SAND2003-3407 

Unlimited Release 

Printed December 2003 

The Disturbed Rock Zone at the Waste 

Isolation Pilot Plant 

Francis D. Hansen 

Carlsbad Programs Group 

Sandia National Laboratories 

P.O. Box 5800 

Albuquerque, NM 87185-1395

Abstract 

The Disturbed Rock Zone constitutes an important geomechanical element of the Waste Isolation 

Pilot Plant. The science and engineering underpinning the disturbed rock zone provide the basis 

for evaluating ongoing operational issues and their impact on performance assessment. 

Contemporary treatment of the disturbed rock zone applied to the evaluation of the panel closure 

system and to a new mining horizon improves the level of detail and quantitative elements 

associated with a damaged zone surrounding the repository openings. Technical advancement 

has been realized by virtue of ongoing experimental investigations and international 

collaboration. The initial portion of this document discusses the disturbed rock zone relative to 

operational issues pertaining to re-certification of the repository. The remaining sections 

summarize and document theoretical and experimental advances that quantify characteristics of 

the disturbed rock zone as applied to nuclear waste repositories in salt. 

3
Contents 

1.0 Introduction ..........................................................................................7

2.0 Option D Modeling ...............................................................................8

2.2 Background of Option D Panel Closure Analyses .............................................................10

2.3 Option D in the Technical Baseline Migration.....................................................................11

2.4 Preliminary Option D Assessment .........................................................................................16

3.0 Clay G Evaluations ............................................................................17

3.1 Background of Clay G Analyses.............................................................................................17

3.2 Results of Clay G Analysis.......................................................................................................19

3.3 Conclusions of Clay G Analyses ............................................................................................23

4.0 Salt Damage Evaluations ..................................................................24

4.1 Principles of Salt Damage ........................................................................................................25

4.2 Hydrologic Properties of Damaged Salt ...............................................................................26

4.3 Laboratory Studies of Salt Damage .......................................................................................27

4.4 Salt Damage Modeling...............................................................................................................30

4.5 Salt Damage Healing in Laboratory Studies........................................................................31

4.6 Salt Damage Healing—In Situ Small Scale...........................................................................32

4.7 DRZ Delineation by Sonic Velocity .......................................................................................33

4.8 Observational Fracture Studies ..............................................................................................36

4.9 Full-Scale Field Analogs ..........................................................................................................39

5.0 Summary.............................................................................................41

6.0 References..........................................................................................42

4
LIST OF TABLES 

Table 1. DRZ Permeability used in the CCA and PAVT .................................................. 9 

Table A.1 Summary of Strength and Permeability Tests on ....................................... 51 

5
LIST OF FIGURES 

Figure 1. Detail of PAVT and TBM grid and properties ...................................................... 12 

Figure 2. Damage in the Floor of Panel 1, Room 2, August 21, 2001.............................. 13 

Figure 3. Stratigraphy near the Repository Horizon (after Kreig, 1984)........................... 14 

Figure 4. Schematic of the Stratigraphy Surrounding the Raised and Unraised Sections 

of the Repository ................................................................................................................ 15 

Figure 5. En Echelon DRZ Fracture Pattern to Clay G....................................................... 19 

Figure 6. Porosity Histories for Raised and Original Horizons Using Various Gas 

Generation Parameters..................................................................................................... 20 

Figure 7: Deformation of Raised Disposal Room Containing Waste with Time for f=0.0

............................................................................................................................................... 21

Figure 8: Anhydrite Shear Failure around the Raised Disposal Room with Time for f=0.0

............................................................................................................................................... 22

Figure 9: Disturbed Rock Zone around a Raised Disposal Room with Time for f=0.0 .. 23

Figure 10. Stress States Known to Cause Dilation of WIPP Salt....................................... 29 

Figure 11. Permeability Versus Dilatant Volumetric Strain for WIPP Salt ........................ 30 

Figure 12. Damage Predicted Around a Typical WIPP Disposal Room 40 Years After 

Excavation (after Van Sambeek et al., 1993b).............................................................. 31 

Figure 13. Layout of Holes for Room Q Alcove, with holes used for ultrasound 

measurements indicated in red........................................................................................ 34 

Figure 14. Same-hole measurements for adjacent holes, one in the left-hand wall (red) 

and in the corner (black) ................................................................................................... 35 

Figure 15. Fractures and Apertures in Three WIPP Cores ................................................ 38 

Figure 16. Fracture Apertures for DRZ Cores from WIPP and Asse................................ 39 

Figure 17. ALOHA2: Permeability Distribution around the Bulkhead and Open Drift.... 40 

Figure A.1. Permeability of SMC, ESC, and MSC Concrete Specimens Versus Gas 

Pressure Difference ........................................................................................................... 52 

Figure A.2. Cumulative Distribution Function for Permeability of SMC (after Repository 

Isolation Systems Department, 1996, WIPP Shaft Seal System Compliance 

Submittal Design Report, Appendix A) ........................................................................... 53 

6
1.0 Introduction 

The Disturbed Rock Zone (DRZ) is an important geomechanical element of the Waste Isolation 

Pilot Plant (WIPP). The DRZ was modeled explicitly in the Compliance Certification 

Application (CCA) and in the Performance Assessment Verification Test (PAVT). On the basis 

of the performance calculations, WIPP was certified by the U.S. Environmental Protection 

Agency (EPA) as meeting regulatory compliance. Since the certification, the scientific 

understanding of the DRZ has progressed by virtue of ongoing experimental investigations, 

further evaluations of published research, and international collaborations. This paper reviews 

the considerable information base on the DRZ and contrasts today’s understanding with the 

representation utilized for the compliance determination. As documented subsequently, DRZ 

properties are bracketed more definitively today than at the time of the compliance certification 

application, thereby making it possible to represent elements of the underground in a more 

realistic manner than represented heretofore. 

To begin the evaluation of the current WIPP operational framework in which DRZ issues are 

addressed, a limited discussion of DRZ evolution helps set the stage. The WIPP is situated in 

primarily rock salt at a depth of 655 meters. Salt, being a plastic medium at this depth, exhibits a 

virgin lithostatic state of stress. Creation of underground openings perturbs the static equilibrium

of the mined regions sufficiently to cause fracturing in rock proximal to the extracted material. 

The DRZ comprises the region near an excavation that experiences a change in hydrologic or 

mechanical properties. The properties that typically define a DRZ include: (1) dilational 

deformation ranging from microscopic to readily visible scales, (2) loss of strength evidenced by 

rib spall, floor heave, roof degradation and collapse, and (3) increased fluid permeability via 

connected porosity. The DRZ can play an important role in the geomechanical response of the 

WIPP underground, particularly where structures are placed to retard fluid flow in the repository. 

Although stress differences tend to decrease over time in a creeping medium, such as rock salt, 

fractures continue to grow and coalesce in an arching pattern around drifts and develop 

preferentially oriented parallel to the opening. As shown in photographs later in this report, the 

manifestation of the DRZ can be observed today in several locations in the WIPP underground. 

Treatment of the DRZ is integral to the evaluation of two features of the operating repository that 

have changed relative to the analyses supporting the initial certification: 

• The Option D panel closure to be implemented as a condition of the certification, and, 

• The operational change elevating the repository disposal room ceiling to Clay Seam G. 

These two considerations, which involve several geomechanical elements, will be referred to as 

Option D and Clay Seam G, respectively. In particular, construction of Option D will create 

conditions substantially different from those modeled in the compliance calculations. Namely, 

the salt DRZ would heal around such a rigid monolith and the anhydrite comprising Marker Bed 

139, a major component of the DRZ, beneath the current repository floor would be mined out. 

Raising the repository horizon by 2.43 meters to Clay G changes the structural setting by 

increasing the thickness of salt in the floor between the repository and MB 139 and decreasing 

the distance from the roof to overlying marker beds, such as Marker Bed 138. Construction of 

Option D within the raised repository setting is not addressed at this time. 

7
The primary motivation for developing this paper derives from the need to incorporate these two 

features in structural analysis of the underground setting and implement the derivative 

information into PA analyses. The EPA certified WIPP compliance previously; however, 

incorporation of these operational features necessitated conceptual model modifications and 

additional detail to the PA models. In anticipation of the scrutiny associated with recertification, the geotechnical aspects of Option D and Clay Seam G features are evaluated to 

ascertain deviations from the certified baseline. Technical documentation demonstrates and 

substantiates that these two changes can be adequately represented and understood and that they 

do not perceptibly change the PA cumulative complementary distribution function. In addition 

to evaluating these operational details, the broader context of a damaged rock in a salt repository 

will be reviewed and updated to include recent work at WIPP and within international repository 

programs. 

In preparation for the compliance re-certification application, a prerequisite to the EPA 

deliberations includes assessment of advances in our knowledge of features, events and 

processes pertaining to WIPP. In technical exchanges between the DOE, EPA and stakeholders 

during the period between the compliance determination and the re-certification application, 

ongoing technical assessment of the DRZ was discussed periodically. Technical understanding 

of the DRZ has been recorded in reference literature, such as external publications, SAND 

documents published by Sandia National Laboratories, and biannual progress reports on 

repository investigations. This document emphasizes present advances with respect to 

quantifying characteristics of the DRZ and provides a literature review, both of which emphasize 

WIPP applications. This document is meant to provide comprehensive documentation and 

technical discussion of the DRZ relative to WIPP re-certification. In particular, the technical 

discourse emphasizes improvement to our understanding of the DRZ at WIPP. 

This document provides a review and assessment of the Project’s understanding of the WIPP 

DRZ. Liberal reference will be made to a large amount of available information. The layout of 

this paper is an attempt to be comprehensive and systematic. Flow of the content begins with 

background information, which contrasts previous and current treatment of the DRZ in 

performance assessment analyses. Then, treatment of the two primary features—Option D and 

Clay G—will be addressed in Sections 2 and 3, respectively. Section 4 presents an overview of

characteristics of the DRZ, which substantiate many of the parameters and modeling treatment of 

the DRZ. Section 4 reviews underlying theory and characteristics of the DRZ, and provides a 

summary updating the understanding of the DRZ. The emphasis of the new treatment is the 

DRZ itself, particularly the “salt” DRZ, but other elements of the underground, such as the 

concrete of Option D and fracture of the anhydrite, are involved in the analyses. These 

geomechanical elements as represented in the baseline compliance calculations and subsequent 

PA verification testing have been updated for re-certification calculations. The updated 

implementation is believed to represent an improvement in accuracy, adequacy and validity of 

the modeling employed for the initial certification. 

2.0 Option D Modeling 

The PA calculation was conducted in 1996 (U.S. DOE, 1996) as part of the overall compliance 

certification process established by the EPA in its radiation protection regulations (U.S. EPA, 

8
1998). In 1997 the EPA required a PAVT to verify and evaluate the results of DOE’s CCA PA 

calculation. In their analysis, EPA addressed DRZ parameter values and distributions. To 

support the upcoming re-certification process, the technical baseline of the CCA and the PAVT 

was converged. 

The table below summarizes the DRZ parameter changes made between the CCA and the PAVT. 

The grid used in CCA calculations implemented a DRZ of constant permeability (10-15

 m

2

) over 

a region 12 meters above and 2.23 meters below the disposal rooms. The grid was continuous 

above panel closure systems, such that the same permeability and thickness existed above and 

below the simulated panel closures. The PAVT changed the DRZ permeability to a uniform

distribution ranging from 10-19.4

 to 10-12.5 m

2

. The geometrical dimensions of the DRZ are the 

same between the CCA and the PAVT. A consensus was reached that the PAVT permeability 

values represented an acceptable range for purposes of those analyses and assumptions 

pertaining thereto. Sandia National Laboratories reconciled all the parameters used in the CCA 

and the PAVT and established a single parameter baseline for the compliance re-certification 

calculations (Hansen and Leigh, 2002). 

Table 1. DRZ Permeability used in the CCA and PAVT. 

DRZ Permeability 

Material ID's 

CCA 

Value 

Description of Change 

for the PAVT

Rationale 

198 - DRZ_1/prmx_log 

199 - DRZ_1/prmy_log 

200 - DRZ_1/prmz_log 

-15 

Log of the DRZ permeability 

(m2

) was changed to a uniform

distribution ranging from -19.4 

to -12.5. 

Based on gas permeability 

testing of anhydrite cores 

from MB 139 (see WPO 

#30603 p. 2; WPO #32038;

WPO #38367 p. 11) 

The EPA documented their reasons for selecting PAVT DRZ permeability distributions, which 

differed from the single permeability value used in CCA calculations. Records from the WIPP 

Project Office (WPO) were used by the EPA to derive the recommended PAVT permeability 

range, which includes the CCA value near the mid-range of PAVT distribution. The WPO 

records are listed in the table. Additional documentation is cited in Sandia National Laboratories 

electronic database (PRAMVIEW). The DRZ parameters now assembled in PRAMVIEW are 

those selected by the EPA for the PAVT. 

A brief review of the WPO documents supporting the PAVT DRZ values supports the magnitude 

and range of the PAVT values. WPO #32038 includes one data set comprising 14 tests, which 

yields a permeability range (log 10) from –12.5 to –21 m2

. The other two WPO packages noted 

in the table include laboratory measurements on Marker Bed 139 anhydrite. From a total of 42 

anhydrite samples, a pressure-sensitive permeability from (log 10) –16 to –21 m2

 was reported. 

Based on these data the range employed by the PAVT is appropriate. 

The CCA and PAVT are documented, extensive, complicated calculations, which underpin the 

compliance determination. In addition, the “record” includes reference documents of many 

types, such as Technical Support Documents (TSDs), and Compliance Application Review 

Documents (CARDS). These records were scrutinized for their applicability to the DRZ model. 

9
A summary of the review of technical discussions existing in the records is included in this 

report (Appendix B). 

2.2 Background of Option D Panel Closure Analyses 

In terms of PA, the most important DRZ parameters are permeability, porosity, and their extent. 

In the period since the compliance application, WIPP personnel have re-examined the DRZ 

model, paying particular attention to implementation of Option D panel closure systems. 

Analysis Plan 087 (Hansen et al., 2002) describes the incorporation of the Option D closure into 

the existing BRAGFLO grid. The migration from the initial representations of the closures and 

DRZ to a more detailed analysis was called a Technical Baseline Migration (TBM). Detail is 

added to simulate more closely the actual geometry of the WIPP underground. Permeability is a 

primary modeling parameter, therefore a contrast will be drawn between treatment of the DRZ 

for compliance certification calculations, PA verification test calculations, and more recent 

calculations performed to reconcile parameters, representations and conceptual models into a 

single baseline. The primary motivation to add detail to the BRAGFLO grid is to incorporate a 

more realistic representation of the geotechnical issues attendant to Option D. 

Implementation of Option D into the PA model necessitated additional detail within the 

BRAGFLO mesh to capture the geotechnical interplay between the DRZ, the anhydrite marker 

beds and the concrete monolith. The salt DRZ and the marker bed response are also integral to 

interpretation of the effects caused by raising the disposal horizon (see Section 3.0). 

Perspectives, background, and data will be provided to guide the arguments toward the analysis 

being undertaken to evaluate incorporation of Option D panel closures into the PA calculations. 

Calculations underway for re-certification refine the detail of the repository and evaluate effects 

of the DRZ in concert with the panel closure Option D. 

Permeability values and geometrical extent of the DRZ are based on observations, measurements 

and an understanding of the mechanical response. The DRZ is also reversible in salt. When a 

rigid plug, such as the Option D panel closure concrete, is placed in a drift, the impinging salt 

experiences a “back-stress”, which reduces stress differences. As the state of stress approaches 

equilibrium, existing microfractures heal within the salt medium. Thus, the expectation is that 

the DRZ around an Option D panel closure would be minimal at the time of construction and 

eliminated essentially immediately after the panel closure is completed. By contrast, the DRZ 

around rooms filled with waste would continue to evolve as the country rock deforms into the 

open space of the room and then compresses the waste stack. In a relatively short time (fewer 

than 100 years), however, the state of stress in the salt around the waste rooms will return to their 

original condition of no shear, and the DRZ around the greater areas of the waste rooms would 

be largely healed as well. Implications of DRZ healing and the underlying theory are discussed 

in Section 4. 

Placement of a rigid structure within a drift, such as provided by the Option D concrete monolith, 

will resist the inward flow of salt and locally return the state of stress to a condition that no 

longer produces a DRZ, rather conditions would favor healing of damaged salt. In addition, the 

DRZ is excavated prior to placement of the concrete structure. Therefore, consideration of the 

10
model for an Option D panel closure must include properties of the structure placed in the drift, 

particularly its permeability, and properties of the surrounding rock. Characteristics of the Salado 

Mass Concrete (SMC) specified for the Option D closure are summarized in Appendix A. 

In the course of WIPP analyses, the DRZ proximal to the disposal rooms and extending into 

panel entry drifts has been (and is proposed to be) represented in the following ways. 

DRZ and panel closure in the CCA. 

• DRZ permeability was held constant at 10-15

 m

2

. 

• The DRZ extended 12 meters above and approximately 2 meters below (bottom of Marker 

Bed 139). 

• The panel closure was represented with a permeability of 10-15 m

2

. 

• Anhydrite fracture occurred when gas pressure approached lithostatic. 

DRZ and panel closure in the PAVT. 

• DRZ permeability was sampled from 10-19.4

 to 10-12.5 m

2

 with a median permeability of 

10-15.95 m

2

. 

• The DRZ extended 12 meters above and approximately 2 meters below (bottom of Marker 

Bed 139). 

• The panel closure was represented with a permeability of 10-15

 m

2

. 

• The pressure-induced fracture model (designed for the anhydrite marker beds) was applied to 

the DRZ. 

DRZ and panel closure in the TBM

• The PAVT permeability distribution was applied to the vast majority of the DRZ. 

• The DRZ extended 12 meters above and approximately 2 meters below the disposal rooms, 

however the DRZ residing above and below placement of the Option D concrete monolith 

assumed a low permeability. 

• The panel closure concrete was represented with an appropriate permeability distribution (10-

17 to 10-21

 m2), as discussed in Appendix A. 

• The pressure-dependent fracture model was applied to the DRZ. Conceptually, fluid could 

access anhydrite marker beds and allow migration around the panel closure through Marker 

Bed 139 or propagate into overlying anhydrite seams, which are underlain by thin clay 

seams. 

2.3 Option D in the Technical Baseline Migration

To implement the various details required to model Option D and to prepare analyses for review 

by independent technical peers, Sandia embarked on an exercise called the TBM. The TBM grid 

refinement represented Option D closures with SMC, the DRZ above and below disposal rooms, 

and the DRZ above and below the Option D closure. SMC is Portland-cement concrete that is 

saturated with respect to NaCl (see Appendix A). Anhydrite characteristics remain the same as 

used in PAVT. Elements of the panel closure system are interrelated. For example, the 

evolution of the DRZ is a function of stress state, which changes as salt creep redistributes the 

superincumbent loading. A rigid concrete monolith further affects the state of stress, which 

rapidly decreases the deviatoric stress component and approaches equilibrium. Therefore, 

11
appropriate parameter selection must include the coupled system. The sketches in Figure 1 

illustrate the differences between the PAVT and the TBM grid. The accompanying parameters 

provide explicit refinement to capture detail of the Option D panel closure systems that is not 

represented in the PAVT. 

12 m

Waste area

Waste area

k=10-15 m2

DRZ

DRZ

DRZ

DRZ

10-12.5 to 10-19.4 m2

10-12.5 to 10-19.4 m2 12 m

10-17 to 2 x 10-21 m2

PAVT

TBM

Figure 1. Detail of PAVT and TBM grid and properties. 

Some fundamental issues with respect to treatment of the DRZ were addressed as the models and 

grid were changed to accommodate the details that Option D introduced. Analyses Plan AP-106 

(Stein and Zelinski, 2003) defined the strategy. Some of the deliberations are reviewed here. 

Previous analyses in the PAVT allowed fracture in the upper salt DRZ to provide a gas pathway 

for high repository pressures. Thereby, the PAVT analysis did not yield unrealistically high 

pressures in the repository. It is equally probable that the floor DRZ would allow flow to Marker 

Bed 139, which resides 1.4 meters below the repository horizon. Marker Bed 139 comprises a 

nominally 1-m anhydrite layer that would not be expected to heal in the same manner as salt 

when it is damaged. Fractures around existing openings, such as shown in the photograph in 

Figure 2, evidence the nature of the damage in the floor of the repository. Extensive floor heave 

was observed as rooms in Panel 1 were reshaped to the original 4X10 meter rectangular cross 

section. Approximately one meter of the floor was removed to re-establish the original height of 

4 meters. Given the extensive damage in the floor and that the rock comprises anhydrite, it is 

probable that brine or gas flow to Marker Bed 139 is possible when high pressure is modeled in 

the repository. 

12
Figure 2. Damage in the Floor of Panel 1, Room 2, August 21, 2001. 

The situation gets a little more complicated when the repository horizon is raised 2.4 meters to 

Clay Seam G. In the raised half of the repository, the distance through the lower DRZ from the 

repository floor downward to Marker Bed 139 will increase from 1.4 meters to approximately 

3.8 meters. This change means that fracturing associated with floor heave will likely be reduced 

in the raised part of the repository. The raised waste rooms will have ready access to the 

Anhydrite “b” layer, which would now be excavated at the crown line of the raised waste rooms. 

Anhydrite “b” is a thin (~6 cm-thick), layer that is present directly above Clay Seam G, as the 

stratigraphy near the repository illustrates in Figure 3. Because of the availability and likely 

connectivity to anhydrite seams both above and below the repository horizon, it was deemed 

appropriate to model potential fluid flow in both the upper and lower DRZ. In the event of high 

repository pressures it is equally likely that a fracture pathway would form (1) parallel to the roof 

of the repository via Anhydrite “b”, (2) vertically through the 2 m-thick DRZ to Anhydrite A--

associated with Clay H, or, (3) into the floor to Marker Bed 139. 

13
Figure 3. Stratigraphy near the Repository Horizon (after Kreig, 1984). 

The phenomenon of high-pressure opening of fractures can be envisioned as hydrofractures that 

tend to open preferentially normal to the direction of the minimum principal stress. To examine 

hydrofracture in more detail, field studies (Wawersik and Stone, 1989) were re-evaluated. The 

results of hydraulic fracturing tests performed in WIPP salt, 3 to 100 meters from excavated 

rooms indicate that the pressures at which hydraulic fracturing is initiated, fall in the same range 

as hydrofracture tests performed in anhydrite Marker Beds 139 and 140 (Wawersik et al., 1997). 

Fracture initiation pressures for the anhydrite tests ranged from 7.36 to 12.46 MPa with an 

average initiation pressure of 10.5 MPa. Fracture initiation pressures for the salt tests ranged 

from 4.14 to 17.24 MPa with an average initiation pressure of 11.98 MPa (Wawersik and Stone, 

1989). One important difference in the fracture behavior of intact salt is that because it is so 

impermeable, fractures in WIPP salt will tend to stop at more permeable anhydrite marker beds 

and change direction, moving along the bed rather than fracturing across beds (Wawersik et al., 

1997). These data indicate that fractures in both materials will typically initiate at pressures 

below lithostatic and thus repository pressures significantly above lithostatic are unjustified and 

unexpected. 

Because the data support the application of the fracture model to intact salt in addition to the 

marker beds, calculations incorporated fracturing in both the upper and lower DRZ. Even in the 

parts of the repository that are not being raised to Clay Seam G, the test results support 

implementing the fracture model to both the upper and lower DRZ, considering the inherent 

uncertainty in exactly how the system will behave under possible near-lithostatic stresses. The 

important process that the fracture model simulates is the bleed off of very high pressures. 

Whether these pressures bleed off through the upper or lower DRZ is not the salient point; rather, 

the important modeling process is one of pressure relief. The parameters used by the BRAGFLO 

fracture model and applied to the marker beds and the DRZ are justified, because they do not 

allow repository pressures to exceed lithostatic pressure significantly. 

14
Figure 4 compares the raised and unraised repository configurations in relation to the 

surrounding stratigraphy. In the grid used for compliance re-certification, regions where the 

Option D panel closures intersect a marker bed are treated as isolated blocks of marker bed 

material. This representation is warranted for two reasons. First, the marker bed material has a 

very similar permeability distribution (10-21

 to 10-17 m

2

) as the concrete portion of the Option D 

panel closures. Second, in the case of high pressures (near lithostatic) it is expected that 

fracturing may occur in the anhydrite marker beds and flow could go “around” the panel closures 

out of the 2-D plane considered in the model grid. In this case the flow would be through the 

marker bed material that is already allowed to fracture in the model. Therefore, treating these 

isolated cells as anhydrite marker bed material is appropriate.

Figure 4. Schematic of the Stratigraphy Surrounding the Raised and Unraised Sections 

of the Repository. Not to scale. (Stein and Zelinski, 2003)

One purpose of the grid change is to incorporate appropriate detail to represent Option D panel 

closures more accurately than either the CCA or the PAVT. As shown in Figure 1, the PAVT 

grid did not include detail associated with Option D, such as the mining to remove the local 

DRZ. The Option D panel closure system calls for removal of DRZ around the circumference of 

the panel entry, and removes anhydrite Marker Bed 139 in the floor, as illustrated by the TBM 

grid shown in Figure 1. Details incorporated in the re-certification calculations include DRZ 

permeability as depicted and permeability values of the SMC, a salt-based concrete included as 

part of the condition for Option D. Properties used for the salt-based concrete are summarized in 

Appendix A. 

Calculations implementing the refined grid were conducted to the point of assessing the 

repository saturations and pressures over the regulatory period of 10,000 years. When detail was 

15
added for the Option D elements, a complex variation of the pressures and saturations was 

observed. These calculations and the underlying modeling rationale were provided to an 

independent peer review panel, which was empanelled consistent with requirements of Title 40 

Code of Federal Regulations (CFR) 1297. The peer review panel’s assessment of these 

conceptual model changes are summarized in Section 2.4. 

2.4 Preliminary Option D Assessment

During the spring of 2002, the DOE directed Sandia to make a preliminary calculation whereby 

Option D was modeled within the PAVT grid simply as a relatively tight plug. This preliminary 

assessment helped kick-start a re-design of the panel closure system. Results were provided to 

CBFO (Hansen, 2002). Assessing the impact of an Option D panel closures on repository 

performance was challenging because the CCA and the PAVT comprise the regulatory baseline 

for WIPP certification. However, neither the CCA nor the PAVT explicitly represented Option 

D panel closures in the calculations. To provide a baseline for assessing the effects of changing 

the panel closure design, the DOE felt a PA that included Option D panel closures must be 

completed and that the accepted PAVT grid be used. 

This assessment explicitly represented the Option D panel closures in the EPA-approved models 

of the repository, using the computational grid and parameter values that were used for the 

PAVT. However, the PAVT grid may be insufficiently detailed to capture all the important 

effects of the Option D panel closures. Subsequently Sandia conducted a second PA in which 

the computational grid was revised to represent the panel closures more realistically. A 

comparison was made between the repository performance with the Option D panel closures and 

the repository performance as calculated using the PAVT grid. In general, results indicate that 

panel closure characteristics are unlikely to affect repository performance significantly. 

Peer review of conceptual models developed by the DOE for the WIPP is required by Title 40 

CFR 194.27. To meet this requirement, the CBFO conducted a peer review of the three 

conceptual models that were changed in response to the Option D requirement and to incorporate 

knowledge gained since the original conceptual models were developed. The peer review panel 

examined the following conceptual models and their implementation: 

• Disposal System Geometry 

• Repository Fluid Flow, and 

• DRZ. 

The peer review process is a documented, critical review performed by peers who possess 

qualifications at least equal to those of the individuals who conducted the original work and 

independent of the work being done (Caporuscio et al., 2003). In most of their considerations the 

peer panel assessed the proposed changes against the existing implementation in the CCA or the 

PAVT. The panel concluded that the technical migration implemented for Option D was 

reasonable and adequate as summarized from their report below: 

Disposal System Geometry. With respect to the disposal system geometry, the system

characterized by the Option D concrete monolith and the explosion wall led to proposed change 

in the grid geometry since the existing grid block discretization was perceived to be too coarse 

for the representation of the specifics of Option D and the interrelated impacts on the DRZ. The 

16
panel concluded that the geometry retains the features of the original conceptual model and grid 

changes appear reasonable and sound. 

Repository Fluid Flow. The panel also determined that the repository fluid flow conceptual 

model was both reasonable and adequate for its intended purpose. 

Disturbed Rock Zone. The panel stated that the DRZ model represents a reasonable development 

of the earlier alternatives. The methods and procedures used in the changed model are 

refinements of the previous models, and modulate the relationship between repository pressure, 

waste degradation and brine inflow in a more realistic and conservative way than preexisting 

models, while integrating the influences of two design changes. The panel’s perception that 

excavation to Clay G is not a significant change in concept will be explored in the following 

Section 3. 

3.0 Clay G Evaluations 

This section summarizes a series of structural calculations executed to examine possible effects 

of raising the WIPP repository horizon from the original design level upward 2.43 meters. These 

calculations allow evaluations to be made of various features involved with the conceptual 

models implemented in WIPP PA. Notably this work addresses issues raised in an EPA letter to 

Carlsbad Field Office dated August 6, 2002. In the subject letter the EPA stated “the conceptual 

model for the repository should reflect the change to raise the level of excavation to clay seam G. 

The conceptual change should be appropriately addressed in the modeling, if warranted” (U.S. 

EPA, 2002). The Clay Seam G analyses included significant efforts to qualify the finite element 

code SANTOS. The primary results involve the production of porosity surfaces for PA. These 

computations also allow evaluation of the DRZ behavior and anhydrite fracture. The 

calculations support the modeling concepts used for the disposal area rock mechanics. In 

addition, details of the geomechanical structural elements provide examples of appropriate 

treatment of these features in PA. 

3.1 Background of Clay G Analyses 

 

Clay Seam G structural evaluations began with qualification of the finite element code SANTOS, 

the finite element code used for calculations supporting the original compliance certification 

porosity surface. At the time of the CCA, this code was executed on a Cray J916 machine. For 

the current analyses of Clay G the code was run on a Linux P4 Intel workstation. The first step 

in the requisite analyses was to replicate the CCA calculation of the porosity surface. These 

calculations verified that identical results can be obtained today, despite use of a new 

computational platform. Concomitantly, the verification and validation test problems were run to 

verify SANTOS functionality. 

The structural analysis models repository behavior of waste-filled disposal rooms raised 2.43 

meters above the present, or original, repository level. The DRZ evolution comprises a 

fundamental component of this analysis. The goal of these analyses is to assess whether or not 

raising the repository to Clay Seam G has any significant impact on the conceptual models used 

17
in PA. Results of these analyses provides an opportunity to review treatment of the DRZ within 

the context of WIPP. 

The analysis period is 10,000 years after waste emplacement. The calculations include 

mechanical creep closure response of a filled disposal room in a manner employed for baseline 

calculations supporting the compliance application. These calculations included construction of 

the three-dimensional porosity surfaces used for WIPP PA activities (Park and Holland, 2003). 

Thus, the primary output of Clay G structural calculation pertains to development of the porosity 

surface for PA. 

The WIPP management and operating contractor, Washington TRU Solutions (WTS), gained 

concurrence of the DOE and EPA to raise the disposal room 2.43 meters above the present level. 

The elevation change means the roof of a disposal room would coincide with the Clay Seam G 

horizon and the floor would be separated from the underlying Marker Bed 139 by 3.81 meters 

instead of 1.38 meters (the existing separation in disposal Panels 1 and 2). The change in 

repository horizon was recommended to ease ground control conditions. Fractures surrounding 

the existing horizon tend to coalesce in an arch, which mimics the shear stress trajectories. These 

patterns can be seen in the underground today where the roof has been taken down along the 

length of the East 140 drift (see Figure 5). The roof rock of the original horizon tends to decouple at Clay G, as exhibited by the shear fracture patterns. Underground operations personnel 

are currently obligated to provide roof support and maintenance that they believe would be 

minimized if the roof of the disposal rooms is raised to Clay G. Raising the repository disposal 

horizon presents a different combination of lithologies intimate to the disposal room than that of 

the compliance baseline. Thus, it is necessary to evaluate the impact of this proposed mining 

change. 

18
Figure 5. En Echelon DRZ Fracture Pattern to Clay G. 

The analysis replicated results reported in “Final Disposal Room Structural Response 

Calculations, SAND97-0795” (Stone, C.M., 1997), which is the referenced baseline report for 

the CCA. Calculation procedures and data of SAND97-0795 were used in this analysis and the 

results of a new, current analysis were compared with the results of SAND97-0795. Therefore, 

the initial calculations replicate room pressure and porosity histories for various gas generation 

rates for a period of 10,000 years following excavation and waste emplacement. 

3.2 Results of Clay G Analysis 

A recent report authored by Park and Holland (2003) provides the comprehensive results of these 

structural analyses. A few notable examples of the analyses are provided here, with an emphasis 

given to the DRZ implications. First the porosity histories for future states of the repository were 

replicated as shown in Figure 6. This figure plots porosity over time for representative gas 

generation factors and superimposes Clay Seam G results over the results obtained for the 

original repository horizon. In detail, many such calculations were executed to obtain porosity 

surfaces, but this example illustrates both replication of the previous results underpinning the 

CCA and the slight influence on these results that raising the repository horizon imparts to these 

baseline results. The CCA grid and material properties were run and results overlay previous 

calculations by Stone (1997). Then the grid was modified slightly to reflect elevation of the 

19
repository horizon by 2.43 m, and the model was re-executed. Recall that the Stone calculations 

included gas generation with rates imposed by a factor f. In Figure 6 the Stone porosity results 

are reproduced for gas generation factors of 0.0 and 0.5. A comparison is made to the porosity 

results derived from the new horizon at 2.43 meters upward. In terms of room closure operating 

in concert with gas generation, Figure 6 demonstrates that the porosity surface for the upper 

horizon is identical, for all practical purposes, to the baseline porosity surface. 

Figure 6. Porosity Histories for Raised and Original Horizons Using Various Gas 

Generation Parameters,. 

The next series of figures illustrates representative geomechanical results from Park and Holland 

(2003). In Figure 7 the original grid and deformation over time are shown for the future without 

gas generation. The deformed mesh helps clarify the physical extent of deformation. Over time 

the surrounding salt deforms over 2 meters into the disposal room compressing the waste inside. 

The anhydrite layers are dragged along with the salt, thus ensuring extensive fracturing within 

these marker beds. Figure 8 focuses on the anhydrite layers themselves, and shows the state of 

stress easily exceeds a Drucker-Prager failure criterion. Note the MSF represents the material 

safety factor, which compares the existing state of stress to the Drucker-Prager criterion and 

MSF>1 denotes failure. Also note in Figure 8 that the state of stress difference would decrease 

over time and less of the anhydrite would reside in failed stress space. Whereas salt has been 

shown to heal as the stress state approaches equilibrium (reducing deviatoric stress), anhydrite 

has not demonstrated similar healing characteristics. 

20
0 year 10 years 25 years

10,000 years 1,000 years 300 years

Figure 7: Deformation of Raised Disposal Room Containing Waste with Time for f=0.0. 

21
0 year 1 day ear

ears ears ears

1 y

10,000 y 100 y 10 y

Failure Condition:

MSF > 1

0 year ay ear

10,000 years 100 years 10 years

1 d 1 y

Failure Condition:

MSF > 1

Figure 8: Anhydrite Shear Failure around the Raised Disposal Room with Time for f=0.0. 

The above two figures show the dramatic deformation involved with the waste repository rooms. 

The primary mechanism of deformation is salt creep, which ensues with damage near the 

opening and without damage further out in the formation. Section 4 of this report will explore 

salt damage evaluation in greater detail. These snapshots of the DRZ over time represent some

of the output of the Clay Seam G analyses. The DRZ model simply relates stress invariants and 

assumes that damage occurs based on the relation given in Figure 9. Thus the DRZ extends to its 

greatest dimensions relatively early in the repository regulatory period of 10,000 years. The 

report by Park and Holland (2003) contains several different situations for gas generation, and in 

all cases the DRZ vanishes early in repository history. 

22
0 year 1 year 17 years

10,000 years 248 years 50 years

Undisturbed Zone:

2 27 1 J ≤ 0. ⋅I

0 year 1 year 17 years

10,000 years 248 years 50 years

Undisturbed Zone:

2 27 1 J ≤ 0. ⋅I

Figure 9: Disturbed Rock Zone around a Raised Disposal Room with Time for f=0.0. 

3.3 Conclusions of Clay G Analyses 

These calculations demonstrate that changing the repository horizon upward 2.43 meters has no 

appreciable effect on the response of the underground relative to the computations made for the 

CCA. This conclusion is drawn by first comparing new results with the previous results that 

underpinned the compliance application. The calculation procedures and input parameters were 

consistent with SAND97-0795 (Stone, 1997). These analyses used the same code, SANTOS, 

that supported the compliance calculations. A new validation and qualification of the software 

and hardware was assembled, as required by Quality Assurance procedures. 

Performance Assessment. The hand-off to PA from the structural (finite element) calculations 

takes the form of a porosity surface. The models include geomechanical response of the Salado 

stratigraphy, the waste material, and gas generation in the disposal rooms. The volume change 

of the disposal room due to the salt creep is strongly dependent on the gas generation factor, f.

The calculations used in the CCA were replicated and then repeated for grid changes appropriate 

for the new horizon to Clay Seam G. Because the CCA porosity surface calculated for the 

original horizon and the new porosity surface calculated for the raised rooms are essentially 

identical, no changes to the porosity surface are recommended to the compliance re-certification 

calculations. 

Disturbed Rock Zone. Calculations of the DRZ illustrate several interesting features. First the 

propagation of the DRZ into the surrounding rock salt passes through Marker Bed 139 in the 

case of the original horizon (Park and Holland, 2003) and does not penetrate Marker Bed 139 in 

the case of the raised room, as shown above in Figure 9. Quantitatively, the extent of the DRZ 

can be summarized as follows: 

• In the case of the raised room, the maximum thickness of DRZ is almost 6 meters above 

the room and 4 meters under the room. 

23
• In the case of the original horizon, the maximum thickness of upper DRZ is about 6 

meters, while the lower DRZ extends 5.6 meters through Marker Bed 139. 

In all models the DRZ grows until the creeping salt impinges on the waste, at which time the 

stresses trend back toward equilibrium and the DRZ diminishes. In all the simulations, the DRZ 

disappears quickly relative to the regulatory period of 10,000 years. 

Anhydrite Fracture. The anhydrite marker beds sustain states of stress that promote failure. In 

addition, deformation into the room by the marker beds is substantial. Therefore, fracture of the 

anhydrite in the proximity of the disposal rooms is most probable and the strain (deformation) 

induced during room closure would ensure some anhydrite fractures would exist in the proximity 

of the disposal room. The internal gas pressure of the room does not affect characteristics of the 

shear failure zone in the anhydrite layer. Deviatoric stress conditions become less severe over 

time, but the damaged anhydrite is not expected to heal in a manner expected of the salt DRZ. 

Anhydrite marker beds reside in the proximity of the disposal rooms, whether the room is at the 

original horizon or at the elevated horizon. Therefore, fractured anhydrite, possessing high 

permeability, resides intimate to the deformed room. High fluid pressure that could develop in 

disposal rooms would be expected to communicate readily and flow preferentially out the 

damaged marker beds. 

4.0 Salt Damage Evaluations 

The first three sections of this report summarize the current understanding of the geomechanical 

setting at WIPP, and the implementation of that state of knowledge against changes made to the 

repository since the initial compliance determination. This section presents much of the 

technical bases that buttress the choices made to address the changes. The discussion begins 

with first principles of the creation, evolution and attendant properties of the DRZ. The theory is 

expanded into laboratory test results, small-scale in situ experiments and full-scale analogs from

industry experiences and international collaborations. These technical arguments provide 

reasoning for the parameter distributions and grid refinements selected for re-certification 

calculations, which must address changes to the underground as well as incorporate any 

advancement benefiting the collective state of knowledge. The ensuing discussion concentrates 

on rock salt damage, modeling, and properties, and provides objective evidence that the theory 

extends into practice sufficiently that the proposed analyses of the operating repository are 

reasonable and justified. 

24
4.1 Principles of Salt Damage 

Similar to underground structures sited in other geologic media, excavation of an opening, such 

as a drift, disposal room or shaft at the WIPP alters the virgin state of stress (i.e., σ1 ≈ σ2 ≈σ3) 

that exists in the rock salt. The rock zone proximal to the opening experiences deviatoric (or 

shear) states of stress (σ1 > σ2 > σ3) after excavation. Because of the stress-concentrating effect 

of the opening itself, the deviatoric stresses are highest in the rock salt near the opening, 

especially near abrupt changes in opening geometry (e.g., corners), and decrease rapidly with 

distance from the opening. In addition to opening geometry and spatial position, other factors 

affecting the magnitude of the induced deviatoric stress include local geology (e.g., 

homogeneous versus layered media) and depth of the opening below ground surface because, 

absent tectonic influences, the stress magnitude is approximately proportional to depth. Because 

salt is a creeping medium, the stress differences are maximized upon excavation, and decrease 

thereafter. 

In salt, deviatoric states of stress activate three deformation processes: (1) elastic, (2) inelastic 

viscoplastic flow, and (3) inelastic damage-induced flow1

. Elastic deformations occur 

instantaneously (time-independent) in response to changes in stress state, while the two inelastic 

mechanisms are time-dependent, which gives salt its well-known creep characteristics. Inelastic 

flow models usually include stress and temperature terms, but the flow rate also depends on 

factors such as stress history and relative humidity. 

Viscoplastic flow of salt has been well characterized for WIPP applications. Much of the most 

pertinent literature derives from WIPP research and development (e.g., Munson, 1979; Carter 

and Hansen, 1983; Munson and Dawson, 1984) but the WIPP history of salt deformation benefits 

from international collaboration (e.g., Langer, 1984; Wallner, 1984; Aubertin et al., 1991; 

Cristescu and Hunsche, 1992, to name a few). Plastic deformation occurs by dislocation motion 

within the salt lattice. The various dislocation mechanisms of concern to repository sciences are 

also well documented and include dislocation multiplication, glide, cross slip, and climb. 

Because viscoplastic flow is an isochoric or incompressible process, it does not induce damage 

to the salt matrix. In salt, dislocation mechanisms are activated by virtually all deviatoric stress 

states regardless of the magnitude of the applied mean stress (average of the three principal 

stresses). The physics and the mathematics are well established for models that represent 

viscoplastic flow. 

In contrast to viscoplastic flow, damage-induced flow in salt is less well understood. Damage 

only occurs when the deviatoric stresses are relatively high compared to the applied mean stress 

and is manifested through the time-dependent initiation, growth, and coalescence of 

microfractures. Modeling approaches have been suggested for the microfracturing process, with 

limited success. For example, predictions of damage space for WIPP applications seem to 

represent what is witnessed in the underground in a qualitative sense. Indeed, point-wise 

geophysical measurements often validate the general sense of the damage model. However, a 

model for spatial and temporal damage evolution that includes prediction of permeability is not 

yet available to salt repository sciences. 

 

1

 Sometimes referred to as stress-induced damage. 

25
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. Damage recovery is often 

referred to as healing in geomechanics parlance. 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 a 

rigid inclusion such as Option D panel closures. 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 

natural analogs as described later. Healing the salt DRZ can readily restore damaged salt to a 

low permeability as discussed in Section 4.5. 

The discussion of salt behavior and deformation processes around WIPP openings lead to the 

following general observations about the DRZ: 

• Microfracturing of the salt initiates immediately upon excavation of the openings and 

continues with time. 

• Microfracture density and growth rates are highest near the opening and decrease with 

distance away from the opening 

• Fracture growth in the DRZ will be anisotropic with fractures aligning parallel to the 

most compressive stress (the most compressive stresses are typically aligned parallel to 

the free surfaces of the openings). 

• Over time, macrofracturing will lead to salt failure including floor heave, roof falls and 

rib slabbing and spalling. 

• Salt damage is reversible. Rigid panel closures placed in WIPP openings will create a 

nearly hydrostatic state of stress in the DRZ adjacent to the inclusion. 

4.2 Hydrologic Properties of Damaged Salt 

Most geologic media, including salt, contain natural porosity in the form of interconnected 

channels and isolated inclusions. Fluid flow through such media is necessarily constrained to the 

interconnected porosity. In pure WIPP salt, the natural porosity is on the order of 1 percent or 

less and not well connected. In argillaceous WIPP salt, the porosity is marginally higher and 

fluid flow has been observed, although at very low rates (Beauheim and Roberts, 2002). The 

porosity of WIPP salt is filled with brine containing dissolved gases, principally nitrogen. 

Because salt creeps, pore pressures in the brine-filled pores would be expected to approach 

lithostatic. At the depth of the repository, the lithostatic pressure has been established at 14.9 

MPa. 

The porosity of the salt in the DRZ is higher than in the surrounding virgin rock because of the 

dilation induced by microfracturing, as explained above. Peach (1991) studied the effects of salt 

dilation using percolation theory and found that small levels of dilation (as little as 0.05 percent) 

26
were sufficient to develop an interconnected pore network that formed primarily along grain 

boundaries. Furthermore, permeability through this network was found to be proportional to 

(εdv)

3

, where (εdv) is the dilatant volumetric strain equivalent to ∆V/V with ∆V and V 

representing the change in volume due to dilation and the initial volume, respectively. Assuming 

a dilatant strain of 0.5 percent (a value that could easily occur in the DRZ), the 0.05 threshold 

strain, and the Peach proportionality, the permeability within the DRZ could increase by at least 

three orders of magnitude. As shown later, Pfeifle et al. (1998) conducted permeability tests on 

WIPP salt specimens that had been deformed in the laboratory to volumetric strains of the order 

of 0.5 percent and estimated permeabilities that ranged from 10-15

 to 10-14 m

2

, at least seven 

orders-of-magnitude higher than observed in the field by Beauheim and Roberts (2002) for 

virgin argillaceous salt emphasizing the extreme sensitivity of WIPP salt permeability to small 

dilatant volumetric strains. 

Utility of this simple model is complicated by the anisotropy of damage in the field. As will be 

shown throughout this section, fractures in salt develop with preferential orientation with respect 

to the stress state. As clearly shown in Figures 2 and 5, fractures in situ are generally parallel to 

the drift and perpendicular to the minimum principal stress. Permeability along the fractures, 

parallel to the drift would be much higher than permeability perpendicular to the drift. The 

anisotropic nature of fractures and the sensitivity to damage (i.e., the permeability increases by 

orders of magnitude with relatively low levels of damage) are two features that complicate 

development of a damage/permeability relationship for field applications. 

Because of the sensitivity between salt permeability and dilation, the DRZ is expected to exhibit 

high permeability immediately adjacent to the WIPP openings and decrease away from the 

opening in direct relation to the level of induced damage and deviatoric stresses. The 

microfracturing will also relieve the pore pressure in the DRZ. At the free surface of the 

opening, the pore pressure will be atmospheric, while at depth the pore pressure will be on the 

order of 14.9 MPa. This pressure gradient through the DRZ will release brine into the opening. 

The pore pressure in the salt some distance beyond the DRZ may be lower than 14.9 MPa 

because the alteration of the stress field resulting from the excavation may relieve some stress 

acting on the isolated brine-filled pores even though the change in stress is not sufficient to 

induce damage. Because healing processes reduce porosity, permeability is expected to decrease 

when hydrostatic states of stress activate healing processes, particularly in the vicinity of rigid 

panel closures. 

4.3 Laboratory Studies of Salt Damage 

Laboratory studies provide the most readily attainable setting for testing material properties. The 

materials of interest to the Option D panel closure system include intact salt, damaged salt, saltbased concrete and anhydrite. The geomechanical calculations being conducted in support of 

WIPP re-certification activities have added detail in the representation of salt damage (and 

healing) and salt-based concrete materials. Both elements are more representative of actual 

conditions than previously modeled in the CCA calculations. Laboratory characterization of salt 

damage and healing is summarized in the following section and discussion of salt-based concrete 

properties is found in Appendix A, Section 4.6 and Section 4.9.

27
Extensive research has been conducted in the laboratory to determine both the deformational and 

hydrological behavior of WIPP salt. Early work focused on the characterization of the elastic 

and inelastic viscoplastic flow properties of salt (e.g., Hansen and Mellegard, 1977; Wawersik 

and Hannum, 1979, Hansen and Mellegard, 1980; Senseny, 1986; Mellegard and Pfeifle, 1993). 

Most of the early studies provided parameters for the WIPP creep model. This model is 

popularly known as the Munson-Dawson (1984) Model, or M-D Model. In fact the author 

(Munson) called the model the M-D Model to denote multimechanism-deformation. The 

constant-volume creep behavior of the underground modeled by M-D was validated against 

large-scale thermomechanical experiments. This background information was available for the 

use in the PA and the compliance certification application. 

The phenomena associated with salt fracture were made obvious from observations in the WIPP 

underground (Section 4.6) and geophysical measurements (Section 4.7). Despite an 

acknowledged importance of salt damage to the WIPP repository, the DRZ was given a rather 

rudimentary treatment in the compliance calculations. As preparations are being made for the recertification of regulatory compliance, additional sophistication is brought to the treatment of the 

DRZ. A large amount of the data available to quantify DRZ properties derives from laboratory 

studies that were performed to parameterize the M-D model. Eventually, systematic studies of 

salt fracture were undertaken in the laboratory. Based on field observations, experiments, and 

theory, salt damage is reversible. Therefore, consideration of the salt DRZ includes its creation, 

growth, and properties, as well as the conditions under which the DRZ would heal. The 

properties of the DRZ provide the crux of the modeling issues for the Option D panel closures. 

Van Sambeek et al. (1993a) re-examined the extensive creep data existing from years of 

experiments on salt. Their hypothesis was that damage could be assessed because volumetric 

strain and principal stresses are carefully controlled test parameters. Stress states that led to 

dilation were defined in terms of stress invariants rather than individual stress components 

because the stress components for one type of test could not be compared directly with the stress 

components of another type of test. The two stress invariants selected were the first invariant of 

the traditional Cauchy stress tensor, I1, and the second invariant of the deviatoric stress tensor, J2. 

These invariants are related to mean (or confining) stress and deviatoric stress, respectively, and 

are defined as follows: 

1 = 3σ m = σ 1 +σ 2 +σ 3 I

[ ] ( ) ( ) ( )

1/ 2

2

3 1

2

2 3

2

1 2

1/ 2

2 6

1

⎭

⎬

⎫

⎩

⎨

⎧ J = σ −σ + σ −σ + σ −σ

where σm is the mean stress and σ1, σ2, and σ3 are the three principal stress components for a 

particular type of test. Using these definitions, Van Sambeek et al. (1993a) plotted the stress 

states (in terms of invariants) that both did and did not induce dilation in WIPP salt as shown in 

Figure 10. In addition, laboratory data for Avery Island, Louisiana, domal salt were plotted, as 

many experiments had been conducted on Avery Island salt over the years. As shown, a clear 

delineation in the I1 – J2 stress space exists between conditions that cause dilation and those that 

do not regardless of the type of salt or type of test considered. Van Sambeek et al. (1993a) 

28
suggested an empirical relationship to divide dilating stress states from non-dilating stress states 

and expressed this empirical relationship as follows: 

2 1 J = 0.27I

This relationship is often referred to as the stress-invariant model and is used to predict dilational 

states of stress for WIPP salt. 

Figure 10. Stress States Known to Cause Dilation of WIPP Salt. 

Stormont (1990) and Pfeifle et al. (1998) conducted laboratory tests on WIPP salt to correlate 

permeability with damage level expressed as dilatant volumetric strain. Figure 11 provides the 

results of these two studies and shows that permeability changes by nearly 10 orders-ofmagnitude from less than 10-21

 m2 to more than 10-12 m2 corresponding to changes in dilatant 

volumetric strain (or porosity) of up to 4 percent. These data are consistent with the range in 

permeability used in the PAVT. 

29
1E-22

1E-21

1E-20

1E-19

1E-18

1E-17

1E-16

1E-15

1E-14

1E-13

1E-12

1E-11

0 0.01 0.02 0.03 0

Dilatant Volumetric Strain

Instrinsic P

erm

e

ability ( m2 )

.04

 Pfeifle et al, 1998

 Stormont, 1990 

Figure 11. Permeability Versus Dilatant Volumetric Strain for WIPP Salt. 

4.4 Salt Damage Modeling 

The investigations of damage evolution are international issues. The WIPP science advisor 

(Sandia National Laboratories) has a long-standing collaboration with peers in European salt 

programs, most notably with the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR). 

Salt researchers at the BGR have led development of a constitutive relationship between 

dilatancy and permeability (e.g., Hunsche and Schulze, 2000; Cristescu and Hunsche, 1998). 

Their experiments and theory show that dilatancy (also called volume change or damage) is 

linearly increasing with creep deformation under dilatant conditions and decreasing or healing 

with time in the compressive domain. This collaborative research is continuing. As noted by the 

Peer Review Panel (See Section 2.4) in their deliberations constitutive models based on 

measurement of the influence of creep damage on hydrologic properties may be feasible in the 

future, but such models are not expected to indicate that the changed model has failed to 

conservatively bound repository performance (Caporuscio et al., 2003).

The stress-invariant dilatancy model has been used in structural calculations for approximately 

10 years and remains a viable tool for engineering purposes and can be coupled with numerical 

analyses to predict disturbed or damaged zones around a typical waste disposal room, as shown 

in Section 3.2. Figure 12 depicts the disturbed zone in terms of a damage factor, D, 40 years 

after excavation. In the region corresponding to D > 1, the stress states fall within the dilational 

zone, while in the region corresponding to 0.8 < D < 1.0, the stress states remain in the isochoric 

zone (non-dilating zone) but are very near the dilational limit expressed by the stress-invariant 

model. As shown, the damaged zone or DRZ (D > 1) extends away from the room

approximately 3 meters or more after 40 years of unobstructed closure. 

30
Figure 12. Damage Predicted Around a Typical WIPP Disposal Room 40 Years After 

Excavation (after Van Sambeek et al., 1993b). 

The stress-invariant model described above can be used to predict the extent of the DRZ around 

openings in salt but quantifies neither the level of damage nor the increase in permeability 

associated with the DRZ. Based on the theoretical discussions provided above, the salt nearest 

an opening is expected to undergo the greatest damage and, as a corollary, will also experience 

the greatest increase in permeability. Salt farther from the opening undergoes much less damage 

and, as a result, experiences a much smaller change in permeability. 

4.5 Salt Damage Healing in Laboratory Studies 

In laboratory tests Costin and Wawersik (1980), Brodsky (1990) and Pfeifle and Hurtado (1998) 

have shown that the damage evolution process in salt is reversible through crack closure and 

healing. In the Costin and Wawersik study, a series of short-rod fracture toughness strength tests 

were performed to determine the tensile load required to initiate and propagate fractures in WIPP 

salt. The fractured test specimens were subsequently subjected to healing hydrostatic 

compressive stresses ranging from 10 to 35 MPa, and then retested in a second series of fracture 

toughness tests after healing times of varying length. The study showed that the healed 

specimens regained from 70 to 80 percent of their initial fracture toughness strength. 

Using the well-known correlation between wave velocity and crack development in geologic 

materials, Brodsky (1990) used compressional ultrasonic wave measurements to study crack 

initiation, propagation and healing of WIPP salt. In general, velocity decreases with increases in 

31
rock dilation and increases in response to crack closure and/or porosity reduction. Microcracks 

were introduced into WIPP salt specimens during constant strain-rate triaxial compression tests 

conducted at low confining pressure. After specified damage levels were induced, hydrostatic 

compressive stresses of 5, 10, or 15 MPa were applied to the damaged specimens to promote 

healing. During both the loading and healing stages of the tests, ultrasonic wave transducers 

were mounted directly on the test specimens to monitor wave velocity parallel and perpendicular 

to the maximum principal compressive stress. During loading, wave velocity parallel to the 

maximum principal stress decreased 1 to 2 percent, while velocity perpendicular to the maximum

principal stress decreased by as much as 10 percent. In contrast, velocity measurements made 

during healing (or fracture closure) increased, with the rate of increase depending on the initial 

level of damage and the magnitude of the applied hydrostatic stress. The rate of increase in the 

wave speeds was slower for the more highly damaged specimens and this finding was attributed 

to shear offsets along the fractures. Rates of increase in velocity were ordered with respect to 

hydrostatic stress with higher rates corresponding to the higher hydrostatic stress levels applied 

during healing. Velocity recovery generally occurred within a few days. 

Pfeifle and Hurtado (1998) studied salt healing through a series of gas and brine permeability 

tests conducted on damaged WIPP salt specimens subjected to compressive hydrostatic stresses 

of 1, 5, 10 and 15 MPa. Damage was initially introduced through constant stress creep tests 

conducted at low confining pressure. The damaged specimens were then loaded hydrostatically 

to promote healing and permeability measurements were made as a function of time. 

Permeability decreased as a function of time with larger decreases corresponding to higher 

hydrostatic stress levels and specimens saturated with brine rather than gas. In some tests, 

permeability decreased by nearly two orders-of-magnitude in less than 30 days. The 

permeability data were used to estimate healing time constants that could then be used to predict 

the time required for complete healing. Based on their results, complete healing requires several 

hundreds of years at very low hydrostatic stress states (1 to 5 MPa), but is of the order of only a 

few years for higher hydrostatic stress states (i.e., 10 and 15 MPa). 

4.6 Salt Damage Healing—In Situ Small Scale 

The laboratory data for salt damage characteristics, healing and salt-based concrete properties are 

all germane to the DRZ issues, particularly as applied for Option D panel closures. However, 

implementation of closures at WIPP involves much larger scales and uncertainties associated 

with up-scaling properties. This section presents additional information regarding the DRZ and 

seal material performance in situ. 

A series of sealing experiments in the WIPP underground were executed over a ten-year period 

from 1985 to 1995. Series A and B are particularly relevant to panel closures, as they comprised 

vertical (A) and lateral (B) placement of salt-based concrete. Many technical publications on the 

Small Scale Seal Performance Test (SSSPT) program have been prepared and are summarized in 

Finley and Tillerson (1992). Series A and B utilized nine emplacement holes located in the floor 

of the D Room Alcove and in the west rib of Room M. The seal material was an expansive-salt 

concrete developed by Waterways Experiment Station (Wakeley and Walley, 1986). 

32
All nine salt-based concrete seals performed well (Knowles and Howard, 1996). The larger (91-

cm diameter) horizontal seals are most closely analogous to panel closures, and are described in 

more detail here. The concrete was pumped into forms and was not vibrated (Stormont and 

Howard, 1986). The seal system consists of the seal material, the seal/host rock interface, the 

zone of rock immediately surrounding the seal, and the far-field host rock. The seals were tested 

for gas and brine permeability from 1985 to 1987 and again from 1993 to 1995. The tests did not 

provide information regarding the flow paths of the test fluid, so the calculated system

permeability represents a composite fluid barrier presented by all components of the seal system. 

Gas permeability determined in 1985-1987 ranged from 10-17

 to 10-20 m2 and improved to 10-19

to 10-23 m2 when re-tested between 1993-1995. Additional geophysical and petrographic studies 

conducted in concert with the flow testing of the concrete seals (Knowles et al., 1998) provided 

evidence that the damage existed on both sides of the concrete plug. Therefore, the rigid 

concrete inclusion provided the requisite back stress to heal the extant DRZ. 

4.7 DRZ Delineation by Sonic Velocity

A considerable body of geophysical investigative work has been completed in the WIPP 

underground in the period since the initial certification (Holcomb, 1999, Hardy and Holcomb, 

2000, Holcomb and Hardy, 2001). In most investigations, Holcomb and co-workers delineated 

the WIPP DRZ as a function of depth orthogonal to a drift wall and along vertical and horizontal 

paths parallel to the wall. In one campaign, they measured velocity in holes oriented at angle to 

the walls. The borehole array and the transducer assemblies allow measurement of elastic wave 

velocities necessary to detect the anisotropy of cracking associated with the DRZ. Velocity and 

attenuation of elastic waves in the salt are a function of the density of cracks, as is the 

permeability. 

Cross-hole and same-hole velocity measurements give a consistent picture of the DRZ around 

the Q room access drift. The DRZ is well developed at mid-height on the rib, extending into the 

rock 2 meters and possibly as much as 4 meters. Near the back and floor, the DRZ is shallow (1 

meter or less) or not detectable. Compressional mode (P) waves in same-hole measurements are 

most sensitive to the DRZ because of favorable orientation of particle motion perpendicular to 

the cracking. Changes in VP as large as 22 percent were observed for P waves propagating 

perpendicular to the drift axis at room mid-height. 

Open cracks and loosened grain boundaries decrease elastic moduli and therefore, elastic wave 

velocities. The effect on elastic wave velocities is strongest for cracks oriented perpendicular to 

the particle motion induced by the wave. Thus the physical extent of the disturbed zone can be 

determined by propagating elastic waves through successive portions of the formation until an 

undisturbed zone is reached, as indicated by a constant velocity with increasing depth from the 

rib. Cracking responsible for the disturbed zone is expected to vary as a function of distance 

from the walls of the Room Q alcove and to depend on the position of the measurement path 

relative to the back, floor and corner. 

Cross-hole measurement paths were nominally one meter long, while the same-hole 

measurements all had the same fixed path length of 33 cm. Figure 13 shows the arrangement 

33
and naming scheme for the measurement holes, QGU30, QGU31, ... QGU41. Travel time 

measurements were made using the technique commonly used for laboratory determinations of 

sound speed in rock; a sound pulse was applied to the rock at a known time and place and, after 

traveling through the rock, was received by a transducer at a known distance. The travel time 

and distance combine to give the average velocity over that path. 

The most recent work completed at WIPP probed twelve holes cored in the Room Q alcove 

corner (see Figure 13). Two rows of holes, 1 and 3 counting from the top, were in halite, while 

rows 2 and 4 were in argillaceous salt. Each hole was 10.16 cm (4 inches) in diameter, 6+ 

meters deep and as nearly horizontal as possible. Hole locations were chosen to sample the map 

units present (labeled halite and argillaceous in Figure 13), and also the expected variation in 

damage around the corner. 

4

4 4 4

4 4

4 4 4

Q ALCOVE SOUTHEAST CORNER BOREHOLES

TERRY MACDONALD & WES DEYONGE

SANDIA NATIONAL LABORATORIES, DEPT. 6821

DRZ CHAR. TEST PLAN

04/10/00

(HALITE)

(ARGILLACEOUS)

4 4 4

(ARGILLACEOUS)

(HALITE)

FLOOR

(SOUTHEAST CORNER)

BACK

(MARKER BED)

QGD30 QGD31

QGD32 QGD33

QGD34 QGD35

QGD36 QGD37

QGU30 QGU31 QGU32

QGU33 QGU34 QGU35

QGU36 QGU37 QGU38

QGU39 QGU40 QGU41

Figure 13. Layout of Holes for Room Q Alcove, with holes used for ultrasound 

measurements indicated in red. Other holes indicated are for proposed 

hydrological studies.

Sonic velocities can be measured vertically and horizontally across holes, resulting in 9 sets of

measurements for vertical paths and 8 horizontal paths in planes parallel to the corner walls. In 

addition, twelve same-hole measurement sets were completed. Typical same-hole, P-wave 

results are shown in Figure 14. The DRZ of less than 2 meters developed along the wall (red 

dots) is typical for WIPP openings. The unique aspect of these measurements is the lack of DRZ 

34
in the zone directly outside the room corner. As seen in Section 4.8, the damage fracture 

orientations also reflect stress states along the walls toward the corner. 

7

0 1 2 3 4 5 6 7

Depth (m)

0

V

P (km/sec)

4

4.5

QGU36 --> QGU36, P

column 1 

4

4.5

QGU37 --> QGU37, P

Figure 14. Same-hole measurements for adjacent holes, one in the left-hand wall (red) 

and in the corner (black). 

Results show that velocity at depths greater than about 1 meter vary from the mean by less than 

0.5%, which is close to the attainable accuracy. Similarly constant velocities are observed in the 

other paths through halite. In contrast, VP along paths in the “argillaceous” halite layers varies 

by several percent even at depths beyond the DRZ. All four data sets for the horizontal crosshole VP measurements made in halite layers indicate a constant velocity as the measurement 

depth approaches 6 meters. Two data sets show clear evidence of a disturbed zone extending in 

about one meter. Little or no evidence for a DRZ was found in the other two measurements in 

halite. In contrast to horizontal paths, damage measured along vertical paths is less extensive, 

reaching shallower depths and producing smaller changes in VP. The general pattern of damage 

is similar and slightly asymmetric, with greatest damage observed in the upper portion of the left 

wall and the lower portion of the right wall. 

Previous work (Holcomb and Hardy, 2001) in the access drift leading into the Q room alcove, 

showed a simpler pattern of DRZ development and a more extensive damaged zone. In the 

access drift, where the geometry is essentially 2-dimensional, the DRZ was observed to be best 

developed at mid-height of the drift and to extend as much as two meters. The complexity 

35
observed in the corners reflects the influence of the 3-dimensional geometry on the stress state 

and subsequent development of the DRZ. 

Damage along the measurement path contributes to velocity decrease, which is a signature of the 

DRZ. Thus the constant VP observed in the alcove corner along vertical paths indicates that no 

point from ceiling to floor has experienced significant damage in the form of cracks that could 

decrease the speed of a compressional wave propagating vertically. Cracks oriented 

perpendicular to the direction of propagation are most effective in decreasing VP ; in this case, 

horizontal cracks would be most effective. Thus it appears that little or no horizontal cracking 

has occurred near the bisecting plane of the corner, at any depth, even 12 years after excavation. 

A meter away, the stress state is sufficiently different that VP in the vertical direction is 

decreased, indicating some horizontal, or at least non-vertical, cracking did occur. Near the floor 

and ceiling the DRZ was less pronounced than in similar zones closer to the mid-height of the 

room. Damage was clearly anisotropic, with the maximum decrease in VP being observed in 

directions more nearly perpendicular to the walls. This fits with the assumption that the DRZ is 

the result of cracks opening in the direction of minimum compressive stress. In previous work, 

velocity measurements typically indicate a DRZ extending in about 2 meters. An exception to 

that rule was found in the AIS (Hardy and Holcomb, 2000) where the DRZ only extends 0.5 to 1 

meters. In the corner of the Room Q alcove the DRZ only extended in about 1 meter and there 

were many areas that did not appear to be damaged. 

It is expected that the current results will be useful to other studies of the long-term deformation 

characteristics of salt. The data delineate the DRZ as a function of depth from the alcove corner 

and as a function of the varying stress state around a rectangular alcove corner cross-section. 

The significance of the results lies in the length of time the DRZ has had to develop 

(approximately 12 years), the geometrical complexity of the alcove corner, which will allow a 

more rigorous test of models than is possible in simpler geometries. Understanding the timedependent changes in damage, and thus permeability, as the DRZ develops is important because 

these properties affect sealing and PA models of underground openings at the WIPP. 

Previous work had examined the DRZ in simple geometries, typically a room wall or a long drift. 

More recent work is an extensive look at what happens in the corner of a room, an area 

deliberately chosen for its complexity. As expected, the pattern of damage was found to be more 

complex than in the simpler geometries previously studied. Two features were unexpected: 

damage did not extend in nearly as far as in the previous studies, and along the bisecting axis of 

the corner, no DRZ at all was observed. 

4.8 Observational Fracture Studies 

The WIPP site itself provides an underground research setting that has been exploited to quantify 

spatial and temporal characteristics of the disturbed rock zone. In concert with the work of 

Holcomb and coworkers as summarized in the previous section, we have continued petrofabric 

analyses of salt core recovered from the sonic velocity holes. To complement these studies, 

international partners provided cores from the Asse Mine of interest to their programs. Together, 

these cores avail an opportunity to assess the nature of damaged core from the proximity of 

36
underground openings in salt workings. In this section we present petrophysical evidence of the 

structural state of the DRZ and excavation disturbed zone cores drilled from two different sites. 

The comprehensive microstructural examinations that include fracture, free dislocation density 

and subgrain boundaries have been submitted to the European Union for publication with their 

sponsored research on salt repositories. However, the relevant observations concern the 

manifestation of damage, which is described and quantified in terms of fractures. In addition to 

salt cores from WIPP, samples were provided by German colleagues from the ALOHA II Project 

(Wieczorek and Zimmer, 1999), and from the Northern Test Drift B of the German Thermal and 

Structural Demonstration Experiment (TSDE) Test Field. The TSDE was conducted at the Asse 

Mine, near Braunschweig, Germany, by Gesellschaft fur Anlagen- und Reaktorsicherheit mbH 

(GRS). BAMBUS II (Backfill and Material Behavior in Underground Salt repositories) is the 

post-facto evaluation of the TSDE, and addresses the behavior of the DRZ, as well as backfill 

material within a geologic repository for heat-generating radioactive waste in rock salt. Fracture 

analyses entail petrographic fracture mapping; creation of thick sections to investigate fracture 

densities, fracture apertures, fracture angles and the spatial distribution of fractures. For the most 

part scanning electron microscopy (SEM) was used to capture and quantify the images. 

A larger suite of observational studies (Chapin and Hansen, 2002) focused on microstructural 

analyses of seven salt cores: (1) WIPP Core QGU14 (6.07 m), (2) WIPP Core QGU36 (7.33 m), 

(3) WIPP Core QGU39 (2.25 m), (4) Asse Mine Core DJ-V (6.97 m), (5) Asse Mine Core HD-V 

(6.83 m), (6) TSDE Core VVS-A-Mi4 (0.72 m), and (7) TSDE Core VVS-D1-Mi4 (0.77 m). 

The dimensions in parentheses indicate the lengths of the cores referenced from the opening or 

drift face in which the cores were recovered. As can be seen, most cores extend from a free 

surface to a considerable depth into the country rock. The TSDE cores were selected from the 

near field of the heater experiment. These cores exhibited little fracturing, despite being adjacent 

to a free surface. The associated elevated temperature gave rise to thermally activated 

deformational processes, thereby minimizing the brittle manifestations of fracture. 

The geology of WIPP QGU14 and QGU36 are similar; both comprise elongate, coarse, clear 

halite and minor amounts of anhydrite. WIPP QGU39 derives from the so-called “argillaceous” 

salt zone. All WIPP core was obtained by dry drilling (horizontally) through the inside rib of the 

4-m high repository drift. WIPP Core QGU14 was drilled normal to the rib at mid-height, 

whereas cores QGU36 and QGU39 were recovered from boreholes drilled into the corner of the 

Q-Room access drift at an angle of 45°–50° to the inside rib faces. The German cores derive 

from lined and unlined portions of 80-year-old drifts in the Asse research mine, at a depth of 700 

meters (see Section 4.10). The TSDE cores were extracted from the Asse Mine’s Northern Drift 

B, at the 800-m level as part of ongoing international collaborations. 

37
Of the seven cores studied, three cores were analyzed over their entire length at a shallow 

distance into the rib: (1) WIPP Core QGU39 (2.25 m), (2) TSDE Core VVS-A-Mi4 (0.72 m), 

and (3) TSDE Core VVS-D1-Mi4 (0.77 m). The four remaining cores, WIPP Cores QGU14 

(6.07 m) and QGU36 (7.33 m), as well as the ALOHA II Cores DJ-V (6.97 m) and HD-V (6.83 

m) were analyzed differently. The complete first meter of each core was examined, and then 

subsequent fracture analyses were performed at 1-m intervals until the core length was 

exhausted. For display purposes Figure 15 plots the fracture distribution for the WIPP cores 

alone. Of the 744 fractures measured in the three WIPP cores, only two fractures at a depth of 

greater than 2 meters have measured apertures wider than 125 μm. In all the cores measured, 

fracture apertures are predominantly wider proximal to the rib face (at approximately 0.1 meters 

and 1.25 m). Cores QGU36 and QGU39 were oriented nearly 45o

 to the drift face. The 

measured fracture angles qualitatively oriented parallel to the drift wall, and thus could be 

categorized as stress induced fractures and clearly not coring damage. Fracture angles closest to 

the rib face lie subparallel to the rib face for both cores; at approximately 60° to the core axis in 

QGU36 and approximately 50° in core QGU39. At approximately 2 m, the fracture angles in 

both cores have rotated essentially normal to the core axis. Results of the fracture analyses of the 

WIPP, ALOHA II and TSDE salt cores are presented in Figure 16. 

0

100

200

300

400

500

600

700

800

0 1 2 3 4 5 6 7 8

Disturbed Rock Zone Fracture Analyses:

WIPP Repository Cores QGU14, QGU36 and QGU39

WIPP Core QGU 14

WIPP Core QGU 36

WIPP Core QGU 39

Fr

a

cture A

pertur

e (microns)

Distance from Rib Face (m)

Figure 15. Fractures and Apertures in Three WIPP Cores. 

rather surprising result is that the fracture distributions and fracture apertures between

the

A

ALOHA II Cores DJ-V and HD-V were found to be similar. One would hypothesize that

core obtained from behind the rigid tunnel lining (details given in Section 4.9) would have 

completely healed the fractures. Permeability measurements showed that permeability was

38
reduced behind the liner, despite the presence of fractures measured in the cores. Except for a 

few wide fractures measured proximal to the rib wall in core DJ-V, there does not appear to be a 

large disparity between fracture density and fracture aperture as a function of depth between 

either the ALOHA II lined (DJ-V) and unlined (HD-V) drift samples. Fracture distributions and 

fracture apertures are similar for both TSDE cores and minimal compared to the unheated cores. 

A comparison of all seven cores is presented in Figure 16. The highest density of fractures is 

observed closest to the rib walls, at an approximate distance < 2 meters. Fracture apertures at a 

depth of 2 meters or greater are predominantly < 100 μm wide.

0 1 2 3 4 5 6 7 8 0

100

200

300

400

500

600

700

800

DRZ and EDZ Fracture Analyses:

WIPP and German Repository Cores

WIPP Core QGU 14

WIPP Core QGU 36

WIPP Core QGU 39

ALOHA II Core DJ-V

ALOHA II Core HD-V

TSDE Core VVS-A-Mi4

TSDE Core VVS-D1-Mi4

Distance from Rib Face (m)

Fra

cture A

p

erture (microns)

Figure 16. Fracture Apertures for DRZ Cores from WIPP and Asse 

The microstructural analyses performed on cores reveals that the distribution of fractures is 

higher and that fracture apertures are wider proximal (approximately < 2 meters) to the rib fa

Fracture apertures existing at a depth of 2 meters or greater are predominantly 

ces.

< 100 μm wide. 

A clear, though qualitative relationship defining the DRZ exists between velocity and damage. 

Sonic velocity increases as damage decreases and the shapes of the curves are inversely 

proportional. It would appear that the DRZ exists as deep as 2 meters in the clean zones

near the rib midheight, and to a relatively lesser extent near the floor, near the back and near the

corners. 

of salt

.9 Full-Scale Field Analogs

alt damage healing has been demonstrated in the laboratory and in 1-m-scale field tests on 

WIPP salt. Field evidence of damage healing on a large scale has not been demonstrated within 

4

S

39
the confines of WIPP. Indeed, in the world this type of information is sparse. The Germans

have published an excellent example of healing around a rigid enclosure. This case study is 

known as ALOHA (Untersuchungen zur Auflockerungeszone um Hohlräume im

Steinzalzgebirge). These investigations were conducted in the Asse salt mine near 

Braunschweig, Germany (Wieczorek and Zimmer, 1999). 

The in situ permeability tests were conducted on the 700-m level of the Asse salt mine, where a 

ast steel bulkhead was placed in a drift during the 1920’s. Tests were conducted in open

nd a

c

sections of the drift and behind the steel liner. Permeability magnitudes are diagramed in Figure

17. As can be readily ascertained, the permeability tests evidence healing of the DRZ arou

rigid structure, at a depth comparable to WIPP. The extension and the hydraulic properties of the

DRZ around a drift were investigated by means of gas and liquid injection testing. 

10 10 -15 m 2 10 -16 m 2 -21 m 2 10 -20 m 2 10 -19 m 2 10 -18 m 2 10 -17 m 2

Permeability

1.5

1.3

8.0 1.5 5.0

7.0

9.0

1.8

5.7

1.0

Bulkhead Open Drift

Figure 17. ALOHA2: Permeability Distribution around the Bulkhead and Open Drift. 

Co

oth construction and performance. The most pertinent experience noted during a 

yerman et al., 

e seal

ncrete bulkheads placed in Canadian potash mines also provide important case studies for 

b

reconnaissance in 1994 occurred in the PCS Rocanville potash mine. Additional analog 

observations regarding Canadian bulkheads and other case studies are reported in E

1995. The experience at the Rocanville mine is particularly illuminating because concret

construction was performed quickly, and success was critical to survival of the mine itself. This 

successful deployment of a drift seal constructed of brine-based concrete is analogous to panel 

closure construction at the WIPP. 

40
The Rocanville bulkhead was constructed in halite, following water inflow from an overlying 

aquifer. A concrete bulkhead was designed to contain the inflow and prevent additional inflow 

to the mine. A “temporary” bulkhead located 120 ft from the face (point of inflow) was 

d

d

e

its

verwhelming success. These factors demonstrate that basic salt concrete is 

ighly impermeable and construction methods need not be overly elaborate to be successful.

s

ry

r field tests. The fact that salt mines creep closed is well known. Ancient sections of the 

d is

he treatment of operational changes at the WIPP that include the 

g technical considerations. The flow of the document is chronological 

om the compliance certification, through the performance assessment verification, to the 

ent 

rred

to

nt

llowed the CCA. At the same time, the DRZ model was updated to depict more accurate 

.

in

constructed, and has functioned perfectly since its emplacement in 1985. Total hydrostatic hea

is monitored by various accesses through the bulkhead. Design and construction of the bulkhea

took only a few weeks, and the conditions for the construction were less than ideal. Despit

these factors, the bulkhead has resisted water pressures approaching 10 MPa and has not leaked 

since construction. This does not demonstrate that the DRZ developed and then healed, but does 

demonstrate a full-scale salt-based concrete bulkhead in salt that is impermeable to a full 

hydrostatic head. 

The principal reason this case study is so important to the future panel closure at WIPP is

simplicity and its o

h

The most relevant analogs to the case at hand include similar scale, setting, time and materials a

the WIPP Option D Panel Closure. Time represents one element beyond the reach of laborato

o

Hallstatt salt mine have preserved holdings dating from the Late Iron Age (500 B.C. to 0), 

including an unfortunate Celtic miner encapsulated in salt, whose “fully preserved body...was 

found in the Hallstatt salt mine” (DHP-Design, 2003). The fact that salt cavities creep close

well recognized. Two pertinent analogs presented here illustrate that on a large scale, rigid

inclusions tend to heal damaged salt and when functioning in tandem with salt provide 

essentially impermeable barriers. 

 

5.0 Summary 

This document presents t

disturbed rock zone amon

fr

technical migration of the baseline in preparation for the re-certification calculations. 

Information within this report provides justification and reasonableness for the DRZ model in 

Salado flow calculations, parameters, and level of detail that will represent major changes 

experienced in the WIPP underground, namely, incorporation into performance assessm

calculations 1) the EPA mandated Option D panel closure and 2) the advent of raising the 

repository horizon 2.43 meters to Clay G. Incorporation of these changes, which have occu

since the original compliance certification five years ago, required additional detail be added

the analysis scheme and that improvement to our understanding of the DRZ be included to

reflect more accurately the actual conditions experienced in the WIPP nuclear waste repository.

These changes, particularly the Option D condition of the certification, represented significa

departure from the analyses run for the original compliance PA and the verification test that 

fo

geometries and properties of the DRZ. The operational reality of mining to Clay G was 

evaluated in terms of room closure and the resulting porosity, which in turn is sampled in PA

41
Details of the Clay G analyses also provided insight to the local behavior of the DRZ evoluti

and devolution and the distortion of the anhydrite layers near the disposal rooms. This 

information supports the analytical treatment of the Option D panel closure and its incorporatio

into the Salado flow conceptual model. The updated modeling approaches and the concepts for 

the DRZ were subjected to independent peer review in accord with regulatory procedure

found to be acceptable. 

The rest of this document provides a summary of technical information pertaining to the DRZ 

and emphasizes knowled

on

n

s and

ge pertaining to WIPP that might change the methods implemented in 

revious analyses. Calculations show that prediction of the one-way evolution of the DRZ 

of

lt

he

to assess various official positions on the DRZ as a matter of “record”. Places within 

e record that mention the DRZ are listed in Appendix B. Contents of this document and its 

B. Ladanyi. 1991. “Unified Viscoplastic Model for the Inelastic

es,” Mechanics of Materials. Vol. 11, no. 1, 63-82. 

s. SAND90-

7076. Albuquerque, NM: Sandia National Laboratories. 

Brodsk he

, NM: Sandia National

Laboratories. 

p

replicates observations in the WIPP underground. The size and shape of the DRZ around an 

opening based on a stress invariant criterion are similar to the size and shape derived from sonic

velocity studies and from microscopy of core damage. The model output does not provide 

permeability directly, but the trend and magnitude of permeability around WIPP openings are

understood in considerable detail. For WIPP applications, the high permeability in zones near 

the skin of a room is of little consequence. On the other hand, over estimation of the extent

the DRZ could impart significant fictitious effects, if modeled improperly. Healing of the 

DRZ—entombment of the waste—is a far more important concept to PA. Eventually DRZ 

evolution will reverse as the creeping salt approaches equilibrium with the disposal room

contents—a condition that could arise quickly if a rigid panel closure were constructed. Sa

healing will ensue and the technical bases, from theory to practice, for this fact are given in t

main text. 

A review of the compliance supporting documents and the compliance submittal itself was 

performed

th

references include all the significant advancements pertaining to the DRZ and sufficient 

technical justification for model and parameter changes proposed for WIPP re-certification. 

6.0 References 

Aubertin, M., D.E. Gill, and

Flow of Alkali Halid

Beauheim, R.L., and R.M. Roberts. 2002. “Hydrology and Hydraulic Properties of a Bedded 

Evaporite Formation,” Journal of Hydrology. Vol. 259, no. 1-4, 66-88. 

Brodsky, N.S. 1990. Crack Closure and Healing Studies in WIPP Salt Using Compressional 

Wave Velocity and Attenuation Measurements: Test Methods and Result

y, N.S. 1995. Thermomechanical Damage Recovery Parameters for Rock Salt from t

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42
Bryan, C.R., F.D. Hansen, D.M. Chapin, and A.C. Snider. 2001. “Characteristics of the 

Disturbed Rock Zone in Salt at the Waste Isolation Pilot Plant,” Rock Mechanics in

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th

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st: Proceedings of the 38 U.S. Rock Mechanics Symposium, DC Rocks 

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fice

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ristescu, N. 1993. “A General Constitutive Equation for Transient and Stationary Creep of

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any, August 1991. Eds. D. Besdo and 

E. Stein. New York, NY: Springer-Verlag. 511-523. 

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Peer Review Report.” Carlsbad, NM: U.S. Department of Energy, Carlsbad Field Of

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“Sandia National Laboratories Technical Baseline Reports, WBS 1.3.5.3.” “Compliance 

Moni

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L.S., and W.R. Wawersik. 1980. Crack Healing of Fractures in Rock Salt. SAND80-

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Rock Salt,” International Journal of Rock Mechanics and Mining Sciences & 

Geomechanics Abstracts. Vol. 30, no. 2, 125-140. 

Cristescu, N., and U. Hunsche. 1992. “Determination of a Nonassociated Constitutive Equatio

for Rock Salt from Experiments,” Finite Inelastic Deformations – Theory and 

Applications, IUTAM Symposium, Hannover, Germ

cu, N., and U. Hunsche. 1998. Time Effects in Rock Mechanics. Series: Materi

Modeling and Computation. New York, NY: Wiley. 

D

Mechanical Behavior of Salt, Proceedings of the Fourth Conference, Ecole 

Polytechnique, Montreal, Quebec, Canada, June 17 an

esign. 2003. “Short History of Hallstatt.” Hallstatt-Online.

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2003).

Eyermann, T.J., L.L. Van Sambeek, and F.D. Hansen. 1995. Case St

and Materials Used in the Salt and Potash Mining Industries. SAND95-1120. 

Albuqu

udies of Sealing Methods

erque, NM: Sandia National Laboratories.

43
Finley, R.E., and J.R. Tillerson. 1992. WIPP Small Scale Seal Performance Tests - Status and 

Impacts. SAND91-2247. Albuquerque, NM: Sandia National Laboratories. 

ansen, C.W. 2002. “Estimate of Change in Repository Releases Due to Changes in 

boratories

(Copy on file in the Sandia WIPP Records Center as ERMS# 522233). 

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opy on file in

the Sandia WIPP Records Center as ERMS# 524694). 

Hansen ent of 

WIPP Records Center as 

ERMS# 522493).. 

Hansen

es.

NM:

tories.

und a

h North American Rock Mechanics Symposium, NARMS

2000, Seattle, Washington, USA, 30 July-3 August, 2000. Eds. J. Girard, M. Liebman, C. 

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o, 6-9 June, 1999. 

Eds. B. Amadei, R.L. Kranz, G.A. Scott, and P.H. Smeallie. Brookfield, VT: A.A. 

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Washington, D.C., USA, 7-10 July, 2001. Eds. D. Elsworth, J.P. Tinucci, and K.A. 

H

BRAGFLO Modeling.” Memorandum to Kathryn Knowles, Sandia National 

Laboratories, Carlsbad, NM, 9 May 2002. Carlsbad, NM: Sandia National La

, C.W., and C.D. Leigh. 2002. “Sandia National Laboratories Carlsbad Progra

Waste Isolation Pilot Plant, A Reconciliation of the CCA and PAVT Parameter 

Baselines, Revision 2.” Carlsbad, NM: Sandia National Laboratories (C

, C.W., C.L. Leigh, and J.S. Stein. 2002. “Analysis Plan for the Impact Assessm

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49
Appendix A: Salt-Based Concrete 

Salt-based concrete constitutes the major engineered material in the Option D panel closure 

design. Because the behavior of the salt DRZ depends upon interaction with the concrete 

monolith, characteristics of the salt-based concrete are essential for incorporation into the 

analyses. Portland cement concrete has exceptionally low permeability and is widely used for 

hydraulic applications. Salt-based concrete, such as the SMC specified for the Option D closure, 

is essentially Portland cement concrete with the mixing water saturated with respect to NaCl. 

Salt-saturated concrete has been used successfully as a seal material in potash and salt mining 

applications. Salt-based concrete has received less attention than ordinary Portland cement 

(OPC) concrete, however several specific investigations provide a comparison between saltbased and OPC concrete. Upon hydration, unfractured concrete is nearly impermeable, having a 

permeability of less than 10-20

 m2. From laboratory and field experiments, it has been 

demonstrated that salt-based concrete possesses engineering properties similar to OPC concrete. 

And, salt-based concrete is compatible with the salt mine environment. 

The following text establishes performance expectations for the SMC used in the Option D panel 

closure construction. It is included in this document as an appendix to the DRZ discussion, 

because the analysis necessary for PA involves a system comprising intact salt, damaged salt, 

and the concrete monolith. Properties of salt-based concrete are established in the laboratory, in 

scale-model field tests (Section 4.6) and at the full scale (Section 4.9). 

Pfeifle et al. (1996) conducted tests on two salt-based concretes: (1) SMC and (2) cured concrete 

recovered from the shaft plug of an existing salt mine (referred to as MSC concrete). The SMC 

was specifically designed for use in the WIPP shaft sealing system and was tailored to have 

limited shrinkage and to be compatible with WIPP salt through the addition of salt to the mixing 

water (Wakeley et al., 1994). The MSC concrete was originally placed as a shaft plug in a 

commercial salt mine located near the St. Lawrence seaway and consisted of two types of 

mixtures, MSC(1) and MSC(2). The MSC(1) concrete comprised a typical 27.6 MPa (4,000 psi) 

design batch using coarse and fine (sand) aggregates and Type I/II cement. The water for the 

MSC(1) was mixed with salt in a truck to produce a saturated brine before the solid components 

were added to the batch. MSC(2) concrete comprised a sand/cement mix that was placed in the 

shaft by tremie line under 70 meters of water. Granular salt was added to this batch to form brine 

during mixing. 

Table A.1 summarizes the strength and permeability testing conducted on the SMC and MSC 

cores. Figure A.1 plots permeability as a function of the gas pressure difference applied during 

the permeability testing of the SMC and MSC specimens as well as ESC specimens, which are 

described further in the discussion of small-scale seal performance tests (Section 4.6). The 

permeability of the SMC was typically of the order of 10-21

 m2, while the permeability of the 

MSC was approximately four orders-of-magnitude higher, i.e., 10-17

 m2. This difference in 

permeability was attributed to two factors: (1) the stringent design requirements established to 

limit fluid flow through the WIPP SMC shaft sealing components and (2) the limited quality 

control used in the placement of the MSC concrete under extreme conditions (i.e., placement 

under water). The permeability of the ESC from the SSSPT (Section 4.6) is approximately 

50
10-19

m2, which falls between the permeability for the SMC and MSC tests. The strengths of the 

two types of concrete are comparable, and increase appreciably when confined. 

Table A.1 Summary of Strength and Permeability Tests on 

SMC and MSC Concrete Specimens.

Specimen 

I.D. 

Permeability 

(m2

) 

Confining

Pressure 

(MPa) 

Stress 

Difference 

At Failure 

(MPa) 

Elastic 

Modulus, 

E 

(GPa) 

Poisson’s 

Ratio, ν

Salado Mass Concrete 

40SM4-19/2-

1/1 

2×10-21

 – 8 ×10-21 0 44.2 36.3 0.19

32SM4-25/1-

1/1 

– 5 75.8 30.5 0.20 

40SM4-11/2-

1/1 

9×10-22 10 80.5 36.7 0.35

40SM4-2/1-

1/1 

– 15 111.4 32.2 0.20

MSC Shaft Concrete 

MSC/D-1 4×10-17

 – 10 ×10-

17

0 60.2 18.3 0.15

MSC/O-2/2 2×10-17

 – 4 ×10-17 0 45.3 22.6 0.23

MSC/K-2/2 2×10-17

 – 4 ×10-17 0 56.4 32.8 0.17

51
1.E-21

1.E-20

1.E-19

1.E-18

1.E-17

1.E-16

1.E-15

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Gas Pressure Difference (MPa)

P

erm

e

a

bility (m2

)

SMC Concrete ESC Concrete MSC(1) & MSC(2) Concrete

Figure A.1. Permeability of SMC, ESC, and MSC Concrete Specimens Versus Gas 

Pressure Difference. 

52
The permeability of salt-based concrete was measured in the Small Scale Seal Performance Test 

(SSSPT) for a decade and corroborated by laboratory measurements. From these tests, values 

and ranges of concrete permeability have been developed. For PA calculations, permeability of

SMC seal components is treated as a sampled variable, for which the probability distribution 

function is plotted in Figure A.2. 

Figure A.2. Cumulative Distribution Function for Permeability of SMC (after Repository

Isolation Systems Department, 1996, WIPP Shaft Seal System Compliance 

Submittal Design Report, Appendix A). 

53
Appendix B: DRZ Issues Addressed in the CCA 

The disturbed rock zone was addressed in several compliance documents. Because these 

references comprise the basis for the EPA compliance determination, a review of the disturbed 

rock zone discussions as they exist in the compliance record is appropriate. The conceptual 

model implemented at the time of the compliance submittal has been advanced in certain ways, 

as discussed in the main paper. Modest research effort has continued in the underground at the 

repository horizon as well as collaborative research on the international frontier. Based on recent 

information obtained since the CCA coupled with historical information, the current 

understanding and description of the DRZ differ somewhat from the concepts put forward in the 

CCA. A word search on DRZ was conducted for the CCA and supporting documents. The 

following reference sections of the CCA were examined in preparation of the DRZ discussions in 

the main text to ensure consistency between the CCA baseline and the current discussions of the 

DRZ. These documents are identified below and a brief evaluation or summary is provided. 

Thus, the bases of the DRZ considerations in the CCA have been reviewed in preparation of this 

memorandum. 

The Compliance Application: 

Section 2.2.1.3 Hydrology of the Salado: summarizes hydraulic tests in salt and anhydrite. 

Measured permeabilities are all lower than 10-18

 m2. Other discussion acknowledges that flow 

observations are complex. 

Section 3.2 Repository Configuration: states that the panel closure system “will prevent further 

development of the DRZ in panel entries.” When the Option D panel closure is constructed, this 

statement should be modified to include the fact that the DRZ would be mined out and any 

existing DRZ would heal shortly thereafter. 

Section 3.3.1.3.2 Clay Columns: clay column stiffness is sufficient to heal fractures, thus 

removing the DRZ. 

Section 3.3.1.5.1 DRZ Behavior: discusses DRZ healing as accounted for in the Shaft Seal 

Design. 

Section 3.3.2 Panel Closure System: again notes that the PCS would prevent the existing DRZ 

from increasing in permeability. Option D would change this position. Also, this section notes 

that the panel concrete would not degrade to a condition that is more permeable than the DRZ. 

Section 6.0.2.2 Undisturbed Performance: presents arguments for DRZ healing around the 

concrete components. In the absence of elevated pressure in the repository, salt creep would also 

eventually result in substantial compaction of the waste. 

Section 6.4.3.1 Creep Closure: discusses creep closure and development of the porosity surface. 

Section 6.4.4 This section discusses the Shaft Seal System (from Appendix SEAL) and its 

representation in BRAGFLO. 

54
Section 6.4.5 The Salado: discusses modeling interbeds and fracturing. 

Section 6.4.5.1 Impure Halite: begins by noting that gas will not flow in halite. 

Section 6.4.5.2 Salado Interbeds: identifies the distinct anhydrite interbeds modeled in 

BRAGFLO (MB 138, MB 139, and anhydrite layers a and b). MB 139 and anhydrite a and b are 

included within the DRZ. The DRZ is extended to reach MB 138 “because of uncertainty in the 

extent and properties of the DRZ and the associated long-term isolation of MB 138 from the 

repository.” The extent of the DRZ as modeled in the CCA and PAVT is much larger than 

practical observation, geophysical measurement, and modeling would suggest. 

Section 6.4.5.3 DRZ: states that PA approximates the effects of the DRZ conservatively by 

extending it from MB138 to MB 139, thus creating a permanent high-permeability region that 

does not significantly impede flow between the repository and affected interbeds. Table 6-17 

lists the DRZ parameter values as discussed in the main CCA text. The DRZ representation has 

been modified for the re-certification calculations to include Option D closures. Therefore, 

permeability near the Option D closure has been assigned values consistent with the best 

available information since the CCA. 

Section 6.4.7.1.1 Direct Brine Release During Drilling: presents arbitrarily assumed DRZ for 

pillars. 

Section 6.4.10.1 Disposal System Flow and Transport Modeling (BRAGFLO and NUTS): 

discusses start-up permeabilities, constant permeabilities and other initial conditions, such as gas 

reaction rates. 

Section 6.5.4 Uncertainty: basically states that PCS and DRZ are assigned permeability of 

10-15 m2

. 

Section 7.2 Monitoring: states that “Monitoring the DRZ hydrologic properties would not 

provide relevant information of verify assumptions used in PA; therefore, they will not be 

monitored during the operational period nor during the postclosure period.” This statement was 

presumptuous, as ongoing evaluation of DRZ provides more realistic appreciation of the DRZ 

than reflected in the CCA. 

Section 7.2.3.1 Geomechanical Monitoring Program: countermands the previous statement by 

acknowledging “...geotechnical measurements will be useful to detect deviations in ...DRZ 

development. 

Section 9.3.1.1 Adequate Models: “concludes that the present DRZ model is adequate to be 

implemented in performance calculations.” 

Section 9.3.1.2.2.3 Third Peer Review Panel Concern-Repository Fluid Flow: presented and 

discussed the issue stated as “Consolidation of the waste, panel seals, and repository disturbed 

rock zone (DRZ) over time would result in lower permeabilities for these regions.” The effects 

55
of dynamic permeability of the DRZ were modeled and “results in computed releases to the 

accessible environment that are essentially equivalent to the baseline case. In addition, dynamic 

alteration of the DRZ/TZ has an insignificant effect on waste room conditions relevant to 

blowout cuttings, and spalling releases.” 

Section 9.3.1.2.8.3 Third Peer Review Panel Concerns: revisits direct brine release owing to 

penetration into the DRZ. 

Appendices 

Appendix SOTERM 7.1.2 Use of Brine End Members: Material here is of no consequence to 

DRZ considered in the repository horizon. 

Appendix SEAL (contains 210 call outs of DRZ): Discussion in Appendix SEAL concerns the 

shaft seal system. In the design and analysis of the shaft system, the DRZ was incorporated into 

the analysis in considerable detail. The shaft seal design thoroughly accounted for the DRZ, as 

noted by the EPA comments found in other sections; however, the DRZ near the disposal rooms 

is complicated by the horizontal stratigraphy and the size and shape of openings. 

Appendix MASS.2.4 CM Development (1982 to Present): The modeling concept for panel 

closures and an “imperfectly healed DRZ” are noted here. 

Appendix MASS.3.1 Darcy’s Law: Not applicable for DRZ discussions. 

Appendix MASS.13.0 Salado: Flow in the Salado is modeled to occur through interbeds that 

intersect the DRZ. The conceptual model for Salado fluid flow has primary interactions with 

three other conceptual models. The interbed fracture conceptual model allows porosity and 

permeability of the interbeds to increase as a function of pressure. 

Appendix MASS Table 1.0 General Modeling Assumptions: Modeling assumptions for various 

treatment of the DRZ are listed in this table. First, the shaft is surrounded by a DRZ, which heals 

with time. The DRZ is represented through the permeabilities of the shaft system itself, rather 

than as a discrete zone. Second, panel closures are modeled with the same properties as the 

surrounding DRZ. Third, the permeability of the DRZ is constant and higher than intact Salado. 

Fourth, excavation and waste emplacement result in partial drainage of the DRZ. The treatment 

of the shaft within the BRAGFLO model will be simplified for purposes of the re-certification 

PA. 

Appendix MASS.13.4 Flow in the Disturbed Rock Zone: Along with Section 6.4.5.3 this text 

presents the basic treatment of the DRZ in CCA calculations. The conceptual model 

implemented in the PA uses values for the permeablility and porosity of the DRZ that do not 

vary with time. A screening analysis examined an alternative conceptual model for the DRZ in 

which permeability and porosity changed dynamically in response to changes in pressure 

(Vaughn et al., 1995). The Vaughn et al. report implemented a fracturing model in BRAGFLO 

for the DRZ. This fracturing model is identical to the existing anhydrite interbed alteration 

model. They concluded that the DRZ fracture model yielded results “essentially equivalent” to 

those with the DRZ constant. Treatment of anhydrite fracture and the interplay with the DRZ is 

56
being treated in some detail in the re-certification calculations and changes to the conceptual 

models for Salado flow were subjected to Peer Review consistent with 40 CFR 194.27 and 

NUREG-1297. 

Appendix PAR 11 Log Intrinsic Permeability—All Clay Shaft Materials: This section discusses 

how the DRZ permeability was incorporated into the model element for the clay shaft seal 

component. 

Appendix PAR 9 Log Intrinsic Permeability—Asphalt: This section discusses how the DRZ 

permeability was incorporated into the model element for the asphalt shaft seal component. 

Appendix PAR 12 Intrinsic Permeability-Shaft Disturbed Rock Zone: Along with parameters 9 

and 11, this discusses in situ measurements made on the Air Intake Shaft (Dale and Hurtado, 

1998) and in Room D (Knowles and Howard, 1996). 

Appendix PAR Tables PAR-2 and PAR-3: These tables are identical and list seal materials and 

DRZ extent. This information is not applicable to treatment of the DRZ in the repository. 

Appendix PAR Tables PAR-6: This table provides permeabilities of various anhydrite layers 

(MB 139, MB 140 and anhydrite b). 

Appendix Peer Conceptual Models: Section 3.7 Disturbed Rock Zone. As noted in the text 

(Section 2.3) the updated treatment of the DRZ comprised a portion of the independent peer 

review process. 

Technical Support Documents 

TSD 23 Section 1.3.24 Disturbed Rock Zone Conceptual Model: here the EPA was not satisfied 

with DOE’s assumption that the permeability of the DRZ remained constant with time. 

Consequently, this parameter was treated as a variable in the EPA mandated PA verification test. 

TSD 23 Section 3.3 198 DRZ_1-PRMX_LOG:DRZ Permeability 

Compliance Application Review Documents 

CARD 23 Section 4.4.9.1 DOE’s Implementation of the Salado Interbeds Conceptual Model in 

CCA 

CARD 23 Section 1.3.25.1 DOE’s Model Description 

CARD 23 Table 2.3.1 Alternative CM’s Seriously Considered for PA 

CARD 23 Section 4.4.7.1 DOE’s Implementation of the Salado Conceptual Model into CCA 

CARD 23 Section 4.4.11 Shaft and Shaft Seal CM 

CARD 23 Section 4.4.12 Disturbed Rock Zone (DRZ) Conceptual Model 

57
CARD 23 Section 7.3.2.3 Salado CM 

CARD 14 Section 14.B.4 DOE Methodology and Conclusions, Rustler, Dewey Lake, and Santa 

Rosa Formation Hydrology 

CARD 14 Section 14.E.4 DOE Methodology and Conclusions 

CARD 14 Section 14.E.5 EPA Compliance Review 

PAVT 

WPO#46674 Rev. 1. Summary of EPA Mandated PAVT 

58
Distribution List

Federal Agencies

US Department of Energy (1) 

Office of Civilian Radioactive Waste Mgmt. 

Attn: Deputy Director, RW-2 

Forrestal Building 

Washington, DC 20585 

US Department of Energy (7) 

Carlsbad Field Office 

Attn: I. Triay 

 G. Basabilvazo 

 S. Casey 

 D. Mercer 

 R. Nelson 

 R. Patterson 

 Mailroom

P.O. Box 3090 

Carlsbad, NM 88221-3090 

US Department of Energy 

Office of Environmental Restoration and 

 Waste Management 

Attn: P. Bubar, EM-20 

Forrestal Building 

Washington, DC 20585-0002 

US Department of Energy 

Office of Environmental Restoration and 

 Waste Management 

Attn: Mary Bisesi/Lynne Smith, EM-23 

Washington, DC 20585-0002 

US Environmental Protection Agency (1) 

Radiation Protection Programs 

Attn: B. Forinash 

ANR-460 

Washington, DC 20460 

Boards

Defense Nuclear Facilities Safety Board 

Attn: D. Winters 

625 Indiana Ave. NW, Suite 700 

Washington, DC 20004 

State Agencies

Attorney General of New Mexico 

P.O. Drawer 1508 

Santa Fe, NM 87504-1508 

Environmental Evaluation Group (2) 

Attn: Library 

7007 Wyoming NE 

Suite F-2 

Albuquerque, NM 87109 

NM Environment Department (1) 

Secretary of the Environment 

1190 St. Francis Drive 

Santa Fe, NM 87503-0968 

NM Bureau of Geology & Mineral 

Resources 

801 Leroy Place 

Socorro, NM 87801 

Laboratories/Corporations

Battelle Pacific Northwest Laboratories 

Battelle Blvd. 

Richland, WA 99352 

Los Alamos National Laboratory 

Attn: B. Erdal, INC-12 

P.O. Box 1663 

Los Alamos, NM 87544 

Washington TRU Solutions (3) 

Attn: Library, GSA-214 

P.O. Box 2078 

Carlsbad, NM 88221

Distribution List – Page 1 of 3 
National Academy of Sciences

WIPP Panel

National Academies 

Attn: Barbara Pastina (1) 

Committee on WIPP 

Board on Radioactive Waste Management 

500 Fifth Ave NW; Keck 634 

Washington, DC 20001 

Universities

University of New Mexico 

Geology Department 

Attn: Library 

141 Northrop Hall 

Albuquerque, NM 87131 

Libraries

Government Information Department 

Zimmerman Library 

MSC05 3020 

University of New Mexico 

Albuquerque, NM 87131-0001 

New Mexico Junior College 

Pannell Library 

Attn: Earl Dye 

5317 Lovington Highway 

Hobbs, NM 88240 

New Mexico State Library 

Attn: L. Canepa 

1209 Camino Carlos Rey 

Santa Fe, NM 87507 

New Mexico Tech 

Joseph R. Skeen Library 

801 Leroy Place 

Socorro, NM 87801 

Distribution List – Page 2 of 3 
Foreign Addresses

Francois Chenevier (2) 

ANDRA 

Parc de la Croix Blanche 

1-7 rue Jean Monnet 

92298 Chatenay-Malabry Cedex 

FRANCE 

Commissariat a L’Energie Atomique 

Attn: D. Alexandre 

Centre d’Etudes de Cadarache 

13108 Saint Paul Lez Durance Cedex 

FRANCE 

Bundesanstalt fur Geowissenschaften und 

Rohstoffe 

Attn: M. Wallner 

Postfach 510 153 

D-30631 Hannover 

GERMANY 

Bundesministerium fur Forschung und 

Technologie 

Postfach 200 706 

5300 Bonn 2 

GERMANY 

Gesellschaft fur Anlagen und 

Reaktorsicherheit 

(GRS) 

Attn: B. Baltes 

Schwertnergasse 1 

D-50667 Cologne 

GERMANY 

Dr.-Ing. Klaus Kuhn 

TU Clausthal Institut fur Bergbau 

Erzstr. 20 

D-38678 Clausthal-Zellerfeld 

GERMANY 

Distribution List – Page 3 of 3 
Dr. Susumu Muraoka 

Nuclear Material Control Center 

Tokai-Mura, Ibaraki-Ken, 319-11 

JAPAN 

Nationale Genossenschaft fur die Lagerung 

Radioaktiver Abfalle (2) 

Attn: NAGRA Library 

Hardstrasse 73 

CH-5430 Wettingen 

SWITZERLAND 

AEA Technology 

Attn: W. R. Rodwell 

424-4 Harwell 

Didcot, Oxfordshire OX11 OQJ 

UNITED KINGDOM 

Internal

MS Org.

0701 6100 P. B. Davies 

0731 6800 823 Library (2) 

0771 6800 D. Berry 

1395 6820 P. E. Shoemaker 

1395 6821 D. Kessel 

1395 6822 M. Rigali 

1395 6820 F. Hansen (4) 

1395 6820 WIPP Library (10) 

9018 8945-1 Central Technical Files 

0899 9616 Technical Library (2) 

Distribution List – Page 4 of 3