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Twin Lake Tracer Tests: Longitudinal dispersion
Author(s) -
Moltyaner G. L.,
Killey R. W. D.
Publication year - 1988
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr024i010p01613
Subject(s) - aquifer , tracer , dispersion (optics) , hydrology (agriculture) , soil science , geology , water well , groundwater , advection , scale (ratio) , environmental science , geotechnical engineering , physics , optics , nuclear physics , quantum mechanics , thermodynamics
Two natural gradient dispersion tests were conducted at the Chalk River Nuclear Laboratories, Ontario, in 1982 and 1983 in order to quantify field‐scale dispersion processes over a 20‐ and 40‐m distance of a radiotracer migration. The patterns of dispersion that were observed in the field using a dry access tube monitoring technique were compared with patterns predicted by the advection‐dispersion model with constant parameters. Analysis of the time‐concentration profiles of the tracer at observation wells located along the mean direction of the longitudinal spreading showed that the dispersion model adequately describes the dispersion patterns actually observed and averaged over the aquifer depth. The values of longitudinal dispersivity determined from continuous time‐concentration profiles were virtually equal to those obtained from laboratory‐scale columns. The dispersive properties of the aquifer were characterized at the local scale by a constant independent of travel distance dispersivity value of 0.0045 m. Averaging the test data over the aquifer depth, analogous to the information provided by a fully penetrating pumping well, yielded a full‐aquifer dispersivity varying in an irregular fashion from 0.16 to 0.06 m. The scale effect observed between local‐scale and full‐aquifer dispersivities is the result of inhomogeneity of the aquifer and the concentration averaging produced by the sampling instrumentation. The results of two tracer tests also showed that the use of the dry access tube monitoring technique for field experimentation provides detailed representation of spatial and temporal distribution of a radiotracer's activity and, consequently, provides a practical means to determine the groundwater velocity field and dispersive properties of porous materials.