NAPL spill modeling and simulation of pumping remediation : NAPL modellering och simulering av pumpning

Abstract

This Master Thesis presents TMVOC simulations of a NAPL-spill (non-aqueous phase liquid) and following pumping remediation. TMVOC is a simulation program for three-phase non-isothermal multicomponent flow in saturated-unsaturated heterogeneous media. The models presented are based on an actual remediation project. The aim of the thesis was to study if the historical development of the NAPL-spill could be simulated and how long time the pumping remediation would take. A 3D-model and a radially symmetric cylindrical model were created. A large effort of the work done was in taking the complex TMVOC model in use and modifying it for the problem at hand. Therefore, the numerical results of the simulations should be considered as preliminary and as forming basis for future studies. The results from the spill simulation and historical pumping simulation indicated that the spill volume could be less than the estimated 1400 m3, perhaps around 700 m3, assuming a leakage time of 30 years. The historical pumping simulation of a 700 m3 diesel spill showed good agreement with measured values for some wells, but overestimated the recovery in other wells. The overestimation could be due to the fact that the 3D-model did not take seasonal changes in the groundwater level into consideration. Also, the model did not account for any heterogeneity or compartmentalization in soil material properties that could explain the differences between the wells.  Assuming the same spill of 700 m3, future pumping was simulated. The results from these simulations indicated the remediation time to be long due to fast decreasing mobility of the NAPL phase. The NAPL flow rate to the wells was halved in a couple of years. Much of the NAPL was distributed over a large area at near residual saturation with the highest NAPL saturation found at the opposite side of the pumping wells in the model.   Future simulation studies should address the effect of discretization as well as the effect of uncertainties in material properties e.g. conductivity, residual NAPL saturation and soil heterogeneity