Integrated approach in the management of a jet fuel contaminated site. The Decimomannu air base (CA, Sardinia)

Usually, the design of remediation interventions in polluted sites is carried out based on the characterization data, which are aimed at acquiring the necessary parameters for the Risk Assessment, often utilized for the defiition of the remediation targets. These data are often, unfortunately, insuffient to identify the best remediation strategy. In particular, the remediation strategy/plan is usually defied based on characterization data collected (many) years before and that do not take into account the natural “aging” of potential secondary sources of contamination. This aspect is particularly relevant in the case of fuel contamination, complex mixtures of hydrocarbons that contain categories of substances with signifiantly diffrent chemical / physical and biodegradability properties. In the initial phase of the spill, or however when the primary source is active, the most soluble components (i.e. BTEX) are mobilizable in the groundwater flw and aerobic biodegradation processes are active on the more readily degradable fractions (linear hydrocarbons with shorter chain). The progressive aging of the contamination source corresponds to a depletion of the more mobile and degradable fractions, with the accumulation of high molecular weight fractions, less transferable to both aqueous and soil gaseous phase. Therefore, the accurate characterization of the residual phase’s real characteristics allows the defiition of the best remediation strategy. An illustrative case history is here presented concerning the Military Airport of Decimomannu (CA), affcted by various aviation fuel (JP8) spills in 2007 (40000 l), in 2009 (5000 l) and in 2010 (5000 l). The creation of a “4D” geographical database (which also considers the timing factor) allows the integrated management, representation and analysis of diffrent data (geological, hydrogeological, hydrogeochemical and geophysical). The data used for the construction of a georeferenced database, have been enriched by fild hydraulic tests and detailed speciation, through GC-MS, of supernatant that has been occasionally detected over the years in the piezometric monitoring network. A campaign has been conducted on the site with the UVOST-LIF (Laser Induced Fluorescence) technology, the fist performed in our country, which allowed to delimit the volumes of subsoil previously impacted by the primary spills. The laboratory and fild investigations carried out have made it possible to identify the presence of contaminants in the residual phase. Based on the results, an in situ enhanced chemical desorption strategy was implemented to increase the desorption of hydrocarbons adsorbed to saturated soils or at the capillary fringe and to increase the product recoverability in a separate phase. The hydrocarbons are made available in the dissolved phase or in a separate phase with lower viscosity, allowing a subsequent rapid and effctive physical recovery. The integration of the large amount of information has allowed to outline a conceptual model of the site more representative of the current situation and essential for defiing the correct intervention strategy.