A high-speed subterranean problem
Beneath the fertile Friulian Plain in northeastern Italy, a vast and swift-moving plume of industrial pollution travels unseen through the groundwater. This contamination consists primarily of chlorinated aliphatic hydrocarbons, specifically the industrial solvents tetrachloroethylene (PCE) and trichloroethylene (TCE). These chemicals, widely used for metal degreasing and dry cleaning, have seeped into one of the region's most important freshwater resources. The source of the pollution traces back to decades of industrial activity in the upper plain.
The hydrogeology of the region is the principal reason for the plume's rapid and extensive spread. The Friulian Plain is divided into two distinct zones: the High Plain and the Low Plain. The High Plain is a succession of alluvial fans created by Alpine rivers, composed of coarse-grained sediments like gravel and sand. This composition creates an unconfined aquifer with extremely high permeability—in some areas, hydraulic conductivity is as high as 10⁻² meters per second. This geological setting allows the dissolved solvents to travel with the groundwater flow at an exceptional speed of approximately 500 meters per year. Over four decades, this has resulted in a contaminant plume stretching more than 20 kilometers.
Tracking invisible toxins
Mapping and understanding the full extent of this contamination is a complex hydrogeological task undertaken by environmental agencies like ARPA FVG. The process involves a network of monitoring wells to sample groundwater and measure the concentration of PCE, TCE, and their degradation products. These chemicals are denser than water and can sink deep into an aquifer, forming what are known as Dense Non-Aqueous Phase Liquids (DNAPLs), making tracking and remediation exceptionally difficult.
The concentrations of these solvents in affected areas have been found to far exceed legal limits for drinking water. The European Union's drinking water directive sets a combined limit for PCE and TCE at 10 micrograms per liter (µg/L). The presence of these compounds restricts the use of the groundwater for drinking and agricultural purposes, impacting a resource important for the region's population and economy. The contamination primarily affects the shallow, unconfined aquifer of the High Plain, which directly feeds the multilayered artesian aquifer system of the Low Plain, risking the entire groundwater system. Remediation strategies are challenging due to the scale and depth of the plume and include methods like "pump and treat" systems or in-situ bioremediation, where microorganisms are used to break down the contaminants.