Monitoring composition of LNAPL. Essential tool for the estimation of free LNAPL specific volumes

In an aquifer contaminated by LNAPLs, several types of LNAPL can been find with different composition and features, which influence its fate and transport in groundwater and the estimation of its volume. Over time, two different models have been developed for the free phase volume estimation: Pancake Model and Vertical Equilibrium Model. A sensitivity analysis has been carried out, using both models, to evaluate the influence of LNAPL type on volume estimation. This analysis has been carried out applying in every examined monitoring well the features of three different LNAPL types: gasoline, diesel and their mixtures. The results show a sensible variation of estimated specific volumes as LNAPL type varies. Hence, as it can been deduced, the knowledge of LNAPL type and its characteristics are fundamental for a reliable volume estimation. In addition, since the LNAPL type can change over the time, when a contaminated site is monitored for the evaluation of LNAPL volumes, it is fundamental observe during the time, not only the supernatant thickness in the well, but also the compounds constituting the LNAPL, through the sampling of supernatant and its analysis.