A quantitative framework based on a set of dimensionless numbers was developed to capture the effects of competing interfacial and biokinetic processes and define limits on the application of in situ bioremediation. An integrated numerical modeling and experimental approach was utilized to evaluate the quantitative framework. Experiments were conducted to examine the transport and biodegradation of naphthalene in a saturated, heterogeneous intermediate-scale flow cell with two layers of contrasting hydraulic conductivities. The experiments were carried out in two phases: Phase I, simulating intrinsic biodegradation; and Phase II, simulating an engineered in situ bioremediation. In Phase I, dispersion was identified as the overall rate-limiting process based on the proposed quantitative framework. Two engineered perturbations to the system were selected in Phase II to examine their abilities to enhance in situ biodegradation. In the first perturbation, nitrogen and phosphorus were spiked into the influent solution in excess of the required stoichiometric amounts. This perturbation did not have a significant impact because dispersion, not biokinetics, was the overall rate-limiting process. However, in the second perturbation, advection was increased, resulting in increased longitudinal and vertical transverse dispersion, thereby alleviating the rate-limiting process, and enhancing the overall biotransformation rate.