Spectrofluorometric characterisation of Non-Acqueous Phase Liquid contaminations

The reclamation of polluted sites is a very complex operation, in which many different aspects have to be taken simultaneously in consideration. These vary from the hydrodynamic characterization of the subsurface where the contamination is detected, to the spread of the contamination and the properties of the contaminants themselves. Therefore, high resolution characterisation techniques are widely used for the reclamation of polluted sites. Their advantage consist in collecting many and detailed information in order to localise precisely the contamination and proceed to its reclamation. Fluorescence detection instruments are rising increasing interest in this sector, among which the most performing is the Optical Image Profiler tool by Geoprobe, “OIP”, able to detect in real time the presence and the spread of a contamination, once mounted on a logging tool. This work focuses on high resolution characterisation of contaminants, based on fluorescence detection techniques, with the aim of obtaining a quick, wide and detailed fingerprint of contaminants. Firstly, lab measurements of pure samples of gasolines, diesels and oils were conducted using an Agilent Cary Eclipse spectrofluorometer. The fluorescent spectra and the Excitation Emission Matrices of several compounds were studied, obtaining their fluorescent emission over the entire spectrum. This result has been achieved by exciting with a fixed wavelength step the samples, and registering the subsequent emission in a wavelength range between 200 nm and 800 nm. The front-face analysis mode resulted to be more performing compared to the traditional right-angle one, allowing also to retrieve a match with the site’s results obtained through the OIP probe used on field. Then, the study focused on the interaction of these pure hydrocarbons’ samples once placed in contact with a soil matrix collected on field. The aim was to ascertain whether changes in the fluorescent behaviour of these substances might be observed. Effectively, consistent differences could be retrieved between the observation of the supernatant fraction and the analysis of a hydrocarbon’s saturated soil. Ultimately, the behaviour of a real polluted site’s sample was analysed to verify whether a match between lab analysis and the effective complexity presented by a pollutes sites could be found. In conclusion, the research procedure applied to the samples resulted to be quick and efficient, allowing to acquire a wide mole of information, which led to the acquisition of a proper database of the emissive contaminants’ response. This innovative characterisation approach permits to distinguish and recognise pollutants according to their typical fluorescent emission, finding similarities and common patterns among same contaminants. Moreover, this permitted to avoid a previous preparation and treatment of the analysed samples. Such approach represents a great advantage, that allows to reduce the complex and time-consuming operation usually needed for the study of a detected contamination. From the results obtained from this study, future developments might be foreseen, widening the applicability of the fluorescence-based techniques for the detailed characterisation of polluted site’s samples.