Transport and biodegradation modeling of gasoline spills in soil–aquifer system

The leakage from the oil pipeline and storage tank could get into soil and groundwater and lead to contamination. An understanding of the fate of gasoline spills in soil and groundwater is necessary for designing better monitoring systems and remediation strategies. In this paper, the numerical simulation method for the transport and biodegradation of gasoline spills was built by combining Hydrocarbon Spill Screening Model (HSSM) in vadose zone and modified MT3DMS (a Modular Three-Dimensional Multispecies Transport Model) in saturated zone. First, sensitivity analysis of the required time for gasoline through vadose zone was performed. Then, a three-dimensional soil–aquifer system contaminated by a gasoline spill was simulated, the vertical migration and dissolution of gasoline in vadose zone was analyzed by HSSM, and the transport and biodegradation of dissolved benzene in groundwater was computed by modified MT3DMS. The results demonstrate that the transport and biodegradation of gasoline in soil–aquifer system could be simulated by combining HSSM and modified MT3DMS. The sensitivity analysis shows that (1) if the leakage rate is much higher, the required time of gasoline through vadose zone is much shorter, and that (2) if water saturation is much higher, the required time of gasoline through vadose zone is also much shorter. The results for three-dimensional soil–aquifer system show that: (1) Vertical migration of gasoline takes 10.9 days to pass through the 5-m-high vadose zone; (2) the area of oil lens on the groundwater table enlarges about 31 times than that of source in land surface; (3) there are 94.7 % of the total mass of gasoline spills intercepted by vadose zone, and 27 % of the total mass of benzene enters and pollutes more groundwater; and (4) the microbes could grow and propagate rapidly at the place where dissolved benzene and DO (dissolved oxygen) are enough, and the contaminant plumes of dissolved benzene focus on the vicinity of groundwater table.