Despite analytical and interpretive challenges, groundwaterage data can be valuable for improving groundwater fl owmodels, reducing model uncertainty, and providing deeperinsights into subsurface fl ow dynamics, recharge sources,and aquifer vulnerability. This study applies groundwater agetracers to enhance a Modfl ow numerical model of theMuravera coastal plain aquifer (SE Sardinia, Italy), which isaffected by saltwater intrusion. Multiple tracers were used(3H, He, CFC, SF6, and noble gases) in combination withisotopic and geochemical data. Measured noble gasconcentrations in saline samples were corrected in a pre-processing step to remove the infl uence of seawater, then thePANGA code was used to compute recharge parameters forthe freshwater component. Minimum values for samplemean ages were estimated using the TracerLPM software,which indicated that tracer concentrations are consistentwith a bimodal mixing model that includes a premoderncomponent (recharged prior to 1950) and modern componentof variable age. These measured minimum sample meanages were compared to the simulated mean age of water atthe same well locations computed in the numerical modelusing Modpath particle tracking. Modelled heads werecompared to over 4000 head observations from roughly 350wells with weights assigned to account for data qualityvariability. Adjusted parameters included riverbedconductance values (governing river recharge), general headboundaries, irrigation well yields, areal and lateral rechargerates, and hydraulic conductivity. Inclusion of thegroundwater ages revealed important recharge contributionsfrom specifi c stream segments where infi ltration waspreviously considered minor. The dating methods thus substantially improved model representation of interactionsbetween groundwater and the streams in the plain, makingthe fl ow model a more reliable and valuable tool formanaging this alluvial aquifer threatened by intense salineintrusion.
Improving a numerical model with groundwater age tracers: a case study from the Muravera coastal plain (Italy)
Porru Maria Chiara;Arras Claudio;Piscedda Fabrizio Antonio;Biddau Riccardo;Da Pelo Stefania
2024-01-01
Abstract
Despite analytical and interpretive challenges, groundwaterage data can be valuable for improving groundwater fl owmodels, reducing model uncertainty, and providing deeperinsights into subsurface fl ow dynamics, recharge sources,and aquifer vulnerability. This study applies groundwater agetracers to enhance a Modfl ow numerical model of theMuravera coastal plain aquifer (SE Sardinia, Italy), which isaffected by saltwater intrusion. Multiple tracers were used(3H, He, CFC, SF6, and noble gases) in combination withisotopic and geochemical data. Measured noble gasconcentrations in saline samples were corrected in a pre-processing step to remove the infl uence of seawater, then thePANGA code was used to compute recharge parameters forthe freshwater component. Minimum values for samplemean ages were estimated using the TracerLPM software,which indicated that tracer concentrations are consistentwith a bimodal mixing model that includes a premoderncomponent (recharged prior to 1950) and modern componentof variable age. These measured minimum sample meanages were compared to the simulated mean age of water atthe same well locations computed in the numerical modelusing Modpath particle tracking. Modelled heads werecompared to over 4000 head observations from roughly 350wells with weights assigned to account for data qualityvariability. Adjusted parameters included riverbedconductance values (governing river recharge), general headboundaries, irrigation well yields, areal and lateral rechargerates, and hydraulic conductivity. Inclusion of thegroundwater ages revealed important recharge contributionsfrom specifi c stream segments where infi ltration waspreviously considered minor. The dating methods thus substantially improved model representation of interactionsbetween groundwater and the streams in the plain, makingthe fl ow model a more reliable and valuable tool formanaging this alluvial aquifer threatened by intense salineintrusion.
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