Pb on groundwater particles, Door County, Wisconsin

Pb was detected on groundwater particles larger than 0.45 μm. Pb concentration (micrograms per liter) showed positive correlations with particle concentration (milligrams per liter) at five sampled wells, although the slopes of the best-fit lines were different. X-ray fluorescence scans suggested that the particles primarily consist of K-Al silicate minerals, and that Pb is absorbed onto Fe oxyhydroxide coatings on Mg-rich silicates. Particle compositions varied at wells, but remained consistent at each well through the sampling period of a month. The particulate nature of Pb in groundwater could cause the spatial and temporal variations due to: (1) the unique composition of particles at wells, (2) the irregular pathways for groundwater particles, (3) the unpredictable amount of Pb-carrying particles entering the groundwater system during recharge events, and (4) the irregular sampling of groundwater particles subsequently dispersed along the advective flow path.