A push-pull test involves the injection (push) of a prepared test solution into an aquifer followed by the extraction (pull) of the test solution/groundwater mixture from the same location (Figure 1). Tests may be performed in existing monitoring wells or multilevel samplers. The test solution consists of water containing one or more tracers and one or more other solutes; the type, combination, and concentration of solutes are selected to investigate specific aquifer characteristics. During the injection phase, the test solution is injected into the aquifer where it flows away from the well and penetrates a roughly cylindrical volume of aquifer (Figure 1A). During the extraction phase, flow is reversed concentrations of tracer, reactive solutes, and possible reaction products are measured as a function of time at the same well (Figure 1B). Tracer concentrations are used to adjust concentrations of test solution components for dilution. Mass balances are computed by integrating dilution-adjusted concentrations during the extraction phase. Reaction rates are computed from the mass of solute consumed and/or product formed.