characterization systems approved by EPA. DOE implemented site-
specific waste characterization programs to (a) characterize physical 
and radiological components in individual waste containers; and (b) 
demonstrate compliance with the WIPP waste disposal requirements at 40 
CFR 194.24 and 194.8. Since the last recertification (CRA-2014), EPA 
conducted inspections of various site-specific waste characterization 
programs and requests for changes in accordance with 40 CFR 194.24 and 
194.8 and concluded they were technically adequate (see Table 1 in CARD 
8 and CARD 24 for further details). During the period covered by CRA-
2019, all site-specific waste characterization systems of controls at 
active waste generator sites had necessary baseline approvals.
4. Passive Institutional Controls
    While DOE provided information on potential passive institutional 
control designs at the time of the certification, Certification 
Condition 4 requires DOE to submit a schedule and plan for implementing 
passive institutional controls, including markers and other measures 
indicating the presence of the repository, but DOE is not required to 
provide such information until the final CRA prior to the closure of 
the WIPP. EPA anticipates that it will evaluate DOE's compliance with 
Condition 4 of the certification when DOE submits a revised schedule 
and additional documentation regarding the

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implementation of passive institutional controls. EPA has not received 
any submissions from DOE during the period addressed by CRA-2019 and 
has not taken any actions relating to Condition 4 (see CARD 43).

V. The 2019 CRA

A. DOE's 2019 CRA

    On March 26, 2019, DOE submitted the most recent CRA as required by 
40 CFR 194.15(a), updating its previous 2014 submission. On September 
25, 2019, EPA gave public notice of DOE's submittal of CRA-2019 and 
opened the official public comment period (84 FR 50367). On December 
20, 2019, DOE submitted a performance assessment (PA) and supporting 
documentation. This deferred PA was previously agreed upon by EPA and 
DOE so that the Department could address technical issues identified in 
the previous CRA. EPA submitted to DOE six (6) letters with questions 
that DOE responded to between June 2020 to June 2021, with 2 additional 
sets of follow up questions communicated through email. This 
information supplements the documentation DOE submitted in March and 
December 2019. On November 17, 2021, EPA sent a letter to DOE stating 
that DOE's recertification application was complete. On November 26, 
2021, EPA issued a Federal Register document announcing the 
completeness determination and stating that the public comment period 
would close on December 27, 2021. See 86 FR 67424. The CRA-2019 
completeness-related correspondence can be found in the WIPP public 
docket at Docket ID No. EPA-HQ-OAR-2019-0534 at https://www.regulations.gov.\8\
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    \8\ In accordance with 40 CFR 194.67, EPA maintains public 
dockets via https://www.regulations.gov that contain all the 
information used to support the Agency's decision on 
recertification. The Agency maintains the formal docket in 
Washington, DC, as well as informational legacy/paper dockets 
related to the original certification decision (R-89-01, A-92-56, 
and A-93-02) in three locations in the State of New Mexico 
(Carlsbad, Albuquerque, and Santa Fe). The docket as a whole 
consists of all relevant, significant information received to date 
from outside parties and all significant information considered by 
EPA in reaching a WIPP recertification decision.
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    Since September 2019, EPA has published and disseminated numerous 
announcements regarding the recertification schedule and availability 
of WIPP-related documents on the EPA WIPP website and the dockets.\9\ 
EPA held an on-line, or virtual, informal stakeholder meeting on August 
17, 2021, to allow additional opportunity for public participation 
during the recertification process (see the EPA WIPP website for slides 
and documents from the informal meeting). The meeting consisted of one 
three-hour evening session to allow for time-zone differences between 
headquarters in Washington, DC and stakeholders in New Mexico. To make 
this meeting informative to all attending parties, EPA listened to 
stakeholder input and concerns and tailored the meeting around the 
public as much as possible.\10\
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    \9\ A variety of general information, pertinent new information, 
and updates on EPA's WIPP activities is available at the WIPP 
internet homepage at https://www.epa.gov/radiation/epas-role-waste-isolation-pilot-plant-wipp. All pertinent recertification-related 
documents (including the DOE-submitted recertification materials, 
letters, Federal Register notices, outreach materials, etc.) are 
available for review or download (in Adobe PDF format) via the 
electronic docket dedicated to the 2019 recertification process 
(https://www.regulations.gov, Docket ID No. EPA-HQ-OAR-2019-0534). 
The Agency's WIPP-NEWS email listserv, which automatically sends 
messages to subscribers with up to date WIPP announcements and 
information, is also available online. Any individuals wishing to 
subscribe to the listserv can join by visiting https://lists.epa.gov/read/all_forums/subscribe?name=wipp-news and providing 
all requested information to register.
    \10\ Although EPA has provided opportunities for public 
engagement, including a virtual meeting and an opportunity to 
comment, under section 8(f)(2) of the LWA, the periodic (every five 
years) recertification of the WIPP and EPA's recertification 
determination are not subject to rulemaking. In accordance with the 
LWA, EPA is not and has not engaged in rulemaking in connection with 
its recertification determination and did not intend to do so simply 
by seeking and providing opportunity for public participation.
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    The main purpose of the stakeholder meeting was to provide 
information and further opportunity to address questions about EPA's 
recertification process and timeline, as well as DOE's application and 
important changes at the WIPP since the last recertification in 2017. 
The meeting featured brief EPA presentations followed by a question-
and-answer session. In response to stakeholder suggestions, DOE staff 
members were also on hand to provide information and respond to 
stakeholder questions related to DOE's application and current WIPP 
activities. Staff from the New Mexico Environment Department attended 
as observers. Public participants were encouraged to provide comments 
to EPA for consideration during the review of DOE's CRA-2019. The 
issues raised at this virtual meeting have been considered and 
addressed by EPA in this document and within the CARDs, which are 
available in the public recertification docket. EPA received 11 
substantial public comments and has considered and appropriately 
responded to those comments. See Appendix 15-B of CARD 15.

B. EPA Evaluation of the 2019 CRA

    This EPA recertification decision is based on the entire record 
compiled by the Agency, which is available in the public docket 
dedicated to this recertification (Docket ID No. EPA-HQ-OAR-2019-0534 
at https://www.regulations.gov). The record consists of the CRA-2019, 
supplementary information submitted by DOE in response to EPA requests, 
technical reports generated by EPA, EPA audit and inspection reports, 
documentation from technical exchanges between EPA and DOE staff to 
better understand some of DOE's responses to requests for additional 
information, independent EPA calculations, and comments submitted on 
DOE's application and EPA's completeness review during the public 
comment period. All pertinent CRA-2019 correspondence was placed in the 
public recertification docket and linked on EPA's WIPP recertification 
website https://www.epa.gov/radiation/certification-and-recertification-wipp.
    The focus of EPA's technical review relating to the CRA-2019 was on 
topical areas identified by DOE and confirmed by EPA as having been 
changed since the CRA-2014 (see Section VI of this document for further 
discussion of EPA's technical review). EPA produced multiple documents 
during the technical review and evaluation of the CRA. These documents 
included CARDs along with technical support documents (TSDs).\11\ 
Together, EPA's completeness comments, CARDs, and TSDs thoroughly 
document EPA's review of DOE's CRA-2019 and the technical basis for the 
Agency's decisions. In addition, EPA used DOE performance assessment 
computer codes to independently investigate the impact (i.e., 
sensitivity) of parameter changes on the calculated releases from the 
repository. The results of these sensitivity calculations are discussed 
in Section VI.E of this document and in Section 4.0 of the EPA TSD 
Overview of EPA Review of U.S. Department of Energy 2019 WIPP 
Compliance

[[Page 26130]]

Recertification Application Performance Assessment (Docket ID No. EPA-
HQ-OAR-2019-0534).
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    \11\ The CARDs discuss DOE's compliance with each of the 
individual requirements of the WIPP Compliance Criteria and 
correspond in number to the sections of 40 CFR part 194 to which the 
documents primarily relate. Each CARD reviews the changes made by 
DOE and describes EPA's evaluations and conclusions. The CARDs also 
list the EPA TSDs and any other references used by EPA. For more 
detailed information on the technical issues considered in EPA's 
recertification decision, see the TSDs. All CARDs, TSDs, and 
references are available in the public recertification docket, via 
Regulations.gov (Docket ID No. EPA-HQ-OAR-2019-0534), with the 
exception of generally available references and those documents 
already maintained by DOE or its contractors in locations accessible 
to the public.
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C. EPA's 2019 Recertification Decision

    In response to the CRA-2019 and after consideration of all the 
materials and information described in this document, EPA determines, 
in accordance with LWA section 8(f)(2), that the WIPP facility is in 
compliance with the final disposal regulations, subparts B and C of 40 
CFR part 191. The calculated releases contained in the PA demonstrate 
that the WIPP will not exceed regulatory limits on releases of 
radionuclides to the accessible environment \12\ during the 10,000-year 
performance period. Compliance recertification ensures that accurate 
and up-to-date information is considered in the determination that WIPP 
remains in compliance with these radioactive waste disposal 
regulations. EPA makes this recertification and determination of 
continued compliance following the ``Criteria for the Certification and 
Re-Certification of the Waste Isolation Pilot Plant's Compliance With 
the 40 CFR part 191 Disposal Regulations'' (WIPP Compliance Criteria, 
40 CFR part 194), including the WIPP certification conditions (40 CFR 
part 194, appendix A). The Agency's review has also identified 
instances where aspects of the PA could be enhanced or improved, most 
notably in connection with the geochemistry database. The results of 
EPA's review of the CRA-2019, including descriptions of EPA's review 
process, expanded discussions of selected topics of interest, and 
supplemental confirmatory modeling carried out by EPA staff, are 
contained in Section VI of this document.
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    \12\ The accessible environment is defined in 40 CFR 191.12 as 
(1) The atmosphere; (2) land surfaces; (3) surface waters; (4) 
oceans; and (5) all of the lithosphere that is beyond the controlled 
area.
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VI. EPA's Technical Review

A. Performance Assessment and EPA Standards

    The disposal regulations at 40 CFR part 191 include requirements 
for the containment of radionuclides. The numerical containment 
requirements at 40 CFR 191.13 specify that releases of radionuclides to 
the accessible environment must be unlikely to exceed specific limits 
for 10,000 years after disposal. As noted previously, DOE assesses the 
likelihood that the WIPP will meet these release limits through a 
performance assessment.
    The disposal regulations provide that there must be a reasonable 
expectation that cumulative releases of radionuclides from the WIPP and 
into the environment over 10,000 years will not exceed specified 
quantities of these radionuclides (40 CFR 191.13 and appendix A). A 
reasonable expectation standard is used because of the long time period 
involved and because the nature of the events and processes at 
radioactive waste disposal facilities lead to uncertainties about 
future performance. DOE's probabilistic performance assessments 
calculate the likelihood of an environmental radionuclide release by 
accounting for future uncertainties through the use of alternative 
scenarios and variations in values of uncertain parameters via 
probability distributions.
    The containment requirements in 40 CFR 191.13 are expressed in 
terms of ``normalized releases.'' At the WIPP, the specific release 
limits are based on the estimated amount of waste in the repository at 
the time of closure, and the projected releases are ``normalized'' 
against these limits (Sec.  194.31). Normalized releases are expressed 
as ``EPA units.''
    DOE must demonstrate, in each CRA, that the total average of 
combined releases is below two compliance criteria at a higher 
probability of occurrence and a lower probability of occurrence. These 
probability compliance points are as follows:
    1. For a probability of 0.1 (a 1 in 10 chance) in 10,000 years, 
cumulative releases to the accessible environment will not exceed 1 EPA 
unit, and
    2. For a probability of 0.001 (a 1 in 1,000 chance) in 10,000 
years, cumulative releases to the accessible environment will not 
exceed 10 EPA units.
    In the undisturbed case, that is if there is no drilling into the 
repository, no releases are expected as the salt will isolate the waste 
very effectively. For the disturbed case, DOE evaluates four release 
mechanisms in the WIPP performance assessment modeling:
    Cuttings and cavings. These consist of waste material that gets 
brought to the surface when a borehole intersects waste in a WIPP waste 
panel. Cuttings are waste materials intersected by the borehole itself 
and cavings are waste materials that fail around the borehole, collapse 
into it, and are brought to the surface.
    Spallings. These are the solid materials that fail and are brought 
to the surface under high-pressure conditions in the repository. This 
only occurs when the pressure is above 8 megapascals \13\ (MPa).
---------------------------------------------------------------------------

    \13\ ``Pascal'' is a unit of pressure, defined as 1 kg/m-sec\2\. 
A megapascal is one million pascals.
---------------------------------------------------------------------------

    Direct Brine Releases. These are releases of dissolved actinides in 
brine when the pressure in the repository is high (i.e., above 8 MPa) 
and brine saturations are above residual saturation (i.e., brine is not 
``trapped'' between pore spaces) through a borehole that intersects a 
waste panel. The contaminated fluid is brought to the surface over a 
period of hours to days.
    Releases to the Culebra. These occur when contaminated brine from 
the repository is introduced via a borehole to the Culebra Dolomite (a 
geological unit, stratum or layer) and then moves to the edge of the 
accessible environment.
    DOE estimates the potential cumulative releases from these release 
mechanisms and compares them with the specified limits provided in 
Table 1 of 40 CFR part 191, appendix A. DOE is to provide in the 
application overall mean calculated releases and the upper 95th 
confidence limit of that mean.

B. Status of EPA Identified Areas for Improvement From the 2017 
Recertification Decision

1. Plutonium Oxidation States
    Since the original Compliance Certification Application (CCA), WIPP 
Pu solubility calculations have assumed a 50/50 split between aqueous 
Pu(IV) in equilibrium with solid Pu(IV) and aqueous Pu(III) in 
equilibrium with solid Pu(III). There is growing evidence in the 
published scientific literature that suggests the chemical conditions 
at the WIPP will favor Pu(III) over other oxidation states. Pu(III) has 
a higher solubility than Pu(IV), and the preference for Pu(III) over 
Pu(IV) results in higher calculated releases under the direct brine 
release scenario. EPA flagged this issue in its review of CRA-2014 and 
the Agency now considers the case to be stronger for the dominance of 
Pu(III), as documented in EPA's independent literature evaluation and 
modeling study on Pu oxidation states at the WIPP \14\ that concluded 
that conditions at the repository will overwhelmingly support Pu(III) 
over Pu(IV). Pending more robust technical justification for its 
current or an alternative approach, DOE should assume Pu(III) solids 
control dissolved

[[Page 26131]]

Pu concentrations in future PA calculations.
---------------------------------------------------------------------------

    \14\ Schramke, J.A., E.F.U. Santillan, R.T. Peake, ``Plutonium 
Oxidation States in the Waste Isolation Pilot Plant Repository,'' 
Applied Geochemistry, 116:104561, 2020.
---------------------------------------------------------------------------

2. Geochemistry Database
    In its 2017 recertification decision, EPA noted multiple technical 
issues in the geochemistry database that is used to calculate actinide 
solubility, many of which were to be addressed in the CRA-2019 (e.g., 
organic ligands, iron, and lead). DOE has provided updates to address 
these issues. See Section VI.D.1 of this document for more details.
3. Microbial Colloids
    During EPA's 2017 recertification, the Agency noted that DOE's 
microbial colloids parameter did not sufficiently address multiple 
uncertainties. Both EPA and DOE have worked to address these 
uncertainties for CRA-2019. See Section VI.C.4 of this document for 
more details.
4. Creep Closure of Open Areas
    Creep closure of mined openings in deeply buried salt deposits is a 
natural process that is certain to occur after WIPP operations cease, 
but the rate of closure and the final salt properties are uncertain. 
The exclusion of explicit modeling of creep closure processes for open 
areas was accepted by EPA in the early WIPP performance models because 
it eased the computational burden and this exclusion appeared to result 
in estimates of higher releases by reducing the isolation of individual 
waste panels. This leads to conservatism in modeling results. However, 
as a result of the abandonment of the south end of the repository, more 
open areas will be present with the elimination of panel closures in 
the south end and the increased size of the operations and experimental 
areas than postulated in the current 10-panel repository design. 
Because the characterization of the salt creep closure is still 
uncertain at WIPP, EPA recommended, in connection with the prior 
recertification, that DOE improve its understanding of the creep 
processes and develop a more reliable model in the PA calculation. DOE 
is investigating the creep closure process to better understand it for 
more explicit inclusion in the CRA-2024.\15\ Because DOE is still 
investigating the creep closure process,\16\ DOE addressed the creep 
closure uncertainties in the CRA-2019 by using the interim Abandonment 
of Panel Closures in the South (APCS) approach (described in Section 
VI.C.1).
---------------------------------------------------------------------------

    \15\ DOE Response 6 to EPA CRA19 completeness comment CC3-SCR-3, 
October 26, 2020, Document ID. No. EPA-HQ-OAR-2019-0534-0017.
    \16\ Status of Waste Isolation Pilot Plant Rock Mechanics 
Research, Sandia National Laboratories, May 20, 2020, SAND2020-5269 
CTF.
---------------------------------------------------------------------------

C. Changes to the Disposal System Identified by DOE for CRA-2019

    In Section 15 of the CRA-2019, DOE identified changes to the 
disposal system between CRA-2014 and CRA-2019, as well as changes to 
technical information relevant to Sec. Sec.  194.14 and 194.15. 
Noteworthy changes identified by DOE since CRA-2014 include the 
following: The decision not to install final panel closures in multiple 
panels, the abandonment of Panel 9 in the south end of the repository, 
and the development of the APCS approach to model those abandoned 
areas; updated borehole drilling rates and plugging patterns; a revised 
probability of encountering pressurized brine per EPA direction; 
revised baseline radionuclide solubilities; revised colloid parameters; 
and inclusion of brine radiolysis in the gas generation model. The 
addition of six metric tons of surplus Pu to the inventory (Waste 
Stream SR-KAC-PuOx) led DOE to include gas generation from brine 
radiolysis, as the concentration of Pu was not high enough during prior 
recertification applications for gas generation to be a concern in 
terms of repository performance. See both Sections VI.C.5 and VI.F for 
more discussion.
    Before determining that the CRA-2019 was complete, EPA raised 
technical questions with DOE, as described below. For each topic, a 
brief summary is provided of how DOE addressed the issue in the 2019 
application, followed by EPA's perspective on the change, including any 
follow-up sensitivity studies conducted by EPA. However, the calculated 
releases in the CRA-2019 PA were higher than those calculated in the 
CRA-2014 PA, in part due to the assumptions used in the 2019 PA models 
to account for abandonment of the southern end of the repository. DOE's 
approach was intended to bound potential releases, and DOE provided 
separate calculations to demonstrate that its approach was 
conservative, tending to estimate higher releases in the CRA-2019 
calculations. As in the EPA recertification decision for the 2014 
application, in this recertification EPA identifies future analyses DOE 
will need to conduct in order to address this topic in more detail.
1. Abandonment of Panel Closures and Waste Panel 9
    The WIPP repository was closed between February 2014 to January 
2017 following an accidental release of radionuclides that contaminated 
the south end of the underground repository waste area. Access to the 
contaminated areas was limited for an extended period of time and 
routine ground control could not be conducted. This resulted in unsafe 
conditions that led to a DOE decision to seal off and abandon the part 
of the waste area designated as Panel 9, to cancel the planned 
installation of run-of-mine salt panel closures in Panels 3, 4, 5 and 
6, and to identify the need for a replacement for Panel 9. DOE 
addressed the impacts of these design changes in the CRA-2019 PA using 
the APCS approach.
    The APCS approach incorporated conservative assumptions that were 
intended to estimate somewhat higher releases than would be expected 
given that no waste will actually be in Panel 9. DOE proposed this 
interim approach for this CRA because (1) DOE had not developed the 
concept to replace Panel 9 at the time the calculations needed to be 
started and (2) a long lead time was required to develop replacement 
models coupled with developing the new design. The primary elements of 
this approach were to treat abandoned Panel 9 as a surrogate for its 
replacement (i.e., modeling as though waste had actually been emplaced 
in the abandoned panel) and to treat the now-empty waste panel access 
drifts as having relatively high porosities and permeabilities for the 
10,000-year EPA regulatory period. In addition, to help ensure that 
repository releases would not be underestimated by this approach, the 
isolation functions of the remaining single panel closures, including 
the important closures between Panels 9 and 10, were not modeled.
    Upon review, EPA found that the assumptions in the APCS approach 
were not physically realistic but did compensate for inherent 
uncertainties in modeling the design changes. In accepting the APCS 
approach, EPA also evaluated DOE's parallel model (CRA19_CL), which 
assumed all panel access drifts without constructed closures would 
immediately creep close and have the very low porosity and permeability 
properties of intact halite.
    DOE's model CRA19_CL did calculate lower repository releases 
compared to DOE's CRA-2019 PA model, but the Agency found that the 
CRA19_CL model did not address the consolidation and healing of the 
disturbed rock zones (DRZs) surrounding the empty drifts. EPA 
separately analyzed the effects of DRZ healing using the Agency's 
CRA19_COMP model, which modified DOE's model to also treat the DRZs as 
immediately creep closing to the same properties of intact halite, 
consistent with the process described previously

[[Page 26132]]

for the empty drifts (see Section VI.E.1 of this document for more 
detail). The results confirmed that the APCS approach calculated higher 
repository releases as compared with empty drifts that were assumed to 
creep close over longer periods to the similar low porosity and 
permeability endpoints as intact halite.
    Additional discussion can be found in the EPA TSD for Sec.  194.23, 
Review of the APCS Approach to Analyzing WIPP Repository Performance in 
the CRA-2019 Performance Assessment (Docket ID No. EPA-HQ-OAR-2019-
0534).
2. Updated Plugging Patterns and Borehole Drilling Rates
    Plugging Patterns. As a general matter, and unrelated to WIPP-
specific regulations and requirements, before wells are abandoned or 
permanently closed, various state and Federal regulations require that 
the boreholes must be plugged and surface equipment removed. Releases 
could occur through a borehole that penetrates the waste repository 
after it has been plugged and abandoned. The depths and stratigraphic 
horizons of installed plugs (plugging pattern) in abandoned boreholes 
impact the migration of fluids in and out of the repository, which in 
turn have significant effects on releases modeled in the PA. If a 
borehole has one continuous plug, no releases are assumed to occur. Up 
to CRA-2014, DOE evaluated plugging patterns in boreholes abandoned 
since 1988 for each CRA based on an updated dataset of the entire New 
Mexico portion of the Delaware Basin. EPA previously accepted this 
basis for calculating plugging pattern probabilities.
    In CRA-2019, DOE changed the method for calculating plugging 
pattern probabilities to a narrower one based only on the part of the 
Delaware Basin within New Mexico's Known Potash Leasing Area (KPLA). 
DOE justified this change because the WIPP site is within the KPLA 
boundary, and this area could therefore be considered to represent an 
appropriate regulatory and geologic analog for future plugging 
practices at the WIPP. DOE's implementation of this change in the PA 
contributed to the probability of continuous plug use increasing from 
4% in the CRA-2014 PA to 40% in the CRA-2019 PA, based on the field 
data collected by DOE. This significantly reduced calculated releases. 
Because this was a major change, EPA paid special attention to the 
basis for the change.
    EPA found that, in the KPLA, boreholes are required to be abandoned 
with continuous plugs if they are located within known potash reserves, 
but waivers from this requirement are allowed for boreholes in potash 
``barren'' areas, and waivers to the requirement for continuous plugs 
are frequently granted in New Mexico. Based on DOE's borehole database, 
approximately 60% of the boreholes plugged in the KPLA since 1988 did 
not have continuous plugs installed, presumably due to waivers. In 
preparing the 1996 CCA, DOE found that the repository is in a 
``barren'' area without economical potash reserves, meaning it would 
qualify for a waiver. The DOE's CRA-2019 approach does not specifically 
consider that current law provides for this waiver possibility. Based 
on current regulations and practices, EPA expects that a borehole 
through the WIPP repository would likely be granted a waiver from the 
continuous plug requirement because it is in a barren area. Therefore, 
future boreholes through the repository most likely would not be 
abandoned with a continuous plug and the probability of such a borehole 
being abandoned with a continuous plug would be much less than the 40% 
used in the CRA-2019 PA. In addition, the new approach ignores a number 
of abandoned boreholes directly southeast of WIPP but just outside the 
KPLA that may otherwise be relevant geological analogs.
     EPA concludes that the new approach used by DOE to calculate 
plugging pattern probabilities is not adequately supported by 
regulatory considerations or actual practice (e.g., exemptions to the 
solid plugging requirement) in the KPLA, and it further fails to 
consider representative, relevant boreholes in the vicinity of WIPP. 
EPA conducted a sensitivity PA study with the plugging pattern 
probabilities calculated with the original methodology and the release 
results show that WIPP still complies (see Section VI.E.2 of this 
document). EPA expects DOE to use the previously approved methodology 
for calculating plugging pattern probabilities in future PAs, or 
otherwise propose alternative methods that may be approved by EPA prior 
to that time.
    Drilling Rates. The average areal density (i.e., average over an 
area) of boreholes drilled in the Delaware Basin in Texas and New 
Mexico over the past 100 years is called the ``drilling rate'' in the 
PA. This rate is used to estimate the number of deep boreholes that 
might intersect WIPP waste during the 10,000-year post-closure period. 
Deep borehole intrusion into the repository is the only mechanism for 
significant releases from the repository, so a greater number of 
boreholes would increase calculated releases in the PA.
    When the drilling rate is recalculated for each CRA, all boreholes 
without depth information listed at the time are categorized by DOE as 
shallow ``drilling or waiting on paperwork.'' Noting that, based on 
historical trends, the majority of boreholes would eventually be 
categorized as deep, EPA evaluated the impact of this assumption in 
DOE's methodology. These boreholes will eventually get incorporated 
into the PA, but the Agency found the DOE methodology results in 
additional lag time between when drilling actually occurs and when DOE 
incorporates it into the deep drilling rate in the PA. The Agency 
requests that DOE re-evaluate its methodology to better address the lag 
time between the drilling of boreholes and its capture in the PA for 
CRA-2024.
    A more detailed discussion of EPA's review of DOE's plugging 
pattern and drilling rate frequency calculations is presented in the 
EPA TSD Review of Borehole Drilling Rate and Plugging Pattern Frequency 
Calculations in the CRA-2019 Performance Assessment (Docket ID No. EPA-
HQ-OAR-2019-0534).
3. Radionuclide Solubilities
    The solubilities of actinide elements affect actinide mobilization 
as dissolved species, microbial colloids, and humic colloids in WIPP 
brines. The parameters used to represent actinide solubilities were 
updated in the CRA-2019 PA. EPA reviewed the actinide solubility 
calculations and identified a number of issues related to the 
geochemical database and assumptions used to make the solubility 
calculations, resulting in an underprediction of calculated actinide 
solubilities (see Section VI.D.2 of this document). While these issues 
did not result in the WIPP exceeding future regulatory release limits, 
their effects on actinide mobilization in WIPP brines are of concern to 
EPA and are addressed in detail in Section 7.8 and Attachment B of the 
EPA TSD Evaluation of the Compliance Recertification Application (CRA-
2019) Actinide Source Term, Gas Generation, Backfill Efficacy, Water 
Balance, and Culebra Dolomite Distribution Coefficient Values (Docket 
ID No. EPA-HQ-OAR-2019-0534).
4. Revised Colloid Parameters
    DOE updated microbial colloid parameters based on new laboratory 
data and changed intrinsic colloid parameters based on a review of 
existing laboratory data since the previous CRA. Both sets of changes 
do not reflect the full range of values EPA has seen in DOE's existing 
data or in the case of

[[Page 26133]]

microbial colloids, the broader literature. Although there is large 
variability in proportionality constants reported in the scientific 
literature, the variability was not reflected in the CRA-2019 PA 
microbial colloid proportionality constants since DOE determined these 
parameters based on a single organism. EPA's review also found that the 
microbial colloid enhancement parameters used in the CCA provided more 
defensible and bounding maximum microbial colloid concentrations. 
Further, EPA found that the parameters for Americium (Am) (III) and 
Thorium (Th) (IV) intrinsic colloids did not adequately represent the 
available laboratory data. While these issues will not lead to the WIPP 
being out of compliance, they are less technically defensible based on 
the available information. For future PAs, unless DOE proposes an 
acceptable alternative, DOE should use microbial colloid 
proportionality constants that adequately address the variability in 
the literature, CCA-based microbial colloid maximum values, and revised 
Am(III) and Th(IV) intrinsic colloid parameters that bound laboratory 
data. Additional discussion of colloid parameters in the CRA-2019 PA 
can be found in Section 8.3 of the EPA TSD Evaluation of the Compliance 
Recertification Application (CRA-2019) Actinide Source Term, Gas 
Generation, Backfill Efficacy, Water Balance, and Culebra Dolomite 
Distribution Coefficient Values (Docket ID No. EPA-HQ-OAR-2019-0534).
5. Inclusion of Brine Radiolysis in the Gas Generation Model
    Gas generation from radiolysis of brine in the WIPP repository 
results primarily from the decay of Am and Pu isotopes. Gas generation 
is important to repository performance because elevated gas pressure is 
a driver of the primary release pathways, except for the cuttings and 
cavings release pathways. An increased mass of Pu projected for 
disposal in the CRA-2019 waste inventory (Waste Stream SR-KAC-PuOx), as 
well as a decreased contribution of microbial gas generation to 
repository gas pressures, prompted DOE to reevaluate the significance 
of radiolysis to repository performance. Brine radiolysis by Pu in 
saturated waste was added to the gas generation process model in 
response to that evaluation and EPA found it to be incorporated 
appropriately for CRA-2019. However, with the increased importance of 
Pu in the waste inventory, EPA believes that DOE should continue to 
refine this set of parameters for the next PA. Additional discussion of 
the implementation of radiolytic gas generation and brine consumption 
in the CRA-2019 PA can be found in Section 3.6 of the EPA TSD 
Evaluation of the Compliance Recertification Application (CRA-2019) 
Actinide Source Term, Gas Generation, Backfill Efficacy, Water Balance, 
and Culebra Dolomite Distribution Coefficient Values (Docket ID No. 
EPA-HQ-OAR-2019-0534).

D. Other Issues Identified by EPA During Review

    EPA identified several topics where the Agency believes new 
information can be incorporated into future CRAs to improve 
defensibility of the calculated PA results. These topics relate to the 
chemical conditions within the repository and are important in 
determining the potential for releases of radionuclides from the 
disposal system. Although these are important concerns that should be 
addressed in the future by DOE, for its decision on this CRA, EPA was 
nonetheless able to adequately evaluate the WIPP's continued compliance 
with the final disposal regulations and make a sound recertification 
determination. The following subsections briefly describe each of these 
topics, and more detail is provided in the EPA TSD Evaluation of the 
Compliance Recertification Application (CRA-2019) Actinide Source Term, 
Gas Generation, Backfill Efficacy, Water Balance, and Culebra Dolomite 
Distribution Coefficient Values (Docket ID No. EPA-HQ-OAR-2019-0534).
1. Geochemistry Database
    The Agency has identified errors in the geochemical database used 
to perform actinide solubility calculations for the PA, including 
errors in DOE's selection of organic ligand stability constants and the 
inclusion of lead solubility and aqueous speciation data. These errors 
result in lower predicted releases, especially for the +III actinides. 
EPA investigated the impacts of database issues in a sensitivity study 
(see Section VI.E of this document for more detail).
2. Initial Assumptions for Solubility Calculations
    DOE actinide solubility calculations assumed calcite in brine would 
precipitate to saturation even though calcite oversaturation (i.e., 
non-precipitation) is common in low temperature aqueous systems. 
Although this assumption did not significantly affect releases, the 
assumption of calcite precipitation also caused significant cement 
precipitation, consuming up to 83% of water in ERDA-6 brine. These 
results are unrepresentative of the WIPP system, were not reflected in 
the rest of the PA, and have important implications towards repository 
water balance, the availability of radionuclides for transport, the 
effectiveness of the magnesium oxide barrier used to control carbon 
dioxide and pH, and on the physical properties of room closure. This is 
further discussed in Section 7.8 of the EPA TSD Evaluation of the 
Compliance Recertification Application (CRA-2019) Actinide Source Term, 
Gas Generation, Backfill Efficacy, Water Balance, and Culebra Dolomite 
Distribution Coefficient Values (Docket ID No. EPA-HQ-OAR-2019-0534).
3. Actinide Solubility Uncertainty
    DOE represents uncertainty in actinide solubility by sampling from 
a distribution that compares modeled solubility to experimental data 
from multiple reports and peer-reviewed studies. For CRA-2019, DOE used 
a modified distribution from CRA-2014 which did not include any new 
studies since the previous recertification. DOE provided an updated 
distribution following discussions with DOE during EPA's completeness 
determination process in which the Agency asked the Department to 
include new data from publicly available literature (e.g., journal 
articles, government reports) since CRA-2014. EPA's evaluation of DOE's 
response concluded that the update skewed solubility calculations 
towards an overly conservative and unrepresentative increase and that 
DOE's use of the original modified CRA-2014 distribution was sufficient 
for CRA-2019, even without more recent data. Prior to the next CRA, EPA 
recommends that DOE perform an evaluation of the relative advantages 
and disadvantages of other potential approaches for addressing +III and 
+IV actinide solubility uncertainties to improve confidence in the 
current approach. This issue and recommendation are discussed in more 
detail in Section 7.8 of the EPA TSD Evaluation of the Compliance 
Recertification Application (CRA-2019) Actinide Source Term, Gas 
Generation, Backfill Efficacy, Water Balance, and Culebra Dolomite 
Distribution Coefficient Values (Docket ID No. EPA-HQ-OAR-2019-0534).

E. EPA Sensitivity Studies

    In connection with the prior CRA, EPA identified issues with model 
parameters and approaches used by DOE and requested that DOE conduct 
additional calculations so the EPA could better understand how 
alternative

[[Page 26134]]

parameter values and approaches would affect repository performance. 
These calculations were treated as sensitivity studies. To support the 
EPA assessment of the CRA-2019, EPA conducted modeling calculations to 
determine the sensitivity of releases to the previously noted issues 
identified during its review. In combination with other information, 
the sensitivity studies aided EPA in determining whether the WIPP would 
continue to comply with the radioactive waste disposal regulations at 
40 CFR part 191 and the compliance criteria at 40 CFR part 194. Based 
on these sensitivity studies, EPA concludes that WIPP continues to 
comply with EPA's radioactive waste disposal regulatory release limits.
    The results from the EPA sensitivity studies are expressed as 
changes in mean total repository releases in EPA units for comparison 
with DOE's CRA-2019 results. For reference, the EPA release limits are 
1.0 EPA units at the upper probability compliance point of a 0.1 
probability of the release and 10.0 EPA units at the lower probability 
compliance point of a 0.001 probability of the release.
    EPA's sensitivity studies examined the technical issues in the CRA-
2019 PA that potentially had greater impacts on repository releases. 
The Agency's modifications to the selected parameters increased 
calculated releases. However, the total mean releases and the upper 95% 
confidence limit on those means remained below EPA's WIPP regulatory 
release limits. The major issues identified in EPA's review primarily 
influence the importance of the direct brine release pathway and how 
the PA simulates those releases. EPA found that direct brine releases 
are strongly influenced by the degree of waste panel isolation. By 
treating the now-empty waste panel access drifts in the south end of 
the repository as retaining high permeability and porosity for the 
10,000-year EPA regulatory period and discounting most of the isolation 
capabilities of the constructed panel seals that remained, the DOE's 
APCS methodology, described in Section VI.C.1 of this document, did not 
simulate the isolation of waste panels that is likely to exist. As a 
result, DOE's use of the APCS methodology in this CRA provided a 
conservative starting point for evaluating the sensitivity of releases 
to EPA concerns; that is, the APCS approach calculates higher releases 
than would be expected to occur. When the previously discussed non-
conservative borehole plugging, chemistry, and microbial assumptions in 
the CRA were removed in EPA's sensitivity studies, the conservatisms of 
the APCS approach remained. Because of this, EPA believes that the 
sensitivity study results were influenced by the conservatism of the 
APCS approach and those results also conservatively estimated 
repository releases. EPA's CRA19_COMP analysis demonstrated that DOE's 
use of the APCS methodology in the CRA-2019 PA resulted in greater 
repository releases compared to modeling approaches that included 
parameters that assumed less porous and permeable access drifts due to 
creep closure. EPA's CRA19_COMB analysis subsequently demonstrated that 
when the cumulative effects of the Agency's parameter changes were 
added to DOE's CRA-2019 PA releases, total releases remained below 
regulatory limits.
    In the past, DOE has used the previous CRA PA as the point of 
comparison with the current PA. However, given the issues identified by 
EPA for this PA, DOE should not use DOE's CRA-2019 assessment as a new 
baseline for WIPP performance without appropriate adjustments that 
address EPA's recertification review comments. EPA will work with DOE, 
as needed, to develop an appropriate model to use for comparisons with 
future PA calculations.
    Summaries of each of the sensitivity studies are provided in the 
following subsections. More detailed analyses of these studies can be 
found in Section 4.0 of the EPA TSD Overview of EPA Review of U.S. 
Department of Energy 2019 WIPP Compliance Recertification Application 
Performance Assessment (Docket ID No. EPA-HQ-OAR-2019-0534).
1. Sensitivity to Creep Closure of Empty Rooms (CRA19_COMP Analysis)
    EPA prepared the CRA19_COMP model to study the sensitivity of 
repository releases to access drift closure and disturbed rock zone 
(DRZ) healing due to salt creep of empty areas in the WIPP repository. 
This model supplemented DOE's CRA19_CL model \17\ by treating the DRZ 
as immediately creep closing to the same properties of intact halite as 
the empty rooms. The results demonstrate that the CRA-2019 PA model 
using the APCS approach (see Section VI.C.1 of this document) 
calculated greater repository releases than if the empty repository 
rooms had been treated as fully creep closed to intact halite 
properties.
---------------------------------------------------------------------------

    \17\ Zeitler, T.R., J. Bethune, S. Brunell, B. Day, D. Kicker, 
J. Long, and R. Sarathi. 2019. Summary Report for the 2019 
Compliance Recertification Application Performance Assessment (CRA-
2019 PA). 2019. Carlsbad, NM: Sandia National Laboratories. ERMS 
571376.
---------------------------------------------------------------------------

2. Sensitivity to Borehole Plugging Frequency (PLG_PROB Analysis)
    The sensitivity of calculated repository releases to DOE's new 
approach to plugging pattern frequency was evaluated by EPA through a 
comparison of mean total releases calculated by DOE in the CRA-2019 PA, 
which used DOE's new approach, with mean total releases that would have 
been calculated in the CRA-2019 PA if the historic approach previously 
approved by EPA had been used. The results showed that DOE's new 
approach underestimated repository releases compared to the previous 
approach. Mean total releases in the PLG_PROB analysis increased from 
0.06853 to 0.07924 EPA units at EPA's upper probability compliance 
point and from 0.7505 to 0.8954 EPA units at EPA's lower probability 
compliance point. The results of this sensitivity study showed that 
DOE's new approach materially affected calculated repository releases, 
though they remained within the regulatory release limits.
3. Sensitivity to Actinide Solubility (GCHM_S0 Analysis)
    The GCHM_S0 calculations inform EPA how sensitive releases are to 
changes in baseline actinide solubility values. Recalculated baseline 
solubility values incorporated stability constants from an EPA-updated 
geochemical database and used changes in initial modeling assumptions 
about calcite precipitation (see Sections VI.D.1 and VI.D.2 of this 
document). These EPA-recalculated solubilities were verified by DOE in 
a separate calculation.\18\ The resultant solubilities increased both 
+III and +IV actinide releases. The incorrect values in the database 
for the Am-, Mg-, and Ca-EDTA constants caused the biggest impact on 
actinide solubility, underestimating dissolved concentrations by 
approximately an order of magnitude for the +III actinides. When 
recalculated solubilities were incorporated into the PA, the results 
showed increases in direct brine releases and total releases. Mean 
total releases in the GCHM_S0 analysis increased from 0.06853 to 
0.07788 EPA units at the EPA's upper probability compliance point and 
from 0.7505 to 1.186 EPA units at EPA's lower probability compliance 
point. EPA expects DOE to update the database and

[[Page 26135]]

its assumptions regarding calcite precipitation for future PAs.
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    \18\ Domski, P.S., 2021. EPA Requested Changes to the CRA-2019 
DPA Thermodynamic Database and Actinide Solubility Model. December 
9, 2021. Sandia National Laboratory. ERMS 576365.
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4. Sensitivity to Actinide Solubility and Colloid Parameters (GCHM_S2 
Analysis)
    EPA used the GCHM_S2 analysis to evaluate the impact of combining 
the increase in baseline +III actinide solubility in the GCHM_S0 
analysis with updated microbial colloid parameters that are 
proportional to actinide solubility (see Section VI.C.4 of this 
document). This study also assessed the impact of increased intrinsic 
colloid values. The results showed that updating the colloid values 
noticeably increased calculated releases. Mean total releases in the 
GCHM_S2 analysis increased from 0.06853 to 0.09497 EPA units at EPA's 
upper probability compliance point and from 0.7505 to 1.238 EPA units 
at EPA's lower probability compliance point.
5. Sensitivity to Actinide Solubility, Colloid Parameters, and Actinide 
Oxidation State (GCHM_S3 Analysis)
    GCHM_S3 is a CRA-2019 PA-based, comprehensive geochemistry 
sensitivity analysis that combines the impacts of a revised baseline 
actinide solubility, revised intrinsic and microbial colloid 
parameters, and revised actinide oxidation state parameters to include 
only Pu(III), Np(IV), and U(IV) oxidation states in all realizations. 
The combined chemistry parameter changes resulted in increased direct 
brine releases at all probabilities and increased total releases at low 
probabilities. The combined results of these changes showed that the 
chemical conditions assumed by DOE in the CRA-2019 PA led to lower 
projected repository releases than GCHM_S3. Mean total releases in the 
GCHM_S3 analysis increased from 0.06853 to 0.1165 EPA units at EPA's 
upper probability compliance point and from 0.7505 to 1.516 EPA units 
at EPA's lower probability compliance point.
6. Sensitivity to Combined Geotechnical and Geochemical Parameter 
Changes (CRA19_COMB Analysis)
    While EPA conducted individual sensitivity analyses that looked at 
specific changes, the Agency also conducted a sensitivity study that 
encompassed all changes that EPA determined appropriate to incorporate 
into a summary PA designated as CRA19_COMB. This sensitivity study was 
based on the CRA-2019 PA but with the following parameter changes:
     Used the previously established methodology for 
calculating plugging pattern probabilities (see Section VI.C.2 of this 
document);
     Used revised actinide solubility parameters (see Section 
VI.C.3 of this document);
     Used revised colloid parameters (see Section VI.C.4 of 
this document);
     Used revised actinide oxidation state parameters (see 
Section VI.B.1 of this document).
    The cumulative effects of the changes were to increase calculated 
total mean repository releases from 0.06853 to 0.1669 EPA units at 
EPA's upper probability compliance point and from 0.7505 to 1.766 EPA 
units at EPA's lower probability compliance point.

F. Waste Characterization

    Section 194.24 generally requires DOE to identify, quantify and 
track the important chemical, radiological and physical components of 
the waste destined for disposal at the WIPP. DOE collects data from 
generator sites and compiles the waste inventory on an annual basis. 
DOE developed the waste inventory used in the PA using data provided in 
ATWIR (DOE 2018) \19\ and PAIR 2018 (Van Soest 2018b).\20\ The 
Comprehensive Inventory Database is used to store and manage all WIPP 
inventory data and is updated annually using data from the Waste Data 
System for emplaced WIPP waste, and data from the waste generator sites 
for anticipated waste.
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    \19\ DOE (U.S. Department of Energy). 2018. Annual Transuranic 
Waste Inventory Report--2018. Revision 0. U.S. Department of Energy, 
Carlsbad Field Office, DOE/TRU-18-3425.
    \20\ Van Soest, G.D. 2018. Performance Assessment Inventory 
Report--2018. Los Alamos National Laboratory Carlsbad Operations 
INV-PA-18, Revision 0, December 12, 2018.
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    The Agency evaluated DOE's inventory update process and 
documentation. EPA also conducted quality assurance (QA) and waste 
characterization inspections, observations and technical reviews 
between October 2012 and May 2017 to evaluate compliance with the 
requirements of 40 CFR 194.8 and 40 CFR 194.24. The Agency finds that 
DOE has a comprehensive array of QA procedures in place to ensure the 
accuracy of data published in the annual inventory reports. During EPA 
site visits, a number of records were reviewed and were found to be 
consistent with the relevant QA procedures. Based on DOE's inventory 
updating process, inventory reporting is being conducted in a manner 
that produces an inventory suitable for use in the PA.
    The Agency examined the changes in the WIPP inventory since CRA-
2014 and compared the CRA-2014 PA and CRA-2019 PA inventories, where 
appropriate. Changes in the inventory between the CRA-2014 PA and CRA-
2019 PA have been adequately explained based on changes in waste stream 
information. The most significant changes include the addition of Waste 
Stream SR-KAC-PuOx, which increased the quantity of radioactivity (Pu-
239 primarily), and projected waste packaging changes, mainly due to 
increased remote handled (RH) waste shielded containers, that have 
increased the amount of packaging steel and lead in the inventory.
    The Agency notes that the SR-KAC-PuOx waste stream is composed of 
Pu oxides that have been downblended using a proprietary adulterant. 
CRA-2019 does not explicitly discuss the adulterant, but it is included 
in the calculations as part of the SR-KAC-PuOx waste stream. The 
downblended Pu waste form will contain, in addition to the Pu, iron-
base metal alloys, inorganic materials, other non-ferrous metals, and 
plastics. EPA staff have been able to review a preliminary DOE report 
on the waste stream's impacts on repository compliance and conclude 
that the adulterant should not affect the repository conditions in any 
unique way for EPA's CRA-2019 recertification decision. Specifically, 
interactions of this waste stream with the repository will be heavily 
dominated by its high iron content, which is not expected to alter the 
expected repository chemical conditions represented in the PA.
    The use of all inventory-related parameters in the PA was reviewed 
by EPA. All inventory-related parameters were correctly implemented in 
the PA. On the basis of its review, EPA concludes that DOE has 
appropriate QA procedures in place to accurately document the WIPP 
waste inventory on an annual basis. EPA further concludes that the PAIR 
2018 inventory is appropriate for use in the CRA-2019 PA calculations.
    EPA accepts this updated inventory, which is relatively similar to 
the one used in CRA-2014. These topics are discussed in more detail in 
TSD for Sec.  194.24: Review of The Baseline Inventory Used in the 
Compliance Recertification Application (CRA-2019) (Docket ID No. EPA-
HQ-OAR-2019-0534).

G. Peer Review

    Section 194.27 requires DOE to conduct peer review evaluations, 
when warranted, of conceptual models, waste characterization analyses, 
and a comparative study of engineered barriers. The required peer 
reviews must be performed in accordance with the Nuclear Regulatory 
Commission's

[[Page 26136]]

NUREG-1297, ``Peer Review for High-Level Nuclear Waste Repositories,'' 
which establishes guidelines for the conduct of a peer review exercise. 
DOE conducted no peer reviews for inclusion in CRA-2019.

H. Individual and Groundwater Protection Requirements

    Sections 194.51 through 194.55 implement the individual protection 
requirements of 40 CFR 191.15 and the groundwater protection 
requirements of subpart C of 40 CFR part 191. Assessment of the 
likelihood that the WIPP will meet the individual dose limits and 
radionuclide concentration limits for groundwater is conducted through 
a process known as compliance assessment. Compliance assessment uses 
methods similar to those of performance assessment (for the containment 
requirements in 40 CFR 191.13 and appendix A) and can be considered a 
``subset'' of performance assessment since it considers only natural 
(undisturbed) conditions and past or near-future human activities (such 
as existing boreholes) but does not include the long-term future human 
activities that are addressed in performance assessment.
    In this CRA, DOE updated the data for groundwater quantity 
determination to define an underground source of drinking water for 
purposes of calculating groundwater concentrations and doses. DOE used 
2016 U.S. Bureau of Census data to update the average number of persons 
per household to 2.51 and used 2013 data from the New Mexico Office of 
the State Engineer to update the average household water consumption to 
272 gallons per person per day. DOE concluded that the sub-criterion of 
5 gallons per minute rate of production from a well continued to 
accurately define an underground source of drinking water.
    The updates made by DOE in CRA-2019 did not significantly impact 
the conclusions regarding the groundwater standard in the 1996 CCA. DOE 
did not change the criteria for making underground source of drinking 
water determinations. For the CRA-2019 evaluation, the maximum 
potential dose remained below the CCA calculated value, and DOE 
concluded that continued compliance with the individual protection 
standard is maintained. EPA found that DOE is in continued compliance 
with 40 CFR 194.51 through 194.55 requirements.

VII. What is EPA's role in future WIPP activities?

    EPA's regulatory role at the WIPP does not end with this 
recertification decision. The Agency's future WIPP activities include 
recertifications every five years (the next scheduled to be submitted 
by DOE in March 2024), review of DOE reports on conditions and 
activities at the WIPP, assessment of waste characterization, quality 
assurance programs at waste generator sites, announced and unannounced 
inspections of the WIPP and other facilities and, if necessary, 
modification, revocation or suspension of the certification.
    Although not required by the Administrative Procedure Act, the WIPP 
LWA, or the WIPP Compliance Criteria, the EPA intends to continue to 
make all inspection or audit reports and annual reports and other 
significant documents on conditions and activities at the WIPP, as well 
as formal communications between the two agencies available in the 
public docket.

Jonathan Edwards,
Director, Office of Radiation and Indoor Air.
[FR Doc. 2022-09209 Filed 5-2-22; 8:45 am]
BILLING CODE 6560-50-P