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EPA Comment

1-C-1 LANL Waste Stream With Added Cellulosic Material.

Organic kitty litter was used as an absorbent for nitrate salts for Waste Stream LA-MIN02-V.001 (NMED 

2014) and 349 drums of this waste were placed in Panels 6 and 7 (Wallace 2014). Please address the 

following:

1. Provide a complete waste profile for the kitty litter; including; cellulosic content and other 

ingredients; emplaced volume and mass.

2. Specify the number of drums with kitty litter placed in either Panel 6 or 7.

3. Identify the type of waste emplaced in the drums with the kitty litter.

4. Indicate whether this cellulosic kitty litter has been used in other waste streams and whether the 

corresponding waste profile reports adequately describe the waste material parameters.

5. Describe the effects of omitting the organic kitty litter in the waste stream(s) on the CPR 

inventory and consequent effects on gas generation rates calculated for the CRA-2014 PA.

6. Provide information of the quantities of soluble organics, such as organic ligands or surfactants 

that could affect actinide solubilities when this material is leached.

DOE Response

The Department of Energy (DOE) is currently working through an Extent of Condition Review1and do 

not currently have all of the nitrate salt bearing waste data from Los Alamos National Laboratory

(LANL). However, DOE, Carlsbad Field Office (DOE/CBFO) is providing the potential impacts of 

organic kitty litter on the Culebra Kd values from EPA comment 1-23-1 as part of the response to 1-C-1, 

since the questions address both LANL’s nitrate salt bearing waste and organic sorbents.

Responses to the EPA’s nitrate salt waste comments are discussed below and are identified by the 

comments number.

1. Pet Care Systems, Inc., is the manufacturer of Swheat Scoop®(“kitty litter”). The composition of 

the Swheat Scoop®is: wheat 74.498%, wheat midds 12.0%, moisture (maximum) 13.5% and 

natural soybean oil .0025%. Attachment 1 contains the manufacturer’s profile for Swheat 

Scoop®.

2. Previous LANL reports and presentations may contain emplaced data for LA-MIN02-V.001 

waste stream, but DOE/CBFO is not in the position to defend or justify these data. DOE/CBFO

relies on the WIPP Waste Data System (WDS), which is the official database of record, to report 

emplaced data. WDS reports the number of emplaced containers for waste stream LA-MIN02-

V.001 in Panels 6 and 7 as 257 55-gallon drums, 77 55-gallon pipe overpacks, and 15 standard 

waste boxes containing a total of 34 55-gallon drums. The total emplaced drum volume is 77.28

m

3

and the emplaced waste mass is 30,723.70 kg for the 55-gallon drums for waste stream LAMIN02-V.001. The total mass of the Swheat Scoop®

used in the emplaced LA-MIN02-V.001 

waste containers is not currently known. LANL has reported that the total amount of Swheat 

Scoop®used in all TRU waste remediation activities at LANL is approximately 41,000 lbs 

(18,597 kg).

3. Waste material parameters that are reported in the WDS for emplaced waste stream LA-MIN02-

V.001 are shown in Table 1.

 

1 Extent of Condition Review is being performed on the nitrate salt waste at LANL to determine the extent to which 

the actual condition exists with other containers and waste streams.
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Table 1

LA-MIN02-V.001

(Solidified Inorganic)

Iron Base Metal Alloys

Aluminum Base Metals/Alloys

Other Metals/Alloys

Other Inorganic Materials

Cellulosics

Rubber

Plastics

Solidified Inorganic Materials

Solidified Organic Materials

4. Thus far, LANL has reported three additional waste streams that contain nitrate salt waste in a 

portion of the containers in those waste streams. The three waste streams are LA-CIN01.001, 

LA-MHD01.001 and LA-MIN04-S.001. The number of containers and the amount of Swheat

Scoop®for these three waste streams is currently unknown. The waste material parameters that 

describe these waste streams as reported in the WDS are shown in Table 2.

Table 2

LA-CIN01.001

(Solidified Inorganics)

LA-MHD01.001

(Heterogeneous Debris)

LA-MIN04-S.001

(Salt Waste)

Iron Base Metal Alloys Iron Base Metal Alloys Iron Base Metal Alloys

Aluminum Base 

Metals/Alloys

Aluminum Base 

Metals/Alloys Other Metals/Alloys

Other Metals/Alloys Other Metals/Alloys Other Inorganic Materials

Other Inorganic Materials Other Inorganic Materials Cellulosics

Cellulosics Cellulosics Plastics

Rubber Rubber Solidified Inorganic 

Materials

Plastics Plastics

Solidified Inorganic Materials Solidified Inorganic Materials

Soils Solidified Organic Materials

Soils

5. The response on the potential impacts of organic kitty litter on the Culebra Kd values from EPA 

comment 1-23-1 and 1-C-1 sub-comment 5 are addressed together in the following response. 

These comments deal with the impacts of waste stream CPR (LA-MIN02-V.001) and the effects 

of organic kitty litter on the CPR inventory, on gas generation rates and on Kds in the Culebra.
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The cellulose in the organic absorbent makes up less than 0.4% of the currently expected (based 

on a scaled full repository volume) total amount of cellulose and 0.1% of the total CPR2. 

Historically, the estimates of the CPR used in previous recertification PAs have varied by as 

much as 33% with no impact on the CCDFs (DOE 2010) (the mass of CPR in the LA-MIN02-

V.001 waste stream is listed in Table 4). This minor addition of cellulose will not impact 

assumptions made in the PA concerning CPR inventory, gas generation or Kds.

Microbial consumption of the organic carbon in CPR can produce CO2 and other gases. The 

presence of CO2 in the repository affects gas pressure and chemical conditions of the brine in the 

repository which could be released to the Culebra. Changes to the chemical conditions of the 

brine in the Culebra could impact Kds. Specifically, CO2 can impact brine pH which could affect 

these assumptions. MgO is emplaced as an engineered barrier that sequesters CO2 in the 

repository resulting in essentially no increase in pressure from CO2. Additionally, MgO reduces 

the possible concentration of CO2 in repository brine to essentially zero. A significant excess 

amount of MgO is emplaced in the repository, based on the CPR content of each waste container 

and associated emplacement materials such that there is more than enough MgO to react with all 

the CPR in the repository. By continually emplacing excess MgO in each disposal room, the 

chemical conditions modeled in the performance assessment will be maintained regardless of the 

amount of CPR. Additionally, there are conservative assumptions regarding the amount of MgO 

that is to be emplaced. For example, it is assumed that all carbon in the waste will be converted

100% to CO2 which is improbable. Since the MgO maintains stable repository brine conditions 

with essentially no CO2, the impact of a minor addition of cellulose from the LANL waste will 

not impact repository chemical conditions and therefore will not impact Culebra chemical 

conditions due to potential brine releases to the Culebra. Since these chemical conditions are 

maintained, there is no change in the chemical characteristics of the Culebra brine that would 

affect Kd assumptions.

In response to a similar comment from EPA on the CRA-2004, DOE assessed the impact of 

additional CPR on gas generation and repository performance. The CPR mass was increased by 

250% with only a minor impact on repository performance (EPA 2004 and Dunagan et al. 2004). 

Changes in the quantity of CPR by the minor amount added from the LANL waste (i.e., 0.1% 

increase of the total CPR) will not impact repository performance.

References:

Dunagan, S., Hansen, C. and Zelinski, W. 2004. Effects of Increasing Cellulosics, Plastics, and 

Rubbers on WIPP Performance Assessment. ERMS 535941. Sandia National Laboratories, 

Carlsbad, NM. 

McInroy, W. Email correspondence to S. Wagner dated January 14, 2015. ERMS 563787. Los 

Alamos National Laboratory, Carlsbad, NM.

U.S. Department of Energy (DOE). 2010. 5th Response Submittal to EPA, Enclosure 1, 

Comment 3-24-1. ERMS 553145. February 19, 2010.

U.S. Environmental Protection Agency (EPA). 2004. First CRA-2004 EPA completeness letter 

from E. Cotsworth to P. Detwiler dated May 20, 2004. ERMS 535554.

 

2 Based on the possible 41,000 lbs of kitty litter in the LANL waste (McInroy 2015) and total CPR and C from the 

2012 PAIR (Van Soest 2012).
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Van Soest, G.D. 2012. Performance Assessment Inventory Report, INV-PA-12, Revision 0, LAUR-12-26643. Los Alamos National Laboratory Carlsbad Operations, Carlsbad, NM.

6. The following tables specify the quantities of organics in the LA-MIN02-V.001 waste stream.

Table 3 – Organic Ligands (from McInroy 2015a)

Waste Stream Acetic Acid 

(kg)

Citric Acid 

(kg)

Oxalic Acid 

(kg)

Acetate 

(kg)

Citrate 

(kg)

EDTA 

(kg)

Oxalate 

(kg)

LA-MIN02-V.001 0.354045962 38.93036512 484.7932261 0 0 0 0

Table 4 – Organic Waste Material Parameters (from McInroy 2015b)

Waste Stream Waste Material Parameter Mass (kg)

LA-MIN02-V.001 Cellulosics 445.9

LA-MIN02-V.001 Plastic 1,433.2

LA-MIN02-V.001 Rubber 204.5

LA-MIN02-V.001 Solidified Organics 92.1

References:

McInroy, W. 2015a. Email correspondence dated April 14, 2015, from McInroy to S. Wagner re: 

Organic Ligands Inventory Information. ERMS 563809. Los Alamos National Laboratory, 

Carlsbad, NM.

McInroy, W. 2015b. Email correspondence dated April 14, 2015, from McInroy to S. Wagner re: 

WDS Waste Material Parameters. ERMS 563808. Los Alamos National Laboratory, Carlsbad, 

NM.
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Attachment 1

Guaranteed Analysis

Product Name: Swheat Scoop Cat Litter

Composition of wheat litter:

Wheat 74.498%

Wheat Midds 12.0%

Moisture (maximum) 13.5%

Natural Soybean oil .0025%

TOTAL 100.00%

We certify that the above product is composed of these ingredients.

A Material Safety Data Sheet (MSDS) is not required on wheat litter.

Pet Care Systems, Inc. • 1421 Richwood Road • Detroit Lakes, MN 56502-1529 • 1-800-794-3287

www.swheatscoop.com
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EPA Comment

2-23-1 ROM Salt Panel Closures Locations. 

Please provide the WIPP configuration layout (a plan view) used for the 2014 CRA that includes all 

locations where the ROM salt panel closures are to be placed. Provide text that provides the exact 

location, dimensions and properties for the set of panel closures that lie furthest north in the repository.

DOE Response

A plan view of the WIPP configuration layout used for 2014 CRA calculations was included as Figure 3-

2, Plan View of WIPP Underground Facility and Panel Closure Systems, in the EPA’s Approval of the 

ROM Salt Panel Closure System (ROMPCS) (U.S. EPA 2014). The figure (included here as Figure 1) 

provides locations where the ROM salt panel closures are to be placed. This is consistent with current 

WIPP project planning. Panel closures will have the same basic properties as the closures approved by 

EPA (U.S. EPA 2014) for the panels in Panel Closure System Design (DOE 2011). 

The northernmost panel closures would be located in north-south access drifts W-170, W-30, E-140 and 

E-300 just north of S-700 and just south of the waste and exhaust shafts. The approximate dimensions of 

the access drifts for the closures are as follows: W-170 – 16 feet wide, 13 feet tall, ROM salt length 100 

feet. W-30 – 20 feet wide, 14 feet tall, ROM salt length 100 feet. E-140 – 24 feet wide, 18 feet tall, 

ROM salt length 100 feet. E-300 – 13 feet wide, 16 feet tall, ROM salt length 100 feet.
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Figure 1 Plan View of WIPP Underground Facility and Panel Closure Systems.
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References:

U.S. Environmental Protection Agency (EPA). 2014. Title 40 CFR Part 194: Criteria for the 

Certification and Recertification of the Waste Isolation Pilot Plant’s Compliance With the Disposal 

Regulations; Panel Closure Redesign. Federal Register, Vol. 79, No, 195. (October 8, 2014): 60750-

60756.

U.S. Department of Energy (DOE). 2011. Panel Closure System Design Planned Change Request to the 

EPA 40 CFR Part 194 Certification of the Waste Isolation Pilot Plant. DOE/CBFO-11-3479. . Carlsbad 

Field Office, Carlsbad, NM..
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EPA Comment

2-23-2 Provide An Update of the Derivation of the Shaft Properties at the Repository Horizon. 

In the BRAGFLO grid for the 2004 and 2009 CRA Performance Assessments (PAs), the modeled lower 

portion of the shaft included an effective permeability that incorporated both the concrete portion of the 

shaft (at the repository horizon level) and the furthest north panel closures located just south of the waste 

and exhaust shafts. The material properties of the modeled shaft (the concrete monolith segment) were 

combinations of the shaft properties and the Option D panel closure properties (Camphouse and Clayton 

2011, ERMS 555204). Now, however, there is a new panel closure system that uses run of mine salt 

instead of the Option D design, and the properties of new panel closure system are different than that of 

the concrete portion in the lower shaft. In the CRA 2014 PA, however, it appears the material properties 

of the shaft at the repository horizon have not been updated to reflect the change. Please confirm this and 

identify how the properties would change to reflect the change in the panel closure design.

DOE Response

There are two issues that are relevant to EPA's comment; each is described in detail in the following DOE 

response:

1. Material properties of CONC_MON. The material properties of the concrete monolith at the base of 

the shaft, identified as material CONC_MON for BRAGFLO, are defined correctly. However, there is an 

error in the documentation of the basis for the CONC_MON properties.

2. Size of Northernmost ROMPCS. DOE has identified an error in the BRAGFLO grid for the CRA2014. The northernmost panel closures should have been 200-feet long, rather than 100-feet long, as in 

the BRAGFLO model for CRA-2014. However, DOE has performed BRAGFLO calculations to 

demonstrate that this error has no significant impact on BRAGFLO results for CRA-2014.

Material Properties of CONC_MON (Concrete Portion of Lower Shaft)

There was an error in the description of the properties of CONC_MON in Camphouse and Clayton 

(2011). That document claimed that the properties of the lower shaft region in the BRAGFLO grid came 

from the “Option D” panel closure properties and the lower shaft properties: “the operations (Ops) and 

experimental (Exp) regions have been separated by a material [CONC_MON] combining panel closure 

and waste shaft properties.” However, the properties of the shaft concrete material do not in fact reflect a 

combination of panel closure and waste shaft properties, but solely waste shaft properties. The properties 

of the northernmost set of panel closures were not incorporated into the properties for CONC_MON, at 

the base of the shaft. Thus, there is no need to update the properties of the lower shaft (i.e., 

CONC_MON), but the properties of the northernmost set of panel closures will be changed because of an 

error in the BRAGFLO grid, described next. 

Updating the Size of the Northernmost ROMPCS

The BRAGFLO grid used in the CRA-2014 PA did not take into account the properties of the 

northernmost set of panel closures. In order to account for these properties, we now implement the 

strategy used in the transition from the Technical Baseline Migration (TBM) BRAGFLO grid to the grid 

used for the CRA-2004 (Stein 2003). This strategy was peer-reviewed and accepted during the TBM 

modifications and carried forward for use in the CRA-2004 and CRA-2009. From the analysis report that 

examined the change to the BRAGFLO grid (Stein 2003):
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“To account for this panel closure that is immediately south of the shaft, the dimensions of the concrete 

portion of the panel closure located between the northern rest of repository (nRoR) and the operations 

area was doubled (7.9 m x 2 = 15.8 m). This ensures that gas produced in the waste regions must 

effectively travel though [sic] the same number of panel closures to reach the experimental area as was 

modeled in the TBM. This is an important part of the revised conceptual model of repository geometry 

that was presented to the Salado Flow Peer Review panel.”

This strategy resulted in three sets of panel closures in the BRAGFLO grid. In the TBM grid (and the 

CRA-2004 and CRA-2009 representations of the repository), the northernmost set of panel closures 

(located between the northern rest of repository and the operations area) had a length twice that of the 

other two. When the ROMPCS was implemented in the grid used for the PCS-2012 analysis, all three sets 

of “Option D” panel closures were replaced in the BRAGFLO grid with the ROMPCS having a length of 

30.48 m (Camphouse et al. 2012). To be consistent with the representation of the northernmost panel 

closures as modeled in the TBM, the CRA-2004, and the CRA-2009, the northernmost set of panel 

closures should have had twice the length of the other two (i.e., 60.96 m) in the CRA-2014 PA.

Updated BRAGFLO Calculations

Here, we have modified the CRA-2014 BRAGFLO grid (Figure 1) in order to double the length of the 

northernmost set of panel closures. The BRAGFLO calculations were performed as deviations under AP164 (Camphouse 2013) and the calculation details are summarized in Zeitler (2015). We present an 

analysis of the impact of this change in the BRAGFLO grid on the pressure and brine saturation in the 

NRoR, south rest of repository (SRoR), and waste panel as compared to the CRA-2014 PA. We compare 

the mean results for 100 vectors in each of three scenarios (1, 2, and 4) for replicate 1.

Figure 2. Computational grid used in BRAGFLO for this analysis.
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Figure 2 shows the impact of the increased size of the northernmost ROMPCS on pressure in the NRoR 

for scenarios 1, 2, and 4. Overall, there is a small increase in mean pressure in the NRoR, as expected, 

because the increased length of the relatively low-permeability ROMPCS (after 200 years) makes the 

barrier to gas and brine flow greater in the northern direction. The increased pressure results in a very 

small decrease in brine saturation (Figure 3).

Figure 3. Replicate 1 means of NRoR pressure for scenarios 1, 2, and 4.

Figure 4. Replicate 1 means of NRoR brine saturation for scenarios 1, 2, and 4.

Figure 4 shows the impact of the increased size of the northernmost ROMPCS on pressure in the SRoR 

for scenarios 1, 2, and 4. Overall, there is a very small increase in mean pressure in the SRoR, as 

expected, because the increased length of the relatively low-permeability ROMPCS (after 200 years) 

makes the barrier to gas and brine flow greater in the northern direction. The small pressure increase 

results in a barely noticeable decrease in brine saturation (Figure 5). The differences in pressure and brine 
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saturation are smaller in the SRoR than in the NRoR. This is expected, as the SRoR is separated from the 

OPS/EXP areas by an additional set of ROMPCS compared to the NRoR.

Figure 5. Replicate 1 means of SRoR pressure for scenarios 1, 2, and 4.

Figure 6. Replicate 1 means of SRoR brine saturation for scenarios 1, 2, and 4.

Figure 6 shows the impact of the increased size of the northernmost ROMPCS on pressure in the waste 

panel for scenarios 1, 2, and 4. Overall, there is a negligible change in mean pressure in the waste panel. 

The differences in pressure and brine saturation are smaller in the waste panel than in the SRoR. This is 

expected, as the waste panel is separated from the OPS/EXP areas by an additional set of ROMPCS 

compared to the SRoR. The negligible difference in pressures results in a negligible difference in brine 

saturation (Figure 7). Additionally, there are only small changes in the 10th and 90th percentile values for 

pressure and brine saturations (Figures 8-11). Due to the negligible effect of the change in length of the 

northernmost ROMPCS on waste panel pressures and brine saturations, there is no impact on releases 

from the repository that result from a hypothetical drilling intrusion.
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Figure 7. Replicate 1 means of waste panel pressure for scenarios 1, 2, and 4.

Figure 8. Replicate 1 means of waste panel brine saturation for scenarios 1, 2, and 4.
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Figure 9. Replicate 1 10th percentiles of waste panel pressure for scenarios 1, 2, and 4.

Figure 10. Replicate 1 90th percentiles of waste panel pressure for scenarios 1, 2, and 4.
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Figure 11. Replicate 1 10th percentiles of waste panel brine saturation for scenarios 1, 2, 

and 4.

Figure 12. Replicate 1 90th percentiles of waste panel brine saturation for scenarios 1, 2, 

and 4.

Conclusion

The EPA’s comment that the material properties of the concrete portion of the lower shaft should be 

updated to reflect the change in panel closure system was based on an error in Camphouse and Clayton 

(2011) that incorrectly described the properties of the “Option D” panel closure as being incorporated into 

the properties of the lower shaft. There is no need to update the properties of the lower shaft (i.e., 

CONC_MON).

However, EPA’s comment has brought to light that there was an error in implementation of the ROMPCS 

in PCS-2012, which carried through to the CRA-2014. The BRAGFLO grid should have represented the 
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northernmost set of ROMPCS as being twice as long as the other two ROMPCS representations. Here, we 

have updated the BRAGFLO grid and run BRAGFLO calculations to judge the impact of the grid change 

on pressures and brine saturations in the repository. The update to the size of the northernmost ROMPCS 

has negligible effect on pressures and brine saturations in the waste panel during the 10,000-year 

regulatory period. Our judgment is that there is therefore no impact of the grid change on radionuclide 

releases. The corrected length of the northernmost set of panel closures will be implemented in future PA 

calculations and will be tracked in Enclosure 4, CRA-2014 Errata Tracking.

References:

Camphouse, R.C. and D. Clayton. 2011. Analysis Package for Salado Flow Modeling Done in the AP151 (PC3R) Performance Assessment. ERMS 555204. Sandia National Laboratories, Carlsbad, NM.

Camphouse, R.C. 2013. Analysis Plan for the 2014 WIPP Compliance Recertification Application 

Performance Assessment. ERMS 559198. Sandia National Laboratories, Carlsbad, NM.

Camphouse, R.C., D. Kicker, T. Kirchner, J. Long, B. Malama, and T. Zeitler. 2012. Summary Report 

and Run Control for the 2012 WIPP Panel Closure System Performance Assessment. ERMS 558365. 

Sandia National Laboratories, Carlsbad, NM.

Stein, J.S. and W. Zelinski. 2003. Analysis Report for: Testing of a Proposed BRAGFLO Grid to be used 

for the Compliance Recertification Application Performance Assessment Calculations. ERMS 526868. 

Sandia National Laboratories, Carlsbad, NM.

Zeitler, T.R. 2015. Memo to Records: BRAGFLO calculations for updated northernmost ROMPCS 

representation. ERMS 563875. Sandia National Laboratories, Carlsbad, NM.
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EPA Comment

2-33-1 Future Drilling Into Nitrate Waste. 

Please provide the probability and describe the potential consequence(s) to PA calculation of drilling 

into the nitrate waste.

DOE Response

With respect to Los Alamos National Laboratory waste, four CH waste streams have been identified as 

containing some amount of nitrate waste. The number of drums with nitrate-containing waste in each of 

these waste streams is currently not known, but is expected to be less than the total number of drums, 

such that the probability of hitting a nitrate-containing drum in a waste stream would be less than the 

probability of hitting the waste stream. Until the number of drums that contain nitrate waste is known for 

each waste stream, the probability of hitting nitrate waste in a given waste stream will not be known.

However, an upper limit of the probability of hitting nitrate waste can be calculated by assuming that all 

containers in these four waste streams contain nitrate waste. The waste stream volumes and hit 

probabilities that were used in the CRA-2014 PA calculations for the four nitrate-containing waste 

streams are summarized in Table 1. The probability of a drilling event hitting an individual waste stream 

(given that the drilling event results in an intrusion into a waste-containing area1), as implemented in 

WIPP PA calculations, is equal to the ratio of the volume of the waste stream to the total inventory 

volume for that type of waste (CH or RH). (The nitrate containing waste streams are all CH waste.) That 

probability is then multiplied by the probability of a drilling event resulting in a waste encounter (17.7%)

1

to result in the probability of a single drilling event hitting a given waste stream. The total probability of 

1.4% represents an absolute maximum probability of a drilling event hitting nitrate waste for a randomly 

placed drilling intrusion within the WIPP repository footprint. This upper bound is based on the total 

volume of the nitrate-containing waste streams, but the probability of hitting nitrate waste is expected to 

be lower, because as mentioned earlier, it is expected that only a fraction of the containers in these four 

waste streams contain nitrate waste.

 

1

In WIPP PA, the probability of a drilling event resulting in a waste encounter is equal to the ratio of the excavated 

region of the repository (sum of parameters REFCON:AREA_CH and REFCON:AREA_RH, the areas associated 

with CH and RH waste, respectively) to the area of the footprint of the entire repository (parameter 

REFCON:ABERM). For the CRA-2014, this ratio is (111,500 + 15,760 m2)/628,500 m2= 0.202. Thus, there is only 

a 20.2% chance of a single drilling event within the WIPP footprint resulting in a waste encounter (17.7 % for CH 

waste and 2.5 % for RH waste). The probabilities presented in column 5 of Table 1 are representative of drilling

events that indeed encounter CH waste. So, for a single drilling event, the probability of a drilling event resulting in 

the hitting of one of the waste streams in Table 1 is equal to the probability of hitting the waste stream (given a 

waste hit) multiplied by the probability of a drilling event resulting in a CH waste encounter (0.177). For context, 

there is an average of about 7.5 drilling events per 10,000 year future for the CRA-2014.
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Table 1. Waste stream volumes and hit probabilities for nitrate-containing waste streams

TRU Waste 

Stream

Waste 

Stream 

Volume 

(m3)

Total CH 

Inventory 

Volume 

(m3)

Percent 

Volume

Probability of 

Hitting Waste 

Stream (Given 

a CH Waste 

Hit)*

Probability 

of Hitting 

Waste 

Stream

LA-CIN01.001** 826 168496 0.490 0.00490 0.00087

LA-MHD01.001** 12720 168496 7.549 0.07549 0.01339

LA-MIN02-V.001 10.2 168496 0.006 0.00006 0.00001

LA-MIN04-S.001 14.4 168496 0.009 0.00009 0.00002

Total 8.054 0.08054 0.01429

*The volume ratio expressed as a fraction (i.e., the value in the previous column divided by 100).

**The volume of the LA-CIN01.001 and LA-MHD01.001 waste streams include the emplaced volume from those waste streams, denoted as 

separate waste streams (WP-LA-CIN01.001 and WP-LA-MHD01.001, respectively) in Van Soest (2012).

In regard to the potential consequences to PA calculations of drilling into nitrate waste, there is no 

difference in hitting a nitrate-containing waste stream or a waste stream that does not contain nitrates. In 

regard to the waste inventory, a drilling event in WIPP PA calculations is solely dependent on the waste 

stream properties of volume and activity per unit volume. The PA calculations do not consider a release 

mechanism that is specific to nitrate-containing waste; thus the PA calculations do not depend on the 

likelihood that a drilling event into the repository encounters a nitrate-containing waste stream.

Reference:

Van Soest, G.D. 2012. Performance Assessment Inventory Report, INV-PA-12, Revision 0, LA-UR-12-

26643. Los Alamos National Laboratory Carlsbad Operations, Carlsbad, NM.
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EPA Comment

2-44-1 MgO Physical Segregation. 

In Franco (2012) DOE notified EPA that MgO emplacement has been modified by placing a 3,000 pound 

supersack of MgO on every other waste stack or on each waste stack in every other row. In the Franco 

2012 letter the “effective diffusion penetration length of CO2” was considered but the information on 

physical segregation is limited.

Please provide updated documentation to more explicitly and clearly address whether the larger lateral 

separation distance still allows sufficient reactions between MgO and CO2.

References:

Franco, J.R. 2012. Letter to A. Perrin (Subject: “Planned Change Notice for Placement of MgO 

Supersacks,” with enclosure (Analysis of an alternative placement scheme for MgO supersacks). 

February 14, 2012. Carlsbad, NM: U.S. Department of Energy Carlsbad Field Office.

U.S. Department of Energy (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. DOE/WIPP 09-3424. Carlsbad, NM: Carlsbad Field Office.

Vugrin, E.D., M.B. Nemer, and S.W. Wagner. 2006. Uncertainties Affecting MgO Effectiveness and 

Calculation of the MgO Effective Excess Factor (Rev. 0, November 17). ERMS 544781. Carlsbad, NM: 

Sandia National Laboratories.

DOE Response

Introduction

The WIPP repository uses magnesium oxide (MgO) backfill as the engineered barrier. MgO is emplaced 

in the WIPP repository along with the waste as a chemical control agent. The presence of adequate 

amounts of MgO ensures that favorable and consistent conditions are maintained in WIPP brines by 

reacting with any carbon dioxide (CO2) produced by microbial consumption of organic carbon in the 

waste materials. The reaction of MgO with CO2 and water ensures that the pH of WIPP brines remains in 

a limited range that provides predictable brine conditions that support relatively low solubility limits for 

the actinides in transuranic waste.

WIPP’s current operational procedures require DOE to emplace a supersack with 3,000 or 4,200 pounds 

of MgO on top of each stack of waste containers, beginning with the even numbered rows in a room. The 

amount of MgO (3,000 or 4,200 pounds per sack) is based on the masses of cellulose, plastic and rubber 

emplaced in the room. DOE tracks the emplaced masses of MgO and organic carbon on a room-by-room 

basis at the end of each waste emplacement shift. Additional supersacks are emplaced on odd numbered 

rows if required to maintain an MgO excess factor of 1.2 or greater in the repository (NWP 2013, Section 

3.0, Backfill).

The supersacks holding MgO are hexagonal in shape and are made of woven polypropylene material 

(WTS 2009). The mean thickness of the polypropylene is 0.017 inches (Batchelder 2014). The supersacks 

are expected to fail when room closure applies compressive loads to the waste containers and supersacks. 

After failure of the supersacks, MgO can directly react with CO2 generated by microbial degradation of 

waste, and the presence of the supersacks is not considered in this diffusion mixing analysis. 
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Microbially generated CO2 can be transported away from the point of generation by several mixing 

processes. Bulk movement of brine in the repository will transport dissolved CO2 by advection. 

Hydrodynamic dispersion (mixing caused by pore-scale velocity variations as the brine flows through the 

tortuous pore spaces of the waste and backfill) will cause dissolved CO2 to spread both longitudinally and 

transverse to the direction of the bulk flow. Dissolved CO2 will also be transported via molecular 

diffusion from brine regions with higher CO2 concentrations to regions with lower CO2 concentrations. In 

the absence of significant brine flow, molecular diffusion will be the dominant mixing mechanism and its 

effectiveness has been analyzed in two previous studies.

In Effectiveness of Mixing Processes in the Waste Isolation Pilot Plant Repository, Wang (2000)

concluded that, during a minimum hydraulic residence time for brine in the repository, diffusion alone is 

sufficient to mix CO2 with WIPP brine over a distance greater than the final room height after creep 

closure. This result means that MgO emplaced on top of waste stacks will be effective in sequestering the 

CO2 generated by all the containers beneath the supersack. In Updated Analysis of Characteristic Time 

and Length Scales for Mixing Processes in the WIPP Repository to Reflect the CRA-2004 PABC 

Technical Baseline and the Impact of Supercompacted Mixed Waste and Heterogeneous Waste 

Emplacement, Kanney and Vugrin (2006) updated Wang’s analysis based on the Performance 

Assessment Baseline Calculation for the 2004 Compliance Recertification Application (CRA-2004). They 

concluded that the range of diffusion penetration distances bracketed the range of final room heights, and 

that diffusion alone provided sufficient mixing of CO2 over the final room height during the minimum 

hydraulic residence time. They also confirmed that the presence of supercompacted waste and 

heterogeneous waste emplacement did not change their conclusions.

Microbially generated CO2 can also be transported away from the point of generation by gaseous 

diffusion if all CO2 is not dissolved in brine. The focus of this analysis is on the mixing of CO2 dissolved 

in brine because the primary purpose of the MgO backfill is to limit actinide concentrations in brine. 

However, diffusive transport will efficiently mix any CO2 remaining in the gaseous state on a panel-wide 

scale, as shown later in this document. 

Update of Diffusion Mixing Analysis for the CRA-2014

The diffusion analysis of Kanney and Vugrin (2006) has been updated to reflect changes in the 

performance assessment for the 2014 Compliance Recertification Application (CRA-2014) (DOE 2014). 

BRAGFLO simulations for the CRA-2014 performance assessment provide the input data for the updated 

mixing analysis. The methodology for the analysis follows the technical approach in Kanney and Vugrin 

(2006) and in Wang (2000), with appropriate parameter changes for the CRA-2014.

Waste panel porosities, pore volumes, and brine flow are based on the BRAGFLO simulations for 

Replicate R1, Scenario S2 (R1S2) of the CRA-2014. Replicate 1 has 100 vectors whose input parameters 

are sampled from distributions using Latin Hypercube Sampling. Scenario 2 has a borehole intrusion that 

intersects the waste panel and a brine pocket in the Castile at 350 years after closure. Scenario 2 is a 

reasonable choice for this analysis because vectors with high flow up the intrusion borehole result in 

lower hydraulic residence times and lower diffusion penetration lengths in comparison to an undisturbed 

scenario.

Attachment A to this response provides the BRAGFLO output data for waste panel porosity, waste panel 

pore volume, and cumulative brine flow up the intrusion borehole for each of the 100 vectors in R1S2. 

Attachment A also provides the calculated hydraulic residence times and diffusion penetration lengths for 

the 100 vectors in R1S2. The key output parameter from this analysis is the diffusion penetration length, 

which varies from 1.43 m for vector 17 to 453 m for vector 99. The output for vector 17 provides the 

basis for this analysis, and the use of data from vector 17, with the minimum diffusion penetration length 
4

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over 100 vectors, is a lower bound on the effectiveness of diffusive mixing. To put this conservatism in 

perspective, the second smallest diffusion penetration length is 1.87 m (for vector 7) and the mean 

diffusion penetration length is 108 m for all 100 vectors (see Table A-1 in Attachment A).

Calculations for Vector 17

The diffusion penetration distance is a function of the characteristic hydraulic residence time for brine in 

the repository and the effective diffusivity of CO2 in brine in a waste-filled panel. The hydraulic residence 

time is defined as:

,

Q

V

T

brine

pore

hr 

(1)

where Thr is the hydraulic residence time [T], Vp is the waste panel pore volume [L3], and Qbrine is the 

volumetric flow rate up the intrusion borehole to the Culebra [m3/year]. The cumulative brine flow up the 

intrusion borehole in vector 17 is 1.73x105 m

3

at 10,000 years after closure (see Table A-1 in Attachment 

A). This flow occurs over a duration of (10,000 years – 350 years) = 9,650 years, resulting in a 

characteristic brine flow rate of Qbrine = (1.73x105 m

3

)/(9,650 years) = 17.9 m3/year. The waste panel 

porosity at 10,000 years in vector 17 is 0.1247 (see Table A-1), resulting in a waste panel pore volume1of 

5,750 m3.

The hydraulic residence time is calculated to be 320 years (see Table 1). This is also the minimum 

hydraulic residence time over all 100 vectors in R1S2 (see Table A-1).

Table 1. Hydraulic residence time in the waste panel for vector 17 (CRA-2014)

Vpore Qbrine brine

pore

hr Q

V

T 

5,750 m317.9 m

3

/year 320 years

Assuming Fickian (linear) diffusion, the one-dimensional equation for solute diffusion through a 

homogeneous porous medium can be written as:

2

2

x

C

D

t

C

eff 









(2)

where 

C

is the concentration of the diffusing species [M/L3], t is time [T], x is distance [L], and Deff is the 

effective diffusion coefficient [L

2

/T]. The effective diffusion coefficient accounts for two features: 1) 

diffusion occurs only through fluid-filled pores and not throughout the entire volume of the porous 

medium; and 2) the diffusion pathway at the pore scale is a complicated and tortuous network, not a 

straight line.

The effective diffusion coefficient is often modeled as:

D F D eff f

(3)

 

1 The excavated volume of the waste panel is 46,136 m3

(DOE 2014, Appendix PA-2014, Figure PA-12). The pore 

volume is the product of BRAGFLO waste porosity and panel volume: (0.1247)(46,136 m3) = 5,753 m3~ 5,750 m3.
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where Ffis a “formation factor” (dimensionless) and D is the free liquid diffusion coefficient [L

2

/T]. The 

free liquid diffusion coefficient for CO2 in sea water is approximately 2x10-5cm2/sec (Li and Gregory 

1974). The formation factor is a function of the porosity, tortuosity of the pores, and the constrictivity of 

the pores, but is often modeled as a function of porosity alone:

F .

f

2

 

(4)

Combining Equations (3) and (4), the effective diffusion coefficient in a porous medium is:

D D.

eff

2

 

(5)

To calculate the effective diffusion coefficient in Equation (5), BRAGFLO porosity must be converted to 

actual (intrinsic) porosity using the following relation:

,

B

B

1  0





 



(6)

where  is the intrinsic porosity [-], B is the BRAGFLO porosity [-], and 0 is the initial porosity [-]. The 

initial porosity of the waste-filled rooms is 0.848. Substituting the BRAGFLO porosity of 0.1247 at 

10,000 years for vector 17 into Equation (6), the intrinsic porosity in the waste panel at 10,000 years is 

0.451. The effective diffusion coefficient for CO2 in WIPP brine is:

Deff = 

2D, (7)

= (0.451)2(1⁄2)(2×10-5cm2/s),

= 2.03×10-6cm2/s,

= 6.4×10-3 m

2

/year.

In Equation (7), the free liquid diffusion coefficient is reduced by a factor of one-half from the published 

value for diffusion of CO2 in seawater (Wang 2000). This is reasonable correction because the ionic 

strength of WIPP brines is greater than that of seawater.

The characteristic diffusion penetration distance, L, is defined as:

L D T , eff hr

(8)

where Deff is the effective diffusivity in the waste-filled panel and Thr is the characteristic hydraulic 

residence time. The physical meaning of L derives from an analytical solution to the one-dimensional 

diffusion equation for a semi-infinite slab when the concentration at one end is held at a fixed value, C0

(Cussler 1997, Section 2.3):

 

    ,

Dt

x

erf erfc ,

C

C x,t

4

1

0

      

(9)

where 

erfc

is the complimentary error function (Abramowitz and Stegun 1972, Section 7). When 

distance 

x  Dt ,

then 

  0.5

and 

C/C0  0.5

(Abramovitz and Stegun 1972, page 310). Thus, 

L  Deff Thr

corresponds to the distance over which the concentration of CO2 in brine is reduced to 
4

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approximately half of its concentration at its source. Stated differently, the aqueous concentration of CO2

will be greater than one-half of the CO2 concentration at the waste within a distance L from the waste.

The 50 percent reduction in source concentration at distance L is another conservative element of this 

analysis. In a room, the reduction in CO2 concentrations within distance L from the source may be less

than 50% because the physical domain for diffusion is not the semi-infinite region of the analytic 

solution.

Using Equation (8), the characteristic diffusion penetration distance for vector 17 is 1.43 m (4.7 feet) (see 

Table 2). This is the minimum characteristic diffusion penetration distance for the 100 vectors in R1S2 

that are shown in Table A-1 in Attachment A.

Table 2. Diffusion penetration distance in the waste panel for vector 17 (CRA-2014)

Deff Thr L  Deff Thr

6.4×10-3 m

3

/year 320 years 1.43 m (4.7 feet)

Figure 1 illustrates the lateral coverage provided by MgO supersacks for an actual waste emplacement 

scheme. Figure 1 is based on the as-emplaced waste containers in Room 7 of Panel 7. Room 7 is only 

partly filled with waste, but provides a realistic example of supersack emplacement for a variety of waste 

container types with varying lateral separations between adjacent waste stacks. The light green regions 

surrounding each supersack of MgO illustrate the diffusive penetration length of 1.43 m for CO2 and the 

darker green regions indicate where there is overlap from two supersacks. The dissolved CO2 that is 

generated by waste containers within the green regions is within the minimum distance L that provides 

efficient diffusive mixing of CO2 with MgO supersacks during the minimum hydraulic residence time for 

the R1S2 scenario in BRAGFLO. Figure 1 shows that the minimum diffusive penetration length of 1.43 

m provides efficient lateral mixing of CO2 over all of the waste containers in Room 7. In addition, lateral 

diffusion and mixing of dissolved CO2 is enhanced by: (1) the supersacks will fail during room closure, 

allowing some MgO to fall into the lateral separation between adjacent waste stacks and accumulate on 

the floor, (2) channels are likely to exist within the consolidated waste after the drums collapse, providing 

higher porosity pathways for diffusion of CO2 in brine, and (3) if the waste is not fully saturated, gaseous 

diffusion provides a mechanism that rapidly mixes gaseous CO2 over panel-scale distances2. These effects 

provide added assurance of efficient lateral mixing throughout each room.

Summary

Molecular diffusion (alone) is sufficient to mix CO2 with WIPP brines over time and length scales 

characteristic of conditions in a waste panel. This mixing will occur laterally around each MgO 

supersack, and will also occur vertically as discussed by Wang (2000) and by Kanney and Vugrin (2006). 

This analysis has a number of assumptions that provide a high level of confidence that sufficient mixing 

of CO2 will occur throughout the regulatory period:

 The minimum diffusion penetration length for CO2 in brine is 1.43 m for vector 17 in BRAGFLO 

simulations for R1S2 of CRA-2014. The second smallest diffusion penetration length is 1.87 m

 

2

The gaseous diffusion coefficient of CO2 in H2 is 0.55 cm2/s at standard temperature and pressure conditions (AIP 

1972, Table 2s-1). The gaseous diffusion coefficient of CO2 is a factor of 55,000 greater than the brine diffusion 

coefficient of CO2, 1×10-5cm2/s. The corresponding gaseous diffusion penetration distance for CO2 in the waste is 

336 m, so diffusion maintains uniform CO2 gaseous concentrations throughout a panel.
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(for vector 7) and the mean diffusion penetration length is 108 m for all 100 vectors, so the 

effective penetration length is very likely to be greater than the minimum value for this analysis.

 The interpretation of the diffusion penetration length is based on an analytic solution for a semiinfinite domain. Within the finite confines of waste emplacement rooms, CO2 concentrations 

should exceed the predictions of the analytic solution for a given residence time and for a given 

distance from the MgO supersack.

 Mixing from advection and dispersion will increase the mixing of CO2 beyond that predicted for 

diffusion alone.

 If the waste is not fully saturated, any concentrations of gaseous CO2 will rapidly equilibrate 

throughout a panel because the gaseous diffusion coefficient of CO2 is 55,000 times greater than 

diffusion coefficient of CO2 in brine. The gaseous diffusion penetration distance for CO2 in the 

waste is 336 m, ensuring effective mixing on a panel scale.
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Figure 1. Diffusive mixing in the lateral direction provides high CO2 concentrations near 

the MgO supersacks. This figure is based on the actual waste emplacement and supersack 

configuration in the air exhaust drift for Room 7 of Panel 7.

1.43 m
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References:

Abramovitz, M., and I.A. Stegun. 1964. Handbook of Mathematical Functions with Formulas, Graphs, 

and Mathematical Tables. National Bureau of Standards, Applied Mathematics Series 55. U.S. 

Government Printing Office, Washington, D.C.

American Institute of Physics (AIP). 1972. American Institute of Physics Handbook. McGraw-Hill 

Book Company, New York, NY.*

Batchelder, T. 2014. Personal communication via E-Mail dated September 8, 2014, from Mr. Terry 

Batchelder of Nuclear Waste Partnership, LLC, to Mr. Steve Kouba of URS Professional Solutions LLC -

Regulatory Environmental Services.

Cussler, E.L. 1997. Diffusion Mass Transfer in Fluid Systems. Second Edition. Cambridge University 

Press, New York, NY.*

Kanney, J.F., and E.D. Vugrin. 2006. Updated Analysis of Characteristic Time and Length Scales for 

Mixing Processes in the WIPP Repository to Reflect the CRA-2004 PABC Technical Baseline and the 

Impact of Supercompacted Mixed Waste and Heterogeneous Waste Emplacement. ERMS 544248. 

Sandia National Laboratories, Carlsbad, NM.

Li, Y.H. and S. Gregory. 1974. Diffusion of Ions in Sea Water and in Deep Sea Sediments. Geochemica 

et Cosmochimica Acta 38: 703-714.*

Nuclear Waste Partnership LLC (NWP). 2013. CH Waste Downloading and Emplacement, Revision 12. 

WP 05-WH1025. Effective Date: November 18, 2013. Nuclear Waste Partnership LLC, Carlsbad, NM.

Sandia National Laboratories (SNL). 1992. Preliminary Performance Assessment for the Waste Isolation 

Pilot Plant, December 1992. SAND92-0700/3. Sandia National Laboratories, Albuquerque, NM.

U.S. Department of Energy (DOE). 2014. Title 40 CFR Part 191 Subparts B and C Compliance 

Recertification Application-2014 for the Waste Isolation Pilot Plant (March). DOE/WIPP-14-3503. U.S. 

Department of Energy, Carlsbad Field Office, Carlsbad, NM.

Wang, Y. 2000. Effectiveness of Mixing Processes in the Waste Isolation Pilot Plant Repository. ERMS 

512401. Sandia National Laboratories, Carlsbad, NM.

Washington TRU Solutions, LLC (WTS). 2009. Specification for Prepackaged MgO Backfill. 

Specification D-0101, Revision 8, February 11, 2009. Washington TRU Solutions, Carlsbad, NM.

Zeitler, T. 2015. Summarized BRAGFLO Results for R1S2 of CR-2014 Analysis. ERMS 563788. Sandia 

National Laboratories, Carlsbad, NM. .

 

* Copyrighted reference not provided in Enclosure 2.
4

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ATTACHMENT A

BRAGFLO OUTPUT FOR R1S2 OF CRA-2014 AND CALCULATION OF DIFFUSION 

PENETRATION LENGTH FOR ALL VECTORS

Table A-1 provides the BRAGFLO output data for waste panel porosity, waste panel pore volume, and 

cumulative brine flow up the intrusion borehole for each of the 100 vectors in R1S2. Table A-1 also 

provides the calculated hydraulic residence time and diffusion penetration length for each vector in R1S2. 

The calculations of hydraulic residence time and diffusion penetration length require parameter values for 

the following quantities:

 Volume of the waste panel is 46,136 m

3

 Initial waste porosity is 0.848

 Duration of the flow in the intrusion borehole is 9,650 years

 Free diffusion coefficient for CO2 in WIPP brine is 1×10-5cm2/s [3.16×10-2 m

2

/year]. The free 

diffusion coefficient for CO2 in WIPP brine is one-half of the free diffusion coefficient for CO2 in 

seawater.

Exact BRAGFLO output values were used for the calculations of residence time and diffusion length in 

Table A-1, and results have been rounded for presentation purposes. Any small discrepancies are due to 

this round-off process. For example, the exact calculation of panel pore volume for vector 17 is 

(0.1246707)(46,135.568 m3) = 5,751.75 m3, while a calculation using rounded values in footnote 1 on 

page 3 of this document gives: (0.1247)(46,136. m

3

) = 5,753 m3.

The key output parameter from this analysis is the diffusion penetration length, which varies from 1.43 m 

for vector 17 to 453 m for vector 99. The output for vector 17 provides the basis for this analysis, and the 

use of data from vector 17, with the minimum diffusion penetration length, provides a conservative bias 

(i.e., underestimates) the effectiveness of diffusive mixing.

The two rightmost columns of Table A-1 provide the output from the 100 vectors, sorted by the smallest 

to the largest values of diffusion penetration length.

The BRAGFLO output for R1S2 is in file: cra14_r1_s2_results.xlsx that was provided by Sandia 

National Laboratories (Zeitler 2015).
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Table A-1. BRAGFLO Output for R1S2 of the CRA-2014 and Calculation of Diffusion Penetration Length

Cumulative Panel

Flow Up Waste Pore Borehole Effective Sorted

Borehole Porosity Volume Flow Rate Residence Intrinsic Diffusion Diffusion Diffusion

(10k yrs) (10k yrs) (10k yrs) (10k yrs) Time Porosity Coefficient Length Sorted Length

Vector m

3

(-) (-) m

3

/yr yrs (-) (m2/yr) (m) Vector (m)

1 877.82 0.1232 5684.44 0.09 62490 0.4477 6.33E-03 19.88 17 1.43

2 5791.36 0.1404 6475.85 0.60 10791 0.4801 7.27E-03 8.86 7 1.87

3 4405.10 0.1220 5629.81 0.46 12333 0.4453 6.26E-03 8.79 36 1.88

4 5.77 0.1806 8332.38 0.00 13939868 0.5430 9.30E-03 360.15 22 2.24

5 29.63 0.1793 8273.59 0.00 2694933 0.5412 9.24E-03 157.84 50 2.34

6 2625.43 0.1846 8518.78 0.27 31312 0.5485 9.49E-03 17.24 12 2.51

7 100595.30 0.1240 5718.91 10.42 549 0.4492 6.37E-03 1.87 98 2.75

8 5306.25 0.1497 6905.73 0.55 12559 0.4962 7.77E-03 9.88 9 2.80

9 43702.39 0.1226 5658.27 4.53 1249 0.4466 6.29E-03 2.80 45 2.99

10 5.62 0.1277 5891.84 0.00 10122213 0.4566 6.58E-03 258.05 30 3.20

11 896.47 0.1261 5819.26 0.09 62641 0.4535 6.49E-03 20.16 27 3.31

12 54949.82 0.1229 5670.81 5.69 996 0.4471 6.31E-03 2.51 78 3.85

13 5811.01 0.1225 5650.11 0.60 9383 0.4462 6.28E-03 7.68 66 3.97

14 4183.25 0.1274 5875.49 0.43 13554 0.4559 6.56E-03 9.43 28 4.89

15 5.74 0.1415 6526.87 0.00 10975209 0.4821 7.33E-03 283.70 67 5.13

16 777.48 0.1691 7799.84 0.08 96810 0.5266 8.75E-03 29.10 20 5.19

17 173205.10 0.1247 5751.75 17.95 320 0.4506 6.41E-03 1.43 82 5.25

18 3.86 0.1802 8314.47 0.00 20778502 0.5425 9.29E-03 439.27 83 5.38

19 37.48 0.1435 6622.03 0.00 1704984 0.4857 7.44E-03 112.66 55 5.51

20 13877.29 0.1276 5886.04 1.44 4093 0.4563 6.57E-03 5.19 79 6.39

21 7.06 0.1462 6743.64 0.00 9222042 0.4902 7.58E-03 264.46 34 6.49

22 72249.68 0.1257 5799.42 7.49 775 0.4527 6.47E-03 2.24 63 6.52

23 3116.97 0.1249 5764.33 0.32 17846 0.4512 6.42E-03 10.71 58 6.63

24 338.12 0.1376 6346.08 0.04 181116 0.4751 7.12E-03 35.91 89 6.67

25 250.77 0.1677 7737.19 0.03 297734 0.5246 8.68E-03 50.85 54 7.12

26 530.61 0.1113 5135.95 0.05 93405 0.4228 5.64E-03 22.95 13 7.68

27 30644.34 0.1212 5593.25 3.18 1761 0.4437 6.21E-03 3.31 76 7.91

28 14071.58 0.1214 5598.88 1.46 3840 0.4440 6.22E-03 4.89 3 8.79

29 311.38 0.1154 5325.51 0.03 165044 0.4316 5.88E-03 31.15 2 8.86
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Cumulative Panel

Flow Up Waste Pore Borehole Effective Sorted

Borehole Porosity Volume Flow Rate Residence Intrinsic Diffusion Diffusion Diffusion

(10k yrs) (10k yrs) (10k yrs) (10k yrs) Time Porosity Coefficient Length Sorted Length

Vector m

3

(-) (-) m

3

/yr yrs (-) (m2/yr) (m) Vector (m)

30 34001.92 0.1235 5695.91 3.52 1617 0.4482 6.34E-03 3.20 14 9.43

31 6.49 0.1814 8371.07 0.00 12440241 0.5442 9.34E-03 340.94 8 9.88

32 5.70 0.1527 7044.16 0.00 11932109 0.5011 7.92E-03 307.50 86 10.42

33 7.50 0.1180 5443.57 0.00 7006394 0.4370 6.03E-03 205.49 23 10.71

34 9064.57 0.1290 5949.34 0.94 6334 0.4590 6.65E-03 6.49 46 11.95

35 38.05 0.1117 5154.87 0.00 1307479 0.4237 5.66E-03 86.06 70 12.15

36 97005.37 0.1227 5662.27 10.05 563 0.4467 6.30E-03 1.88 80 12.93

37 13.09 0.1491 6878.53 0.00 5071889 0.4952 7.74E-03 198.10 90 13.83

38 66.51 0.1914 8831.23 0.01 1281399 0.5574 9.80E-03 112.09 69 13.88

39 100.69 0.1551 7154.87 0.01 685704 0.5050 8.05E-03 74.29 6 17.24

40 6.52 0.1105 5097.92 0.00 7547411 0.4209 5.59E-03 205.44 93 17.41

41 210.28 0.1439 6639.08 0.02 304677 0.4863 7.46E-03 47.69 52 17.42

42 9.97 0.1090 5029.15 0.00 4866706 0.4176 5.50E-03 163.67 84 17.72

43 317.12 0.1236 5701.78 0.03 173508 0.4485 6.35E-03 33.18 1 19.88

44 287.95 0.1741 8033.66 0.03 269229 0.5339 9.00E-03 49.21 11 20.16

45 36031.22 0.1189 5486.88 3.73 1470 0.4390 6.08E-03 2.99 26 22.95

46 2662.66 0.1287 5937.85 0.28 21520 0.4585 6.63E-03 11.95 62 26.01

47 111.66 0.1187 5475.38 0.01 473179 0.4385 6.07E-03 53.58 16 29.10

48 9.29 0.1460 6734.33 0.00 6997079 0.4899 7.57E-03 230.19 74 30.51

49 9.08 0.1081 4988.42 0.00 5301234 0.4157 5.45E-03 170.01 29 31.15

50 60055.71 0.1203 5550.94 6.22 892 0.4418 6.16E-03 2.34 43 33.18

51 8.34 0.1645 7588.41 0.00 8776410 0.5197 8.52E-03 273.51 24 35.91

52 1449.37 0.1381 6371.45 0.15 42422 0.4760 7.15E-03 17.42 71 44.61

53 8.61 0.1986 9162.83 0.00 10268764 0.5665 1.01E-02 322.46 41 47.69

54 6706.32 0.1221 5631.75 0.69 8104 0.4454 6.26E-03 7.12 44 49.21

55 10756.29 0.1197 5523.31 1.11 4955 0.4406 6.13E-03 5.51 25 50.85

56 8.00 0.1296 5977.76 0.00 7214414 0.4602 6.68E-03 219.57 47 53.58

57 6.78 0.1359 6268.02 0.00 8922378 0.4720 7.03E-03 250.44 61 54.68

58 11180.96 0.1460 6733.96 1.16 5812 0.4899 7.57E-03 6.63 59 61.32

59 123.22 0.1417 6537.39 0.01 511975 0.4825 7.35E-03 61.32 97 71.21

60 32.92 0.0971 4481.64 0.00 1313545 0.3899 4.80E-03 79.38 39 74.29
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Cumulative Panel

Flow Up Waste Pore Borehole Effective Sorted

Borehole Porosity Volume Flow Rate Residence Intrinsic Diffusion Diffusion Diffusion

(10k yrs) (10k yrs) (10k yrs) (10k yrs) Time Porosity Coefficient Length Sorted Length

Vector m

3

(-) (-) m

3

/yr yrs (-) (m2/yr) (m) Vector (m)

61 107.05 0.1186 5471.28 0.01 493197 0.4383 6.06E-03 54.68 60 79.38

62 489.84 0.1206 5561.97 0.05 109573 0.4423 6.17E-03 26.01 35 86.06

63 8588.80 0.1262 5823.82 0.89 6543 0.4537 6.50E-03 6.52 77 90.54

64 6.15 0.1268 5849.87 0.00 9174791 0.4548 6.53E-03 244.72 94 107.02

65 6.81 0.2249 10374.78 0.00 14701723 0.5967 1.12E-02 406.42 38 112.09

66 21488.24 0.1218 5617.10 2.23 2523 0.4448 6.24E-03 3.97 19 112.66

67 12266.73 0.1191 5495.42 1.27 4323 0.4394 6.09E-03 5.13 72 144.14

68 17.32 0.1867 8615.57 0.00 4801148 0.5513 9.59E-03 214.58 5 157.84

69 2114.23 0.1330 6136.90 0.22 28011 0.4667 6.87E-03 13.88 42 163.67

70 2275.45 0.1213 5597.82 0.24 23740 0.4439 6.22E-03 12.15 49 170.01

71 129.86 0.1074 4953.01 0.01 368071 0.4139 5.41E-03 44.61 87 177.11

72 18.84 0.1305 6022.54 0.00 3084328 0.4620 6.74E-03 144.14 95 195.79

73 6.24 0.1854 8552.09 0.00 13225200 0.5495 9.53E-03 354.96 37 198.10

74 225.38 0.0976 4503.82 0.02 192840 0.3911 4.83E-03 30.51 40 205.44

75 7.91 0.1398 6447.99 0.00 7865792 0.4790 7.24E-03 238.66 33 205.49

76 6437.11 0.1324 6109.20 0.67 9158 0.4656 6.84E-03 7.91 68 214.58

77 50.79 0.1345 6204.49 0.01 1178848 0.4694 6.95E-03 90.54 56 219.57

78 22847.74 0.1218 5617.44 2.37 2373 0.4448 6.24E-03 3.85 48 230.19

79 8806.50 0.1253 5782.39 0.91 6336 0.4519 6.45E-03 6.39 96 235.62

80 1902.83 0.1183 5456.74 0.20 27673 0.4376 6.04E-03 12.93 75 238.66

81 6.99 0.1714 7908.09 0.00 10924550 0.5300 8.86E-03 311.19 64 244.72

82 12395.68 0.1224 5647.33 1.28 4396 0.4461 6.28E-03 5.25 57 250.44

83 12180.46 0.1242 5730.55 1.26 4540 0.4497 6.38E-03 5.38 10 258.05

84 1138.41 0.1250 5765.46 0.12 48872 0.4512 6.42E-03 17.72 92 262.85

85 5.46 0.1385 6390.46 0.00 11292550 0.4768 7.17E-03 284.62 21 264.46

86 3541.73 0.1294 5968.19 0.37 16261 0.4598 6.67E-03 10.42 51 273.51

87 27.78 0.1957 9030.11 0.00 3137325 0.5629 1.00E-02 177.11 100 277.55

88 7.38 0.1616 7456.50 0.00 9752255 0.5153 8.38E-03 285.89 15 283.70

89 7868.99 0.1237 5707.87 0.82 7000 0.4487 6.35E-03 6.67 85 284.62

90 2121.72 0.1328 6127.01 0.22 27867 0.4663 6.86E-03 13.83 88 285.89

91 5.53 0.1754 8092.15 0.00 14125682 0.5357 9.06E-03 357.69 32 307.50
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Cumulative Panel

Flow Up Waste Pore Borehole Effective Sorted

Borehole Porosity Volume Flow Rate Residence Intrinsic Diffusion Diffusion Diffusion

(10k yrs) (10k yrs) (10k yrs) (10k yrs) Time Porosity Coefficient Length Sorted Length

Vector m

3

(-) (-) m

3

/yr yrs (-) (m2/yr) (m) Vector (m)

92 9.47 0.1685 7773.50 0.00 7921438 0.5257 8.72E-03 262.85 81 311.19

93 1734.27 0.1508 6959.35 0.18 38724 0.4981 7.83E-03 17.41 53 322.46

94 53.22 0.1625 7497.23 0.01 1359333 0.5167 8.42E-03 107.02 31 340.94

95 13.23 0.1481 6834.88 0.00 4986024 0.4936 7.69E-03 195.79 73 354.96

96 7.67 0.1360 6274.04 0.00 7889904 0.4722 7.04E-03 235.62 91 357.69

97 50.35 0.1068 4925.47 0.01 944042 0.4126 5.37E-03 71.21 4 360.15

98 52353.46 0.1314 6061.37 5.43 1117 0.4636 6.78E-03 2.75 65 406.42

99 3.99 0.1894 8739.83 0.00 21145638 0.5548 9.71E-03 453.22 18 439.27

100 10.99 0.1927 8891.54 0.00 7810272 0.5591 9.86E-03 277.55 99 453.22

MIN 3.86 0.0971 4481.64 0.00 320.45 0.390 4.80E-03 1.43

MAX 173205.10 0.2249 10374.78 17.95 21145638.22 0.597 1.12E-02 453.22

MEAN 9902.45 0.1392 6421.63 1.03 3300217.46 0.474 7.16E-03 107.54
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EPA Comment

2-C-4 Hydromagnesite Conversion Rate. 

Clayton (2013) formulated the conversion reaction from hydromagnesite to magnesite for inclusion in the 

BRAGFLO calculations as:

Mg5(CO3)4(OH)2•4H2O(s) → 4 MgCO3(s) + Mg(OH)2(s) + 4 H2O(l) (5)

Clayton (2013) calculates a range for the hydromagnesite conversion rate based on reaction times of 100 

years to 10,000 years. However, the minimum reaction time for this conversion is uncertain. SCA (2008) 

reviewed the available experimental and natural analogue data and concluded that hydromagnesite 

conversion is best represented by a range of zero conversion (only hydromagnesite remains after 10,000 

years) to complete conversion (only magnesite remains after 10,000 years), with a uniform distribution 

across this range. Please provide an explanation as to why the specific upper and lower limits used in the 

PA were picked.

The effect of using zero rather than 100 years as the minimum conversion rate is likely to be less brine 

production in the water balance, based on equation (5). Please provide an explanation of the effects on 

PA if the lower limit of the hydromagnesite conversion rate is set to zero while the upper limit is 

decreased by a variety of plausible factors that are less than what Clayton had adopted.

References:

Clayton, D.J. 2013. Justification of Chemistry Parameters for Use in BRAGFLO for AP-164, Rev. 1. 

Sandia National Laboratories, ERMS 559466.

SCA (S. Cohen and Associates). 2008. Review of MgO-Related Uncertainties in the Waste Isolation Pilot 

Plant. Final Report prepared for the U.S. Environmental Protection Agency Office of Radiation and 

Indoor Air, Washington, D.C., January 24, 2008.

DOE Response

As discussed in the Justification of Chemistry Parameters for Use in BRAGFLO for AP-164, Revision 1

(Clayton 2013), the range used for the hydromagnesite conversion rate was derived from the Technical 

Support Document for Section 194.24: EPA’s Evaluation of DOE’s Actinide Source Term (EPA 1998). 

In section 3 of EPA (1998) the following conceptualization was given.

“Based on a review of the literature, the Agency developed the following conceptualization of the 

sequence and time scales of reactions between infiltrating brine and MgO backfill in the WIPP 

repository:

1. Rapid reaction of MgO with brine to produce brucite (hours to days);

2. Rapid carbonation of brucite to produce nesquehonite and possibly hydromagnesite (hours to 

days);

3. Rapid conversion of nesquehonite to hydromagnesite (days to weeks);

4. Slow conversion of hydromagnesite to magnesite (hundreds to thousands of years).”

In order to capture the stated reaction time range of “hundreds to thousands of years,” versus tens or tens 

of thousands, the reaction time range of 100 to 10,000 years was used. While the range in reaction time

could be bounded by 0 (instantly to magnesite) to infinity (remains as hydromagnesite), we chose to 
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follow the conceptualization discussed in EPA (1998). In the Review of MgO-Related Uncertainties in 

the Waste Isolation Pilot Plant (SCA 2008), S. Cohen and Associates discuss potential reaction time 

ranges for the hydromagnesite conversion rate between a 73 years half-life (time required to convert half 

the hydromagnesite) and 6,200 years required for complete conversion. This is in line with the 

conceptualization discussed above. The discussion of using the bounding assumptions of all 

hydromagnesite or all magnesite appears to be limited to estimating the overall amount of carbon dioxide 

consumed by the magnesium oxide after 10,000 years.

Reducing the minimum reaction time to zero would result in an instantaneous conversion of 

hydromagnesite to magnesite, freeing the bound water molecules at an earlier time. This would result in 

an increase in the volume of brine to occur 100 years earlier, but should have a minimal effect on overall 

performance assessment results. The potential effects on performance assessment can be estimated by 

examining the impact of the sampled hydromagnesite conversion rate on the final output. In the 

Sensitivity of the CRA-2014 Performance Assessment Releases to Parameters (Kirchner 2013), Kirchner

documents the sensitivity of releases to sampled input parameters. The parameter used to represent the 

hydromagnesite conversion rate (WAS_AREA:HYMAGCON) did not show any correlation with releases 

from the repository. Therefore, the potential effects on performance assessment with the current range of 

the sampled hydromagnesite conversion rate are minimal.

References:

Clayton, D.J. 2013. Justification of Chemistry Parameters for Use in BRAGFLO for AP-164, Revision

1. ERMS 559466. Sandia National Laboratories, Carlsbad, NM.

Kirchner, T. 2013. Sensitivity of the CRA-2014 Performance Assessment Releases to Parameters. 

ERMS 560043. Sandia National Laboratories, Carlsbad, NM.

S. Cohen and Associates (SCA). 2008. Review of MgO-Related Uncertainties in the Waste Isolation 

Pilot Plant. January 24, 2008. Final Report prepared for the U.S. Environmental Protection Agency 

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

U.S. Environmental Protection Agency (EPA). 1998. Technical Support Document for Section 194.24: 

EPA’s Evaluation of DOE’s Actinide Source Term. Docket A-93-02, Item V-B-17. Environmental 

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

2-C-6 MgO Hydration Rate. 

MgO has been supplied for the WIPP engineered barrier by three vendors: National Magnesia 

Chemicals, Premier Chemicals, and, currently, from Martin Marietta Magnesia Specialties (Martin 

Marietta). The majority of the MgO in the repository is from Premier Chemicals and Martin Marietta. 

Clayton (2013) used MgO hydration rates obtained from experiments conducted with MgO supplied by 

Premier Chemicals to establish the hydration rates used in PA. However, Wall (2005) performed 

preliminary tests with the Martin Marietta MgO and concluded that it reacted to form brucite faster than 

Premier MgO. Given the multiple vendors that supply MgO a summary of the following information 

needs to be provided;

 The inundated and humid MgO hydration rates for MgO from the three vendors.

 The potential effects of the variable MgO hydration rates on repository performance.

 The amounts of National Magnesia Chemicals, Premier MgO and Martin Marietta MgO that will 

be present in the WIPP repository at the time of closure, and assumptions regarding the future 

source(s) of MgO.

References:

Clayton, D.J. 2013. Justification of Chemistry Parameters for Use in BRAGFLO for AP-164, Rev. 1. 

Sandia National Laboratories, ERMS 559466.

Deng, H., M. Nemer, and Y. Xiong. 2007. Experimental Study of MgO Reaction Pathways and Kinetics 

Rev. 1. Sandia National Laboratories TP 06-03.

Deng, H., Y. Xiong, M. Nemer and S. Johnsen. 2009. Experimental Work Conducted on MgO Long-Term 

Hydration. Sandia National Laboratories ERMS 551421.

Wall, N.A. 2005. Preliminary Results for the Evaluation of Potential New MgO. Sandia National 

Laboratories ERMS 538514.

DOE Response

As mentioned in Appendix MgO-2014 (DOE 2014), there are three vendors for the MgO in the WIPP, 

i.e., National Magnesia Chemicals, Premier Chemicals, and Martin Marietta Magnesia Specialties. As 

National Magnesia Chemicals supplied MgO for only a short time (about one year) and this source

accounts for only 0.41% of the MgO in the repository (see Table 1), its hydration rates were not 

systematically characterized. The hydration rates for Martin Marietta MgO are faster than those for 

Premier MgO. As a direct comparison, for instance, Martin Marietta MgO reached complete hydration 

for the reactive portion of the industrial grade MgO in 43 days at 70oC in deionized (DI) water in the 

accelerated inundated hydration test described in Experimental Work Conducted on MgO 

Characterization and Hydration (Deng et al. 2009), whereas Premier MgO reached complete hydration for 

the reactive portion of the industrial grade MgO in 78 days under the same conditions described in 

Hydration of Magnesium Oxide in the Waste Isolation Plant (Snider 2002). In general, faster MgO 

hydration rates would reduce the amount of brine in the repository at earlier times, but would not change 

the total amount of brine that could be consumed by the MgO.

The experiments for MgO hydration rates at the repository temperature with Premier MgO were 

completed as described in Analysis of MgO Hydration Laboratory Results and Calculation of Extent of 

Hydration and Resulting Water Uptake versus Time under Postulated WIPP Conditions (Nowak and 
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Clayton 2007, and references therein), and their hydration rates were implemented in performance 

assessment (PA). Experiments for determination of MgO hydration rates at the repository temperature 

with Martin Marietta MgO have not been completed, so their hydration rate data have not been included 

in MgO hydration rate parameters. Using the slower hydration rates for Premier MgO for PA is a 

conservative assumption.

Table 1. Amounts of MgO from three vendors that were already emplaced in WIPP (from 

Kouba 2015)

Vendor Amounts of MgO Procured 

and Emplaced in WIPP (Tons)

Percentage 

(%)

National Magnesia Chemicals 148 0.41

Premier Chemicals 10856.4 30.14

Martin Marietta Magnesia Specialties 25016.1 69.45

Sensitivity of the CRA-2014 Performance Assessment Releases to Parameters (Kirchner 2013) 

documents the sensitivity of releases to sampled input parameters (see Table 9 in Kirchner 2013). The 

variables used to represent the MgO hydration rates in the various brines showed that the releases from 

the repository are at best only weakly correlated with the MgO hydration rates over the range sampled. 

Therefore, the potential effects on performance assessment by changing the MgO hydration rates should 

be minimal.

At the time of closure, the amounts of MgO from National Magnesia Chemicals and Premier Chemicals

in the WIPP listed in Table 1 will remain unchanged, but their percentages will change as the amounts of 

MgO from Martin Marietta Magnesia Specialties will increase. At this time, the final, exact amounts of 

MgO from Martin Marietta Magnesia Specialties that will be present in the WIPP at the closure are not 

available. The future provider of MgO is expected to be Martin Marietta Magnesia Specialties. This 

assumption is based on continued availability of the raw materials for their production, and the outcome 

of competitive procurements as required by the Federal Acquisition Regulations and the Department of 

Energy Acquisition Regulations.

References:

Deng, H.-R., Y.-L. Xiong, M.B. Nemer, and S. Johnsen. 2009. Experimental Work Conducted on MgO 

Characterization and Hydration. Materials Res. Soc. Symp. Proc. 1124, Q05-05 (6 pages).*

Kirchner, T. 2013. Sensitivity of the CRA-2014 Performance Assessment Releases to Parameters. 

ERMS 560043. Sandia National Laboratories, Carlsbad, NM.

Kouba, S. 2015. E-mail from Steve Kouba dated March 9, 2015, to Yongliang Xiong, Todd Zeitler, and 

Steve Wagner regarding the input for 2-C-6. ERMS 563786. Sandia National Laboratories, Carlsbad, 

NM.

Nowak, E.J. and D.J. Clayton. 2007. Analysis of MgO Hydration Laboratory Results and Calculation of 

Extent of Hydration and Resulting Water Uptake versus Time under Postulated WIPP Conditions. ERMS 

546769. Sandia National Laboratories, Carlsbad, NM.

 

*

Copyrighted reference not provided in Enclosure 2.
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Snider, A.C. 2002. Hydration of Magnesium Oxide in the Waste Isolation Plant. SAND2002-1645P. 

Sandia National Laboratories, Albuquerque, NM.*

U.S. Department of Energy (DOE). 2014. Title 40 CFR Part 191 Subparts B and C Compliance 

Recertification Application 2014 for the Waste Isolation Pilot Plant, Appendix MgO-2014, Magnesium 

Oxide as an Engineered Barrier, United States Department of Energy, Waste Isolation Pilot Plant.

Carlsbad Field Office, Carlsbad, NM.
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EPA Comment

2-32-G1 Obsolete FEP Screening Arguments, Curtailed FEP Screening Arguments, and 

Completeness Considerations. 

The screening arguments in the CRA-2014, Appendix SCR-2014 for many FEPs have been carried 

forward from past baseline reviews and do not necessarily reflect changes that have occurred in the past 

several years. This especially applies to information on how some FEPs are accounted for in PA. Some 

FEPs need to be updated to reflect current repository design and new knowledge of repository behavior. 

These are identified in Table FEP-1.

For some FEPs, the screening argument needs to provide a more complete discussion of the FEP and 

how it is determined to be screened-in or screened-out. The supporting arguments, along with documents 

incorporated by references, need to provide a basic understanding of how the FEP is accounted for in PA 

calculations, where the FEP is accounted for in the repository region and surrounding geosphere, and 

when in the regulatory time frame the FEP is accounted for. Those FEPs with inadequate or curtailed 

screening arguments are provided in Table FEP-1.

For some FEPs that DOE has reported “no change”, EPA disagrees and believes that DOE should 

reconsider and update the FEP discussion. Table FEP-1 includes those FEPs in this category that EPA 

has identified, to date, as being incomplete.

DOE Response

Since the Compliance Certification Application (CCA), Appendix SCR is a screening document for 

individual FEPs, and therefore contains only the description, screening argument, and decision as to 

whether the FEP is to be included (screened-in) or excluded (screened-out) within PA scenarios. For 

those FEPs that are screened-in, an attempt has been made to point to the appropriate location within the 

compliance documentation that describes and justifies the implementation of the FEP with the appropriate 

model(s). Because the screening document is quite large, and because FEPs span a myriad of technical 

and scientific disciplines, attempting to describe the implementation of each FEP within the screening 

document would: 1) result in a document of unmanageable size, 2) create redundancy within the 

compliance documentation, and 3) create the opportunity for inconsistency and error within the 

compliance baseline.

The FEPs baseline is reviewed any time a change to the baseline is proposed, or any time that new data or 

conditions affect or relate to screening arguments or decisions. Since recertification applications are an 

opportunity to “roll-up” and account for any changes that have occurred since the last recertification, 

updates to the FEPs baseline are reflected cumulatively in Appendix SCR. Requests by the EPA to 

describe the implementation methodology of specific FEPs in Appendix SCR-2014 are not consistent 

with the current FEP program or format and content of Appendix SCR. The DOE agrees and understands 

that such information must be included within the compliance documentation; however, Appendix SCR is 

not the correct place to provide this information, rather pointers should be given to the correct source 

material as appropriate. Such information has historically been found within Chapter 6 of the CCA, 

Appendix MASS of the CCA, or their updated successor documents (Appendix PA-2004 and Attachment 

MASS-2004, Appendix PA-2009, Appendix PA-2014, etc.). Again, this is mostly a practical matter that 

has to do with managing the compliance documentation in a way that avoids duplication and 

inconsistency.

The DOE will continue to document any new data and information with each Compliance Recertification 

Application. Whenever new data or new information are available, the affected FEPs and their screening 

decisions will be updated. This process is consistent with EPA’s comments as provided in its February 

27, 2015, letter and accompanying FEPs table. In cases where we update FEPs as a result of addressing 

EPA’s comments, we will provide updated excerpts from Appendix SCR-2014.
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EPA Comment

2-32-S4 FEP H28 Enhanced Oil and Gas Production. 

Please address whether enhanced production techniques are being used in the Delaware basin and in the 

vicinity of WIPP. Please also address the potential for these techniques to create a preferential pathway 

for radionuclide releases through a second well.

DOE Response

Enhanced production refers to methods used to enhance production in a well after the primary production 

rate becomes unsatisfactory. Enhanced production techniques employed in the Delaware Basin include 

water injection, waterflood, and carbon-dioxide (CO2) miscible flooding. These techniques have been 

commonly used in the Delaware Basin, but only small-scale pilot injection1occurs near the WIPP. No 

unitized floods have been identified or planned2. As stated in Melzer (2013), carbon dioxide miscible 

flooding is not an attractive production enhancement technique near the WIPP due to unfavorable 

reservoir characteristics (channel sands). These same characteristics make widespread waterflooding 

unlikely as well.

In the mid-1990s, WIPP stakeholders suggested including an injection well into WIPP performance 

assessment scenarios. The DOE did not agree that the scenario was technically credible, and conducted 

very conservative analyses assuming a faulty injection well operated at extreme pressures for a very long 

time period located at the WIPP boundary to simulate a worse-case injection scenario. These analyses 

concluded that such activities do not jeopardize the ability of the WIPP to perform as expected (Stoelzel 

and Obrien [1996], and Stoelzel and Swift [1997]). EPA concurred with this analysis in its Technical 

Support Document for Section 194.32: Fluid Injection Analysis (EPA 1998) and stated, “...fluid injection 

was appropriately screened out of performance assessment by DOE.”

EPA’s question asks whether these techniques can create pathways for radionuclide releases through a 

second well. It is assumed that the second well is located outside the WIPP boundary and then employs 

enhanced recovery methods later in the life of the well. Due to the reservoir characteristics cited above, 

only pilot injection (single-point injection) would be employed near the WIPP, not a widespread 

waterflood project. In this case, water would be injected into the target formation to move oil or gas 

toward a neighboring producing well (not for disposal purposes). Because injection wells are permitted to 

pressures safely below the fracture threshold, fractures will not occur and therefore will not create any 

pathway that would connect the repository to the injection well. In waterflood or “pilot flood” projects 

such as this, exceeding the fracture threshold is not only in violation of the operating permit3, but also 

detrimental to the purposes of enhancing production. Therefore, operators ensure that these threshold 

pressures are not exceeded. Given these limitations, it is not expected a well near the WIPP employing 

enhanced production techniques would create a release pathway or connection to the other wells outside 

the WIPP boundary or waste panels within the boundary. Scenarios where wells within the boundary that 

do not intersect WIPP waste are explicitly exempted from consideration of enhanced production 

techniques under 40 CFR 194.33(d), where it states, “With respect to future drilling events, performance 

assessments need not analyze the effects of techniques used for resource recovery subsequent to the 

 

1 Note: “Pilot injection” refers to a single injection well, not an expansive, multi-injection-site waterflood project 

intended to influence several producing wells. 

2 Unitization provides for the development of an entire geologic structure or area by a single operator so that drilling 

and production may proceed in the most efficient and economic manner. Unitized waterfloods are typically 

designated for large, continuous reservoir types. 

3

Permits to inject are issued by the New Mexico Oil Conservation Division and limit injection pressures based on 

depth, fracture pressures, and other rock and reservoir characteristics.
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drilling of the borehole.” (See also Appendix SCR-2014 Section SCR-5.2.1.7, FEPs H60 Liquid Waste 

Disposal – Inside Boundary, and H61 Enhanced Oil and Gas Production – Inside Boundary.) 

References:

Melzer, L.S. 2013. An Updated Assessment of the CO2-Enhanced Oil Recovery Potential in the Vicinity 

of the Waste Isolation Pilot Plant (June). Melzer Consulting, Midland, TX.

Stoelzel, D.M., and D.G. O’Brien. 1996. The Effects of Salt Water Disposal and Waterflooding on 

WIPP. Summary Memorandum of Record for NS-7a. ERMS 240837. Sandia National Laboratories, 

Albuquerque, NM.

Stoelzel, D.M., and P.N. Swift. 1997. Supplementary Analyses of the Effect of Salt Water Disposal and 

Waterflooding on the WIPP. ERMS 244158. Sandia National Laboratories, Albuquerque, NM.

U.S. Environmental Protection Agency (EPA). 1998. Technical Support Document for Section 193.32: 

Fluid Injection Analysis (May). Environmental Protection Agency Office of Radiation and Indoor Air, 

Washington, D.C.
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EPA Comment

2-32-S5 FEP H58 Solution Mining. 

This FEP is screened out partially on the basis that solution mining will not occur in low ambient 

temperature conditions. However, solution mining is occurring in the nearby Eddy mine under similar 

conditions that exist in the vicinity of WIPP. Please provide text that reconciles the basis of the screening 

argument and the conditions at the Eddy mine where solution mining is taking place.

DOE Response

The official screening decision for this FEP, as stated in Appendix SCR-2014, is based on regulatory 

grounds under the “future states assumption” found in 40 CFR 194.25. That is, from a strictly regulatorybased perspective, the solution mining project currently underway by Intrepid Mining can be screened out 

because it is located geographically outside of the Delaware Basin boundary, and regulatory guidance is 

clear that areas outside the basin boundary are, by definition, not in the vicinity of WIPP and therefore not 

to be considered in compliance applications due to their geographic and geologic differences from the 

WIPP site. This position is supported by the EPA in its Response to Comments, Section 8, Issue GG 

(EPA 1998d):

“...However, the Agency emphasizes that, in accordance with the WIPP compliance 

criteria, solution mining does not need to be included in the PA. As previously discussed, 

potash solution mining is not an ongoing activity in the Delaware Basin. Section 

194.32(b) of the rule limits assessment of mining effects to excavation mining. Thus the 

solution mining scenarios proposed are excluded on regulatory grounds after repository 

closure. Prior to or soon after disposal, solution mining is an activity that could be 

considered under Section 194.32(c). However, DOE found that potash solution mining is 

not an ongoing activity in the Delaware Basin; and one pilot project examining solution 

mining in the Basin is not substantive evidence that such mining is expected to occur in 

the near future.”

For many FEPs within WIPP’s baseline, screening can sometimes be accomplished based on more than 

one screening criterion. In such cases, the DOE often opts for the regulatory screening, if appropriate. 

Such is the case for H58. However, in the interest of completeness and comprehensiveness, the DOE felt 

it worthwhile to discuss the Intrepid solution mining project in Appendix SCR-2009. The DOE again 

updated this project’s progress in Appendix SCR-2014. DOE has followed the development of this 

project from its inception, and has verified that the solution mining activity remains outside the Delaware 

Basin boundary, thus supporting the screening decision of SO-R (screened-out, based on regulatory 

grounds).

While the screening decision of SO-R is the “decision of record,” a technical discussion is also presented 

about both the probability and consequence of solution mining for potash at the WIPP within Appendix 

SCR-2014. The DOE feels that while these arguments are not the basis of the current screening decision, 

they are valuable in understanding the nature and impact of this activity should it occur at or near the 

WIPP in the future. Appendix SCR-2014 provides additional information regarding the possible 

consequences of solution mining near the WIPP, however this information does not affect the current 

screening decision.
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References:

U.S. Environmental Protection Agency (EPA). 1998. Response to Comments: Criteria for the 

Certification and Recertification of the Waste Isolation Pilot Plant’s Compliance with the 40 CFR Part 

191 Disposal Regulations (May). Environmental Protection Agency Office of Radiation and Indoor Air, 

Washington, D.C.
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EPA Comment

2-32-S7 FEP W3 Heterogeneity of Waste Forms. 

The screening argument citation of the CCA as the source of information on the heterogeneity of waste 

forms ignores changes that have occurred in the past 15 years, including supercompacted waste and 

mingling RH waste in shielded containers with CH waste. Please update the information to reflect current 

waste forms.

DOE Response

The screening argument for W3 Heterogeneity of Waste Forms has been revised to reflect new 

information regarding the variety of waste forms and types that are approved for disposal. However, the 

details regarding the implementation of the waste inventory and waste heterogeneity are presented 

elsewhere within the compliance documentation, and are referenced in the revised Appendix SCR text. 

Waste heterogeneity from an activity standpoint is accounted for in disturbed performance scenarios (see

Appendix PA-2014, Section PA-3.8). Any new information related to the heterogeneity of wastes and 

variations to their physical form has been updated with each CRA as appropriate. These variations have 

been discussed historically in other areas of the CCA and subsequent CRAs, as appropriate. This 

information continues to be represented within the compliance baseline, as all previous compliance 

submittals and correspondence remain part of the certification basis.

With regard to EPA’s specific request about current waste forms, Hansen et al. (2004) discusses the 

effects of supercompacted waste and heterogeneous waste emplacement on repository performance. In 

that report, the DOE “assessed the baseline features, events and processes (FEPs) to identify specific 

components of performance assessment that could be affected by supercompacted waste.” The DOE

found that “no changes to the waste-related FEPs were warranted in the new performance assessment.” 

The results of that assessment have not been superseded, so the DOE continues to support that finding, 

and no changes to the waste-related FEPs based on supercompacted waste and heterogeneous waste 

emplacement are currently warranted. The EPA’s review (EPA 2004) and approval (Marcinowski 2004) 

of this analysis concurred with DOE’s findings that these wastes are suitable for disposal in WIPP and are 

adequately represented within performance assessment. 

More recently, the approval to dispose shielded RH containers was granted by EPA in Edwards (2013). 

This approval was based, in part, upon a bounding analysis (Dunagan et al. 2007) that evaluated the 

effects of 1) disposing all of the RH waste in the walls as originally assumed; 2) disposing all of the RH 

waste in shielded containers on the room floors, and 3) disposing half of the RH waste in shielded 

containers and the other half in the walls. The bounding analysis concludes that the packaging and 

emplacement of RH waste in shielded containers has no discernible impact to all release pathways (i.e., 

cuttings, cavings, spallings, direct brine releases, groundwater releases, and total releases).

SCR-6.1.2.1.2 Summary of New Information

The waste inventory used for the CRA-2014 PA calculations has been updated as provided in Kicker and 

Zeitler (2013). Since these FEPs are accounted for in PA, inventory-related parameters may differ from 

those used in previous PAs; however, the screening decisions have not changed and these FEPs are 

represented in PA calculations. The EPA approved the use of the shielded RH container as an allowable 

disposal container in WIPP (Edwards 2013). The impacts of this container upon WIPP performance were 

evaluated in Dunagan et al. (2007).
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SCR-6.1.2.1.3 Screening Argument

Waste characteristics, comprising the waste inventory and heterogeneity of waste forms, are described in 

the CCA, Appendix BIR. The waste inventory is accounted for in PA calculations in deriving the 

dissolved actinide source term and gas generation rates. The distribution of contact-handled transuranic 

(CH-TRU) and remote-handled transuranic (RH-TRU) waste within the repository leads to room-scale 

heterogeneity of the waste forms, which is accounted for in PA calculations when considering the 

potential activity of waste material encountered during inadvertent borehole intrusion (Appendix PA2014, Section PA-3.8). The DOE implements waste heterogeneity in waste forms through the assumption 

of random placement of TRU waste in the repository. This assumption includes all waste container forms 

and types. Details regarding the implementation of this assumption are provided in the CRA-2009, 

Appendix MASS-2009, Section MASS-21.0. This implementation methodology has not changed as a 

result of the addition of the shielded RH-waste container. 

This change has been added to Enclosure 4, CRA-2014 Errata Tracking.

References:

Dunagan, S.C., G.T. Roselle, E.D. Vugrin, and J.T. Long. 2007. Analysis Report for Shielded Container 

Performance Assessment. ERMS 547197. October 31, 2007. Sandia National Laboratories, Carlsbad, 

NM.

Edwards, J.D. 2013. Letter to J. Franco, Carlsbad Field Office, approving the disposal of the shielded 

container assembly. September 3, 2013. U.S. Environmental Protection Agency, Washington, D.C.

Hansen, C.W., L.H. Brush, M.B. Gross, F.D. Hansen, B.Y. Park, J.S. Stein and T. W. Thompson. 2004. 

Effects of Supercompacted Waste and Heterogeneous Waste Emplacement on Repository Performance.

ERMS 533551.

Marcinowski, F. 2004. Letter to R. P. Detwiler, Carlsbad Field Office, approving the disposal of 

compressed waste from the Idaho National Environmental and Engineering Laboratory’s Advanced 

Mixed Waste Treatment Facility at the Waste Isolation Pilot Plant. March 26, 2004. U.S. Environmental 

Protection Agency, Washington, D.C.

Trinity Engineering Associates. 2004. Review of Effects of Supercompacted Waste and Heterogeneous 

Waste Emplacement on WIPP Repository Performance, Final Report. March 17, 2004. U.S. 

Environmental Protection Agency, Washington, D.C.
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EPA Comment

2-32-S8 FEP W5 Container Material Inventory. 

Please supplement the screening argument with an explanation of the implementation in PA of the 

material inventory of shielded containers containing RH waste.

DOE Response

Appendix SCR is not intended to provide comprehensive explanations on how a FEP is represented in PA 

models, but does provide pointers to other compliance documents that contain this information. The 

implementation and impact of the addition of shielded containers to the inventory was discussed in the 

CRA-2009, Section 15.6.4.3, and with more recent information in Section 15.8.4.3 of the CRA-2014. 

Analyses evaluating shielded containers on WIPP performance are found in Dunagan et al. (2007). The 

masses of shielded container material parameters are represented in PA the same way as for other RH 

containers. Changes to Appendix SCR-2014 text that points to the implementation details of waste 

containers within performance assessment has been made and is provided in the revised text below.

SCR-6.1.3.2 FEP Number: W5

FEP Title: Container Material Inventory

SCR-6.1.3.2.1 Screening Decision: UP

The Container Material Inventory is accounted for in PA calculations.

SCR-6.1.3.2.2 Summary of New Information

The masses of container materials associated with the waste inventory for the CRA-2014 have been 

updated as detailed in Van Soest (2012). The EPA approved the use of the shielded RH container as an 

allowable disposal container in WIPP (Edwards 2013). The impacts of this container upon WIPP 

performance were evaluated in Dunagan et al. (2007). 

SCR-6.1.3.2.3 Screening Argument

The container material inventory is described in Van Soest (2012) and is accounted for in PA calculations 

through the estimation of gas generation rates (see Appendix PA-2014, Section PA-4.2.5). In the CCA, 

Appendix WCL, a minimum quantity of metallic Fe was specified to ensure sufficient reactants to reduce 

radionuclides to lower and less soluble oxidation states. This requirement is met as long as there are no 

substantial changes in container materials. The inventory used for the CRA-2014 contains 3.69 x 107 kg 

of steel in packaging (includes containers) materials. This value is up slightly from 3.59 x 107 kg 

reported in 2008 (Van Soest 2012). Modeling assumptions related to the implementation of waste 

container materials can be found in Appendix MASS-2014, Table MASS-5.

This change has been added to Enclosure 4, CRA-2014 Errata Tracking.

Reference:

Dunagan, S.C., G.T. Roselle, E.D. Vugrin, and J.T. Long. 2007. Analysis Report for Shielded Container 

Performance Assessment. ERMS 547197. October 31, 2007. Sandia National Laboratories, Carlsbad, 

NM.
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EPA Comment

2-32-S9 FEP W18 Disturbed Rock Zone (DRZ). 

The screening argument for this FEP states “This excavation-induced, host-rock fracturing is accounted 

for in PA calculations (the CCA, Chapter 6.0, Section 6.4.5.3).” The cited CCA text indicates that the 

DRZ is modeled in the same way around all repository excavations. However, the DRZ is now expected to 

vary spatially. Provide an updated description of the DRZ in the waste and non-waste locations of the 

repository.

2-32-S10 FEP W19 Excavation-Induced Changes in Stress. Screening argument was combined with 

that for W18 Disturbed Rock Zone (DRZ); please see comments for FEP W18.

DOE Response

FEPs W18 and W19 have been screened in since the CCA (Chapter 6.0, Section 6.4.5.3). The status of 

these FEPs did not change for CRA-2014, and host-rock fracturing resulting from excavation-induced 

changes in stress has always been included in PA calculations. Its detailed implementation in PA 

calculations is discussed in other parts of WIPP compliance documentation, as described below. The 

screening argument for these FEPs (Appendix SCR-2014) refers to the CCA (Chapter 6.0, Section 

6.4.5.3) to note that excavation-induced, host-rock fracturing has been included in PA calculations (as a 

disturbed rock zone, DRZ), but does not describe the specific details of how this fracturing has been 

implemented in PA calculations. In the “Summary of New Information” for these FEPs (Appendix SCR2014), AP-164 (Camphouse 2013) is cited as providing a description of the DRZ, including the DRZ in 

both the waste and non-waste locations of the repository and in locations beyond the panel closures (i.e., 

operational and experimental areas). Further, Camphouse (2013) describes how the spatial variation in 

the DRZ is implemented in different parameter values for the DRZ in the waste locations (material 

DRZ_1) and in the non-waste locations around the ROMPCS (material DRZ_PCS):

For the first 200 years post-closure, the disturbed rock zone (DRZ) above and below the 

ROMPCS maintained the same properties as specified to the DRZ surrounding the

disposal rooms (PA material DRZ_1). After 200 years, the DRZ above and below the 

ROMPCS was modeled as having healed, and was represented by material DRZ_PCS.

And also:

It is expected that healing of the DRZ region above and below the ROMPCS after 200 

years will not yield an increase in permeability when compared to the damaged DRZ. A 

relationship will be implemented in the CRA-2014 PA to enforce that the permeability of 

material DRZ_PCS is never greater than the permeability of material DRZ_1.

Although there is an updated implementation and updated parameters for the DRZ, there is no change to 

the screening argument or screening decision for these FEPs. 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. 

Reference:

Camphouse, R.C. 2013. Analysis Plan for the 2014 WIPP Compliance Recertification Application 

Performance Assessment. ERMS 559198. Sandia National Laboratories, Carlsbad, NM.
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EPA Comment

2-32-S15 FEP W28 Nuclear Explosions. 

Please modify the screening argument to address whether, in addition to “a reduction of TRU 

radionuclides from previous estimates”, the quantities of fissile radionuclides have also been reduced.

DOE Response

This screening argument is based on the lack of a mechanism for rapid compression of fissile mass to a 

high density; this remains true. It would be reasonable to assume, however, that since the overall TRU 

inventory has declined, the fissile radionuclide inventory has also declined. In response to the EPA’s 

comment, we have taken the fissile radionuclides as identified in the WIPP TRAMPAC (DOE 2012) as 

having a fissile gram equivalent of greater than 0.00,1and summed the total curies (CH and RH) for these 

radionuclides from the Performance Assessment Inventory Report-2008 (PAIR)2(Crawford et al. 2008) 

used in the 2009 PABC, and then compared them to the same curie totals3from the PAIR-2012 (Van 

Soest 2012) used in the CRA-2014. Fissile radionuclides have indeed reduced from approximately 3.1 

million curies for the PABC-2009 to 2.7 million curies for the CRA-2014. The Appendix SCR-2014 text 

has been updated with this information and is provided below.

SCR-6.3.3.2 FEP Number: W28

FEP Title: Nuclear Explosions

SCR-6.3.3.2.1 Screening Decision: SO-P

Nuclear explosions have been eliminated from PA calculations on the basis of low probability of 

occurrence over 10,000 yrs.

SCR-6.3.3.2.2 Summary of New Information

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

Zeitler (2013). This new information does not change the screening argument or decision for this FEP.

SCR-6.3.3.2.3 Screening Argument

Nuclear explosions have been eliminated from PA calculations on the basis of low probability of 

occurrence over 10,000 yrs. For a nuclear explosion to occur, a critical mass of Pu would have to undergo 

rapid compression to a high density. Even if a critical mass of Pu could form in the system, there is no 

mechanism for rapid compression. Inventory information used for the CRA-2014 is presented in Kicker 

and Zeitler (2013). The updated inventory information for the CRA-2014 shows a reduction of TRU 

radionuclides from previous estimates. Fissile radionuclides have reduced from approximately 3.1 

million curies for the PABC-2009 to 2.7 million curies for the CRA-2014. Thus, current criticality 

screening arguments are conservatively bounded by the previous CCA screening arguments (Rechard et 

al. 1996, 2000, and 2001).

This change has been added to Enclosure 4, CRA-2014 Errata Tracking.

 

1

See the WIPP TRUPACT Authorized Methods of Payload Control (TRAMPAC), Table 3.1-2. 

2 Data from Table A 4 (decayed to 2033) from the PAIR-2008 was used.

3 Data from Table 5-3 and 5-4 (decayed to 2033) from the PAIR-2012 was used.
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References:

Crawford, B.A., D. Guerin, S. Lott, B. McInroy, J. McTaggart, G. Van Soest. 2008. Performance 

Assessment Inventory Report, INV-PA-08, Revision 0. LA-UR-09-02260. Los Alamos National 

Laboratory, Carlsbad, NM

U.S. DOE (Department of Energy). 2012. Contact-Handled Transuranic Waste Authorized Methods for 

Payload Control (CH-TRAMPAC), Revision 4. December 2012. U.S. Department of Energy Carlsbad 

Field Office, Carlsbad, NM.

Van Soest, G.D. 2012. Performance Assessment Inventory Report, Revision 0, LA-UR-12-26643. Los 

Alamos National Laboratory Carlsbad Operations, Carlsbad, NM.
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EPA Comment

2-32-S16 FEP W40 Brine Inflow. 

Please supplement the screening argument with information on the impacts of changes in 

GLOBAL:PBRINE and the PCS on brine inflow.

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. The change in the PA parameter 

distribution for PBRINE does not affect the screening argument or decision for this FEP. The parameter 

distribution has changed, however the implementation of PBRINE within PA models has not changed. 

Therefore, no changes have been made to the screening argument or decision for this FEP.

The impacts on repository performance due to implementation of the PCS were discussed in the DOE’s 

planned change request documentation (DOE 2011) and were specifically approved by EPA (per 

condition 1 of 40 CFR 194) in its October 8, 2014, Federal Register notice (EPA 2014). Furthermore,

EPA agreed with the way DOE addressed FEPs in the PCS change notice in its TSD, which stated,

“The Agency agrees that for screened-in FEPs, the details of conceptual and numerical 

implementation and parameterization can be considered modeling issues, and can be 

documented and justified in analysis plans and reports. (S. Cohen and Associates 2013)”

Details regarding the overall impacts of the PCS to WIPP performance can be found at: 

http://www.epa.gov/radiation/news/wipp-news.html#panelclosure.

References:

S. Cohen and Associates. 2013. Review of DOE’s Planned Change Request to Modify the WIPP Panel 

Closure System. November 2013. Vienna, VA.

U.S. Department of Energy (DOE). 2011. Transmittal of Planned Change Request to Panel Closures 

Redesign, E. Ziemianski, DOE Interim Manager, to J. Edwards, EPA ORIA. September 8, 2011.

U.S. Environmental Protection Agency (EPA). 2014. Title 40 CFR Part 194: Criteria for the 

Certification and Recertification of the Waste Isolation Pilot Plant’s Compliance With the Disposal 

Regulations; Panel Closure Redesign. Federal Register, vol. 79 (October 8, 2014): 60750-756.
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EPA Comment

2-32-S17 FEP W42 Fluid Flow Due to Gas Production. 

Please supplement the screening argument with information on the impacts of changes in 

GLOBAL:PBRINE and the PCS on the availability of brine in the waste panels.

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. Also, as discussed in the DOE’s 

response to comment 2-32-S16, the change in the PA parameter PBRINE does not affect the screening 

argument or decision for this FEP. Implementation of PBRINE within PA models has not changed. 

Therefore, no changes have been made to the screening argument or decision for this FEP.

Information on the impacts of the PCS implementation on Salado flow modeling can be found at: 

http://www.epa.gov/radiation/news/wipp-news.html#panelclosure.
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EPA Comment

2-32-S18 FEP W44 Degradation of Organic Material. 

Please supplement the screening argument with an expanded discussion of the importance of the 

availability of brine on the degradation of organic material. Changes that affect the availability of brine 

in a waste panel, such as the water balance implementation, the revised value of GLOBAL:PBRINE, and 

the properties of the ROMPCS and associated DRZ, will affect this FEP.

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. While changes in the availability 

of brine to support the degradation processes of organic material will indeed affect the amount of gases 

generated, these processes are already accounted for in PA calculations. However, the screening 

argument and decision are not affected by these changes. The implementation of the chemical models 

that represent these processes is described elsewhere within the compliance documentation and PCS 

documentation (see Appendix PA-2014, Section PA-4.2.5).
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EPA Comment

2-32-S19 FEP W45 Effects of Temperature on Microbial Gas Generation. 

Please modify the screening argument to acknowledge the reduced thermal impact of seal concrete 

hydration because of the elimination of additional explosion walls and the Option D monolith.

DOE Response

This is a revision to Appendix SCR-2014, Section SCR-6.5.1.1.3.1. The revised text has been changed to 

read:

This thermal rise is considered bounding due to the elimination of concrete from the 

panel closure systems. Because the new panel closures will be constructed of mined salt, 

the overall mass of concrete emplaced within the repository will be significantly 

decreased. More importantly, the emplacement of any constructed element (e.g., shaft 

seals) of the repository will be done at or before repository closure. Therefore, any 

increase in temperature due to concrete hydration will have abated by the time AICs are 

assumed to no longer prevent drilling into the repository.

The revised text has been added to Enclosure 4, CRA-2014 Errata Tracking.
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EPA Comment

2-32-S20 FEP W53 Radiolysis of Cellulose. 

The reported reason for the screening argument update is not consistent between Table SCR-1, where the 

update is due to new radionuclide inventory, and Section SCR-6.5.1.7.2 where the update is due to new 

cellulose inventory. The screening argument in Section SCR-6.5.1.7.3 refers only to the new radionuclide 

inventory. Please reconcile the information.

DOE Response

This is a revision to Appendix SCR-2014. The revised text of Section SCR-6.5.1.7.2 has been changed to 

read:

SCR-6.5.1.7.2 Summary of New Information

This FEP has been updated with new waste inventory data. Decreasing waste inventory 

values lower the overall activity for all TRU radionuclides which indicate that radiolysis 

of cellulose will not be a significant process. The screening argument and decision are 

not affected by this change in inventory information.

This change has been added to Enclosure 4, CRA-2014 Errata Tracking.
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EPA Comment

2-32-S23 FEP W110 Panel Closure Physical Properties. 

Please update the screening argument to provide a description of the as-emplaced properties of the ROM 

salt now that in situ testing has been completed.

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. The results of in situ testing have 

not been documented at this time. At this point, the screening argument and decision remain unchanged.
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EPA Comment

2-32-S25 FEP W113 Consolidation of Panel Closures. 

Please supplement the screening argument with information on consolidation specific to the ROM salt in 

the ROMPCS. Such a discussion can be found in Camphouse et al. (2012, Section 2.0. ERMS 557396).

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. The screening argument in 

Appendix SCR-2014 states in Section SCR-6.3.5.1.3: “Consolidation of shaft seals, consolidation of the 

ROM salt PCS, mechanical degradation of shaft seals, and mechanical degradation of panel closures are 

accounted for in PA calculations through the permeability ranges assumed for the seal and closure 

systems (Appendix PA-2014, Section PA-4.2.7 and Section PA-4.2.8).” Appendix PA, Section PA-4.2.8 

then cites Camphouse et al. (2012) for more discussion on the ROMPCS consolidation.