From Groundwater Vulnerability Mapping to Investigation Priorities: A DRASTIC-Inspired Sensitivity Analysis in Debrecen, Hungary

Spatial investigation planning under data scarcity requires a clear separation of source evidence, pathway assumptions, and decision preferences. We evaluated conditional groundwater investigation priorities in Debrecen, Hungary, using published As and Pb topsoil screening rasters, a DRASTIC-inspired pathway proxy, and heuristic soil-retention scenarios. The reference depth scenario combined 14 stations of the Municipal Environmental Control System (KER) and 16 water-authority monitoring stations covering 1 September 2025–22 August 2026, with separate network scenarios used to examine sensitivity to the monitoring source. At 500 m spatial support, using a nominal 20% area quota within each decision rule, the screening-only and multiplicative selections differed across 11.8% of the study area for As and 9.5% for Pb. Depending on the weighting assigned to the decision rules, areas with a preference-weighted mean selection frequency of at least 0.80 covered 4.2–5.0% of the study area for As and 2.5–4.1% for Pb. Groundwater observations from the KER network showed persistent As exceedance at KER04, while Pb and Cd remained below their comparison thresholds at the locations and sampling occasions assessed within the study polygon. The results demonstrate that investigation priorities depend on the decision rule and the assumptions used to represent subsurface pathways.