Variation of geochemical risk associated with the use of ophiolitic washing muds as refilling material in a basalt quarry of the Northern Appennine (Italy).

Ophiolitic sequences in Northern Apennines are usually exploited as source of raw material for civil engineering works. Grinding procedures of basalts imply the production of dusts with relatively high concentration of PHES. This paper studied the increase of geochemical risk when washing mud produced at Sasso di Castro quarry site (Tuscany) is reused as rock keeper in a near dismissed quarry and highlighted geochemical fractionation produced on the base of different mineral hardness. Co, Cr, Ni and V concentration measured in washing mud were higher than the limits fixed by the Italian law but compatible with background values. The mobility of these four elements during future weathering processes were estimated by considering the element transfer coefficients and assuming weathered rocks and soils as two different natural analogues of the future state of washing mud. The future concentration was estimated by considering the average lifetime of mineral grains calculated through their dissolution rate, molar volume and grain diameter. The variations of geochemical concentrations were used to estimate the percentage increase of the geochemical risk at the displacement place. After 50 years the associated geochemical risk is still considerably lower than the probability to be damaged by a single landslide event.