Lead (Pb) occurrence and sources and aqueous geochemistry were assessed in private wellhead and tap water at a targeted area of concern for possible exceedances and at a control area in the same geologic formation, and in wells at a nearby landfill in south-central Massachusetts (MA). Total Pb concentrations were below the U.S. Environmental Protection Agency (USEPA) Action Level of 15 μg/L in all samples, and about 6% of unfiltered samples contained Pb concentrations that exceeded 1.0 μg/L. Pb concentrations were higher under conditions that are acidic and oxic (pH ≤ 6.5 and dissolved oxygen [DO] ≥ 2 mg/L), in which minerals that could sequester lead or manganese typically are undersaturated, and adsorption by hydrous ferric oxide is limited. Under more neutral to alkaline conditions, the precipitation of Pb in solid solution series minerals such as (Ca,Pb)CO3 and (Ba,Pb)SO4 2, and adsorption by amorphous ferric hydroxides, could limit Pb solubility in the bedrock aquifer or in t ...