Physical pollution of karst aquifers caused by marble quarrying: the case of the Apuan Alps, Italy

Abstract

The Apuan Alps are a mountain range in northern Tuscany exploited for the famous Carrara marble since the Roman age. The Apuan quarrying district currently comprises about 150 quarries and most of them are located at high elevations. Marble blocks are cut and re-squared by means of line drilling and various sawing techniques, diamond wire and chain saw being the most used. Such quarrying activities produce a fine marble powder that frequently mixes up with meteoric water, producing a slurry that can easily infiltrate into the karst aquifers through solution-enlarged fractures. Depending on the aquifer hydrodynamics, the marble slurry can eventually reach the karst springs, thus contaminating high quality waters generally used for the human consumption. Several samples of marble powder, karst spring deposits, and stream sediments were collected and analyzed for their mineralogical, morphological and sedimentological characterization, to evaluate the degree of pollution of the Apuan karst aquifers. Quarry powder samples are mainly made up of calcite crystals, whereas spring and stream sediment samples have variable proportions of calcite, silicates, and dolomite grains. The clasts from marble powder produced by diamond wire and chain sawing have constant morphological features, whereas the sediments collected in filtering tanks and disposal bags exhibit more heterogeneous characteristics. The quarry powders are generally finer than the sediments, although some overlap occurs probably because of marble powder contamination in the sediments themselves. The most polluted spring samples are characterized by a predominant calcite component that is finer than the silicate one. The same occurs also for the stream samples. Spring samples also show homogeneous morphometric features that are probably related to both marble powder contamination and the transport mechanisms through the karst aquifers. Marble powder pollution appears to be widespread in most of the Apuan karst springs, thus affecting the aquifer hydrodynamics and water quality.