Date: M

To: 

From: 

Technica

QA Revie

Managem

Subject: 

1.0 Int

The Wa

develope

disposal 

U.S. Env

the Code

containm

means of

(SNL). 

radionuc

10,000 y

informati

features, 

and the p

therein a

repositor

first wast

WIPP w

WIPP PA

(CCA) o

May 3, 2012

WIPP Reco

R. Chris Ca

Michael Gr

Courtney G

Dwayne C. 

Bill Thomp

al Review: 

ew: 

ment Review

Recommen

Panel Closu

roduction 

ste Isolation

ed by the U

of transuran

vironmental P

e of Federal 

ment requirem

f performanc

WIPP PA

lide releases

ears after fa

ion as part 

events, and

parameters 

also result in

ry recertifica

te shipment 

aste panel c

A regulatory

of 1996. Pa

2 

rds Center

amphouse (6

ross, WTS Su

G. Herrick, S

Kicker, The

pson, Golder 

Ross Kirke

Shelly Nie

w: Janis Tron

dations and 

ure System D

n Pilot Pla

U.S. Departm

nic (TRU) wa

Protection A

Regulations

ments accor

ce assessmen

A calculatio

s from the re

cility closur

of an ongoi

d processes t

used in them

n updates to

ation proces

at the site in

closures com

y compliance

anel closures

6211) 

ubcontractor

andia Nation

e S.M. Stolle

Associates

es 

elsen 

ne 

Justification

Design Mode

ant (WIPP), 

ment of En

aste. Contai

Agency (EPA

s (CFR), Par

rding to the 

nt (PA) calc

ons estimate

epository to t

e. The mod

ing process.

typically resu

m. Planned

 WIPP PA 

s that occur

n 1999. 

mprise a fea

e demonstra

s are include

1

r

nal Labs (62

er Corporatio

ns of Parame

eled in the P

located in

nergy (DOE)

inment of TR

A) according

rt 191. The 

Certificatio

culations per

e the prob

the accessibl

dels used in P

 Improved 

ults in refin

d changes to

models. W

rs at five-ye

ature of the 

ation since th

ed in the rep

Opera

211) 

on 

eter Values f

PCS-2012 PA

n southeaste

) for the g

RU waste at 

g to the regul

DOE demo

on Criteria in

rformed by S

bability and

le environm

PA are main

information

nements and 

o the reposi

WIPP PA mo

ear intervals 

repository t

he Complian

pository as 

ated for the U.S. De

Sandia Co

Defense Waste Ma

4100 National Park

Carlsbad, New Me

for the Run-o

A

ern New M

geologic (de

the WIPP is

lations set fo

onstrates com

n Title 40 C

Sandia Natio

d consequen

ment for a reg

ntained and u

n regarding 

modificatio

itory and/or

odels are use

following t

that has bee

nce Certifica

a safety me

epartment of Energ

rporation 

anagement Progra

ks Highway 

exico 88220 

of-Mine Salt

Mexico, has 

ep undergro

s regulated b

orth in Title 

mpliance wit

CFR Part 19

onal Laborat

nce of pote

gulatory peri

updated with

important W

ons to PA m

r the compo

ed to suppor

the receipt o

en represent

ation Applic

easure durin

gy by the

ms 

t

been 

ound) 

by the 

40 of 

th the 

94 by 

tories 

ential 

iod of 

h new 

WIPP 

models 

nents 

rt the 

of the 

ted in 

cation 

ng the 
2

operational period. In particular, their presence in the repository is a means to protect workers 

from exposure to two potential hazards: 1) volatile organic compounds that may be present in 

emplaced waste materials and 2) an explosion which has been hypothesized to occur from gas 

generation causing methane concentration in the waste panels to reach a sufficiently high level. 

Panel closures were not developed to isolate radionuclides in the repository after closure. The 

DOE stated in the CCA (DOE 1996) that “The panel closure system was not designed or 

intended to support long-term repository performance.” Panel closures are included in WIPP 

PA models principally because they are part of the disposal system, not because they play a 

substantive role in inhibiting the release of radionuclides to the outside environment. 

The WIPP was certified to receive TRU waste in 1998. The 1998 rulemaking had several 

conditions, one of which involved the design of the panel closure system (PCS) implemented in 

the repository. The DOE presented four design options in the CCA, and 

“The EPA based its certification decision on the condition that DOE 

implement the most robust design [referred to in the CCA as “Option D”]. 

The Agency found the Option D design to be adequate, but also determined 

that the use of a Salado Mass Concrete- using brine rather than fresh waterwould produce concrete seal permeabilities in the repository more consistent 

with the values used in DOE’s performance assessment. Therefore, Condition 

1 of the EPA’s certification requires DOE to implement the Option D PCS at 

the WIPP, with Salado Mass Concrete” (EPA 1998). 

The Option D panel closure system consists of three primary components: 1) a concrete block 

wall (the explosion wall), 2) open drift, and 3) a concrete monolith. The arrangement and 

dimensions of these components are illustrated in Figure 1. 

Figure 1: A Schematic of the “Option D” Panel Closure 

Extensive refinement to WIPP panel closure modeling in PA has occurred since the 

implementation used in the CCA (Vugrin and Wagner 2006). In the CCA and the PAVT 

(MacKinnon and Freeze 1997) that followed, regulatory compliance was demonstrated with a 

generic panel closure that was not Option D. Following certification of the WIPP in 1998, and 

the mandate that Option D be implemented as the panel closure in WIPP, a PA was conducted in 

2002 (Hansen 2002) with the aim of implementing an Option D panel closure into the repository 

W a s te d is p o s a l O p e n D rift

C o n cre te

M o n o lith

9 .1 m 7 .9 m

E x p lo s io n

W a ll

3 .7 m

40 m

2 .4 o r 2 .7 m

2 .4 m

DRZ

DRZ

O p e n D rift
3

models used in WIPP PA, and to assess the impacts of panel closure design on long-term 

repository performance.  Two panel closure cases were considered. The first was modeled upon 

the mandated Option D panel closure design. The second was the generic panel closure design 

implemented in the CCA and PAVT. Upon completion of the analysis, it was found that total 

normalized releases resulting from the two panel closure cases were nearly identical. Moreover, 

nearly identical distributions for each release component were calculated in the two panel closure 

cases. A more granular representation of the Option D panel closure was developed during the 

2002 – 2003 Technical Baseline Migration (TBM) PA. Upon completion of the TBM PA, it was 

found that the TBM and PAVT produced releases that are nearly identical, indicating that 

repository performance is not significantly affected by changes in the panel closure properties 

(Dunagan 2003). The Option D panel closure representation developed during the TBM was 

used for the panel closure representation in the 2004 and 2009 Compliance Recertification 

Applications (CRA-2004 and CRA-2009, respectively).   

Panel closures are represented in PA by way of their material properties and spatial extent. Due 

to the regulatory time scale of 10,000 years for which regulatory compliance must be 

demonstrated, there are uncertainties associated with panel closure material properties. These 

uncertainties in material properties are incorporated in PA. A material property with an 

associated uncertainty is assigned a distribution, and this distribution is randomly sampled. This 

sampling process allows for repository performance to be quantified over a range of material 

conditions, as well as an analysis of performance sensitivity to changes in material properties. 

As briefly described above, numerous studies have been conducted to date, often by way of full 

PA analyses, to quantify the impact of changes in panel closure material properties on regulatory 

compliance. In addition, several PA analyses have been performed (Hansen 2002, Vugrin & 

Dunagan 2006, Camphouse et al 2011) with the aim of determining the impact of panel closure 

redesigns on repository performance. Regulatory compliance has been met in all PA analyses 

performed to date, including those that incorporated changes to panel closure modeling. 

Regulatory compliance has been repeatedly shown to be primarily insensitive to panel closure 

material properties. A future PA is planned that incorporates a new panel closure design into the 

current PA baseline established by the 2009 Performance Assessment Baseline Calculation 

(PABC-2009) (Clayton et al., 2010). The name given to this planned panel closure PA is PCS2012. 

The PCS-2012 will quantify impacts of a run-of-mine (ROM) salt panel closure design by 

comparing total normalized releases to those found in the PABC-2009 where Option D was 

implemented as the panel closure. Calculations and analyses have been performed to develop 

material properties to be used in the PCS-2012, and are documented in DOE (2012) and Herrick 

(2012). This memorandum provides hydrologic and pore compressibility parameter values for 

the revised PCS in the PCS-2012 PA. Parameters are created as discussed in NP 9-2, 

Parameters. PCS-2012 parameters not listed in the memorandum will be equal to the values 

prescribed to them in the PABC-2009. In the discussion that follows, material parameters and 

timings are developed to account for the following physical processes and accepted rock 

mechanics principles: 

1. Creep closure of the salt rock surrounding panel entries will cause consolidation of 

ROM salt emplaced in panel entries. 
4

2. Eventually, the ROM salt comprising the closures will approach a condition similar to 

intact salt. 

3. As ROM salt reaches higher fractional densities during consolidation, back stress will 

be imposed on the surrounding rock mass leading to eventual healing of the disturbed 

rock zone (DRZ). 

4. DRZ healing above and below the ROM salt panel closures will reduce DRZ porosity 

and permeability in those areas. 

 

A brief discussion of creep and reconsolidation of run-of-mine salt, and the DRZ healing that 

results, is the topic of the next section. 

2.0 Creep and Reconsolidation of Run-of-Mine Salt 

2.1 Creep Closure in Salt 

The ability of salt to deform with time, eliminate voids, and create an impermeable salt barrier 

around the waste was one of the principal reasons for locating the WIPP repository in a bedded 

salt formation. The creep closure process is a complex and interdependent series of events 

starting after a region within the repository is excavated, which creates a disturbance in the stress 

field. Stress relief results in some degree of brittle fracturing and the formation of a DRZ 

surrounding excavations in all deep mines. For the WIPP, the DRZ is characterized by an 

increase in permeability, and may ultimately extend a few meters from the excavated region. 

Stress relief generates deviatoric stresses in the host rock, causing salt to deform by creep 

processes and to move inward to fill the excavated void. This process of salt creep will continue 

until deviatoric stress is dissipated and the system is once again at stress equilibrium (DOE 1996, 

Section 6.0.2.2 and Appendix PORSURF). Eventually, at equilibrium, deformation ceases, and 

the panel entry and any backfill (such as ROM salt) have undergone as much compaction as is 

possible by the weight of the rock above the repository horizon. 

2.2 Mechanical Behavior of Run-of-Mine Salt 

The mechanical behavior of ROM salt, which is also referred to as crushed salt, has been 

extensively studied and can be divided into three basic categories: elastic deformation, inelastic 

deformation, and failure (Callahan et al. 1995, Section 2.4.1). The inelastic behavior can further 

be divided into time-independent (instantaneous compaction) and time-dependent (creep 

consolidation) deformation. A number of parameters or characteristics are expected to affect the 

mechanical behavior of crushed salt. These parameters include (but are not limited to) density (or 

porosity), grain size and grain size distribution, moisture content, impurity content (such as clay, 

anhydrite, etc.), temperature, stress state (i.e., confining pressure and stress difference), and time. 

Crushed salt is proposed as the main component of the redesigned panel closure, and over time 

this crushed salt will be consolidated by the creep closure of the entry. Crushed salt is also 

proposed as one component of the shaft seal, and an assessment of the mechanical behavior of 

crushed salt is provided as part of the WIPP shaft sealing system design (DOE 1996, Appendix 

SEAL). If salt reconsolidation is unimpeded by fluid pore pressures, the material will eventually 

achieve extremely low permeabilities approaching those of the native Salado Formation. 

Developments in support of the WIPP shaft seal system have produced confirming experimental 

results, constitutive material models, and construction methods that substantiate use of a salt 
5

column to create a low permeability seal component. Other advantages of the use of crushed salt 

for sealing systems is that as a replacement of the natural material in its original setting it ensures 

physical, chemical, and mechanical compatibility with the host formation. 

2.3 Response of the Disturbed Rock Zone 

An underground excavation creates a disturbed zone in the surrounding rock. Microfracturing 

will occur in the rock adjacent to the drift wall, where confining stresses are low or nonexistent. 

The extent of the zone depends on the rock strength and the prevailing stress state, which is 

depth dependent. 

In terms of WIPP repository applications, one of the most important features of salt as an 

isolation medium is its ability to heal previously damaged areas (Hansen 2003, Section 4.1). 

Damage recovery, or healing, arises when the magnitude of the deviatoric stress decreases 

relative to the applied mean stress. A decrease in deviatoric stress occurs as stresses approach 

lithostatic conditions, as would be the circumstance adjacent to the crushed salt barrier when it 

reaches a consolidated state. The healing mechanisms include microfracture closure and bonding 

of fracture surfaces. Microfracture closure is a mechanical response to increased compressive 

stress applied normal to the fractures, while bonding of fracture surfaces occurs either through 

crystal plasticity, a relatively slow process, or pressure solution and redeposition, a relatively 

rapid process (Spiers et al., 1988). Evidence for healing has been obtained in laboratory 

experiments, small-scale tests at WIPP and through observations of field analogs (Hansen 2003, 

Sections 4.5, 4.6, and 4.9). 

2.4 Impact of ROM Salt Reconsolidation on Porosity and Permeability 

Numerical modeling conducted as part of shaft sealing analyses provides density of the 

compacted salt column as a function of depth and time. Many calculations comparing models for 

consolidation of crushed salt were performed to quantify performance of the crushed salt column 

in the shaft seal (DOE 1996, Appendix SEAL; Callahan et al. 1995; Brodsky et al. 1996). From 

the density-permeability relationship of reconsolidating crushed salt, permeability of the 

compacted salt seal component is calculated. In general, results show that the bottom of the salt 

column consolidates rapidly, achieving permeability of 1×10-19 m

2

 in about 50 years. By 100 

years, the middle of the salt column reaches similar permeability. 

Structural analysis calculations were developed to determine the fractional density of the crushed 

salt seal as a function of time and depth and, using these results, to determine permeability of the 

crushed salt as a function of time and depth (DOE 1996, Appendix SEAL, Section 7.4.2.1). The 

results of these calculations indicate that compacted salt will increase from its emplaced 

fractional density of 90% to a density of 95% approximately 40, 80, and 120 years after 

emplacement at the bottom, middle, and top of the shaft seal, respectively. Using the modified 

Sjaardema-Krieg creep consolidation model, the times required to fully reconsolidate the crushed 

salt to 100% fractional density are 70 years, 140 years, and 325 years at the bottom, middle, and 

top of the salt column, respectively. Based on these results, the desired fractional densities 

(hence, permeability) can be achieved over a substantial length of the compacted salt seal in the 

range of 50 to 100 years. 
Addition

and 5.1.2

Section 5

flow pro

damage a

ROM sal

3.0 R

The DOE

Condition

WIPP. F

reassesse

easier to 

Accordin

revised d

design of

feet of ru

from ong

emplaced

as compl

the ROM

permeabi

(a) P

(b) P

nal details on

2. Based on

5.1.1, it is e

perties indis

and heal is 

lt and the sur

Revised Desi

E has submit

n 1 of the F

Following th

ed the engine

construct an

ngly, the PC

design for the

f the PCS, kn

un-of-mine (

going mining

d in a panel 

letely as pra

M salt to con

ility. 

anel closure

anel closure

Figu

n the porosit

n the calcul

expected tha

stinguishable

a time-depe

rrounding D

ign of the PC

tted a planne

Final Certifi

he selection

eering of the

nd equally e

CR submitte

e panel closu

nown as the 

(ROM) salt w

g operations

entry. The R

acticable. A

nsolidate to 

e with 100 fe

e with 100 fe

ure 2. Schem

ty and perm

lations cited

at a complet

e from natur

endent proce

DRZ will retu

CS 

ed change re

fication Rule

n of the Opt

e panel closu

effective at p

ed to EPA r

ures be appr

Run-of-Min

with barriers

s at the WIP

ROM salt w

After emplac

a condition 

eet of ROM s

eet of ROM s

matic diagram

6

meability of R

d above and 

tely consolid

ral Salado s

ess; eventual

urn to that of

equest (PCR)

emaking for 

tion D pane

ure and estab

performing 

requested th

roved for use

ne Panel Clo

s at each end

PP and may 

will be empla

ement, creep

approachin

salt between

salt between

m of the revi

ROM salt ar

on in situ 

dated ROM 

salt. The ab

lly, the perm

f intact salt.

) to the EPA

40 CFR Pa

el closure de

blished a rev

its operation

hat Conditio

e in all pane

osure System

d (Figure 2)

be compact

aced to all sa

p closure of

g intact salt

n two ventila

n a ventilatio

sed panel clo

re provided 

observations

salt-filled d

bility of salt

meability of

A requesting 

art 194 (EPA

esign in 199

vised design 

nal-period is

on 1 be chan

ls (DOE, 20

m (ROMPCS

). The ROM

ted and/or m

alt surfaces (

f the panel e

t, with low p

ation bulkhea

on bulkhead 

osure design

in Sections 

s as describ

drift will ach

t to recover 

f the consoli

that EPA m

A, 1998) fo

98, the DOE

which is sim

solating func

nged, and t

011). The re

S), comprise

M salt is gene

moistened as

(back, walls,

entries will c

porosity and

ads 

& explosion

n

Concrete

block wall

5.1.1 

bed in 

hieve 

from 

dated 

modify 

or the 

E has 

mpler, 

ction. 

that a 

evised 

s 100 

erated 

s it is 

, etc.) 

cause 

d low 

n wall 
7

The barriers will consist of ventilation bulkheads, similar to those currently used in the panels as 

room closures (Figure 3). The ventilation bulkheads are designed to restrict air flows and 

prevent personnel access into waste-filled areas during the operational phase. In Panels 1, 2, and 

5, where explosion walls fabricated from concrete blocks have already been emplaced in the 

panel entries, an explosion wall is the inbye barrier and a ventilation bulkhead will be the outbye 

barrier, as shown in Figure 2b. 

The emplacement scheme for the ROM salt will be finalized once in situ testing has been 

completed. It is expected that the final emplacement scheme will involve some degree of inplace compaction, with or without added moisture (moisture may be added because it accelerates 

the consolidation of the crushed salt). The emplacement technique and/or strategy is not

important to long-term repository performance. In particular, the uncertainty in the final panel 

closure emplacement strategy is not a result of consideration of long-term panel closure 

characteristics. Panel closures are emplaced in the repository to protect workers during the 

operational phase of the facility. Emplacement uncertainty is due to current lack of operational 

experience in constructing/emplacing this type of closure system. The method used will be 

based on consideration of various operational variables. Cost, efficiency, short-term 

effectiveness, dust control, and other factors will all play into the final emplacement scheme. A 

range of possible emplacement strategies are being assumed in the PCS-2012 to develop panel 

closure materials, properties, and timings representative of all potential emplacement strategies. 

At one end of the range is emplacement of dry ROM salt without any initial compaction. The 

uncompacted porosity of ROM salt is assumed to be 35%, based on several sources. Callahan 

and Devries (1991, Section 4.1 and Table 2-2) define the initial density of crushed salt as about 

65% of intact density, based on data from (Sjaardema and Krieg, 1987) and (Weatherby, 1989). 

This initial density corresponds to an initial porosity of approximately 35% for the crushed salt. 

Recent work on backfill compaction in the German repository program also assumes an initial 

backfill porosity of 35% (Rothfuchs and Wieczorek, 2010). The uncompacted ROM salt is 

therefore assumed to have an initial porosity of 35%, equivalent to a fractional density of 65%. 

At the other extreme, the ROM salt may be emplaced in compacted layers that are wetted with a 

small amount of moisture to enhance the initial emplacement density and short-term 

consolidation. The average porosity of the compacted layers is estimated to be greater than 20%, 

based on engineering judgment. The values of the hydrologic and mechanical parameters for the 

PCS-2012 PA are intended to encompass both of these extremes. 
The ROM

at the rep

small am

chemical

the repos

the host r

4.0 Mo

A new P

between 

design of

used for 

in the PC

closure im

modeled 

be modif

Option D

The ROM

years to 2

panel clo

Figure 3. T

M salt is che

pository hor

mount of mo

lly similar to

sitory. The m

rock and wit

odeling App

PA baseline 

the PABCf the PCS. M

the PABC-2

CS and the d

mplemented

in the PCSfied slightly

D. 

MPCS prope

200 years, a

osure model

Typical desig

mically com

rizon and be

oisture. The 

o the iron-ba

materials in t

th the materi

proach for P

was establis

-2009 and th

More specifi

2009, but wi

disturbed roc

d in the PAB

2012 is 100 

y to account

erties will b

nd from 200

ling undertak

gn of a venti

mpatible with

ecause it has

sheet metal

ased metals i

the redesigne

ials already i

PCS-2012 PA

shed by the 

he PCS-201

fically, the P

ith new prop

ck zone dire

BC-2009 is 4

feet (30.48 

t for the red

be based on 

0 years to 10

ken in the 2

8

ilation bulkh

h the host roc

s no additive

l in the vent

in the waste

ed PCS will 

in the reposi

A 

PABC-2009

12 PA will 

PCS-2012 PA

perties for th

ectly around

40 meters lo

meters) long

duction in le

three time p

0,000 years. 

2006 PCS P

head that blo

ck because i

es, except f

tilation bulk

e and waste c

therefore be

itory. 

9 (Clayton e

be a direct 

A will use th

he materials

the PCS. N

ong (Figure 

g. The PAB

ength of the

periods: fro

This is a ref

PA (Vugrin 

ocks the pane

it is mined fr

for the possi

khead has sm

containers th

e chemically

et al., 2010)

consequenc

the BRAGFL

 that represe

Note that the

1) while the

BC-2009 BRA

e ROMPCS

m 0 to 100 

finement to t

and Dunaga

el entry 

rom the host

ible addition

mall mass a

hat are alrea

y compatible

. The differe

ce of the re

LO grid that

ent the ROM

e Option D p

e redesigned

AGFLO grid

S as compar

years, from

the granular

an 2006) an

t rock 

n of a 

and is 

ady in 

e with 

ences 

evised 

t was 

M salt 

panel 

d PCS 

d will 

red to 

m 100 

rity of 

nd the 
2011 PC

to consol

the proce

approxim

as PCS_T

years. Si

materials

The vent

These bu

creep clo

This wall

through n

condition

spalling 

the salt. I

under inc

1.2 to 1.5

layer of b

inch behi

3R PA (Cam

lidate the RO

ess to heal fr

mately 200 y

T1 for the fi

imilarly, the

s DRZ_PCS_

tilation bulk

ulkheads are 

osure of the p

l is inspected

numerical m

n of the free

or slabbing 

In contrast, t

creasing load

5 inches and

bricks that h

ind the free s

Figure 4. Su

mphouse et a

OM salt occu

ractures in th

ears. The RO

irst 100 year

e DRZ dire

_T1, DRZ_P

kheads are de

not expecte

panel entries

d on a regula

modeling (e.g

e face in Pan

of the concr

the plastic pr

d due to salt

d quite consi

have become

surface. 

urface spalli

al 2011). Th

urs over a p

he DRZ surr

OM salt will

rs, PCS_T2 f

ectly above 

PCS_T2, and

esigned to p

ed to remain

s. The explo

ar basis, and

g. RockSol, 

nel 1 during

rete blocks a

roperties on 

 creep. The

istent. The ro

e detached a

ing at the bas

Panel 1 dur

9

hree time per

rimary time 

rounding the

l therefore b

for 100 to 2

and below 

d DRZ_PCS

provide isola

n intact 100 y

osion wall is 

d the anticipa

2006). Fig

g February 2

as a result o

the ROMPC

 thickness o

od in Figure

and pushed o

se of the exp

ring Februar

riods are app

 scale of app

e PCS occur

e represente

00 years, an

the ROM 

S_T3. 

ation only du

years after r

also designe

ated conditio

gures 4 and 5

2012. The e

of the loadin

CS will allow

f the slabs s

e 5 is anchor

out by the fo

plosion wall 

ry 2012 

propriate bec

proximately 

rs over a lon

ed by three m

nd PCS_T3 f

salt will be

during the op

repository cl

ed for the op

on of the wal

5 present ph

explosion wa

ng caused by

w it to recon

shown in Fig

red by a nut

ormation of 

in the intake

cause the pr

100 years, w

nger time sca

materials, den

for 200 to 10

e represente

perational pe

losure becau

perational pe

ll is also ass

hotographs o

all shows su

y inward cre

nsolidate and

gure 4 is typi

t resting on a

a crack abo

e drift of 

ocess 

while 

ale of 

noted 

0,000 

ed by 

eriod. 

use of 

eriod. 

essed 

of the 

urface 

eep of 

d heal 

ically 

a thin 

out an 
Fig

Numeric

the rib c

emplacem

out; how

not be si

behavior 

significan

analysis 

during th

through 

explosion

5.0 PC

As discu

this closu

ROM sal

as the R

surround

permeabi

the surro

values fo

ROM sal

gure 5. Surfa

al stress ana

ontacts will 

ment (Rocks

wever, it is ex

gnificant str

of concrete

nt impact on

of material 

he initial 10

the closure 

n wall will b

S Paramete

ussed in Sect

ure will cau

lt will appro

ROM salt re

ding rock ma

ility. These p

ounding DRZ

or a complete

lt and for the

ace spalling 

alysis of the 

be in a con

sol, 2006, Fi

xpected that 

ructures afte

e. The ven

n long-term 

properties f

00 year per

system will

be minimal. 

ers 

tion 2.0, the

use consolid

oach a condi

eaches highe

ass leading 

processes an

Z are discus

e set of hydr

e DRZ direct

at the top co

Panel 1 dur

concrete exp

ndition of pl

gures 7 and 

the spalling 

er the initial 

ntilation bulk

performanc

for the PCS 

riod after re

l be through

e salt rock su

dation of RO

ition equival

er fractiona

to healing 

nd their effec

ssed in Secti

rologic param

tly above an

10

orner of the e

ring February

plosion wall

lastic yield 

10). No lon

and yield w

100 year tim

kheads and 

ce of the pan

and the DR

epository cl

h the DRZ s

urrounding t

OM salt em

lent to intact

l densities, 

of the DRZ

ct on porosit

ion 2.0. Thi

meters and th

nd below the 

explosion wa

ry 2012. 

l has demons

with an uny

ng term stres

will be progre

me period, d

explosion w

nel closures

RZ surround

osure, the p

so any influ

the panel en

mplaced in p

t salt. Durin

a back stre

Z and a redu

ty and perm

is section of

he pore com

PCS. 

all in the int

strated that t

yielded core

ss analyses h

essive, and t

due to the b

walls will th

s and are no

ding the PC

primary pot

uence from t

ntries is cree

panel entries

ng the conso

ess will be 

uction in D

meability of t

f this memo

mpressibility 

ake drift of 

the free face

 by 7 years 

have been ca

that the walls

rittle, non-p

herefore hav

ot included i

S. Addition

tential flow 

the bulkhea

eping closed

s. Eventually

olidation pro

imposed on

DRZ porosity

the ROM sal

orandum pro

parameter fo

es and 

after 

arried 

s will 

plastic 

ve no 

in the 

nally, 

path 

ads or 

d, and 

y the 

ocess, 

n the 

y and 

lt and 

ovides 

or the 
11

5.1 Hydrologic and Pore Compressibility Parameters for the ROM Salt 

5.1.1 Porosity of ROM Salt 

Estimates of the consolidation process have been made in a series of calculations (Herrick 2012) 

carried out using JAS3D (Blanford et al., 2001; DOE, 2012, Figures 4 through 7) with the 

Sjaardema and Krieg (1987) model for crushed salt, modified with a deviatoric creep compaction 

response (Stone, 1997). Separate calculations were performed for initial emplacement porosities 

of 20%, 25%, 30%, and 35%, which correspond to initial fractional densities of 80%, 75%, 70%, 

and 65%, respectively. These calculations show consolidation to a porosity of 5% in 65 years 

from an initial porosity of 20% and in 152 years from an initial porosity of 35%. The results 

from the JAS3D calculations during the first 150 years are summarized in Table 1 as a function 

of time and initial emplacement porosity. 

Table 1. Porosity predicted by JAS3D for ROM salt in a panel entry as a function of time and 

initial emplacement porosity 

Time After 

Emplacement (Years) Porosity 

0 20% 25% 30% 35% 

50 6.6% 10.3% 14.6% 18.7% 

100 1.9% 4.2% 7.3% 10.7% 

150 1.0% 1.2% 2.9% 5.2% 

During the first time period, from 0 to 100 years, the data in Table 1 show that the porosity of the 

ROM salt decreases rapidly. In order to represent this time varying porosity in a way suitable for 

long-term performance assessment calculations, it is reasonable to define the range of porosity of 

the ROM salt at the midpoint of this time interval, 50 years. The porosity range for the first 100 

years is then 6.6% to 18.7%, based on the second row of data in Table 1. This range explicitly 

accounts for the uncertainty in initial emplacement porosity for the ROM salt. 

For the time period from 100 to 200 years, the porosity range is 2.5% to 7.5%, with an expected 

or mean porosity of 5%. The lower limit for the porosity range, 2.5%, is essentially the same as 

the lower limit of porosity from the JAS3D calculations at 100 years, 1.9% (see Table 1). The 

upper limit for the porosity range, 7.5%, is less than the maximum porosity from the JAS3D 

calculations at 100 years, which is 10.7% (see Table 1); however, the JAS3D calculation for 

ROM salt with an initial porosity of 35% predicts a porosity of 7.5% by 126 years after 

emplacement. The value of 7.5% as an upper limit is also consistent with the magnitude of the 

porosity range for intact halite. That is, the magnitude of the porosity range from 100 to 200 

years is 7.5% - 2.5% = 5%, approximately equal to the magnitude of the observed porosity range 

for intact salt, which is 5.19% - 0.1% = 5.09% (DOE 2009, Appendix PA, Parameter 17; Ismail 

2007). Finally, the mean porosity, 5%, is consistent with the JAS3D predictions at 100 years, 

which have a porosity range of 1.9% to 10.7% at 100 years after emplacement (see the 3rd row 

of data in Table 1). 

A number of sources corroborate the use of a reduced upper limit, 7.5% rather than 10.7%, 

during the second time period. Hurtado et al. (1997) carried out a number of consolidation 
12

estimates for the proposed crushed salt component of the shaft seals. The proposed crushed salt 

component of the shaft seals will consist of mined WIPP crushed salt, dynamically precompacted 

with added moisture to a porosity of 10%. Calculations of the consolidation of this component 

due to creep closure of the shaft indicate that the crushed salt will be at an essentially intact 

condition (a fractional density approaching 1) within 100 years at a depth of 515 m and within 60 

years at a depth of 600 m (Hurtado et al. 1997, Figure 2-3). Additional calculations by Callahan 

(1999) show consolidation results for different crushed salt models at depths of 430 m, 515 m, 

and 600 m, indicating similar results to Hurtado et al. (1997). Callahan and DeVries (1991) 

conducted calculations on the closure of disposal rooms backfilled with crushed salt that show 

closure to essentially intact density in about 25 years. Collectively, these alternate calculations 

imply that a mean porosity of 5% and an upper limit of 7.5% by 100 years after emplacement are 

reasonable and conservative values. 

The consolidation process will continue after 200 years, particularly for ROM salt that is 

emplaced dry with minimal compaction. This is accounted for by assigning a third time period, 

200 to 10,000 years, during which consolidation of the ROM salt will continue and achieve a 

porosity similar to that of intact salt regardless of the emplacement strategy. In situ observations 

from the BAMBUS II project at the Sigmundshall mine in Germany indicate consolidation of a 

crushed salt slurry to essentially an intact condition within tens of years (Bechthold et al., 2004, 

Figure 2.57). Consolidation to an essentially intact condition is also confirmed by observations at 

the Rocanville mine, where a consolidated salt plug was emplaced after a water inflow, and has 

been effective in sealing off a hydrostatic groundwater pressure of about 1200 psi (8.3 MPa) 

(Van Sambeek et al., 1995). The state of the intact halite at WIPP therefore provides an analog 

for the long-term consolidated state of ROM salt in a panel entry. Table 2 summarizes the values 

for porosity of the ROM salt as a function of time. 

The values in Table 2 indicate that there is a significant overlap between the porosity ranges for 

the 100 to 200 year and the 200 to 10,000 year time periods. More specifically, the 2.5% to 

5.19% porosity range is included in both time periods, although this range represents the lower 

end of the porosity range from 100 to 200 years and the upper end of the porosity range from 200 

to 10,000 years. This representation is very reasonable because the consolidation process will 

continue after 200 years, particularly for ROM salt that is emplaced with minimal compaction, 

and because the JAS3D predictions show that the rate of consolidation decreases significantly 

after 100 years, making an overlap in the porosity range likely to occur as porosity decreases to 

in situ values. 

Table 2. Porosity of the ROM salt during three time periods 

Parameter Time Period 

Assumed 

Porosity Notes 

PCS_T1:POROSITY 0 to 100 years 6.6% to 18.7% Assumes ROM salt is emplaced with an initial porosity 

of 20% to 35%. An initial porosity of 35% represents 

no compaction during emplacement. 

PCS_T2:POROSITY 100 to 200 yrs 2.5% to 7.5% 2.5% to 7.5% is consistent with the JAS3D calculations 

and is conservative relative to alternate computational 

predictions from several sources. 

PCS_T3:POROSITY 200 to 10,000 

yrs 

0.1% to 5.19% Assumes that the porosity of crushed salt after 200 

years is equal to the porosity for intact halite. 
13

5.1.2 Permeability of ROM Salt 

Laboratory experiments on consolidated cores of crushed salt confirm that the intrinsic 

permeability of crushed salt decreases as the fractional density of the cores increases (Hurtado et 

al. 1997, Figure 2-1). This observation is corroborated by other experiments on the behavior of 

crushed salt under similar conditions to WIPP (Case et al., 1987; Zhang et al., 2007); although 

the cores tested by Zhang et al. (2007) are for salt from the Asse mine and some of the core 

tested by Case et al. (1987) is for salt from Avery Island, the overall behavior of the crushed 

material is expected to be similar. The general observations from testing of crushed salt cores are 

that: (1) intrinsic permeability decreases as the fractional density increases (or as the porosity 

decreases), (2) crushed salt cores with added moisture generally have lower values of intrinsic 

permeability than dry cores, and (3) cores of crushed salt with smaller grain sizes generally have 

lower values of intrinsic permeability than cores with larger grain sizes. The first and third 

observations are generally valid for all granular materials, while the second observation 

specifically relates to the microstructure of the salt cores and requires further explanation. 

At equivalent fractional densities, dry consolidated salt cores are more permeable than wet 

consolidated salt cores because of the difference in the mechanism causing consolidation. Under 

dry conditions, the effective consolidation mechanism is crystal plasticity, while under wet 

conditions the effective consolidation mechanism is pressure solution/redeposition (Hurtado et 

al. 1997, page 2-7; Case et al., 1987, Section 4). Pressure solution/redeposition under wet 

conditions generally produces higher consolidation rates and more deformation than crystal 

plasticity under dry conditions, leading to lower measured permeability for wet consolidated salt 

than for dry consolidated salt at equivalent fractional densities (Hurtado et al. 1997, Figure 2-1; 

Case et al., 1987, data for Test 3 in Figure 1). 

During the first time period, from 0 to 100 years, the porosity of the ROM salt varies from 6.6% 

to 18.7% (see Table 2). Table 3 summarizes permeability data for cores of crushed salt that are 

relevant to the maximum porosity of 18.7%. The data are from three sources: Hurtado et al. 

(1997), Case et al. (1987), and Zhang et al. (2007). Hurtado et al. (1997) summarizes data from 

(Brodsky 1994) and (Brodsky et al., 1996) for wet and dry cores, respectively. The permeability 

data from the three sources are remarkably consistent and provide a basis for defining the 

maximum permeability as approximately 10-12 m

2

 at a porosity of 18.7%. 

Table 3. Permeability data for cores of crushed salt at 18.7% porosity 

Source Porosity 

Permeability 

(m2) Notes 

(Brodsky et al., 1996), 

summarized in Table 

2-1 of (Hurtado et al., 

1997) 

17.8% 4.11×10-13 m2 For dry WIPP salt at fractional density of 0.822 

(porosity of 17.8%). This core has the greatest porosity 

of the data in (Brodsky et al., 1996) and (Brodsky 

1994). 

Case et al., 1987, 

Figure 1 

18.7% 1×10-13 m2 to 

2×10-12 m2 For dry WIPP salt with 0.9 mm and 10 mm maximum 

grain sizes (Tests 1 and 2) and for moistened WIPP 

salt with 20 mm maximum grain size (Test 3). 

Zhang et al., 2007, 

Figure 4 

18.7% 2×10-13 m2 to 

1×10-12 m2 For dry Asse salt cores with maximum grain size of 32 

mm. 

 
14

At the minimum porosity value of 6.6% during the first 100 years after facility closure, the 

measurements have a wide range of permeability because of the microstructure of the cores. 

Table 4 has the measured values that are relevant to a porosity of 6.6%. The gas permeability 

data for dry cores at 6.6% are relatively consistent from the three sources, falling within a 

permeability range of 10-15 m

2

 to 10-14 m

2

. The brine permeability from Case et al. (1987) is 

lower than the brine permeability from Hurtado (1994), which may be caused by the maximum 

grain size for the cores. Test 3 from Case et al. (1987, Table 1) has a maximum grain size of 20 

mm, while the maximum grain size of ROM WIPP salt was measured at 1.5 inches (38 mm) 

(Pettigrew and Associates, 1993), or almost twice as large as the crushed salt for Test 3. Cores 

with finer grain sizes are expected to have lower permeability than cores with larger grain sizes, 

which may explain the observed difference in permeability from different sources. 

Table 4. Permeability data* for cores of crushed salt at 18.7% porosity 

Source Porosity 

Permeability 

(m2) Notes 

(Brodsky et al., 1996) 

& (Brodsky, 1994), 

summarized in Table 

2-1 of (Hurtado et al., 

1997) 

6.61% 

6.67% 

4.95×10-15 m2 

2.14×10-19 m2

For dry WIPP salt at a fractional density of 0.9339 

(porosity of 6.61%)(Brodsky et al., 1996) 

For wet WIPP salt at a fractional density of 0.9333 

(porosity of 6.67%)(Brodsky 1994) 

Case et al., 1987, 

Figure 1 

6.6% 

6.6% 

1×10-15 m2 to 

1×10-14 m2

1×10-21 m2 to 

1×10-20 m2

For dry WIPP salt with 0.9 mm and 10 mm maximum 

grain sizes (Test 1 and Test 2) 

For wet WIPP salt with 20 mm maximum grain size 

(Test 3). 

Zhang et al., 2007, 

Figure 4 

18.7% 1×10-14 m2 For dry Asse salt cores with maximum grain size of 8 

mm. 

*Data on fractional density and permeability from (Brodsky, 1994) and (Brodsky et al., 1996) are reproduced with the same 

number of digits in (Hurtado et al., 1997, Table 2-1) to facilitate identification of specific measurements in the data sets. 

The range of permeability for performance assessment should encompass the range of laboratory 

measurements shown in Tables 3 and 4. At a porosity of 18.7%, the maximum permeability is 

approximately 10-12 m

2

. At a porosity of 6.6%, the brine permeability from Hurtado et al. (1997) 

is about 2×10-19 m

2

. The brine permeability data from Case et al. (1987) are not used here 

because the maximum grain size for Test 3, 20 mm, is somewhat smaller than the measured 

maximum grain size for WIPP salt, 38 mm. We therefore determine that the permeability of the 

ROM salt should be sampled from a log-uniform distribution, [2×10-19 m

2

, 10-12 m

2

], during the 

first time period, from 0 to 100 years. 

During the second and third time periods, the permeability of consolidated ROM salt is based on 

the experimental measurements of consolidated WIPP salt cores summarized in Hurtado et al. 

(1997) and further documented in additional Sandia documents (Brodsky, 1994; Brodsky et al., 

1996; Ahrens and Hansen, 1995). This analysis uses the brine permeability data from Brodsky 

(1994) for two reasons. First, the salt cores are based on ROM salt from the WIPP and provide a 

consistent data set for defining permeability as a function of porosity. Second, the fractional 

densities of the salt cores measured by Brodsky (1994) have a range of 0.8953 to 1.00511

(porosity of 10.47% to ~ 0%, resp.), which encompass the porosity range of interest during the 

second and third time periods (see Table 2). The alternate data sets are either sparsely populated 

                                                            

1

 A fractional density greater than 1 may imply uncertainty in the assumed density of intact salt. 
15

at the porosities of interest during the second and third time periods or are based on crushed salt 

with finer grain sizes than ROM salt from the WIPP. 

The permeability data from Brodsky (1994) are represented as a function of porosity through a 

two-step relationship: (1) a least squares fit to the permeability data as a function of fractional 

density, and (2) a normal distribution that represents the residuals of the data about the least 

squares fit. This approach captures the mean variability of permeability with porosity and 

represents the uncertainty in the data set. Figure 6 shows the least squares fit to the data from 

(Brodsky, 1994). Figure 7 is a quantile-quantile plot showing that a normal distribution provides 

a good representation of the residuals of the individual data points about the least squares fit. 

(The closeness of the individual points to the straight line in Figure 7 indicates the goodness of 

fit by a normal distribution.) This normal distribution has a mean of 0.0 and a standard deviation 

of 0.86. The parameters for the normal distribution are determined by the data, without 

adjustment or expert judgment. Given the limited number of data points from Brodsky (1994), 

the normal distribution will be truncated at plus or minus two standard deviations. 

The relationship between porosity and permeability can be mathematically written as: 

log( )  21.187(1  ) 1.5353, e k (1) 

10 10 , log( )  

e

k k k e    (2) 

where ke is the expected value of permeability from the least squares fit, 

 is the sampled value of porosity, 

 k is the final value of permeability, and

is the sampled value of a normal distribution with a mean of 0, a 

 standard deviation of 0.86, and truncated at ±2 standard deviations.

Figure 6. Least squares fit to brine permeability measurements for WIPP crushed salt 

y = ‐21.187x + 1.5353

R2 = 0.3222

‐22

‐21

‐20

‐19

‐18

‐17

0.88 0.9 0.92 0.94 0.96 0.98 1 1.02

Log10(Permeability [m2])

Fractional Density

Brine Data (Brodsky 1994)

Linear Fit
16

Figure 7. Quantile-quantile plot of the data residuals relative to the linear fit and of the predicted 

residuals for a normal distribution with mean of 0.0 and standard deviation of 0.86 

The following algorithm for representing the values of PCS_T1:PRMX_LOG, 

PCS_T2:PRMX_LOG and PCS_T3:PRMX_LOG in PA should be used: 

1. The value of PCS_T1:POROSITY is sampled from a uniform distribution, [6.6%, 

18.7%], in each realization. 

2. The permeability [m2] of ROM salt from 0 to 100 years, PCS_T1:PRMX, is sampled 

from a log-uniform distribution, [2×10-19 m2

, 10-12 m2], in each realization. The values of 

PCS_T1:PRMY and PCS_T1:PRMZ are set equal to PCS_T1:PRMX. 

3. For each realization, the value for PCS_T2:POROSITY between 100 and 200 years is 

sampled from a uniform distribution with a minimum of 0.025 and a maximum of 0.075. 

The value for PCS_T3:POROSITY between 200 and 10,000 years is sampled from a 

uniform distribution with a minimum of 0.001 and a maximum of 0.0519. 

4. Calculate the expected values of the log10 (ke), the logarithm of the expected permeability, 

using Equation (1) with the sampled values of PCS_T2:POROSITY and 

PCS_T3:POROSITY. 

5. Sample a normal distribution (mean of zero, standard deviation of 0.86) that is truncated 

at ±2 standard deviations and calculate the final value of the permeability, k, using 

Equation (2). This calculation is performed twice, once for 100 to 200 years, and a 

second time for 200 to 10,000 years. This sampling is performed once per realization. 

‐2.5

‐1.5

‐0.5

0.5

1.5

2.5

‐2.5 ‐1.5 ‐0.5 0.5 1.5 2.5

Residual of Log10(K[m2]) from Linear Fit

Residual for a Normal Distribution
17

6. The values of PCS_T2:PRMX, PCS_T2:PRMY, and PCS_T2:PRMZ are set equal to the 

value of k for the second time period. The values of PCS_T3:PRMX, PCS_T3:PRMY, 

and PCS_T3:PRMZ are set equal to the value of k for the 200 to 10,000 year time period. 

Figure 8 shows the range of permeability as a function of fractional density for this algorithm. 

Table 5 presents numerical values of the minimum, and maximum permeability from 0 to 100 

years, from 100 to 200 years, and from 200 to 10,000 years based on this approach. For the latter 

two time periods, the mean permeability is based on the sampled value of porosity (between 0.025 

and 0.075 for 100 to 200 years, and between 0.001 and 0.0519 for 200 to 10,000 years), as defined 

by the least squares fit (Equation (1)). The minimum and maximum permeability values 

correspond to -2 and +2 standard deviations on the normal distribution, respectively (Equation (2)). 

The 2.5% to 5.19% porosity range is included in both the 100 to 200 year and the 200 to 10,000 

year time periods (see discussion in Section 5.1.1), and represents the lower end of the porosity 

range from 100 to 200 years and the upper end of the porosity range from 200 to 10,000 years. 

This provides an overlap in the permeability ranges for these two time periods, although the 

effect is mitigated by sampling the uncertainty in the data about the least squares fit in Figure 8. 

With this algorithm, the calculated permeability value for 200 to 10,000 years may be greater 

than the calculated permeability value for 100 to 200 years. This is not a reasonable outcome, so 

the permeability value for 200 to 10,000 years should be sampled so that it is never greater than 

the permeability value for 100 to 200 years. 

Figure 8. Variation of permeability with fractional density, based on the least squares fit and a 

normal distribution with a mean of 0.0 and a standard deviation of 0.86 

‐22

‐21

‐20

‐19

‐18

‐17

‐16

‐15

0.88 0.9 0.92 0.94 0.96 0.98 1 1.02

Log10(Permeability [m2])

Fractional Density (= 1 ‐ )

Brine Data (Brodsky 1994)

±1 Standard Deviation

±2 Standard Deviations

Linear Fit
18

Table 5. Permeability of the ROM salt during three time periods 

Parameter(s) Porosity 

Fractional 

Density 

Minimuma,b

Permeability 

Maximuma,b

Permeability 

PCS_T1: 

PRMX_LOG, 

PRMY_LOG, 

PRMZ_LOG 

6.6% to 

18.7% 

0.825 to 0.933 -18.7 

(2×10-19 m2

) 

-12 

(1×10-12 m2) 

PCS_T2: 

PRMX_LOG, 

PRMY_LOG, 

PRMZ_LOG 

0.025 0.975 -20.8 

(1.44×10-21) 

-17.4 

(3.96×10-18) 

0.075 0.925 -19.8 

(1.65×10-20) 

-16.3 

(4.55×10-17) 

PCS_T3: 

PRMX_LOG, 

PRMY_LOG, 

PRMZ_LOG 

0.001 0.999 -21.4 

(4.46×10-22) 

-17.9 

(1.23×10-18) 

0.0519 0.9481 -20.3 

(5.34×10-21) 

-16.8 

(1.47×10-17) a

 Each cell has the log(k[m2]) and the corresponding value of k in parentheses. b

 Minimum corresponds to -2 standard deviations below the least squares fit; maximum corresponds to +2 

standard deviations above the least squares fit. 

The permeability values in Table 5 and Figure 8 are reasonable and appropriate and are 

supported from several viewpoints: 

 From 0 to 100 years, the crushed salt is assigned a permeability range of 2×10-19 m

2

 to 10-12

m

2

, representative of the combined test results from Hurtado et al. (1997), Case et al. 

(1987), and Zhang et al. (2007) for loosely consolidated ROM salt. 

 From 100 to 200 years, the permeability range in Table 5 encompasses a wide range of 

possible outcomes, from a minimum permeability of 1.44×10-21

 m

2

 to a maximum 

permeability of 4.55×10-17 m

2

. This range will produce a range of hydrologic responses for 

the ROM salt, from very “tight” to much “looser” in terms of brine and gas flows across 

the closure. This wide range has been chosen because of the uncertainties in emplacement 

of the ROM salt. 

 From 200 to 10,000 years, the permeability range in Table 5 represents the response of 

fully compacted salt, with a minimum permeability of 4.46×10-22

 m

2

 and a maximum 

permeability of 1.47×10-17 m2

. This range of values is purposefully greater than the range 

for intact halite in PA, which is 10-24

 m

2

 to 10-21 m

2

. The consolidation mechanisms for 

moistened versus dry crushed salt are different and can lead to different degrees of 

interconnected porosity and permeability for a given effective porosity. In this situation, the 

very low permeability of intact salt may not be attained for thousands of years by the ROM 

salt. 

 After 100 years, the range of permeability in Table 5 is similar to the permeability range for 

material DRZ_PCS in the PABC-2009, which is 2×10-21 m2

 to 1×10-17 m2 (Clayton et al. 

2010), as discussed in Section 5.2 of this memorandum. The ranges of permeability after 

100 years are therefore consistent with the expected response for a healed DRZ above and 

below a panel closure, as represented in PABC-2009. 
19

5.1.3 Residual Brine Saturation and Residual Gas Saturation of ROM Salt 

The residual gas saturation is the degree of gas saturation necessary to create an incipient 

interconnected pathway for a porous material to be permeable to gas. The residual gas saturation 

for all materials in the original shaft seal model, including crushed salt, was defined for the CCA 

(DOE, 1996, Appendix PAR, Parameter 14). The residual gas saturation was based on a 

literature review for consolidated geologic materials, concrete, and asphalt, and on professional 

judgment. Similarly the residual brine saturation for all shaft seal materials, including crushed 

salt, was defined for the CCA based on a literature review and on professional judgment (DOE, 

1996, Appendix PAR, Parameter 15). The residual brine saturation and residual gas saturation of 

the ROM salt in the PCS will use the same distributions as the corresponding parameters for the 

crushed salt component of the shaft seals. These distributions are summarized in Table 6. 

Table 6. Residual brine saturation and residual gas saturation of the ROM salt 

Parameter Distribution 

PCS_T1:SAT_RBRN 

PCS_T2:SAT_RBRN 

PCS_T3:SAT_RBRN 

Cumulative distribution: 

Probability Value 

 0.0 0.0 

 0.5 0.2 

 1.0 0.6 

PCS_T1:SAT_RGAS 

PCS_T2:SAT_RGAS 

PCS_T3:SAT_RGAS 

Uniform distribution: 

Minimum value: 0.0 

Maximum value: 0.4 

5.1.4 Relative Permeability Model and Capillary Pressure Model for ROM Salt 

Several two phase flow models have been implemented in the BRAGFLO code, and the values 

of the parameters RELP_MOD and CAP_MOD define the relative permeability model and the 

capillary pressure model for a material, respectively. Most materials mapped to the BRAGFLO 

grid use a modified Brooks-Corey model for relative permeability, with the exception of the 

anhydrite Marker Beds and Anhydrite Layers a and b (DOE, 2009, Table PA-4), which switch 

between the Brooks-Corey and Van Genuchten models for relative permeability. The two phase 

flow model for the ROM salt will also use the modified Brooks-Corey model, which corresponds 

to relative permeability model number 4 (i.e., RELP_MOD = 4) (DOE, 2009, footnote to Table 

PA-4) and use capillary pressure model number 2 (i.e., CAP_MOD = 2), which has a fixed 

maximum capillary pressure. The choice of these models is independent of the timing of the 

consolidation process. Table 7 summarizes these values. 

Table 7. Relative permeability model and capillary pressure model for the ROM salt 

Parameters Value 

PCS_T1:RELP_MOD 

PCS_T2:RELP_MOD 

PCS_T3:RELP_MOD 

4 (a modified Brooks –Corey 

model) 

PCS_T1:CAP_MOD 

PCS_T2:CAP_MOD 

PCS_T3:CAP_MOD 

2 (fixed maximum capillary 

pressure) 
20

5.1.5 Other Two Phase Flow Parameters 

Table 8 identifies seven parameters for the relative permeability and capillary pressure models 

for the ROM salt. All WIPP PA materials use the same values for KPT, PC_MAX, and 

PO_MIN. The crushed salt materials and concrete-related materials for the original shaft seal 

model use the same values and distributions for the COMP_RCK, PCT_A, PCT_EXP, and 

PORE_DIS parameters shown in Table 8. The values or distribution in Table 8 will be used for 

the ROM salt, independent of the time period. 

 

Table 8. Two phase flow parameters for the ROM salt 

Parameter Description Type Value 

COMP_RCK Bulk Compressibility Constant 8.0x10-11 Pa-1

KPT Flag for permeability 

determined threshold 

Constant 0.0 (dimensionless) 

PO_MIN Minimum brine pressure for 

capillary model KPC=3 

Constant 1.01325×105 Pa 

PC_MAX Maximum allowable 

capillary pressure 

Constant 1×108 Pa 

PCT_A Threshold pressure linear 

parameter 

Constant 0.56 Pa 

PCT_EXP Threshold pressure 

exponential parameter 

Constant -0.346 (dimensionless) 

PORE_DIS Brooks-Corey pore 

distribution parameter 

Cumulative 

distribution 

Probability Value 

 0.0 0.11 

 0.5 0.94 

 1.0 8.1 

5.2 Hydrologic and Pore Compressibility Parameters of the DRZ Surrounding the 

ROMPCS 

5.2.1 Porosity and Permeability of the DRZ 

Initially it is expected that the DRZ around the PCS will be no different from that around the 

disposal rooms, since there will be only very small back stress from the consolidating ROM salt. 

Calculations for closure of panel entries and consolidation of the ROM salt have been performed 

for two bounding cases: (1) ROM salt that is emplaced and compacted to 20% porosity (80% 

fractional density), and (2) ROM salt that is emplaced without compaction to 35% porosity (65% 

fractional density) (Herrick 2012). The results of these calculations demonstrate that the time 

dependent backstress does not become appreciable until approximately 200 years after 

emplacement. While the back stress is low, the state of the DRZ surrounding the PCS will be 

similar to the state of the DRZ surrounding the disposal rooms, and it is appropriate to maintain 

the same ranges of DRZ porosity and DRZ permeability above and below the PCS as those 

around the disposal rooms during the first 200 years. Thus, the porosity of DRZ surrounding the 

PCS lies between 0.0039 and 0.0548 for the first 200 years (i.e. the same porosity range 

prescribed for material DRZ_1 in the PABC-2009). The permeability of the DRZ surrounding 

the PCS has a range of 10-12.5 m

2

 to 10-19.4 m

2

 for the first 200 years. 
After 20

shown in

rapidly u

For exam







Figu

0 years, bac

n Figures 9 a

under these l

mple, Costin 

Tensile frac

35 MPa), to

fracture pla

The healing

or storage in

The princip

fracture sur

ure 9. Vertic

emplacem

ck pressures

and 10. It h

evels of stre

and Wawers

ctures in salt

o the extent

ane is approx

g process tak

n salt occurs

pal mechanis

rface. 

cal back stre

ment porosit

s will have b

has been sho

ess (e.g., IT 

sik state: 

t will heal w

t that the res

ximately 70-

kes place rap

s. 

sm in healin

ss on the roo

ty of 20% (fr

21

built up to 

wn by sever

Corporation

when subject

sistance to c

80% of that 

pidly compa

ng appears to

of of the pan

fractional den

values of th

ral authors t

n, 1987 and C

ted to nomin

crack propag

through virg

ared to the ti

o be creep o

nel entry for 

nsity of 80%

he order of 

that fractures

Costin and W

nal overburd

gation along

gin material.

ime scale ov

f contact asp

ROM salt w

%) (Herrick 2

6 to 10 MP

s in salt will

Wawersik, 1

den pressures

g the pre-exi

.

ver which m

perities alon

with an initia

2012) 

Pa, as 

l heal 

980). 

s (10-

isting 

mining 

ng the 

l 
22

Figure 10. Vertical back stress on the roof of the panel entry for ROM salt with an initial 

emplacement porosity of 35% (fractional density of 65%) (Herrick 2012) 

Given the values of back stress calculated for closures with some degree of emplaced 

compaction, and the rapid increase of stress even for the most extreme case of salt that is 

emplaced without compaction (see Figure 10), the back stress is expected to heal the DRZ 

directly above and below the ROMPCS, reducing its porosity and its permeability. It is then 

appropriate to assume that the porosity and permeability of the DRZ after 200 years will be 

equivalent to the state of the DRZ surrounding the Option D panel closure in the PA for CRA2009 (DOE, 2009, Appendix PA) and in the PABC-2009. The porosity of the DRZ directly 

above and below the Option D panel closure in the PA for CRA-2009 and in the PABC-2009 has 

a minimum value of 0.0039 and a maximum value of 0.0548 at all times. The permeability of the 

DRZ directly above and below the Option D panel closure has a minimum value of 2×10-21

 m

2

and a maximum value of 1×10-17 m2 (DOE, 2009, Appendix PA, Sections PA-4.2.8.2 and PA4.2.8.3). We have chosen that these ranges be used for the DRZ surrounding the ROMPCS after 

200 years. Table 9 summarizes the ranges for porosity and permeability for the DRZ directly above 

and below the ROMPCS. 

The selected porosity for the DRZ directly above and below the PCS is constant at all times. After 

200 years, it is reasonable to expect that the healing of the DRZ caused by increasing back stress 

will reduce the DRZ porosity. A reduction in DRZ porosity should have minimal impact on the 

PCS-2012 PA because sensitivity calculations have demonstrated that PA results are insensitive to 

the porosity of a panel closure, and by extension to the porosity of the DRZ directly above and 

below the ROMPCS (DOE 2012, Response to EPA Question 1.2b). 
23

Table 9. Porosity and permeability of the DRZ surrounding the PCS 

Parameter Value Notes 

DRZ_PCS_T1:POROSITY 

DRZ_PCS_T2:POROSITY 

DRZ_PCS_T3:POROSITY 

0.0039 to 

0.0548 

Same range in the PA for CRA-2009 and the 

PABC-2009 as for the DRZ (material DRZ_1) 

around disposal rooms at all times. 

DRZ_PCS_T1:PERMEABILITY 

DRZ_PCS_T2:PERMEABILITY 

10-19.4 m2 to 

10-12.5 m2 Same permeability range in the PA for CRA2009 and PABC-2009 for the DRZ (material 

DRZ_1) surrounding disposal rooms from 0 to 

200 years. 

DRZ_PCS_T3:PERMEABILITY 2×10-21 m2 to 

1×10-17 m2 Same permeability range in the PA for CRA2009 and PABC-2009 for the DRZ_PCS above 

and below the Option D panel closures after 

healing of the DRZ. 

5.2.2 Two Phase Flow Parameters for Materials DRZ_PCS_T1 and DRZ_PCS_T2 

During the first 200 years, while the back stress is low, the state of the DRZ surrounding the PCS 

will be similar to the state of the DRZ surrounding the disposal rooms, and it is appropriate to 

maintain the same values for two phase flow parameters for the DRZ directly above and below 

the ROMPCS as those for the DRZ around the disposal rooms. Table 10 identifies the values for 

the two phase flow parameters and their sources during the first 200 years. 

5.2.3 Two Phase Flow Parameters for DRZ_PCS_T3 After 200 Years 

After 200 years, the back pressure from the consolidated ROM salt is expected to heal the 

fractures in the DRZ directly above and below the PCS. In this state, the DRZ above and below 

the consolidated ROM salt is expected to have similar properties to the DRZ above and below 

the Option D monolith in the PA for the CRA-2009 and the PABC-2009. Therefore, the two 

phase flow parameters for the DRZ directly above and below the ROM salt shall be assigned the 

same values and distribution as the DRZ_PCS in the PA for CRA-2009 or the PABC-2009. 

Table 11 identifies the values for the two phase flow parameters and their sources after 200 

years. 
24

Table 10. Two phase flow parameters for the DRZ directly above and below 

the ROMPCS during the first 200 years 

Parameter Description Value Source 

DRZ_PCS_T1:SAT_RBRN 

DRZ_PCS_T2:SAT_RBRN 

Residual brine saturation 0.0 DOE, 2009, Table PA-3 

for material DRZ_1 

DRZ_PCS_T1:SAT_RGAS 

DRZ_PCS_T2:SAT_RGAS 

Residual gas saturation 0.0 DOE, 2009, Table PA-3 

for material DRZ_1 

DRZ_PCS_T1:RELP_MOD 

DRZ_PCS_T2:RELP_MOD 

Relative permeability model 

number 

4 (modified 

BrooksCorey 

model) 

DOE, 2009, Table PA-4 

for material DRZ_1 

DRZ_PCS_T1:CAP_MOD 

DRZ_PCS_T2:CAP_MOD 

Capillary pressure model 

number 

1 (capillary 

pressure is 

unbounded) 

DOE, 2009, Table PA-4 

for material DRZ_1 

DRZ_PCS_T1:KPT 

DRZ_PCS_T2:KPT 

Flag for permeability 

determined threshold 

0.0 Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T1:PO_MIN 

DRZ_PCS_T2:PO_MIN 

Minimum brine pressure for 

capillary model KPC=3 

1.01325x105

(Pa) 

Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T1:PC_MAX 

DRZ_PCS_T2:PC_MAX 

Maximum allowable capillary 

pressure 

1.0x108

(Pa) 

Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T1:PCT_A 

DRZ_PCS_T2:PCT_A 

Threshold pressure linear 

parameter 

0.0 DOE, 2009, Table PA-3 

for material DRZ_1 

DRZ_PCS_T1:PCT_EXP 

DRZ_PCS_T2:PCT_EXP 

Threshold pressure 

exponential parameter 

0.0 DOE, 2009, Table PA-3 

for material DRZ_1 

DRZ_PCS_T1:PORE_DIS 

DRZ_PCS_T2:PORE_DIS 

Brooks-Corey pore distribution 

parameter 

0.7 DOE, 2009, Table PA-3 

for material DRZ_1 

Table 11. Two phase flow parameters for the DRZ directly above and below the ROMPCS after 

200 years 

Parameter Description Value Source 

DRZ_PCS_T3:SAT_RBRN Residual brine saturation 0.0 DOE, 2009, Table PA-3 

for material DRZ_PCS 

DRZ_PCS_T3:SAT_RGAS Residual gas saturation 0.0 DOE, 2009, Table PA-3 

for material DRZ_PCS 

DRZ_PCS_T3:RELP_MOD Relative permeability model 

number 

4 (modified 

BrooksCorey 

model) 

DOE, 2009, Table PA-4 

for material DRZ_PCS 

DRZ_PCS_T3:CAP_MOD Capillary pressure model 

number 

1 (capillary 

pressure is 

unbounded) 

DOE, 2009, Table PA-4 

for material DRZ_PCS 

DRZ_PCS_T3:KPT Flag for permeability 

determined threshold 

0.0 Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T3:PO_MIN Minimum brine pressure for 

capillary model KPC=3 

1.01325x105

(Pa) 

Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T3:PC_MAX Maximum allowable capillary 

pressure 

1.0x108

(Pa) 

Stein, SNL, ERMS 

520524, Table 2 

DRZ_PCS_T3:PCT_A Threshold pressure linear 

parameter 

0.0 DOE, 2009, Table PA-3 

for material DRZ_PCS 

DRZ_PCS_T3:PCT_EXP Threshold pressure 

exponential parameter 

0.0 DOE, 2009, Table PA-3 

for material DRZ_PCS 

DRZ_PCS_T3:PORE_DIS Brooks-Corey pore distribution 

parameter 

0.7 DOE, 2009, Table PA-3 

for material DRZ_PCS 
25

6.0 Summary 

The DOE has submitted a planned change request to the EPA proposing that a revised panel 

closure design be approved for use in all WIPP waste panels. Panel closures are emplaced in the 

WIPP to protect workers during the operational phase of the facility. They are represented in PA 

because they are a significant physical feature of the repository. Long-term repository 

performance has been repeatedly shown to be insensitive to panel closure material properties. 

The revised panel closure design proposed by the DOE is comprised of 100 feet of run-of-mine 

salt with barriers at each end. A performance assessment named the PCS-2012 PA is planned to 

quantify regulatory compliance impacts resulting from the incorporation of the new closure 

design in the repository. PA materials, properties, and timings are developed to allow for 

modeling of the revised panel closure system in the PCS-2012. These parameter choices are 

reasonable values that will adequately represent the PCS within PA, and are based on sound 

science, modeling, and external data sources where available. 

7.0 References

Ahrens, E.H., and F.D. Hansen. 1995. Large-Scale Dynamic Compaction Demonstration Using 

WIPP Salt: Fielding and Preliminary Results. Sandia National Laboratories. Albuquerque, NM. 

SAND95-1941. 

Bechthold, W., E. Smailos, S. Heusermann ,T. Bollingerfehr, B Bazargan Sabet, T. Rothfuchs, P. 

Kamlot, J Grupa, S. Olivella, and F. D. Hansen. 2004. Backfilling and Sealing of Underground 

Repositories for Radioactive Waste in Salt (BAMBUS II Project): final report. European 

Commission, Directorate General for Research, Office for Official Publications of the European 

Communities. Call No: EUR 20621 EN. Showcased in Research for Europe: Successful EUfunded projects by the Directorate General for Research. 

Blanford, M.L., M.W. Heinstein, and S.W. Key. 2001. JAS3D: A Multi-Strategy Iterative Code 

for Solid Mechanics Analysis User’s Instructions, Release 2.0. Sandia National Laboratories. 

ERMS 552358. 

Brodsky, N.S., 1994. Hydrostatic and Shear Consolidation Tests With Permeability 

Measurements on Waste Isolation Pilot Plant Crushed Salt. Sandia National Laboratories. 

Albuquerque, NM. SAND93-7058. 

Brodsky, N.S., F.D. Hansen, and T. Pfeifle. 1996. “Properties of Dynamically Compacted WIPP 

Salt.” Proceedings of the 4th International Conference on the Mechanical Behavior of Salt, 

Montreal, Quebec, Canada, June 17-18, 1996. Sandia National Laboratories. Albuquerque, NM. 

SAND96-0838C. 

Callahan G.D. and K.L. DeVries. 1991. Analyses of Backfilled Transuranic Wastes Disposal 

Rooms. Sandia National Laboratories. SAND91-7052. 
26

Callahan, G.D., M .C. Loken, L.L. Van Sambeek, R. Chen, T.W. Pfeifle, J.D. Nieland, and F.D. 

Hansen. 1995. Evaluation of Potential Crushed-Salt Constitutive Models. Sandia National 

Laboratories. Albuquerque, NM. SAND95-2143. 

Callahan, G.D. 1999. Crushed Salt Constitutive Model. Sandia National Laboratories, SAND98-

2680. 

Camphouse, R.C., Clayton, D.J., Kicker, D.C., and Pasch, J.J. 2011. Summary Report for the 

AP-151 (PC3R) Performance Assessment, Revision 1. Sandia National Laboratories, Carlsbad, 

NM. ERMS 555489. 

Case, John B., Peter C. Kelsall, and James L. Withiam. 1987. Laboratory Investigation of 

Crushed Salt Consolidation. 28th US Symposium on Rock Mechanics, Tucson, Arizona, 29 June 

– 1 July 1987. 

Clayton, D.C., Camphouse, R. C., Garner, J. W., Ismail, A. E., Kirchner, T. B., Kuhlman, K. L., 

and Nemer, M. B.. 2010. Summary Report of the CRA-2009 Performance Assessment Baseline 

Calculation, Revision 1. Sandia National Laboratories. Carlsbad, New Mexico, ERMS 553039. 

Costin, L.S. and W. R. Wawersik. 1980. Creep Healing of Fractures in Rock Salt. Sandia 

National Laboratories. SAND80-0392. 

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

Application for the Waste Isolation Pilot Plant. DOE/CAO-1996-2184. U.S. Department of 

Energy, Waste Isolation Pilot Plant, Carlsbad Area Office. Carlsbad, NM. 

DOE (U.S. Department of Energy). 2004. Title 40 CFR Part 191 Compliance Recertification 

Application for the Waste Isolation Pilot Plant. DOE/WIPP 2004-3231, 10 vols. U.S. 

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

DOE (U.S. Department of Energy). 2009. Title 40 CFR 191 Parts B and C Compliance 

Recertification Application. DOE/WIPP-09-3424. Carlsbad Field Office. Carlsbad, New Mexico. 

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

Request to the EPA 40 CFR Part 194 Certification of the Waste Isolation Pilot Plant. U.S. 

Department of Energy, Carlsbad Field Office. Carlsbad, New Mexico. 

DOE (U.S. Department of Energy), 2012. Response to First Set of EPA Questions to DOE, 

December 22, 2011. Letter from Mr. Juan Franco, Manager, Carlsbad Area Field Office, U.S. 

Department of Energy, to Mr. Jonathan Edwards, Director, Radiation Protection Division, U.S. 

Environmental Protection Agency, dated April 17, 2012. 

Dunagan, S. C. 2003. Complementary Cumulative Distribution Functions (CCDFs) for the 

Technical Baseline Migration (TBM), Revision 0. Sandia National Laboratories, Carlsbad, NM. 

ERMS 525707. 
27

EPA (U.S. Environmental Protection Agency). 1998. Criteria for the Certification and 

Re-Certification of the Waste Isolation Pilot Plants Compliance with the 40 CFR Part 191 

Disposal Regulations: Certification Decision; Final Rule, Federal Register, Vol. 63, No. 95, 

pp. 27353-27406. U.S. Environmental Protection Agency, Office of Air and Radiation, 

Washington, D.C. 

Hansen, C. W. 2002. Analysis Report for the Panel Closure Impact Assessment. Sandia National 

Laboratories, Carlsbad, NM. ERMS 523935. 

Hansen, F.D. 2003. The Disturbed Rock Zone at the Waste Isolation Pilot Plant. Sandia National 

Laboratories. Albuquerque, NM. SAND2003-3407. 

Herrick, C.G. 2012. JAS3D Calculations Performed in Support of the PCS-2012 PA Parameter 

Selections. Sandia National Laboratories, Carlsbad, NM. 

Hurtado, L.D., Knowles, M.K., Kelly, V.A., Jones, T.L., Ogintz, J.B., and T.W. Pfeifle. 1997. 

WIPP Shaft Seal System Parameters Recommended to Support Compliance Calculations. Sandia 

National Laboratories. Albuquerque, New Mexico. SAND97-1287. 

IT Corporation. 1987. Laboratory Investigation of Crushed Salt Consolidation and Fracture 

Healing. Prepared for Office of Nuclear Waste Isolation. BMI/ONWI-631. 

MacKinnon R. and G. Freeze, 1997. Supplemental Summary of EPA-Mandated Performance 

Assessment Verification Test (All Replicates) and Comparison with the Compliance 

Certification Application Calculations, Sandia National Laboratories, Carlsbad, NM. ERMS 

414880. (EPA Docket A-93-02, II-G-28.) 

Pettigrew and Associates. 1993. Sieve Analysis on Salt Backfill Sample #1 and Sieve Analysis on 

Salt Backfill Sample #2. Carlsbad, New Mexico. 

RockSol Consulting Group, Inc. 2006. Further Assessment of the Short-term Stability of the 12 

Foot Explosion Isolation Wall. Report prepared for Washington TRU Solutions, LLC. 

Rothfuchs, Tilmann, and Klaus Wieczorek. 2010. Backfill Compaction and EDZ Recovery. USGerman Workshop on Salt Repository Research, May 25-28, 2010, Jackson, Mississippi. 

Sjaardema, G.D., and R.D. Krieg. 1987. A Constitutive Model for the Consolidation of WIPP 

Crushed Salt and It’s Use in Analyses of Backfilled Shaft and Drift Configurations. Sandia 

National Laboratories. Albuquerque, NM. SAND87-1977. 

Spiers, C.J., J.L. Urai, and G.S. Lister. 1988. “The Effect of Brine (Inherent or Added) on 

Rheology and Deformation Mechanisms in Salt Rock,” The Mechanical Behavior of Salt, 

Proceedings of the Second Conference, Federal Institute for Geosciences and Natural 

Resources, Hanover, Federal Republic of Germany, September 24-28, 1984, 89 to 102. H.R. 

Hardy, Jr. and M. Langer (eds.). Clausthall-Zellerfeld, Germany: Trans Tech Publications. 
28

Van Sambeek, L.L., T. J. Eyerman, and F. D. Hansen. 1995. Case Studies of Sealing Methods 

and Materials Used in the Salt and Potash Mining Industries. Sandia National Laboratories. 

Albuquerque, NM. SAND95-1120. 

Vugrin, E.D. and S.C. Dunagan. 2006. Analysis Package for the Impact Assessment of the 

Redesigned Panel Closure System, Rev. 0. Sandia National Laboratories. Carlsbad, NM. ERMS 

543865. 

Vugrin, E., and S. Wagner. 2006. Panel Closure Summary Report. Sandia National 

Laboratories. Carlsbad, NM. ERMS 544802. 

Weatherby, J. R. 1989. Finite Element Analysis of TRU Storage Rooms Filled With Waste and 

Crushed Salt. Sandia National Laboratories Internal Memorandum to B. M. Butcher, Division 

6332, Albuquerque, NM. 

Zhang, Chun-Liang, Tilman Rothfuchs, and Johannes Droste, 2007. Post-tests on thermomechanically compacted salt backfill. The Mechanical Behavior of Salt – Understanding of 

THMC Processes in Salt, Wallner, Lux, Minkley and Hardy, Jr., Editors.