Skip to Main Content
Skip Nav Destination

Tracer penetration into welded tuff matrix from flowing fractures

Qinhong Hu, Timothy J. Kneafsey, Robert C. Trautz and Joseph S. Y. Wang
Tracer penetration into welded tuff matrix from flowing fractures
Vadose Zone Journal (August 2002) 1 (1): 102-112


Field and laboratory tracer experiments were conducted to investigate the extent of tracer imbibition and penetration into unsaturated, fractured rock matrix at Yucca Mountain, Nevada. Field experiments were carried out in the Exploratory Studies Facility (ESF), an underground tunnel at Yucca Mountain. Water containing dye was released into horizontal boreholes drilled into the wall of the ESF main drift. The region was then mined to observe the flow pathways and to collect dye-stained rock samples for subsequent laboratory quantification. Dye concentration profiles in the rock, measured using a newly developed sampling technique, showed that liquid flowing through the fractures penetrated into the matrix to a depth of several millimeters. Laboratory studies of tracer penetration into the rock matrix were conducted using tracer-free rock samples, collected from the same hydrogeologic unit and machined into cylindrical cores. Tracer-imbibition tests were performed on cores at two different initial water saturations with both sorbing (dyes) and nonsorbing tracers. The travel distance for sorbing dyes was a few millimeters after 16 to 20 h, similar to the extent measured in samples from the field test. The nonsorbing bromide front coincided with the wetting front in the rock core at the initial water saturation of 12%, and the imbibition depth agreed very well with the prediction, using independently measured properties. At the high initial water saturation of 76%, the bromide front lagged significantly behind the wetting front. Sorption coefficients for the dyes in the partially saturated core samples were calculated using two independent approaches, based on tracer travel-distance and mass-distribution calculations, and were found to yield comparable results. Utilization of nonsorbing tracers with different molecular sizes helped to identify the effects of pore-size restriction on tracer transport during imbibition. The results from this work have a direct application to radionuclide transport at Yucca Mountain, and the methods presented are broadly applicable to the investigation of water and solute transport in unsaturated rock.

ISSN: 1539-1663
Serial Title: Vadose Zone Journal
Serial Volume: 1
Serial Issue: 1
Title: Tracer penetration into welded tuff matrix from flowing fractures
Affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA, United States
Pages: 102-112
Published: 200208
Text Language: English
Publisher: Soil Science Society of America, Madison, WI, United States
References: 36
Accession Number: 2002-078860
Categories: Engineering geologyEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Accessed on Oct. 10, 2002
Illustration Description: illus. incl. 3 tables
N36°43'60" - N37°00'00", W116°34'60" - W116°25'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200224
Close Modal

or Create an Account

Close Modal
Close Modal