Influence of fracture truncation on dispersion: A dual permeability model

Simulations with a dual permeability model show that a few discrete fractures can have a Ž . major influence on plume geometry. A limited number of truncated fractures 1–4 within a permeable matrix can create nearly circular plumes, with about the same degree of spreading in the direction transverse to the average hydraulic gradient as in the longitudinal direction. By comparison, continuous fractures in the direction of flow tend to produce elongated plumes, similar to those typically seen in granular materials. Both types of plumes have been observed in tracer experiments in fractured porous media on the Oak Ridge Reservation. Understanding the influence of fracture geometry is important in planning field characterization and subsequent remediation in fractured porous media. q 1998 Elsevier Science B.V. 1. Background and purpose Shales are typically considered adequate barriers against migration of contaminants. Ž . However, on the Oak Ridge Reservation ORR the upper portion of these deposits Ž . usually less than 10 m depth are highly weathered and fractured, which substantially Ž increases the hydraulic conductivity and potential for contaminant migration Solomon . et al., 1991 . For example, tritium migration from shallow low-level radioactive waste ) Corresponding author. Current address: Dept. of Geology, Temple University, Philadelphia, PA 19022, USA. Tel.: q1-215-2048227; fax: q1-215-2043496. 1 Oak Ridge National Laboratory is managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract No. DE-AC05-96OR22464. 0169-7722r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0169-7722 97 00037-5 ( ) P. Stafford et al.rJournal of Contaminant Hydrology 3