In general, in situ remediation techniques require that treatment agents come into contact with contaminants to facilitate the treatment process. Greater contact causes more in situ mixing of the two compounds and greater contaminant reduction. In a recirculation well system featuring an injection/extraction well pair, delivery controls the remedial and economic efficiency of decontamination, and is therefore a key consideration for successful in situ remediation. In this study, we numerically evaluated the remedial and economic efficiency of a recirculation well system with sinusoidal temporally varying pumping and injection rates for enhancing remediation; the results were compared with those of a traditional recirculation well system with constant injection/extraction rates. We performed sensitivity analyses to determine the optimal values of four operational parameters associated with the effects of temporally variable pumping or injection rates on the cumulative swept area of injected chemical amendment for a given operation time or cumulative injected volume, which are good measures of remediation and economic efficiency. The findings of this study provide insight into the mechanical process of plume spreading in response to injection/pumping operational strategies, and demonstrate that enhanced plume spreading is a key requirement for achieving sufficient contact between chemical amendments and contaminants.