Frank W. Schwartz Warren W. Wood S. P. Garabedian D.R. LeBlanc Hubao Zhang 1998 <p><span>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</span>⁻<span>), a nonreactive tracer, and lithium (Li</span>⁺<span>), 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</span>⁺<span><span>&nbsp;</span>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</span>⁻<span><span>&nbsp;</span>and Li</span>⁺<span><span>&nbsp;</span>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</span>⁻<span><span>&nbsp;</span>plume due to gravity slowed significantly because of dilution by dispersion. The downward movement of the Li</span>⁺<span><span>&nbsp;</span>plume was negligible because the two plumes moved in locally different velocity regimes, where Li</span>⁺<span><span>&nbsp;</span>transport was retarded relative to Br</span>⁻<span>. The maximum extent of downward transport of the Li</span>⁺<span><span>&nbsp;</span>plume was less than that of the Br</span>⁻<span><span>&nbsp;</span>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</span>⁻<span><span>&nbsp;</span>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</span>⁺<span><span>&nbsp;</span>plume were simulated by including kinetic adsorption-desorption reactions.</span></p> application/pdf 10.1029/97WR02918 en American Geophysical Union Simulation of variable-density flow and transport of reactive and nonreactive solutes during a tracer test at Cape Cod, Massachusetts article