On-site investigations of hydrocarbon contaminated soil by the Pollut-Eval methodology

The Pollut-Eval method is based on the Rock-Eval pyrolysis method, founded on an IFP patent that has been used for decades for oil prospecting in sedimentary basins all over the world. This equipment provides data on the quantity and the quality of organic matter in sedimentary rocks. With the increasing demand for cost effective and rapid contaminated site diagnosis, it became obvious that the field of application of the Rock-Eval technology should be enlarged to environmental problematic. The Pollut-Eval methodology was developed since 1996 and firstly qualified through the design of a laboratory version. Compared to the previous apparatus dedicated to the geochemistry, innovations allow acquisition of data for accurate quantification of complex organic pollutants and mineral carbon distribution. New methods were developed especially for the characterisation of hydrocarbon pollutants in soil. Compared to kerogen analysis, the characterisation of light petroleum cuts entrapped in soil as pollutants was available by the design of an adapted refrigerated auto-sampler. The prevention of the loss of the high vapour tension pollutants couldn't be avoided for the new environmental field of applications. Site after site, the various experiments involving the 'laboratory' version of the Pollut-Eval analyser extended the application field of the methodology. The efficiency of the thermal extraction applied directly on the soil showed useful advantages compared to conventional solvent extraction techniques, especially for pollutants originating from former gas plants. The method was especially suitable for the determination of the complete carbon mass balance in the case of non-extractable organic pollutant such as coal tar or for heavy petroleum cut such as heavy fuel, vacuum distillation residue and bitumen. By the way, the Pollut-Eval method became rapidly complementary to more conventional GC quantification dedicated to complex organic pollution characterisation. By the lack of sample pre-treatment and the adaptation of a cooled auto-sampler, short time analysis suited for light petroleum pollutant such as gasoline and kerosene. The simple protocol applied to the soil appeared rapidly suitable for keeping the track of depollution process efficiency. During its qualification, the analyser has been involved in rehabilitation process evaluation by analysing various contaminated soils before and after clean-up treatment. From 1999, IFP was frequently asked for on-site diagnosis involving Pollut-Eval methodology. So, IFP installed this lab equipment in a mobile van in order to qualify the methodology through real time and on-site diagnosis. In addition to the qualification program, the aim of the project was also to identify the analytical parameters available in the method and sufficient for field contaminated soil characterisation. During 2 years, all over France, IFP, Gester and Vinci Technologies gathered their effort to ensure 10-site diagnosis. The variety of pollutants encountered has enriched a data base that has been included in a user guide. The gathered experience ended by the design of a compact apparatus dedicated to field analyses. Its small size and weight (less than 20 kg) was designed to perform on-site and autonomous characterisations. (authors)