Transport of four organic solutes was monitored in 15 multilevel points and a partially penetrating well during a forced-gradient test in the Borden aquifer. Simulations assuming equilibrium sorption were unable to match the observed breakthrough curves, particularly for the more highly sorbing solutes. The data were better fit by first-order physical nonequilibrium simulations including mass transfer between mobile and immobile water regions. Assuming 86% of total porosity is mobile, as estimated previously, curve fits yielded estimates of Kd (sorption distribution coefficient) f (fraction of sorption sites within mobile water regions), and &agr; (first-order mass transfer coefficient). Kd and f estimates compare well with those from previous laboratory studies and simulations of the natural gradient test previously conducted nearby. The estimated &agr; values compare reasonably well with those derived from laboratory tests but are considerably higher than the value utilized in simulations of the natural gradient test.