15. Characterization of a Contamination Event

This chapter provides a methodological approach for the characterization of a contamination event. This includes an examination of both the unsaturated (i.e., soil, soil gas and pore water) and the saturated media (i.e., soil and groundwater), and is structured around three main phases, i.e., collection and organization of existing data, development of a conceptual model, verification of the hypotheses made in the conceptual model through targeted investigations and sampling. After illustrating different strategies available for defining the sampling design, sampling techniques for the different phases of the unsaturated and saturated media are described. In the unsaturated medium, soil sampling can be carried out through rotary or direct push techniques; active and passive sampling methods are available for the collection of soil gas samples; lysimeters or filter-tip samplers can be used for sampling pore water. Sampling of the saturated medium should allow to obtain a three-dimensional reconstruction of the contaminated areas. Hence, recommendations on the spatial distribution of monitoring wells, on the available options for vertical sampling and on well-purging prior to sampling are provided. These aspects are fundamental for ensuring the collection of representative samples. Subsequently, the most important aspects that need to be kept into account when planning a sampling campaign are illustrated, in particular as regards sampling rate, sample collection method, sampling devices (e.g., bailers, pumps). On site measurement of water quality parameters is also considered, and the possibility of filtering samples during collection is discussed. Quality assurance and control protocols aimed at ensuring accuracy, precision and defensibility of acquired data are then illustrated. Finally, a brief overview of sample storage, blank collection and sampling materials is provided.