Temporal moment-based approach to understand the dissolved-phase LNAPL recovery and associated characteristics in the porous system under dynamic groundwater table conditions

Abstract

Abstract The dissolved-phase hydrocarbon recovery can be the first step in decontaminating the soil–water system if spilled with light/dense non-aqueous phase liquid (L/D-NAPL). This study proposes a temporal moment-based approach to investigate the effectiveness of groundwater table manipulations for recovering dissolved-phase byproducts of light non-aqueous phase liquid (LNAPL) from the subsurface system. Temporal moments were computed utilizing experimentally observed and HYDRUS-simulated dissolved-phase toluene concentration data, representative of LNAPL, under stable and dynamic groundwater table fluctuation (GWTF) scenarios. Zeroth temporal moment (ZTM) showed that the hydrocarbon mass recovery varied from 1,804 to 5,190.6 mg/L × h, with the highest variation for the rapid GWTF scenario. An increase in the ZTM of hydrocarbon was observed with an increase in the rate of change of magnitude of the water table and pore velocity fluctuation as in the case of a rapid GWTF as compared to a stable GWTF case. The value of mean residence time for the stable groundwater table case was highest for the entire experimental duration, followed by slow, general, and rapid cases. Temporal moment analysis revealed that the high dissolved-phase hydrocarbon recovery could be achieved by manipulating groundwater table conditions. The present study provides a powerful technique to improve dissolved hydrocarbon remediation in mineral aquifers using hydrological restorations.