A center of excellence in earth sciences and engineeringrrM 

Geosciences and Engineering Division 

6220 Culebra Road San Antonio, Texas, U.S.A. 78238-5 166 

(210)522-5160*Fax (210) 522-5155 

March 23, 201 1 

Contract No. NRC-02-07-006 

Account No. 20.14002.01.441 

06300001 

ATTN: Document Control Desk 

U.S. Nuclear Regulatory Commission 

Mr. King Stablein 

Office of Nuclear Material Safety and Safeguards 

Division of High-Level Waste Repository Safety 

Mail Stop (EBB-2-B02) 

Washington, DC 20555-0001 

SUBJECT: Final Version of Intermediate Milestone 14002.01.441.1 14-The Role of Matrix 

Diffusion as a Retardation and Attenuation Process at Yucca Mountain and Other 

Geologic Environments 

Dear Mr. Stablein: 

This letter transmits the final report titled The Role of Matrix Diffusion as a Retardation and 

Attenuation Process at Yucca Mountain and Other Geologic Environments, completed under the 

Knowledge ManagementlCapture project. A previous version of the report, as Intermediate 

Milestone 14002.01 171.1 14, was transmitted on January 27, 201 1. The final version, 

addressing comments by U.S. Nuclear Regulatory Commission (NRC) received by email on 

March 16, 201 1 , is located as a Microsoft@ Word' file in the Center for Nuclear Waste 

Regulatory Analyses and NRC Microsoft Sharepoint' file system at this location 

YM Licensing Review > Knowledge Management > Knowledge Capture Reports > 

Walter-Matrix Diffusion as a Retardation and Attenuation Process-114 

Washington Office 

1801 Rockville Pike. Suite IO5 Rockville. Maryland 20852- 1633 t 
Mr. King Stablein 

March 23, 201 1 

Page 2 

Enclosed with this letter are our staffs specific responses to the NRC comments. Please advise 

me if any other changes are needed. If you have any questions regarding this paper, please 

contact Dr. Gary Walter at (210) 522-3805 or me at (210) 522-5582. 

Sincerely, 

David Pickett, Ph.D. 

Senior Program Manager 

Integrated Spent Fuel Regulatory 

Program-Geologic Disposal 

DP/ar 

Enclosure 

- NRC 

cc: D. DeMarco 

R. Jackson 

V. Whipple 

L. Kokajko 

A. Mohseni 

J. Davis 

J. Rubenstone 

J. Guttmann 

Y. Kim 

B. Hill 

T. McCartin 

J. Bradbury 

R. Fedors 

P. Hall 

CNWRA Letter Only 

W. Patrick 

B. Sagar 

GED Directors 

GED Managers 

G. Walter 

J. McMurry 

M. Padilla 

SwRl 

Record Copy B, IQS 
Responses to NRC Programmatic Comments 

NRC Comment 

1. Overall comment on processes included in field test interpretations and parameterization of 

the effective diffusion coefficient at field scale. 

Throughout the executive summary and main text, effective matrix diffusion coefficient is said to 

incorporate only the effect of diffusion between mobile and relatively "immobile" zones. The 

scale effect between lab and field tests is attributed to the underrepresentation of the mobile 

wate r/matrix contact area. 

The scale effect going from lab to field could also be attributed to alternative fracture pathways 

(small fractures, highly tortuous pathways versus large-fracture direct pathways), which is 

alluded to in the text, but also advective flow/transport into the relatively "immobile" zones. 

Thus, in field tests, the delay in portions of the breakthrough could be attributed to matrix 

diffusion, advection/transport into relatively "immobile" zones, and slow tortuous fracture 

pathways. 

The author needs to present arguments to explain why breakthrough curves from field test data 

can be explained solely by changes to the effective diffusion coefficient (underrepresentation of 

the contact area), rather than a combination of diffusion and advection into the matrix 

("immobile" zone). The perspective of this comment comes from the interpretation of field tests 

hinging on the parameterization of the active fracture model and the diffusion parameters 

(uniqueness issue: changes to the AFM versus changes to effective diffusion coefficient). As 

the author knows, the AFM includes a matrix/fracture area terms and matrix block size. The 

AFM area term would not necessarily be the same as the contact area for the effective diffusion 

term (e.g., effect of transport channeling). Though, changes to the AFM parameters would 

affective estimates of the effective diffusion coefficient in field tests. 

See particularly the first paragraph of section 4.2 and third paragraph of section 6.3. 

Response: 

The comment on the potential significance of advective transports between the fractures and 

matrix is well-taken. A further discussion of the potential significance of this phenomenon on 

the interpretation of field tracer tests has been added to Section .4.2. As noted in Section 4.2, 

the potential confounding effect of advective transport on the interpretation matrix diffusion 

coefficients from field tracer tests is somewhat mitigated when multiple tracers with different free 

aqueous diffusion coefficients, but similar mobilities, are used in the test and considered in the 

its interpretation. 

A mention of the potential effect of advective transport on the interpretation of the active fracture 

parameter has been added to Section 6.3. 

NRC Comment 

2. Typo on page 6-1 1 ; "consisted" should be "consistent" in the llast paragraph of section 

6.1.2.5. 

Response: This typo has been corrected. 
NRC Comment 

3. Typo on page 6-4; “fracture of infiltrating water.. .” should be “fraction of infiltrating water.. .” 

Response: This typo has been corrected.