Remediation procedures of petrol stations: conventional techniques and phytoremediation for reclamation of hydrocarbon based contaminants in the Terni area (Central Italy)

Hydrocarbon contaminants – produced by spillages from storage tanks – are some of the hazardous substances detected in soil and groundwater. The petrol stations in Italy are about 3.4 times higher than the European mean (Tabarelli, 2010). According to the Italian guidelines (DLgs 152/2006), threshold concentrations of contamination are more stringent than in other European countries and USA: thus, due to the high number of potential contaminated areas, the cost for characterization plain and for risk analysis is very high. The present work takes as reference the remediation times and technologies of 25 petrol stations located in the Terni area (Central Italy). The maximum value of total petroleum hydrocarbons (TPHs) in the soil matrix was about 1750 g/l while in groundwater a value of about 184 g/l was registered. The statistical analysis of data from reclamation procedures shows that about 15 sites may be considered – in terms of contaminant levels – as reclaimed. Results showed that the reclamation times are between 5 and 10 years (60% of sites) although some of these are characterized by coarse-grained soils, which increase the efficiency of soil reclamation. So long reclamation periods are due mainly to the delivery of the remediation and risk analysis projects by the companies in charge of remediation, and to the delays by the territorial authorities. The soil removal, the Bioventing and the Soil Vapor Extraction are the most widely used technologies for the unsaturated soil, while Pump & Treat (P&T), the Air Sparging and the Multi Phase Extraction are used to reclaim groundwater. Apart of the costs to remove the contaminated soils, the application of conventional technologies has high management costs and - in some cases - led to a stagnation of the overall remediation process. Taking as reference a site where contaminants in groundwater are present since 1998, a mean cost for the management of reclamation by using P&T and recharge wells has been estimated of about 25,000 Euro/year in period 2010-2013. In order to reduce costs for removing the contaminated soils, the present study proposes, for some sites, the application of phytoremediation technologies by using the plant species: Lolium Multiformum. Although, the phytoremediation of TPHs is still not a proven technology, more in-depth studies on this topic would be useful, because of the low cost and to the low environmental impact of this type of procedure (Collins, 2007). The application of this technique requires a proper evaluation of the soil moisture which has been computed by using the Thornthwaite-Mather method, allowing to define the monthly water to be supplied to the system for an optimal efficiency. Collins C.D. 2007. Implementing Phytoremediation of Petroleum Hydrocarbons. Phytoremediation Methods in Biotechnology, 23, 99-108. Tabarelli D. 2010. La rete carburanti nel 2009: il confronto con l’Europa. Nomisma Energia: www.unionepetrolifera.it (May 23, 2014).