Model-Based Analysis of the Link between Groundwater Table Rising and the Formation of Solute Plumes in a Shallow Stratified Aquifer

Groundwater table rising (GTR) represents a well-known issue that affects several urban
and agricultural areas of the world. This work addresses the link between GTR and the formation of
solute plumes from contaminant sources that are located in the vadose zone, and that water table
rising may help mobilize with time. A case study is analyzed in the stratified pyroclastic-alluvial
aquifer near Naples (Italy), which is notoriously affected by GTR. A dismissed chemical factory
generated a solute plume, which was hydraulically confined by a pump-and-treat (P&T) system.
Since 2011, aqueous concentrations of 1,1-dichloroethene (1,1-DCE) have been found to exceed
regulatory maximum concentration levels in monitoring wells. It has been hypothesized that a
1,1-DCE source may occur as buried waste that has been flushed with time under GTR. To elucidate
this hypothesis and reoptimize the P&T system, flow and transport numerical modeling analysis was
developed using site-specific data. The results indicated that the formulated hypothesis is indeed
plausible. The model shows that water table peaks were reached in 2011 and 2017, which agree
with the 1,1-DCE concentration peaks observed in the site. The model was also able to capture the
simultaneous decrease in the water table levels and concentrations between 2011 and 2014. Scenario-
based analysis suggests that lowering the water table below the elevation of the hypothesized source
is potentially a cost-effective strategy to reschedule the pumping rates of the P&T system.