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EPA Comment

2-C-3 Data Supporting Water Balance Assumptions. The CRA-2014 PA calculations include the 

effects of MgO hydration, microbial degradation of CPR and iron sulfide formation on repository water 

balance. For PA, it is assumed that hydrogen sulfide created by CPR degradation preferentially reacts 

with iron hydroxide versus metallic iron (CRA-2014 Appendix MASS, page MASS-57). These hydrogen 

sulfide reactions are:

Fe(OH)2(s) + H2S(g) → FeS(s) + H2O(l) (1)

Fe(s) + H2S(g) → FeS(s) + H2(g) (2)

The assumption that hydrogen sulfide preferentially reacts with iron hydroxide increases brine 

production and decreases gas production compared to the assumption that all or some of the hydrogen 

sulfide reacts with metallic iron.

It is also assumed for PA that carbon dioxide preferentially reacts with brucite instead of unreacted MgO. 

The carbonation reactions are:

1.25 Mg(OH)2(s) + CO2(g,aq) → 0.25 Mg5(CO3)4(OH)2•4H2O(s) (3)

1.25 MgO(s) + CO2(g,aq) + 1.25 H2O(l) → 0.25 Mg5(CO3)4(OH)2•4H2O(s) (4)

The assumption that carbon dioxide preferentially reacts with brucite increases brine production in the 

repository.

Please provide supporting data for these water-balance assumptions and evaluate the potential 

magnitude of the effects of these assumptions on the water balance.

DOE Response

The water balance assumptions were based on experimental studies and were made to capture the 

transient behavior of the gas and water generation/consumption events. Magnesium oxide hydration, iron 

corrosion and microbial degradation of cellulosics, plastics and rubbers (CPR) all depend on the amount 

of water present. CPR degradation via sulfate reduction generates hydrogen sulfide and carbon dioxide. 

Anoxic iron corrosion generates hydrogen gas and iron hydroxide, while consuming water. Magnesium 

oxide hydration consumes water and produces brucite. The products of these reactions will be generated 

where the water is present in the repository.

The overall reactions for the sulfidation of the iron species used in the performance assessment 

calculations are hydrogen sulfide reacting with iron hydroxide (reaction 1) and metallic iron (reaction 2) 

to form iron sulfide.

Fe(OH)2 + H2S → FeS + 2 H2O (1)

Fe + H2S → FeS + H2 (2)

The iron hydroxide in reaction 1 is produced by the anoxic corrosion of iron (reaction 3).

Fe + 2 H2O → Fe(OH)2 + H2 (3)
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The reaction rates used in performance assessment for reactions 1 and 2 depend on the sampled value of 

the CPR degradation rate because the hydrogen sulfide comes from CPR degradation. The reaction rate 

used in performance assessment for reaction 3 depends on the sampled value of the iron corrosion 

reaction rate. Differences in these reaction rates affect the amount of gas and water that are present. The 

reaction scheme for the iron species used in the performance assessment calculation is best represented by 

reactions 3 and 1, rather than reaction 2, which captures the transient behavior of the gas and water 

generation/consumption.

The above representation is supported by experimental studies. In the reports Hydrogen Generation by 

Metal Corrosion in Simulated Waste Isolation Pilot Plant Environments: Progress Report for the Period 

November 1989 through December 1992 (Telander and Westerman 1993), and Hydrogen Generation by 

Metal Corrosion in Simulated Waste Isolation Pilot Plant Environments (Telander and Westerman 1997), 

the authors experimentally demonstrated that anoxic corrosion of low carbon steel without the presence of 

hydrogen sulfide produced iron hydroxide (reaction 3). They also experimentally demonstrated that low 

carbon steel corrosion in the presence of hydrogen sulfide quickly passivated (order of days), with the 

specimen suspended over the brine (reaction 2) passivating quicker and corroding less than the specimen 

immersed in the brine (reaction 1). The specimen immersed in the brine corroded more due to the 

competition of the iron corrosion reaction (reaction 3) and the sulfidation reaction (reaction 1), indicating 

that reaction 1 would dominate in the long term compared with reaction 2. Since 1) experimental studies 

support the above representation, and 2) it allows the performance assessment calculations to capture the 

transient behavior of the gas and water generation/consumption, it was assumed that reaction 1 would 

dominate reaction 2.

The overall reactions of carbon dioxide produced from CPR degradation with brucite (reaction 4) and 

magnesium oxide (reaction 5) as used in performance assessment calculations are:

1.25 Mg(OH)2 + CO2 → 0.25 Mg5(CO3)4(OH)2∙4H2O (4)

MgO + CO2 → MgCO3 (5)

The brucite in reaction 4 is an intermediate species produced by the hydration of magnesium oxide 

(reaction 6), and the hydromagnesite (5424) in reaction 4 is a metastable species that converts to 

magnesite (reaction 7).

MgO + H2O → Mg(OH)2 (6)

0.25 Mg5(CO3)4(OH)2∙4H2O → MgCO3 + 0.25 Mg(OH)2 + H2O (7)

The reaction rates used in performance assessment for reactions 4 and 5 depend on the sampled value of 

the CPR degradation rate because the carbon dioxide comes from CPR degradation. The reaction rates 

used in performance assessment for reactions 6 and 7 depend on the sampled value of the magnesium 

oxide hydration and hydromagnesite conversion reaction rates. Differences in these reaction rates affect 

the amount of gas and water that are present. The reaction scheme used in the performance assessment 

calculations follows the reaction path of reactions 6, 4 and 7 instead of reaction 5 to capture the transient 

behavior of the gas and water generation/consumption.

The above representation is supported by experimental studies. In Experimental Investigations of the 

Reaction Path in the MgO–CO2–H2O System in Solutions with Various Ionic Strengths, and Their 

Applications to Nuclear Waste Isolation (Xiong and Lord 2008), it was experimentally demonstrated that 

magnesium oxide first hydrates as brucite (reaction 6), then the brucite carbonates as hydromagnesite 

(5424) (reaction 4). The conversion rates from brucite to hydromagnesite (5424) are fast under the 
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WIPP-relevant conditions with regard to the repository performance assessment time scale. For instance, 

the conversion rates for reaction 4 in terms of fraction of conversion for ERDA-6 and GWB brines are 

5.37 × 10–6 hour–1 (4.7% per year) and 2.29 × 10–6 hour–1 (2.0% per year) at room temperature and 

atmospheric partial pressure of carbon dioxide (Xiong and Lord 2003). Furthermore, in Thermokinetic 

Analysis of the MgO Surface Carbonation Process in the Presence of Water Vapor (Torres-Rodriguez and 

Pfeiffer 2011), it is reported that magnesium oxide does not absorb carbon dioxide in dry conditions 

(reaction 5) at lower temperatures (<70 o

C). Since 1) experimental studies support the above 

representation, and 2) it allows the performance assessment calculations to capture the transient behavior 

of the gas and water generation/consumption, it was assumed that reaction 4 would dominate reaction 5.

It is worth mentioning that magnesite is the predicted thermodynamically stable phase under WIPP 

conditions, whereas hydromagnesite (5424) is the metastable phase (Xiong and Lord 2008). However, 

the conversion from hydromagnesite (5424) to magnesite is slow, as described in Appendix MgO-2009,

Magnesium Oxide as an Engineered Barrier (U.S. DOE 2009). During the PA period of 10,000 years, 

hydromagnesite (5424) could convert to magnesite (U.S. DOE 2009).

One evaluation of the potential magnitude of the water balance assumptions is given in Verification of the 

Waste Isolation Pilot Plant Chemistry Conceptual Models (SCA 2008). In their analysis, S. Cohen and 

Associates determined the potential amounts of brine volume change per panel for various water balance 

assumptions, summarized here in Figure 1. The values in the right column of Figure 1 indicate the 

volume of brine in a panel that could be produced or consumed for various assumptions. The potential 

volumes of brine in a panel that could be produced or consumed are on the same order as the maximum 

volume of brine in a panel.

To evaluate the potential magnitude of the water balance assumptions on performance assessment, the 

refinement to the repository water balance implementation was included in the CRA-2014 and the results 

were analyzed. The performance assessment calculations conducted for the CRA-2014 included two 

subsets that are relevant to the EPA’s comment, CRA14-BV and CRA14-0 (Zeitler 2013). The only 

parameter changes between the CRA14-BV and CRA14-0 calculations were the update to the steel (iron)

corrosion rate and the refinement to the repository water balance implementation (implemented 

simultaneously). In the CRA14-BV calculations, the repository water balance implementation included 

iron corrosion (reaction 3) as a gas producing and water consuming reaction, and CPR degradation as a 

gas producing and water neutral reaction. This essentially assumed that the amount of water generated 

from CPR degradation was equal to the amount of water consumed by magnesium oxide hydration 

(reaction 6), and magnesium oxide reacted directly with carbon dioxide (reaction 5). Furthermore, in the 

CRA14-BV, the hydrogen sulfide was assumed to react directly with the iron (reaction 2). The CRA14-0 

calculations included CPR degradation as a gas and water producing reaction and reactions 1-7 as written 

above, with reaction 1 dominating reaction 2 and reaction 4 dominating reaction 5. The reduction of the 

iron corrosion rate for the CRA14-0 calculation should have a similar effect on the water balance as the 

refined repository water balance implementation by reducing the amount of gas produced and increasing 

the amount of water available.

A comparison of the results between the CRA14-BV and CRA14-0 is shown in Figure 2. Comparing the 

curves for the CRA14-BV and CRA14-0 shows that the potential magnitude of the impact of the water 

balance assumptions on the normalized releases from the repository is small. The small effect on 

normalized releases of the water balance assumptions is likely because direct brine releases are dominated 

by scenarios involving intrusions into a brine pocket, which increases repository pressure and floods the 

repository and hence, dominates the amount of water in the repository and overwhelms the gas and water 

balance.
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Table 5-1. GWB Brine Volumes Associated with Repository Chemical Processes and Modeled 

Cumulative Brine Flow for the Undisturbed PABC Scenario

Process Brine Volume Per Panel

Maximum Brine Consumed by MgO 

Hydration and Carbonation

Magnesite 0 m3

Brucite or hydromagnesite 3,175 m3

Maximum Brine Produced by Cellulose 

Degradation

Magnesite 988 m3

Hydromagnesite 649 m3

Maximum Brine Produced by Plastics 

Degradation

Magnesite 1,614 m3

Hydromagnesite 1,291 m3

Maximum Brine Produced by Rubber 

Degradation

Magnesite 170 m3

Hydromagnesite 116 m3

Maximum Total Brine Production by 

CPR Degradation (Cellulose + Plastics + 

Rubber

Magnesite 2,772 m3

Hydromagnesite 2,056 m3

Castile Brine (Clayton 2006) Maximum calculated in PABC 13,267 m3

Salado Brine (Clayton 2006) Maximum calculated in PABC 7,763 m3

Salado or Castile Brine (Clayton 2006) Minimum necessary for direct 

brine release

1,045 m3

Brine Consumed by Anoxic Corrosion Fe(OH)2 4,060 m3

0.25 FeS + 0.75 Fe(OH)2 2,030 m3

Figure 1. Table 5-1 from SCA (2008).

Figure 2. Simplified version of figure 3-46 from Zeitler (2013).
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References:

S. Cohen and Associates (SCA). 2008. Verification of the Waste Isolation Pilot Plant Chemistry 

Conceptual Models. September 19, 2008. Final Report prepared for the U.S. Environmental Protection 

Agency Office of Radiation and Indoor Air, Washington, D.C.

Telander, M.R., and Westerman, R.E. 1993. Hydrogen Generation by Metal Corrosion in Simulated 

Waste Isolation Pilot Plant Environments: Progress Report for the Period November 1989 through 

December 1992. SAND92-7347. Sandia National Laboratories, Albuquerque, NM.

Telander, M.R., and Westerman, R.E. 1997. Hydrogen Generation by Metal Corrosion in Simulated 

Waste Isolation Pilot Plant Environments. SAND96-2538. Sandia National Laboratories, Albuquerque, 

NM.

Torres-Rodríguez, D.A., and Pfeiffer, H. 2011.Thermokinetic Analysis of the MgO Surface Carbonation 

Process in the Presence of Water Vapor. Thermochimica Acta 516: 74–78.

*

U.S. DOE. 2009. Title 40 CFR Part 191 Subparts B and C Compliance Recertification Application for 

the Waste Isolation Pilot Plant Appendix MgO-2009 Magnesium Oxide as an Engineered Barrier. United 

States Department of Energy, Waste Isolation Pilot Plant, Carlsbad Field Office, Carlsbad, NM.

Xiong, Y.-L., and Lord, A.C.S. 2008. Experimental investigations of the reaction path in the MgO–CO2–

H2O system in solutions with various ionic strengths, and their applications to nuclear waste isolation. 

Applied Geochemistry, 23:1634–1659.

Xiong, Y.-L., and Snider, A.C. 2003. 4.3 Carbonation Rates of the Magnesium Oxide Hydration Product 

Brucite in Various Solutions, Sandia National Laboratories Technical Baseline Reports, p. 4.3-1–4.3-11, 

WBS 1.3.5.3, Compliance Monitoring; WBS 1.3.5.4, Repository Investigations, Milestone RI 03-210, 

January 31, 2003. ERMS526049. Sandia National Laboratories, Carlsbad, NM.

Zeitler, T.R. 2013. Analysis Package for CCDFGF: 2014 Compliance Recertification Application 

Performance Assessment (CRA-2014 PA). ERMS 560074. Sandia National Laboratories, Carlsbad, NM.

 

* Copyrighted reference not provided in Enclosure 2.
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EPA Comment

2-C-5 Cumulative Effects of Water Balance Assumptions on PA. The result of several water balance 

assumptions is to increase brine production from waste reactions in the repository. These assumptions 

include that hydrogen sulfide will preferentially react with iron hydroxide instead of metallic iron 

(Comment 2-C-3); that carbon dioxide will preferentially react with brucite instead of MgO (Comment 2-

C-3); and that the minimum rate of hydromagnesite conversion to magnesite is greater than zero 

(Comment 2-C-4). Please provide a description of the cumulative effects of these assumptions on the 

water balance calculations for the CRA-2014 PA.

DOE Response

The effect of assuming hydrogen sulfide will preferentially react with iron hydroxide instead of metallic 

iron on the performance assessment calculations is minimal (see response to comment 2-C-3). The effect 

of assuming carbon dioxide will preferentially react with brucite instead of magnesium oxide on the 

performance assessment calculations is minimal (see response to comment 2-C-3). Performance 

assessment calculations show a minimal effect with the assumption that the minimum rate of 

hydromagnesite conversion to magnesite is greater than zero (see response to comment 2-C-4). Each of 

these assumptions results in an increase in the amount of brine at earlier times, but the cumulative effect

of these three assumptions has a minor effect on performance assessment calculations (see response to 

comment 2-C-3).
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EPA Comment

2-32-S1 FEP H21 Drilling Fluid Flow. Screening argument considers only boreholes intersecting the 

waste region. Please supplement the argument with a discussion of boreholes that intersect the non-waste 

regions and the consequence to PA calculations. Provide references and specific information as to 

whether boreholes penetrating non-waste regions could result in the transport of radionuclides between 

the waste and non-waste regions, to overlying units, or to the surface. Provide information, either directly 

or by reference, as to how deep boreholes penetrating the non-waste and waste regions of the repository 

are accounted for in the PA.

2-32-S2 FEP H22 Drilling Fluid Loss. The screening argument considers flow into the repository from 

boreholes that intercept pressurized fluid in underlying formations but only for boreholes intersecting the 

waste region. In the current BRAGLO model gas and brine readily flow between the waste and non-waste 

regions. A discussion and analysis of boreholes that could intersect the non-waste regions and their 

impact on the PA needs to be provided.

2-32-S3 FEP H23 Blowouts. Screening argument considers only boreholes intersecting the waste region 

and also pressurized Castile brine. In the current BRAGLO model gas and brine readily flow between the 

waste and non-waste regions. Please supplement the argument with a discussion and analysis of 

boreholes that could intersect the non-waste regions on the PA.

DOE Response

Boreholes that intercept the non-waste regions (e.g., the operations and experimental areas) of the 

repository have been screened out of PA calculations since the CCA (DOE 1996). Additionally, early 

screening efforts demonstrated that drilling into a non-repository area of the controlled area 

(independently, within both the Salado and Culebra Formations) resulted in low consequences to the 

performance of the repository (Wallace 1996 and Economy 1996). No known recent events have 

occurred or new information become available that would weaken or render these determinations invalid. 

In fact, a recent analysis by Zeitler (2015), based on BRAGFLO results from the CRA-2014, strengthens 

the determination of drilling into non-repository areas being of low consequence. This analysis included 

the impacts of a run-of-mine (ROM) salt panel closure system (PCS).

The current BRAGFLO model does allow for brine and gas flow between the waste and non-waste 

regions, as has been the case since the CCA. A full discussion and analysis of boreholes intersecting nonwaste regions is contained in the Supplemental Peer Review Report (Wilson et al. 1996), in which the 

Conceptual Models Peer Review Panel (CMPRP) evaluated the conceptual model for the exploration 

borehole and raised questions regarding the justification for excluding inadvertent intrusions into the

operations and experimental areas of the repository from PA calculations. DOE’s response to this issue 

was partially based on the fact that even though intrusions into these areas of the repository could occur, 

since waste will not be disposed in these areas, releases from cuttings, cavings, and spallings could (by 

their definitions) not occur since waste will not be disposed in these areas. Radionuclides present in the 

repository could potentially be transported in brine into the operations and experimental areas and 

contaminated brine could be brought to the surface during drilling. However, because the operations and 

experimental areas of the repository are separated from the waste regions by panel closures that will 

greatly reduce brine flow, insignificant quantities of brine flows across this boundary.

To respond to the CMPRP, the DOE provided intermediate BRAGFLO results that demonstrated that the 

panel closures effectively limited brine movement. In their Supplemental Peer Review Report (Wilson et 

al. 1996), the CMPRP stated:
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“...with very few exceptions, the maximum brine flow through a panel seal was found in 

modeling results to be about 12,000 m3 following an E1 intrusion, and the expected flow 

would be about 3,000 m3

. Under undisturbed conditions, the cumulative brine inflow 

into the operations and experimental areas from all sources ranges from near zero to 

about 10,000 m3

 (see Figures 3-4 and 3-5). This flow would, on the average, be 

expected to result in approximately a twofold dilution of brine flowing in from the waste 

area following an E1 intrusion. Under disturbed conditions with intrusion boreholes 

penetrating the operations and experimental areas, the inflow of uncontaminated brine 

and the dilution of contaminated brine would be even greater.

In the event that the operations and experimental areas are penetrated by intrusion 

boreholes, approximately 12,000 m3 of brine could conceivably flow from these areas 

into the waste area. Performance assessment results indicate that total cumulative brine 

flow into the waste area is typically about 40,000 m3 following an E1 intrusion at 1,000 

years and about 30,000 m3 following an E2 intrusion at 1,000 years. Given that about six 

borehole intrusions are expected to occur during the regulatory time frame, the total 

volume of brine potentially available to flow into the waste area could exceed 100,000 

m3

. Although the actual volume of brine inflow will depend on the interrelationships 

among time of intrusion, repository creep closure, gas generation, repository pressure, 

and other factors, the modeling results indicate that sufficient brine is potentially 

available from other sources that an incremental supply of as much as 12,000 m3 would 

have no consequential effect on performance assessment results. However, if subsequent 

model modifications result in significantly smaller fluid volumes in the repository, the 

significance of this issue should be reevaluated.”

Thus, the CMPRP determined that the DOE had satisfactorily demonstrated that representing exploration 

boreholes and their effects in the experimental and operations areas of the repository was not necessary, 

and the representation of repository fluid flow and the exploration borehole was adequately incorporated 

into PA models.

To update the BRAGFLO results that were used by the CMPRP to make its decision, and verify that it 

remains appropriate to exclude boreholes in the operations and experimental areas from PA calculations, 

BRAGFLO results from replicate 1 of the CRA-2014 PA calculations are examined. The maximum brine 

flow through a panel closure is now about 8,000 m3 following an E1 intrusion, which occurred for brine 

flow across the panel closure separating the waste panel and southern rest of repository (SRoR) (Figure 

1). (BRAGFLO scenarios S2 and S3 consider E1 intrusions.) The expected northward flow across any 

panel closure is about 1,000 m3 (for brine flow across the panel closure separating the waste panel and 

SRoR).1 For undisturbed conditions (S1), the cumulative brine inflow into the operations and 

experimental areas from all sources ranges from 700 to 35,000 (Figure 2). This flow would, on average, 

result in about a seventeen-fold dilution of brine flowing in from the waste area following an E1 intrusion

(comparing (35,000 + 700)m3

/2 = 17,850m3 to 1,000m3).

 1 See Appendix PA-2014, Figure PA-12 for a representation of the BRAGFLO grid and the discrete grid sections 

(including the SRoR).
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Figure 1. Cumulative brine volume passing northward from the waste panel to the SRoR 

through the panel closure for the 100 vectors of replicate 1, scenario 2 (E1 intrusion at 350 

years) (from Zeitler 2015)

Figure 2. Cumulative brine flow into the experimental and operations areas for the 100 

vectors of replicate 1, scenario 1 (undisturbed repository) (from Zeitler 2015)
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The CRA-2014 PA results indicate that a total cumulative brine flow into the waste area (including the 

waste panel, northern rest of repository, and SRoR) is on average about 36,000 m3 following an E1 

intrusion at 1,000 years (S3) and about 20,500 m3 following an E2 intrusion at 1,000 years (S5). Given 

that about 7.5 borehole intrusions are expected to occur during the regulatory period, the total volume of 

brine potentially available to flow into the waste area could exceed 200,000 m3

. Thus, with an 

incremental supply of only 8,000 m3

, the same conclusion as the CMPRP can reached: [the additional 

brine volume] “would have no consequential effect on performance assessment results.” Compared to the 

previous analysis, the maximum brine flow across a panel closure has decreased (12,000 to 8,000 m3

) and 

the total volume of brine potentially available to flow into the waste area has stayed the same (210,000 to 

209,500 m3

). Thus, the relative amount of “incremental supply” of brine has decreased from 

12,000/210,000=0.0571 to 8,000/209,500=0.038, indicating approximately a 33 percent decrease in the 

relative amount of brine available in the non-waste regions of the repository. Therefore, boreholes that 

intersect the non-waste regions of the repository still do not need to be accounted for in PA calculations.

The following text for FEPs H21, H22, and H23 incorporate references to previous screening work 

(Wallace 1996 and Economy 1996), as well as the new analysis using CRA-2014 described above. 

Changes to the text for FEPs H21, H22, and H23 are shown in blue font below.

SCR-5.2.1.1 FEP Number: H21

FEP Title: Drilling Fluid Flow

SCR-5.2.1.1.1 Screening Decision: SO-C (HCN)

DP (Future)

Drilling Fluid Flow associated with historical, current, near-future, and future boreholes 

that do not intersect the waste disposal region has been eliminated from PA calculations 

on the basis of low consequence to the performance of the disposal system. The 

possibility of a future deep borehole penetrating a waste panel, such that drilling-induced 

flow results in transport of radionuclides to the land surface or to overlying hydraulically 

conductive units, is accounted for in PA calculations. The possibility of a deep borehole 

penetrating both the waste disposal region and a Castile brine reservoir is accounted for 

in PA calculations.

SCR-5.2.1.1.2 Summary of New Information

No new information that affects the screening of this FEP has been identified since the 

CRA-2009.The screening argument for this FEP has been updated to reference new 

confirmatory screening analyses (Zeitler 2015) that support the determination by the 

Conceptual Models Peer Review Panel (Wilson et al. 1996) that boreholes into the 

experimental and operational areas do not need to be considered in PA calculations.

SCR-5.2.1.1.3 Screening Argument

Borehole circulation fluid could be lost to thief zones encountered during drilling, or fluid 

could flow from pressurized zones through the borehole to the land surface (blowout) or 

to a thief zone. Such drilling-related EPs could influence groundwater flow and, 

potentially, radionuclide transport in the affected units. Future drilling within the 

controlled area could result in direct releases of radionuclides to the land surface or 

transport of radionuclides between hydraulically conductive units.
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Movement of brine from a pressurized zone through a borehole into potential thief zones 

such as the Salado interbeds or the Culebra could result in geochemical changes and 

altered radionuclide migration rates in these units.

SCR-5.2.1.1.3.1 Historical, Current, and Near-Future Human EPs

Drilling fluid flow is a short-term event that can result in the flow of pressurized fluid 

from one geologic stratum to another. However, long-term flow through abandoned 

boreholes would have a greater hydrological impact in the Culebra than a short-term 

event such as drilling-induced flow outside the controlled area. Wallace (1996a) analyzed 

the potential effects of flow through abandoned boreholes in the future within the 

controlled area, and concluded that interconnections between the Culebra and deep units 

could be eliminated from PA calculations on the basis of low consequence. Thus, the 

HCN of drilling fluid flow associated with boreholes outside the controlled area has been 

screened out on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H25 through H36 (Sections SCR-5.2.1.5, SCR-5.2.1.6, SCR5.2.1.7, SCR-5.2.1.8, SCR-5.2.1.9, SCR-5.2.1.10, SCR-5.2.1.11, SCR-5.2.1.12, and 

SCR-5.2.1.1), drilling associated with water resources exploration, groundwater 

exploitation, potash exploration, oil and gas exploration, oil and gas exploitation, 

enhanced oil and gas recovery, and drilling to explore other resources has taken place or 

is currently taking place outside the controlled area in the Delaware Basin. These drilling 

activities are expected to continue in the vicinity of the WIPP in the near future.

SCR-5.2.1.1.3.2 Future Human EPs

For the future, drill holes may intersect the waste disposal region and their effects could 

be more profound. Thus, the possibility of a future borehole penetrating a waste panel, so 

that drilling fluid flow and, potentially, blowout results in transport of radionuclides to 

the land surface or to overlying hydraulically conductive units, is accounted for in PA 

calculations. Drilling events through the experimental and operational regions of the 

repository are not accounted for in PA calculations as it was determined that they could 

be excluded due to low consequence (Wilson et al. 1996). This conclusion of low 

consequence was recently reconfirmed by Zeitler (2015). This new analysis uses the 

latest PA results and updates the low consequence brine flow justification analyses 

discussed in Wilson et al. (1996), where it was determined that insignificant amounts of 

brine flow from the repository to the non-waste areas do not have a consequence on PA 

results. Additionally, drilling into a contaminated zone outside the waste area but within 

the controlled area was screened out due to low consequence (Economy 1996).

The units intersected by the borehole may provide sources for fluid flow (brine, oil, or 

gas) to the waste panel during drilling. In the vicinity of the WIPP, the Castile that 

underlies the Salado contains isolated volumes of brine at fluid pressures greater than 

hydrostatic. A future borehole that penetrates a Castile brine reservoir could provide a 

connection for brine flow from the reservoir to the waste panel, thus increasing fluid 

pressure and brine volume in the waste panel. The possibility of a deep borehole 

penetrating both a waste panel and a brine reservoir is accounted for in PA calculations.

Penetration of an underpressurized unit underlying the Salado could result in flow and 

radionuclide transport from the waste panel to the underlying unit during drilling, 

although drillers would minimize such fluid loss to a thief zone through the injection of 
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materials to reduce permeability or through the use of casing and cementing. Also, the 

permeabilities of formations underlying the Salado are less than the permeability of the 

Culebra (Wallace 1996a). Thus, the consequences associated with radionuclide transport 

to an underpressurized unit below the waste panels during drilling will be less significant, 

in terms of disposal system performance, than the consequences associated with 

radionuclide transport to the land surface or to the Culebra during drilling. Through this 

comparison, drilling events that result in penetration of underpressurized units below the 

waste-disposal region have been eliminated from PA calculations on the basis of 

beneficial consequence to the performance of the disposal system.

SCR-5.2.1.2 FEP Number: H22

FEP Title: Drilling Fluid Loss

SCR-5.2.1.2.1 Screening Decision: SO-C (HCN)

DP (Future)

Drilling Fluid Loss associated with HCN and future boreholes that do not intersect the 

waste disposal region has been eliminated from PA calculations on the basis of low 

consequence to the performance of the disposal system. The possibility of a future 

Drilling Fluid Loss into waste panels is accounted for in PA calculations.

SCR-5.2.1.2.2 Summary of New Information

No new information that affects the screening of this FEP has been identified since the 

CRA-2009. The screening argument for this FEP has been updated to reference new 

confirmatory screening analyses (Zeitler 2015) that support the determination by the 

Conceptual Models Peer Review Panel (Wilson et al. 1996) that boreholes into the 

experimental and operational areas do not need to be considered in PA calculations.

SCR-5.2.1.2.3 Screening Argument

Drilling fluid loss is a short-term event that can result in the flow of pressurized fluid 

from one geologic stratum to another. Large fluid losses would lead a driller to inject 

materials to reduce permeability, or it would lead to the borehole being cased and 

cemented to limit the loss of drilling fluid. Assuming such operations are successful, 

drilling fluid loss in the near future outside the controlled area will not significantly affect 

the hydrology of the disposal system. Thus, drilling fluid loss associated with historical, 

current, and near-future boreholes has been eliminated from PA calculations on the basis 

of low consequence to the performance of the disposal system.

In evaluating the potential consequences of drilling fluid loss to a waste panel in the 

future, two types of drilling events need to be considered – those that intercept 

pressurized fluid in underlying formations such as the Castile (defined in the CCA, 

Chapter 6.0, Section 6.3.2.2 as E1 events), and those that do not (E2 events). A possible 

hydrological effect would be to make a greater volume of brine available for gas 

generation processes and thereby increase gas volumes at particular times in the future. 

For either type of drilling event, on the basis of current drilling practices, the driller is 

assumed to pass through the repository rapidly. Relatively small amounts of drilling fluid 

loss might not be noticed and might not give rise to concern. Larger fluid losses would 
5th Response Submittal to the EPA Enclosure 1

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lead to the driller injecting materials to reduce permeability, or to the borehole being 

cased and cemented, to limit the loss of drilling fluid.

For boreholes that intersect pressurized brine reservoirs, the volume of fluid available to

flow up a borehole will be significantly greater than the volume of any drilling fluid that 

could be lost. This greater volume of brine is accounted for in PA calculations, and is 

allowed to enter the disposal room (see the CCA, Chapter 6.0, Section 6.4.7). Thus, the 

effects of drilling fluid loss will be small by comparison to the potential flow of brine 

from pressurized brine reservoirs. Therefore, the effects of drilling fluid loss for E1 

drilling events have been eliminated from PA calculations on the basis of low 

consequence to the performance of the disposal system.

The consequences of drilling fluid loss into waste panels in the future are accounted for 

in PA calculations for E2 events.

SCR-5.2.1.2.3.1 Historical, Current, and Near-Future Human EPs

Drilling fluid flow will not affect hydraulic conditions in the disposal system significantly 

unless there is substantial drilling fluid loss to a thief zone, such as the Culebra. 

Typically, zones into which significant borehole circulation fluid is lost are isolated 

through injection of materials to reduce permeability or through casing and cementing 

programs. Assuming such operations are successful, drilling fluid loss in the near future 

outside the controlled area will not affect the hydrology of the disposal system 

significantly and will be of no consequence.

SCR-5.2.1.2.3.2 Future Human EPs

The consequences of drilling within the controlled area in the future will primarily 

depend on the location of the borehole. Potentially, future deep drilling could penetrate 

the waste disposal region. Hydraulic and geochemical conditions in the waste panel 

could be affected as a result of drilling fluid loss to the panel. Drilling fluid loss due to 

drilling through the experimental and operational regions of the repository are not 

accounted for in PA calculations as it was determined that such drillholes could be 

excluded due to low consequence (Wilson et al. 1996). This conclusion of low 

consequence was recently reconfirmed by Zeitler (2015). This new analysis uses the 

latest PA results and updates the low consequence brine flow justification analyses 

discussed in Wilson et al. (1996) where it was determined that insignificant amounts of 

brine flows from the repository to the non-waste areas do not have a consequence on PA 

results.

Penetration of an underpressurized unit underlying the Salado could result in flow and 

radionuclide transport from the waste panel to the underlying unit during drilling, 

although drillers would minimize such fluid loss to a thief zone through the injection of 

materials to reduce permeability or through the use of casing and cementing. Also, the 

permeabilities of formations underlying the Salado are less than the permeability of the 

Culebra (Wallace 1996a). Thus, the consequences associated with radionuclide transport 

to an underpressurized unit below the waste panels during drilling will be less significant, 

in terms of disposal system performance, than the consequences associated with 

radionuclide transport to the land surface or to the Culebra during drilling. Through this 

comparison, drilling events that result in penetration of underpressurized units below the 
5th Response Submittal to the EPA Enclosure 1

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waste-disposal region have been eliminated from PA calculations on the basis of 

beneficial consequence to the performance of the disposal system.

For boreholes that do not intersect pressurized brine reservoirs (but do penetrate the 

waste-disposal region), the treatment of the disposal room implicitly accounts for the 

potential for greater gas generation resulting from drilling fluid loss. Thus, the 

hydrological effects of drilling fluid loss for E2 drilling events are accounted for in PA 

calculations within the conceptual model of the disposal room for drilling intrusions.

SCR-5.2.1.3 FEP Number: H23

FEP Title:Blowouts

SCR-5.2.1.3.1 Screening Decision: SO-C (HCN)

DP (Future)

Blowouts associated with HCN and future boreholes that do not intersect the waste 

disposal region have been eliminated from PA calculations on the basis of low 

consequence to the performance of the disposal system. The possibility of a future deep 

borehole penetrating a waste panel such that drilling-induced flow results in transport of 

radionuclides to the land surface or to overlying hydraulically conductive units is 

accounted for in PA calculations. The possibility of a deep borehole penetrating both the 

waste disposal region and a Castile brine reservoir is accounted for in PA calculations.

SCR-5.2.1.3.2 Summary of New Information

Blowouts are implemented in PA through the parameter GLOBAL:PBRINE, which 

represents the probability of an inadvertent intrusion borehole encountering pressurized 

brine beneath the repository. This parameter has been updated based on new data and 

analysis as reported in Kirchner et al. (2012). This parameter update does not change the 

screening argument or decision; H23 Blowouts continue to be classified as DP for the 

future timeframe. The screening argument for this FEP has also been updated to 

reference new confirmatory screening analyses (Zeitler 2015) that support the 

determination by the Conceptual Models Peer Review Panel (Wilson et al. 1996) that 

boreholes (and any associated blowouts) into the experimental and operational areas do 

not need to be considered in PA calculations. This new analysis uses the latest PA results 

and updates the low consequence brine flow justification analyses discussed in Wilson et 

al. (1996), where it was determined that insignificant amounts of brine flows from the 

repository to the non-waste areas do not have a consequence on PA results.

SCR-5.2.1.3.3 Screening Argument

Blowouts are short-term events that can result in the flow of pressurized fluid from one 

geologic stratum to another. For the near future, a blowout may occur in the vicinity of 

the WIPP but is not likely to affect the disposal system because of the distance from the 

well to the waste panels, assuming that AICs are in place which restrict borehole 

installation to outside the WIPP boundary. Blowouts associated with HCN and future 

boreholes that do not intersect the waste disposal region have been eliminated from PA 

calculations on the basis of low consequence to the performance of the disposal system. 

For the future, the drill holes may intersect the waste disposal region and these effects 

could be more profound. Thus, blowouts that occur in the waste area of the repository are 
5th Response Submittal to the EPA Enclosure 1

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included in the assessment of future activities, and their consequences are accounted for 

in PA calculations. Blowouts that occur in the non-waste regions of the repository in the 

future are not included in PA calculations as both Wilson et al. (1996) and Zeitler (2015) 

have demonstrated that these events are inconsequential to repository performance.

Fluid could flow from pressurized zones through the borehole to the land surface 

(blowout) or to a thief zone. Such drilling-related EPs could influence groundwater flow 

and, potentially, radionuclide transport in the affected units. Movement of brine from a 

pressurized zone through a borehole into potential thief zones such as the Salado 

interbeds or the Culebra could result in geochemical changes and altered radionuclide 

migration rates in these units.

SCR-5.2.1.3.3.1 Historical, Current, and Near-Future Human EPs

Drilling associated with water resources exploration, groundwater exploitation, potash 

exploration, oil and gas exploration, oil and gas exploitation, enhanced oil and gas 

recovery, and drilling to explore other resources has taken place or is currently taking 

place outside the controlled area in the Delaware Basin. These drilling activities are 

expected to continue in the vicinity of the WIPP in the near future.

Naturally occurring brine and gas pockets have been encountered during drilling in the 

Delaware Basin. Brine pockets have been intersected in the Castile (as discussed in the 

CCA, Chapter 2.0, Section 2.2.1.2). Gas blowouts have occurred during drilling in the 

Salado. Usually, such events result in brief interruptions in drilling while the intersected 

fluid pocket is allowed to depressurize through flow to the surface (for a period lasting 

from a few hours to a few days). Drilling then restarts with an increased drilling mud 

weight. Under these conditions, blowouts in the near future will cause isolated hydraulic 

disturbances, but will not affect the hydrology of the disposal system significantly.

Potentially, the most significant disturbance to the disposal system could occur if an 

uncontrolled blowout during drilling resulted in substantial flow through the borehole 

from a pressurized zone to a thief zone. For example, if a borehole penetrates a brine 

reservoir in the Castile, brine could flow through the borehole to the Culebra over the 

long term and, as a result, could affect hydraulic conditions in the Culebra. The potential 

effects of such an event can be compared to the effects of long-term fluid flow from deep 

overpressurized units to the Culebra through abandoned boreholes. Wallace (1996a) 

analyzed the potential effects of flow through abandoned boreholes in the future within 

the controlled area and concluded that interconnections between the Culebra and deep 

units could be eliminated from PA calculations on the basis of low consequence. Longterm flow through abandoned boreholes would have a greater hydrological impact in the 

Culebra than short-term, drilling-induced flow outside the controlled area. Thus, the 

effects of fluid flow during drilling in the near future have been eliminated from PA 

calculations on the basis of low consequence to the performance of the disposal system.

In summary, blowouts associated with historical, current, and near-future boreholes have 

been eliminated from PA calculations on the basis of low consequence to the 

performance of the disposal system.
5th Response Submittal to the EPA Enclosure 1

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SCR-5.2.1.3.3.2 Future Human EPs—Boreholes that Intersect the Waste Disposal 

Region

The consequences of drilling within the controlled area in the future will depend 

primarily on the location of the borehole. Potentially, future deep drilling could penetrate 

the waste disposal region. If the borehole intersects the waste in the disposal rooms, 

radionuclides could be transported as a result of drilling fluid flow, e.g., releases to the 

accessible environment may occur as material entrained in the circulating drilling fluid is 

brought to the surface. Also, during drilling, contaminated brine may flow up the 

borehole and reach the surface, depending on fluid pressure within the waste disposal 

panels; blowout conditions could prevail if the waste panel were sufficiently pressurized 

at the time of intrusion.

SCR-5.2.1.3.3.3 Hydraulic Effects of Drilling-Induced Flow

The possibility of a future borehole penetrating a waste panel, so that drilling fluid flow

and, potentially, blowout result in transport of radionuclides to the land surface or to 

overlying hydraulically conductive units, is accounted for in PA calculations. The 

hydraulic effects of drilling through the experimental and operational regions of the 

repository are not accounted for in PA calculations as it was determined that they could 

be excluded due to low consequence (Wilson et al. 1996). This determination of low 

consequence was recently reconfirmed by Zeitler (2015). This new analysis uses the 

latest PA results and updates the low consequence brine flow justification analyses 

discussed in Wilson et al. (1996), where it was determined that insignificant amounts of 

brine flows from the repository to the non-waste areas do not have a consequence on PA 

results.

The units intersected by the borehole may provide sources for fluid flow (brine, oil, or 

gas) to the waste panel during drilling. In the vicinity of the WIPP, the Castile that 

underlies the Salado contains isolated volumes of brine at fluid pressures greater than 

hydrostatic. A future borehole that penetrates a Castile brine reservoir could provide a 

connection for brine flow from the reservoir to the waste panel, thus increasing fluid 

pressure and brine volume in the waste panel. The possibility of a deep borehole 

penetrating both a waste panel and a brine reservoir is accounted for in PA calculations.

Future boreholes could affect the hydraulic conditions in the disposal system. 

Intersection of pockets of pressurized gas and brine would likely result in short-term, 

isolated hydraulic disturbances, and will not affect the hydrology of the disposal system 

significantly. Potentially the most significant hydraulic disturbance to the disposal 

system could occur if an uncontrolled blowout during drilling resulted in substantial flow 

through the borehole from a pressurized zone to a thief zone. For example, if a borehole 

penetrates a brine reservoir in the Castile, brine could flow through the borehole to the 

Culebra and, as a result, could affect hydraulic conditions in the Culebra. The potential 

effects of such an event can be compared to the effects of long-term fluid flow from deep 

overpressurized units to the Culebra through abandoned boreholes. Wallace (1996a) 

analyzed the potential effects of such interconnections in the future within the controlled 

area (but that do not intersect waste), and concluded that flow through abandoned 

boreholes between the Culebra and deep units could be eliminated from PA calculations 

on the basis of low consequence.

These changes have been added to Enclosure 4, CRA-2014 Errata Tracking.
5th Response Submittal to the EPA Enclosure 1

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References:

Economy, K. 1996. “Drilling Into a Salado Zone of Contamination Within the Controlled Area; Drilling 

Into a Non-Salado Zone of Contamination Within the Controlled Area.” Summary Memo of Record for 

S-9 and NS-6 FEPs Screening. August 21, 1996. ERMS 416368. Sandia National Laboratories,

Albuquerque, NM.

Wallace, M. 1996. “Leakage from Abandoned Boreholes.” Summary Memorandum of Record for NS7b, SWCF-A 1.1.6.3:PA:QA:TSK:NS-7b. ERMS 240819. Sandia National Laboratories, Albuquerque, 

NM.

Wilson, C., D. Porter, J. Gibbons, E. Oswald, G. Sjoblom, and F. Caporuscio. 1996. Conceptual Models 

Supplementary Peer Review Report (December). ERMS 243153. Carlsbad Area Office, Carlsbad, NM.

U.S. Department of Energy (DOE). 1996. Title 40 CFR Part 191 Compliance Certification Application 

for the Waste Isolation Pilot Plant (October). 21 vols. DOE/CAO-1996-2184. Carlsbad Field Office, 

Carlsbad, NM.

Zeitler, T. 2015. “Evaluation of Brine Flow Through Panel Closures using CRA-2014 BRAGFLO 

Results.” Summary Memo to Records. June 2015. ERMS Pending. Sandia National Laboratories,

Carlsbad, NM.
5th Response Submittal to the EPA Enclosure 1

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EPA Comment

2-32-S6 FEP W1 Disposal Geometry. In the screening argument please provide evidence that the 

modeled excavated volume is the expected mined volume of the underground workings at the time of 

closure.

DOE Response

Consistent with the DOE’s response to EPA comment 2-32-G1, this type of information is best left in the 

supporting documentation, rather than within the screening document. With regard to the actual mined 

volume modeled in PA, please see DOE’s response to EPA Comment 1-23-7 (Franco 2015).

Reference:

Franco, J.R. 2015. Letter to J. Edwards (Subject: Response to Environmental Protection Agency Letter 

Dated December 17, 2014 Regarding the 2014 Compliance Recertification Application). March 18, 

2015. U.S. Department of Energy, Carlsbad Field Office, Carlsbad, NM.
5th Response Submittal to the EPA Enclosure 1

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EPA Comment

2-32-S11 FEP W20 Salt Creep. Please supplement the screening argument with a discussion of salt 

creep and consolidation to the ROM salt in the ROMPCS, and healing of the adjacent DRZ. Such a 

discussion can be found in Camphouse et al. (2012, Section 2.0. ERMS 557396). The screening argument 

for this FEP states that “Salt creep in the Salado is accounted for in PA calculations (the CCA, Chapter 

6.0, Section 6.4.3.1).” The cited CCA section discusses these FEPs only in the context of the waste 

region. In addition, this is the only FEP that addresses DRZ healing, which is expected to vary spatially.

2-32-S12 FEP W21 Changes in the Stress. Screening argument was combined with that for W20 Salt 

Creep; please see comments for FEP W20. Additionally, please supplement the screening argument with 

discussions of 1) the coupling between consolidation of the ROM salt in the ROMPCS and healing of the 

adjacent DRZ (DRZ healing cannot occur until the ROM salt is consolidated and applies a back stress 

sufficient to compress and heal the DRZ); and 2) lateral extrusion of the ROM salt when under 

compressive stress from drift creep closure.

DOE Response

The screening argument and decision for these FEPs have not changed, however, the following pointers 

will be placed in Appendix SCR-2014 to more precisely define where the new ROM salt panel closures 

are described and how they are implemented within PA. Changes are shown in blue font below.

SCR-6.3.1.2 FEP Numbers: W20 and W21

FEP Titles: Salt Creep (W20)

Change in the Stress Field

(W21)

SCR-6.3.1.2.1 Screening Decision: UP

Salt Creep in the Salado and any resultant Changes in the Stress Field are accounted for 

in PA calculations.

SCR-6.3.1.2.2 Summary of New Information

Salt creep and changes in stress will affect the consolidation of the ROM salt PCS over 

time. Modifications to relevant parameters are described in Camphouse (2013a). 

Implementation of the new ROM salt PCS is described in Appendix PA-2014, Section 

PA-4.2.8, and Appendix MASS-2014, Section MASS-4.1.3. These changes are 

downstream of the FEPs screening process, and will not change the screening decision; 

these FEPs will remain classified UP.

SCR-6.3.1.2.3 Screening Argument

Salt creep will lead to changes in the stress field, compaction of the waste and containers, 

and consolidation of the long-term components of the sealing system. It will also tend to 

close fractures in the DRZ, leading to reductions in porosity and permeability, increases 

in pore fluid pressure, and reductions in fluid flow rates in the repository. Salt creep in 

the Salado is accounted for in PA calculations (the CCA, Chapter 6.0, Section 6.4.3.1). 

The long-term repository seal system relies on the consolidation of the crushed-salt seal 

material and healing of the DRZ around the shaft seals and in and around the panel 

closures to achieve a low permeability under stresses induced by salt creep. Shaft seal 
5th Response Submittal to the EPA Enclosure 1

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and panel closure performance is discussed further in Section SCR-6.3.5.1 (FEPs W36, 

W37, W113, and W114).

This change has been added to Enclosure 4, CRA-2014 Errata Tracking.
5th Response Submittal to the EPA Enclosure 1

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EPA Comment

2-32-S13 FEP W25 Disruption Due to Gas Effects. Please supplement the screening argument with a 

discussion of the potential for high waste panel gas pressures to delay the consolidation of the ROM salt, 

thereby maintaining a higher permeability in the PCS for a longer period of time.

DOE Response

The current parameters used in the implementation of the ROMPCS are described in Appendix PA, 

Section PA-4.2.8 and its supporting references. Gas pressurization effects were not considered in the 

consolidation of the ROMPCS because physical (creep) closure and complete consolidation are expected 

to occur before significant gas pressures can develop. Figure 6-1 of Camphouse (2013) indicates gas 

pressures will be below lithostatic pressure for 1000 years or more, supporting this assertion. Because 

gas pressures are not expected to affect the ROMPCS final permeability, this FEP argument has not been 

changed.

Reference:

Camphouse, C. 2013. Analysis Package for Salado Flow Modeling Done in the 2014 Compliance 

Recertification Application Performance Assessment (CRA-2014 PA). Revision 0. April 30, 2013. 

ERMS 559980. Sandia National Laboratories, Carlsbad, NM.
5th Response Submittal to the EPA Enclosure 1

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EPA Comment

2-32-S14 FEP W27 Gas Explosions. Please update the screening argument to reflect the LANL 

inventory with nitrates and added organic matter that resulted in an exothermic reaction.

DOE Response

The Accident Investigation Board report (DOE 2015) and the Technical Assistance Team report (SRNL 

2015) specifically say that there was no evidence of an explosion. Both reports cite the steep angle of 

repose for the MgO as good evidence that there was no explosion. Both conclude that the radiological 

release was the result of an incompatible mixture that heated up, pressurizing the drum to the point of 

venting and igniting nearby flammable emplacement materials. Therefore, the DOE believes that this 

type of information is best described in FEP W72, Exothermic Reactions (see following DOE response to 

EPA Comment 2-32-S21).

References:

DOE (U.S. Department of Energy). 2015. Accident Investigation Report. Phase 2. Radiological Release 

Event at the Waste Isolation Pilot Plant, February 14, 2014. April 2015. U.S. Department of Energy, 

Office of Environmental Management. 

SRNL (Savannah River National Laboratory). 2015. Waste Isolation Pilot Plant Technical Assessment 

Team Report. March 17, 2015. Revision 0. SRNL-RP-2014-01198. Savannah River National 

Laboratory, Aiken, SC.
5th Response Submittal to the EPA Enclosure 1

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EPA Comment

2-32-S21 FEP W72 Exothermic Reactions. Please supplement the screening argument with a 

discussion of the impact of exothermic reactions in the waste panels.

DOE Response

It is clear that the event of February 14, 2014, has no effect on compliance with 40 CFR 191 Subparts B 

and C (or the CRA-2014), primarily because it occurred during the operational timeframe and not the 

post-closure disposal period. Additionally, this accident was the result of operational and administrative 

deficiencies and should not be considered a normally anticipated event. Procedural changes and 

safeguards will be implemented to assure that such incompatibilities will not occur within waste drums in 

the future. For these reasons, the screening argument has not been changed to assume that such events 

will occur in the future. The screening argument will, however, be changed to describe the incident and 

the processes that are understood to have occurred. This event and resulting administrative changes 

should be considered as operational period activities and have no bearing upon the long-term conditions 

within the repository.

With regard to this specific event, while nitrate is not depleted by anoxic conditions, it does react with 

cellulose and will likely be reacting during the operational phase of the repository until the nitrate salts 

are depleted. However, rather than resulting in a thermal runaway, the more likely scenario of nitrate 

depletion, which has been observed in sibling containers being stored and monitored at LANL, is by 

smooth oxidation that does not give rise to a thermal runaway. These reactions reduce the nitrate salts,

with a concomitant oxidation of the cellulose, to produce carbon and nitrogen oxides and other products 

of combustion. Although not seen in the gas phase, metal oxides are also produced. The heat of reaction 

on these monitored drums has not been detected by the external thermocouples because it is dissipated as 

fast as it is formed. However, the gaseous products are easily detected by gas chromatography, so it is 

clear that the reaction is ongoing but the rate is slow and therefore the impact is small, resulting in no loss 

of containment. While the oxidation by nitrate does produce heat, this heat load is already bounded by 

the CPR being converted to gas (the calorie release from the nitrate oxidation of cellulose is very similar 

to the calorie release from the air oxidation of cellulose). It is expected that the exothermic heat load 

from these reactions will be fairly small compared to the heat capacity of the quantity of salt in the 

repository. The impact of exothermic reactions from the presence of waste with nitrate salts is expected 

to be insignificant and is not included in PA.

The following text from Appendix SCR-2014 presents an updated screening argument for FEP W72 

Exothermic Reactions has been provided to reflect the February 2014 event. Changes are shown in blue 

font.
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SCR-6.3.4.1 FEP Numbers: W29, W30, W31, W72, and W73

FEP Titles: Thermal Effects on Material 

Properties (W29)

Thermally-Induced Stress Changes

(W30)

Differing Thermal Expansion of 

Repository Components (W31)

Exothermic Reactions (W72)

Concrete Hydration (W73)

SCR-6.3.4.1.1 Screening Decision: SO-C

The effects of Thermally-Induced Stress, Differing Thermal Expansion of Repository 

Components, and Thermal Effects on Material Properties in the repository have been 

eliminated from PA calculations on the basis of low consequence to performance of the 

disposal system.

The thermal effects of Exothermic Reactions, including Concrete Hydration, have been 

eliminated from PA calculations on the basis of low consequence to the performance of 

the disposal system.

SCR-6.3.4.1.2 Summary of New Information

This FEP has been updated to include the most recent inventory information as presented 

in Van Soest (2012). Thermal calculations have been updated with the updated quantities 

of reactants and provided below. Additionally, planned Salt Disposal Investigations 

(SDI) experiments as detailed in Patterson (2011) or the Salt Defense Disposal 

Investigations (SDDI) (Franco 2012) will place heaters in newly excavated tunnels in the 

northern experimental region of the WIPP. Mining has been completed, but heater tests 

have not yet commenced. An evaluation conducted by Kuhlman (2011) for the SDI 

planned change notice (PCN) shows that any thermal pulse from these experiments will 

be very minimal, on the order of 0.02 °C or less. Therefore, the screening argument and 

decision for this FEP is unaffected by the conduct of these experiments. 

On February 14, 2014, an exothermic reaction involving the mixture of the organic 

materials (Swheat Scoop® absorbent and/or neutralizer) and nitrate salts occurred inside a 

waste drum emplaced in Room 7 of Panel 7. This exothermic reaction resulted in 

pressurization of the drum, failure of the drum locking ring, and displacement of the 

drum lid. The visual evidence associated with the identified breach was consistent with 

an exothermic reaction within the drum. This reaction led to pressure buildup of 

combustible gases within the drum. The drum lid extruded beyond the lid retention 

ring, deflected the lid, and resulted in rapid release of the materials from the drum. The 

combustible gases and solids ignited, which then spread to other combustible materials 

within the waste array, i.e., fiberboard and polyethylene slip sheets, reinforcement plates, 

stretch wrap, cardboard stiffeners and polypropylene super sack fabric. The cause of this 

event has been identified by the Accident Investigation Board (DOE 2015) as being a 

specific deficiency that, “if corrected, would prevent recurrence of the same accident.”
5th Response Submittal to the EPA Enclosure 1

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SCR-6.3.4.1.3 Screening Argument

Thermally induced stress could result in pathways for groundwater flow in the DRZ, in 

the anhydrite layers and MBs, and through seals, or it could enhance existing pathways. 

Conversely, elevated temperatures will accelerate the rate of salt creep and mitigate 

fracture development. Thermal expansion could also result in uplift of the rock and 

ground surface overlying the repository, and thermal buoyancy forces could lift the waste 

upward in the salt rock.

The distributions of thermal stress and strain changes depend on the induced temperature 

field and the differing thermal expansion of components of the repository, which depends 

on the components’ elastic properties. Thermal effects on material properties (such as 

permeability and porosity) could potentially affect the behavior of the repository.

Exothermic reactions expected in the WIPP repository include MgO hydration, MgO 

carbonation, aluminum (Al) corrosion, and cement hydration1 (Bennett et al. 1996). 

Wang (1996) has shown that the temperature rise by an individual reaction is 

proportional to , where V is the maximum rate of brine inflow into a waste panel 

for a reaction limited by brine inflow (or a specified maximum reaction rate for a reaction 

limited by its own kinetics) and M is the quantity of the reactant. MgO hydration, cement 

hydration, and Al corrosion are assumed to be limited by brine inflow because they all 

consume water and have high reaction rates. The amounts of reactants are tabulated in 

Table SCR-3.

Table SCR-3. Changes in Inventory Quantities from the CCA to the CRA-2014

SCR-1.1.1Inventory CCA CRA-2004 CRA-2009 CRA-2014

MgO (tons) 85,600a 72,760 (because of the 

elimination of minisacks)a

59,385e 51,430h

Cellulosics (tons) 5,940b 8,120c 8,907f 5,127i

Plastics (tons) 3,740b 8,120c 10,180f 10,487i

Rubber (tons) 1,100b 1,960c 1,885f 1,379i

Aluminum alloys (tons) 1,980b 1,960c 2,030f 504i

Cement (tons) 8,540b 9,971d 13,888g 11872j

a U.S. DOE (2000a) b U.S. DOE (1996b). Only CH-TRU wastes are considered. Total volume of CH-TRU wastes is 1.1 × 105 m3

. This is not scaled to WIPP disposal volume. c Appendix DATA-2004, Attachment F. Only CH-TRU wastes are considered. Total volume of CH-TRU waste is 1.4 × 105 m3

. This is not scaled to WIPP 

disposal volume. d This estimate is derived from data in Leigh (2003) and includes both reacted and unreacted cement (1.2 × 107 kg × 1.4 × 105

/168485/1000 kg/ton = 9971 tons 

cement). e This estimate is derived by assuming that Panel 1 has an MgO excess factor of 1.95, three panel equivalents have a 1.67 excess factor, and the remaining 6 

panel equivalents have a 1.2 excess factor, resulting in a 1.416 projected excess factor for a full repository. The projected excess factor is then multiplied by 

the equivalent cellulose value of 28,098 × (40.3/27) (the MgO molar ratio). f This value is derived using material densities reported in Leigh et al. (2005b), and total CH-TRU waste volume (1.45 × 105 m3 reported in Leigh et al. (2005a)). g This value is derived from data in Leigh (2003) and Leigh et al. (2005a). ((1.2 × 107 kg) × 39/29 × (1.45 × 105

)/168485/1000 kg/ton = 13,888 tons cement). h

 This estimate is derived by assuming that Panel 1 has an MgO excess factor of 1.95, three panel equivalents have a 1.67 excess factor, and the remaining 6 panel 

equivalents have a 1.2 excess factor, resulting in a 1.416 projected excess factor for a full repository. The projected excess factor is then multiplied by the 

equivalent cellulose value of 24,334 × (40.3/27) (the MgO molar ratio). i

 This value is derived from Van Soest (2012) and contains CH, RH, packaging, and emplacement materials. 

j

 This value is derived from Van Soest (2012) and contains reacted and unreacted cements for both CH and RH wastes.

 1 Only materials in the waste are included in these calculations. Other materials such as concrete in shaft seals have 

not been included because their effects occur prior to final repository closure or shortly thereafter and have no 

impact on repository performance. 

VM
5th Response Submittal to the EPA Enclosure 1

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Similarly, MgO carbonation, which consumes CO2, is limited by CO2 generation from 

microbial degradation. Given a biodegradation rate constant, the total CO2 generated per 

year is proportional to the total quantity of biodegradable materials in the repository. For 

the LANL drums, the mass of added desiccant is a small fraction of the total mass of CPR 

in the repository, and will not have a significant impact on long-term performance. 

Using the computational methods in Wang and Brush (1996a and 1996b), the inventory 

of biodegradable materials has been changed from 23,884 (8,120 + 1.7 × 8,120 + 1,960) 

tons for the CRA-20042 to 28,098 (8,907 + 1.7 × 10,180 + 1,885) tons of equivalent 

cellulosics for the CRA-2009.1

 For the CRA-2014, this value changes to 24,334 (5,127 + 

1.7 × 10,487 + 1,379) tons of equivalent cellulosics. This decrease in biodegradable 

materials corresponds to a proportional decrease in CO2 generation, all other factors (such 

as brine saturation) being equal. For MgO carbonation and microbial degradation, the 

calculated temperature rises have been updated for the changes in both microbial gas 

generation and waste inventory and are presented in Table SCR-4. Temperature rises 

(

o

C) by exothermic reactions are revised as follows.

CCA conditions following a drilling event show that Al corrosion could, at most, result in 

a short-lived (two years) temperature increase of about 6 °C (10.8 °F) above ambient 

room temperature (about 27 °C (80 °F)) (Bennett et al. 1996). A temperature rise of 6 °C 

(10.8 °F) represented the maximum that could occur as a result of any combination of 

exothermic reactions occurring simultaneously. Revised maximum temperature rises by 

exothermic reactions for CRA-2014 are still less than 12 oC (22 °F) (as shown in Table 

SCR-4). Such small temperature changes cannot affect material properties. Thus, thermal 

effects on material properties in the repository have been eliminated from PA calculations 

on the basis of low consequence to the performance of the disposal system.

Table SCR-4. CCA and CRA Exothermic Temperature Rises

Reactant CCAa CRA-2004a CRA-2009a CRA-2014a

MgO hydration < 4.5 < 4.7 < 4.2 < 3.9

MgO carbonation < 0.6 < 0.7 < 0.6 < 0.6

Microbial degradation < 0.8 < 1.4 < 1.5 < 1.4

Aluminum corrosion < 6.0 < 6.8 < 6.9 < 3.4

Cement hydration < 2.0 < 2.5 < 3.0 < 2.7 a All values are in degrees Celsius.

All potential sources of heat and elevated temperature have been evaluated and found not 

to produce high enough temperature changes to affect the repository’s performance. 

Sources of heat within the repository include radioactive decay and exothermic chemical 

reactions such as backfill hydration and metal corrosion. The rates of these exothermic 

reactions are limited by the availability of brine in the repository. In general, the various 

sources of heat are not great enough to jeopardize the performance of the disposal 

system.

These changes have been added to Enclosure 4, CRA-2014 Errata Tracking.

 2 The 1.7 molar conversion rate for plastic is based on analyses presented in Wang and Brush (1996a and 1996b).
5th Response Submittal to the EPA Enclosure 1

27

EPA Comment

2-32-S22 FEP W73 Concrete Hydration. Please supplement the screening argument with a discussion 

of the impact on the PA based on a reduced concrete inventory due to DOE now using Option D concrete 

monoliths in the panel closure system. Update the analysis to include where explosion walls are or will be 

installed.

DOE Response

The concrete evaluated within the screening argument reflects only that concrete intrinsic to WIPP waste, 

and does not consider concrete hydration due to panel closures or other engineered repository elements. 

Concrete hydration as it relates to this FEP is solely due to cement (or concrete) within the waste (see for 

example Table SCR-3 in Appendix SCR-2014). The reason that concrete hydration from panel closures 

has not been included in this analysis is because any related thermal rise is considered a short-term 

phenomenon that will only exist during the operational period, or at the very earliest part of the postclosure disposal period. Now that concrete will not be used in the panel closure system, concrete 

hydration from engineered elements of the repository is even less important. The same can be said for 

any explosion walls currently emplaced or that will be emplaced in the future. These elements, which 

consist of concrete blocks with mortar joints, have no effect on the long-term performance of the 

repository. What small amount of cement mortar used will have long been reacted during the operational 

period and will not have any thermal effect during the disposal period.
5th Response Submittal to the EPA Enclosure 1

28

EPA Comment

2-32-S24 FEP W111 Panel Closure Chemical Composition. Please update the screening argument to 

include the chemical composition of the steel bulkheads that are part of the panel closure design.

DOE Response

Steel (iron) bulkheads have been used in each panel for ventilation control and are not considered part of 

the engineered panel closure system. Their presence is primarily to control ventilation during 

construction of the ROMPCS. In cases where a block explosion wall has already been emplaced as part 

of the partial closure process for some panels, a steel bulkhead will not be used, as the block wall will 

serve as the ventilation barrier. In cases where the block walls exist, ROM salt will be placed directly 

against the wall. In cases where the steel bulkhead is used, the ROM salt will have a safe stand-off 

distance so as not to collapse or compromise the steel bulkhead. In either case, these engineered features 

are not considered long-term functional elements of the ROMPCS, and are not factored into PA 

parameters used to represent the closures.

Steel (iron) bulkheads are used throughout the mine for ventilation controls, and may or may not be 

removed prior to repository closure. Any additional iron mass associated with steel bulkheads used in

construction of the ROMPCS is inconsequential to repository performance because modeling predictions 

show un-degraded iron at the end of the 10,000-year performance period (see DOE response to comment 

1-23-5). That is, considering only the iron-based alloys in the waste and waste containers results in a 

significant portion of the iron inventory un-degraded. Therefore, slightly increasing the iron inventory 

due to additional steel bulkheads or other facility elements will result in even more un-degraded iron at 

the end of the performance period. Because of this, and the fact that the steel bulkhead is not considered a 

PCS element, this FEP remains unchanged.
5th Response Submittal to the EPA Enclosure 1

29

EPA Comment

2-32-S26 FEP W115 Chemical Degradation of Panel Closures. The screening decision for this FEP 

was changed from UP (screened in) to SO-P (screened out – low probability). Please supplement the 

screening argument with a discussion of the chemical degradation of the steel bulkheads, which are part 

of the ROM salt panel closure system. Please also provide technical justification for the changed 

screening decision in light of the presence of the bulkheads.

DOE Response

As explained in the response to 2-32-S24, the steel bulkhead is not considered an engineered element of 

the ROMPCS and is only important to control ventilation during construction of the closure. Degradation 

of the steel bulkhead will proceed throughout the performance period, as it will for all steel in the 

repository. This has no effect on the long-term properties of the ROMPCS and is not included in PA. 

However, degradation of steel within the repository is represented in PA and is a desirable process that 

serves to maintain a reducing chemical environment, which in turn supports lower actinide solubilities.
5th Response Submittal to the EPA Enclosure 1

30

EPA Comment

3-C-11. Appendix SOTERM Typographical Errors/Errata. Section SOTERM-3.6.1.3, Page 

SOTERM-67, line 3: Section SOTERM-3.5.1.1 and Section SOTERM-3.5.1.2 should be Section SOTERM3.6.1.1 and Section SOTERM-3.6.1.2

Appendix SOTERM, Section SOTERM-6.0 References: The correct date for the following reference is 

2010: Reed, D.T., J.-F. Lucchini, M. Borkowski, and M.K. Richmann. 20092010. Reduction of Higher 

Valent Plutonium by Iron under Waste Isolation Pilot Plant (WIPP) - Relevant Conditions: Data 

Summary and Recommendations. LCO-ACP-09, LANL\ACRSP Report. Los Alamos, NM: Los Alamos 

National Laboratory.

DOE Response

These are typographical errors in Appendix SOTERM-2014. The cross-references in Section 3.6.1.3 

should be SOTERM-3.6.1.1 and SOTERM-3.6.1.2, as the EPA has noted. This sentence in Appendix 

SOTERM-2014 is changed to read:

The overall issue of a thermodynamic driver for higher-valent Pu oxides, although it has 

received much recent attention in the literature, is not yet resolved, but has a relatively 

insignificant impact on the WIPP regardless of the mechanisms at work. A prolonged 

unsaturated phase in the WIPP could lead to the formation of some PuO2+x, but this will 

be quickly overwhelmed in an aqueous environment and the higher-valent Pu will be 

reduced to Pu(III/IV) species, as described in Section SOTERM-3.6.1.1 and Section 

SOTERM-3.6.1.2. Both DBR and transport-release scenarios assume brine inundation 

and, correspondingly, the rapid introduction of reducing conditions.

Although the plutonium internal report is labeled as a 2009 report, it was finalized in 2010 – so DOE

agrees with the EPA that 2010 is the correct date of reference for the report. The reference for this report 

is changed to the following:

“Reed, D.T., J.-F. Lucchini, M. Borkowski, and M.K. Richmann. 2010. Reduction of 

Higher Valent Plutonium by Iron under Waste Isolation Pilot Plant (WIPP) - Relevant 

Conditions: Data Summary and Recommendations. LCO-ACP-09, LANL\ACRSP 

Report. Los Alamos National Laboratory, Los Alamos, NM.”

A copy of this reference is provided in Enclosure 2.

Also, “Reed et al. 2009” is replaced with “Reed et al. 2010” in the following locations:

SOTERM vi Figure SOTERM-15 caption

SOTERM 18 Line 8

SOTERM 36 Line 27

SOTERM 62 Line 14

SOTERM 65 Line 4 (Figure 15 caption)

These typographical errors have been added to Enclosure 4, CRA-2014 Errata Tracking.