Numerical Modeling of Remediation Scenarios of a Groundwater Cr(VI) Plume in an Alpine Valley Aquifer

This work presents the numerical modeling of remediation scenarios aimed at containing and attenuating the groundwater pollution by Cr(VI) sourced from a steelworks area that affects the Alpine aquifer system in the Aosta Plain (N Italy). Here, groundwater is used for drinking water supply and food and beverage production, so the adoption of remediation works is urgently needed. More specifically, three remediation scenarios were modeled using MODFLOW-2000 and MT3DMS: (a) the activation of a hydraulic barrier to contain the pollution within the source area (Scenario 1); (b) the removal of the pollution sources and the natural attenuation of the residual groundwater plume (Scenario 2); and (c) a combination of the previous two works (Scenario 3). Model results for Scenario 1 showed that a hydraulic barrier composed of five wells located along the eastern border of the steelworks area would contain Cr(VI) concentrations above 5 µg/L (i.e., the Italian regulatory limit) within the steelworks area; the barrier would have a total discharge of 27,500 m3/day, which could be compensated by the deactivation of three steelworks wells; the hydraulic barrier would drop the Cr(VI) concentrations below 5 µg/L in the areas downstream of the steelworks after ~3 years from its start of operation. Results for Scenario 2 highlighted that the removal of the Cr(VI) sources would drop the Cr(VI) concentrations below 5 µg/L in the areas downstream of the steelworks after ~2.5 years, and lead to a full remediation of the Cr(VI) groundwater plume (i.e., total Cr(VI) mass in the aquifer close to zero) after 17 years. Results for Scenario 3 showed that the removal of the Cr(VI) sources accompanied by the activation of the hydraulic barrier would led to a faster remediation within the first 14 years from the starting of the remediation works, with concentrations below 5 µg/L in the areas downstream of the steelworks obtained after ~2.3 years