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From 1979 to 1989, ten million tons of phosphogypsum, a waste by-product of the Greek phosphate fertilizer industry, was disposed into an abandoned limestone quarry in Schistos former waste site, Piraeus (Greece). The quarry has been recently closed and remediated using geomembranes and thick soil cover with vegetation. A part of the deposited phosphogypsum has been exposed due to intense rainfall episodes leading to concerns about how could potentially released radioactivity affect the surrounding environment. This study seeks to assess the environmental impact of the phosphogypsum deposited in the Schistos quarry, using laboratory-based γ-ray spectrometry measurements and geographical information systems. Radioactivity concentrations were mapped onto spatial-data to yield a spatial-distribution of radioactivity in the area. The data indicate elevated (226)Ra concentrations in a specific area on the steep south-eastern cliff of the remediated waste site that comprises uncovered phosphogypsum and is known to be affected by local weather conditions. (226)Ra concentrations range from 162 to 629 Bq/kg, with an average activity being on the low side, compared to the global averages for phosphogypsum. Nevertheless, the low environmental risk may be minimized by remediating this area with geomembranes and thick soil cover with vegetation, a technique, which has worked successfully over the remainder of the remediated quarry.

Abstract. The operation of a phosphate fertilizer industry in Drapetsona, near Piraeus port (Greece), resulted in the deposition of 10 million tons of phosphogypsum(PG) into an old limestone quarry, in the period 1979-1989. The whole deposit has been recently remediated using geomembranes and thick soil cover with vegetation. The purpose of the present study was to characterize representative samples of that phosphogypsum, using diffraction (powder-XRD), microscopic (SEM-EDS), analytical (ICP-MS), and spectroscopic techniques (High-resolution γ-ray spectrometry and XRF). The material contains crystalline gypsum (CaSO 4 .2H 2 O) and Ca-Si-Al-S-F (chukhrovite-type/ meniaylovite) phases. The natural radioactivity is mainly due to the 238 U series and particularly 226 Ra (average: 462 Bq/kg), which is relatively low compared to PG from the rest of the world. Furthermore, leaching experiments using local (Attica) rainwater, together with ICP-MS, were performed to assess the potential release of elements in the environment.

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