Un singolare plume di cloruro di vinile in acquifero confinato: campionamento a basso flusso in sondaggi direct-push e fingerprinting isotopico preliminare.

The paper deals with an alluvial sandy confined aquifer contaminated by vynil chloride and located in the eastern sector of the Padana plain immediately to the south of the Po river and about 3 km to the north of the city of Ferrara (Northern Italy). Plume investigation followed three steps in temporal succession and with a progressive downscaling: 1) a regional hydrogeological characterization of the aquifer watershed, intended as the whole of the recharge and transmission area of the groundwater reservoir; 2) a hydrochemical survey of existing long-filtered boreholes (wells, piezometers) with a gross definition of the plume; 3) a direct-push drillings based horizontal and vertical characterization of the plume conducted according a dynamic investigation work-plan. The investigated land size has been, respectively, 35, 20 and 6 km2; the plume resulted with a length of 3 km and a maximum width of about 0.5 km. The first step of the investigation, based on the interpretation of collected stratigraphic logs, two piezometric surveys in opposite hydrological conditions and one 3 days pumping test, put in evidence lateral recharge of Po river and the leaky character of the aquifer; the second step, based on 37 boreholes sampling, identified, inside a fully urbanized area, 10 boreholes with VC concentration higher than MAC (3 with values higher than 1000 ppb and one higher than 8000 ppb); the third step, with a total of 15 direct-push drillings down to a maximum of 30 m depth with 3 GW samples for each, put in evidence also the vertical occurrence of the contamination. It has been verified also the effectiveness of GW sampling by a combined use of a inertial pump for collecting the sample preceded by a short term low flow purging by peristaltic pump. The implications for the source definition and plume remediation are also discussed.