Groundwater samples directly beneath a waste disposal site have been shown to contain a higher concentration of sulfolane and a relatively low concentration of thiolane. The sulfolane is a source compound of thiolane, a reduced from of sulfolane. In subsequent analyses of groundwater samples, these compounds have been detected from all of the monitoring wells in the study area. Since these compounds are present together in an aquifer, a possible competition, that can happen in such a system has been investigated. Thiolane is a nonpolar heterocyclic organic compound whereas sulfolane is a weakly acidic dipolar solvent. As expected, thiolane adsorbs more strongly onto clay than sulfolane in a single solute system. For regression of bisolute system using Matlab to obtain Q (maximum number of moles of solute adsorbed per unit weight of adsorbent), k₁, (constants related to the energy of adsorption for sulfolane), and k₁, (constants related to the energy of adsorption for thiolane), the k₁ value (sulfolane) is smaller than the k₂, value (thiolane) which reflects that thiolane is more strongly adsorbed than sulfolane. This is strongly consistent with the result obtained from single solute system. The Q for the sulfolane and combined data is the same that indicates that the sulfolane data is dominantly fitted because the concentrations of surfolane are much greater than those of thiolane in the experiments. In combined data regression, the suppression of sulfolane adsorption on clay was also observed by the presence of thiolane.