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© Cyril FRESILLON/ISTO/CNRS Photothèque
Close up of a sediment core taken from the sand filter after being cut lengthwise. The sand filter is a water purification device located under the Quai de la Madeleine in Orléans. It filters some 7 million cubic metres of wastewater and rainwater from the north of the city each year which is then channelled to treatment plants downstream. The conical basin is 17 m deep and is entirely buried underground. The sediment accumulated since the construction of the basin in 1942 will help researchers reconstitute more than 70 years of local history. The renovation of the sand filter was the perfect opportunity to take core samples of the sediment and examine its content. The diversity and the changes in the markers observed over time open up new perspectives on the chronology of events across the catchment area, with the focus on issues of major concern such as public health, pollution, biodiversity, transportation and the power supply.