Numerical simulation of a steam-injection pilot study for a PCP-contaminated aquifer

The following study was focused on the simulation of a steam-injection field pilottest conducted in our past research. The scope of research contained two main subjects: heat transfer and contaminant transport when steam was injected into a pentachlorophenol (PCP)-contaminated aquifer. Numerical simulation of the heat transfer during the field test showed that vertical permeability is more influential to the distribution of water temperature than the horizontal permeability. If the vertical permeability is relatively high, the steam in the aquifer has a higher tendency to migrate upward and cause the aquifer temperature to rise faster. The simulation results also showed that heat convection is very sensitive to the soil permeability. Therefore, high permeability media makes the effect of heat convection more important on applying the steam-injection method. Heat conduction dominates the heat transfer within the hot aqueous zone. However, the hot aqueous zone is relatively smaller than the steam zone when steam is injected into the aquifer. Therefore, heat conduction is not as important as heat convection within the steam zone, which is the same result observed in the field test. Specific heat of soil media is also a sensitive factor. A numerical simulator, T2VOC, was utilized to simulate the PCP transport in the aquifer when steam was injected into the aquifer. The results showed that the shape of PCP distribution was identical to that of steam. It illustrated thatthe steam carried PCP upward and laterally. The high vertical soil permeability causes the steam to migrate upward with PCP easily. A low partitioning coefficient allows PCP to be desorbed easier, also an important factor. A majority of the PCP in the soil was transferred to the aqueous phase as the water temperature increased, showing similar results to those observed in the field test. According to the sensitivity analysis, PCP transport is more sensitive to the vertical permeability than the partitioning coefficient. The steam-injection rate is also an important operation parameter and may determine the success of the remediation work.