EPA PC3R Questions – Set 1 1

Enclosure: First Set of EPA Questions to DOE 

December 22, 2011

1 Parameters Related to Run of Mine (ROM) Panel Closure (PC)

This attachment provides initial questions and comments in EPA’s ongoing review of the

Panel Closure Redesign and Repository Reconfiguration Performance Assessment (PC3R 

PA). The focus of these comments are justifications for the parameters and parameter 

values that are new or have been changed from those in the 2009 Performance 

Assessment Baseline Calculation (PABC 2009 PA).

The starting points for reviewing each parameter are the descriptions and references 

provided in the Summary Report for the AP-151 (PC3R) Performance Assessment, Rev. 1

(Camphouse et al. 2011, ERMS 555489) and in Recommendation and Justification of 

Parameter Values Required for the WIPP Panel Closure Redesign and Repository 

Reconfiguration Performance Assessment (Camphouse 2010b, ERMS 554614). The first 

of these is the principal document describing the PC3R PA and its results, and the second 

is the principal document describing and justifying the parameters and values that were 

used. 

1.1 Duration of Time Period T1

Parameter Name PABC 2009 Value Used in PC3R PA

ERMS 555489

Units

Duration of Time Period T1 Not Applicable 100 years

Technical Question 1.1a: Please clarify the justification of the 100 year duration for T1. 

Different documents have estimated different time periods for run of mine salt to reach 

steady state porosity. Specifically, the PC3R cites Callahan and DeVries (1991, 

SAND91-7052), who predict consolidation of ROM salt to a porosity of 0.05 in about 13 

years, and Hansen and Thompson (2002, ERMS 523476), who predict consolidation of 

ROM salt to a higher porosity of 0.10 within 100 years.

Technical Question 1.1b: Please justify the assumption that loosely placed, ROM salt 

will consolidate to a porosity of 0.05 in 100 years when the cited source Hansen and 

Thompson (2002) concludes that the salt will consolidate to a porosity of only 0.10 

within 100 years.

Technical Question 1.1c: Please justify the use of two time periods to represent 

consolidation of the ROM salt panel closure material, when additional time periods could 

provide a more refined representation of salt consolidation over time.

Completeness Question 1.1d: Please identify the effect of the rock bolts installed at 

WIPP for ground control on the consolidation rate for the ROM salt panel closure 

material.
EPA PC3R Questions – Set 1 2

EPA Concerns 

DOE’s justification for adopting 100 years as the time frame for the T1 time period is not 

clear, especially given the range of values given by different sources.

Hansen and Thompson (2002, p.4 ) estimated that a reduction of ROM salt porosity from 

0.33 to 0.10 would occur within a maximum of 100 years, and indicate that it would take 

more than 100 years for ROM salt porosity to drop to the target value of 0.05.

Numerical simulations conducted by Callahan and DeVries (1991, Figure 4-2 SAND91-

7052) predicted the essentially total reduction in the void volume of a room filled with 

crushed salt within about 25 years. These predictions do not seem to be supported by the 

measured closure rates of Panel 1 access drifts used in Hansen and Thompson (2002). 

In DOE’s proposed 2006 panel closure redesign (which also used 100 feet of loosely 

placed ROM salt for the panel closure material), a value of 200 years was used for creep 

closure to reduce the porosity from an initial value of 0.33 (averaged to 0.27 when 

combined with the porosity of the concrete block explosion wall) to a final value of 0.05 

(Vugrin and Dunagan 2006, Table 3 and p. 15 ERMS 543865). No reason is given for 

reducing the time required to reach a .05 porosity value from 200 years to 100 years in

the PC3R PA.

1.2 Panel Closure Porosity

Parameter Name PABC 2009 Value Used in PC3R PA

ERMS 555489

Units

PCS_T2: POROSITY 0.05 for CONC_PCS 0.05 --

Technical Question 1.2a: Please provide justification that the T2 porosity is an 

appropriate target value that correlates to the permeability and compressibility values 

used in the PC3R PA.

Technical Question 1.2b: How sensitive a parameter is the final porosity of the panel 

closure? That is, how much would changing the value of PCS_T2: POROSITY (e.g. to 

0.01 or 0.075) change calculated results, such as waste area saturation and pressure, that 

are known to impact performance?

EPA Concerns 

DOE’s reasoning in selecting the final T2 porosity value of 0.05 is not explicit. Because 

the assigned porosity of the panel closure at T2 is the value from which the long-term 

permeability and compressibility of the panel closure are defined, EPA is asking for more 

information on the parameter’s justification and the importance of the specific value

used.
EPA PC3R Questions – Set 1 3

1.3 Long-Term Panel Closure Permeability

Parameter Name PABC 2009 Value Used in PC3R PA

ERMS 555489

Units

PCS_T2:PRMX_LOG

PCS_T2:PRMY_LOG

PCS_T2:PRMZ_LOG

-17, -20.8, -18.8 for

CONC_PCS

-17.6,-22.8,-20.2

Triangular 

Distribution

log(m2)

Technical Question 1.3a: Please provide a source for the permeability values assigned to 

the ROM salt panel seal during time period T2 that provides traceability to original 

sources.

Technical Question 1.3b: Please justify the assignment of permeabilities to the ROM 

salt panel seal during time period T2 that represent fully consolidated salt rather than 

ROM salt consolidated to a porosity of 0.05.

Completeness Question 1.3c: Please provide design and performance information that 

justifies the stated assumption that the “substantial barrier” will have no impact on panel 

seal performance during time period T2.

Completeness Question 1.3d: Please justify the unstated assumption that repository gas 

pressure buildup during time period T2 will not inhibit or reverse consolidation of the 

ROM salt panel seal, potentially resulting in higher porosities and therefore higher 

permeabilities than the recommended values. 

Completeness Question 1.3e: Please justify the unstated assumption that backpressure 

reduction through lateral halite movement at the unconstrained ends of the 100-ft panel 

closure backfill can be ignored during the consolidation process.

EPA Concerns

EPA is looking for clarification on the justification of the long-term panel closure 

permeability.

A compilation of laboratory-measured permeability values for WIPP crushed salt at 

various fractional densities was prepared by Hurtado et al. (1997, Table 2-1 SAND97-

1287). The most relevant results were taken from Brodsky (1994, SAND93-7058), who 

measured the permeability of compacted ROM salt at fractional densities near 0.95 

(equivalent to a porosity of 0.05) using brine as the fluid rather than gas. 

Kelley et al. (1996, p. 1 ERMS 230995) provide a summary of permeability values at 

various densities. The T2 permeability values recommended by Camphouse (2010b, p. 

4)) are most similar to those reported by Kelley et al. (1996, Table 6) for 200-years,

which represented full reconsolidation. The values recommended by Camphouse are not 

identical to any of those presented in the 1996 Kelley report.
EPA PC3R Questions – Set 1 4

The PC3R T2 permeability values are similar to the values for fully reconsolidated 

crushed salt reported by Kelley et al. (1996) and Hurtado et al. (1997), but not 

representative of porosities equivalent to 0.05. The T2 permeabilities used to represent 

ROM salt at a porosity of 0.05 are generally 1.5 to 2 orders of magnitude lower than 

those reported by Butcher et al. (1991, reported in Hansen and Callahan, 1993), Brodsky 

(1994), Hurtado et al. (1997, SAND97-1287), and Hansen and Thompson (2002) for 

compacted salt equivalent to a porosity of 0.05.

1.4 Panel Closure DRZ Permeability

Parameter Name PABC 2009 Value Used in PC3R PA

ERMS 555489

Units

Long Term T2 Values for the PCS DRZ

PCS_T2:PRMX_LOG

PCS_T2:PRMY_LOG

PCS_T2:PRMZ_LOG

-20.7, -18.8, -17.0

for material 

CONC_PCS

-22.8, -20.2, -17.6

Triangular 

Distribution 

log(m2)

Technical Question 1.4a: Please justify the assignment of permeability values to the 

PCS DRZ during time period T2 that appear to represent a fully reconsolidated material, 

when the ROM salt panel closure itself has not yet fully reconsolidated and stress 

equilibrium has not yet been achieved.

Completeness Question 1.4b: Please explain why the anhydrite marker beds 

surrounding the ROM salt panel seal are not treated in the same manner as those within 

the waste panel DRZ. 

EPA Concerns 

EPA cannot trace the justification for assigned permeabilities provided by Camphouse 

(2010, p. 5 ERMS 554614) to supporting documentation. Both the panel closure and the 

surrounding rock consist of essentially similar material, disturbed Salado halite. The 

porosity and permeability of the disturbed halite around an ROM salt panel closure will 

begin to decrease when back pressure from the compacting ROM salt begins to 

significantly increase. 

As noted by Hansen and Callahan (1993, p. 7), laboratory results indicate that little 

resistance is created by crushed salt during consolidation until fractional densities on the 

order of 0.90 are achieved. According to Hansen and Thompson (2002, p. 2), a fractional 

density of 0.90 is equivalent to a porosity of 0.10 and a permeability on the order of 10-15

m2

. Full reconsolidation of the PCS DRZ halite would be unlikely to occur until the ROM 

salt panel closure is itself fully reconsolidated and stress equilibrium is achieved. The T2 

permeabilities assigned to the ROM PC, and therefore, also to the T2 PCS DRZ halite, 

are more closely representative of fully reconsolidated salt at a porosity of about 0.01 

than of a partially reconsolidated salt at a porosity of 0.05.