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Simulation of variable‐density flow and transport of reactive and nonreactive solutes during a tracer test at Cape Cod, Massachusetts
Author(s) -
Zhang Hubao,
Schwartz Frank W.,
Wood Warren W.,
Garabedian S. P.,
LeBlanc D. R.
Publication year - 1998
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 - 10.1029/97wr02918
Subject(s) - plume , tracer , aquifer , flow (mathematics) , geology , advection , dispersion (optics) , panache , non linear least squares , mechanics , mass flux , flux (metallurgy) , dilution , hydrology (agriculture) , chemistry , meteorology , geotechnical engineering , thermodynamics , groundwater , physics , optics , organic chemistry , machine learning , explained sum of squares , computer science , nuclear physics
A multispecies numerical code was developed to simulate flow and mass transport with kinetic adsorption in variable‐density flow systems. The two‐dimensional code simulated the transport of bromide (Br − ), a nonreactive tracer, and lithium (Li + ), a reactive tracer, in a large‐scale tracer test performed in a sand‐and‐gravel aquifer at Cape Cod, Massachusetts. A two‐fraction kinetic adsorption model was implemented to simulate the interaction of Li + with the aquifer solids. Initial estimates for some of the transport parameters were obtained from a nonlinear least squares curve‐fitting procedure, where the breakthrough curves from column experiments were matched with one‐dimensional theoretical models. The numerical code successfully simulated the basic characteristics of the two plumes in the tracer test. At early times the centers of mass of Br − and Li + sank because the two plumes were closely coupled to the density‐driven velocity field. At later times the rate of downward movement in the Br − plume due to gravity slowed significantly because of dilution by dispersion. The downward movement of the Li + plume was negligible because the two plumes moved in locally different velocity regimes, where Li + transport was retarded relative to Br − . The maximum extent of downward transport of the Li + plume was less than that of the Br − plume. This study also found that at early times the downward movement of a plume created by a three‐dimensional source could be much more extensive than the case with a two‐dimensional source having the same cross‐sectional area. The observed shape of the Br − plume at Cape Cod was simulated by adding two layers with different hydraulic conductivities at shallow depth across the region. The large dispersion and asymmetrical shape of the Li + plume were simulated by including kinetic adsorption‐desorption reactions.