Estimation of emission from an LNAPL contaminated zone considering groundwater recharge

The aim of this work was to develop an easy to handle semi-analytical method to estimate the temporal development of emission from a multi-component LNAPL pool considering groundwater recharge. The presented approach allows the estimation of the total mass flux out of an LNAPL pool into the gas and the water phase, the latter including the mass fluxes from groundwater recharge, advection through and diffusion out of the LNAPL zone. Therefore, the known set of constitutive relationships to determine fluid saturation profiles of 2- and 3-phase systems is extended in this work to account for dynamic conditions due to groundwater recharge. The methodology is applied to a kerosene pool at a former military airfield and it is found that the mass flux due to groundwater recharge dominates the aqueous mass flux from the kerosene contaminated zone. A sensitivity study using field parameters shows, that the apparent kerosene thicknesses observed in monitoring wells and the lithology control mass flux into the gas phase, whereas the mass flux into groundwater mainly depends on the groundwater recharge rate. For the kerosene found at the site, source emission into the soil gas is estimated to last longer than the emission into groundwater, the latter varying between less than 100 and 400 years.