The Potential Heavy Metal Pollution Transfer to Surface Water and Groundwater in an Old Mining Area of Hubei, China

As a typical historical mining city, Daye, Hubei, faces potential heavy metal migration risks from legacy mining activities. This study conducted a grid-based survey in 2020, analyzing 389 soil and 137 water samples using the Nemerow Pollution Index (NPI) and spatial statistics to assess pollution and transfer mechanisms. Results show that soils were significantly contaminated (average NPI = 5.40), with 71.03% of samples exceeding the pollution threshold (NPI > 1), whereas surface water (0.18) and groundwater (0.11) maintained good quality. Despite limited direct soil migration, atmospheric wet deposition was identified as the probably dominant pathway driving higher concentrations of Cu, Cd, Pb, and As in surface water than in groundwater (e.g., on average, Cu and Cd levels in surface water were ~1.7-fold and ~5-fold those in groundwater, respectively, all well below Class III limits of national water quality standards). This study clarifies the mechanism protecting water bodies amid severe soil contamination and provides a scientific basis for integrated soil–water management in post-mining regions.