A 1984-1985 investigation by the New Jersey Department of Environmental Protection and the Sussex County Health Department revealed that 13 out of 56 private well owners in Lafayette Township, New Jersey, had lead concentrations in their plumbing tap water exceeding 50 parts per billion (ppb). Plumbing system sources for lead were rejected because high concentrations persisted even after water continuously flowed through the system for 15 min before sample collection. Investigators concluded that the source of the elevated concentrations of lead was groundwater. It was proposed that lead was being released into groundwater from galena (PbS)-mineralized fracture zones in the local dolomite aquifer. In 1994, the New Jersey Geological Survey initiated a study to determine the mobilization and transport of lead from the galenamineralized fractures to local wells. Preliminary sampling at 74 sites revealed that groundwater is not transporting significant concentrations of lead (90% <3 ppb and 0% >50 ppb), as concluded a decade earlier. This disparity resulted in plumbing system sources of lead also being investigated. Results of time-series sampling at three sites indicated that well water has much lower lead concentrations (<3 to 6 ppb) than connected plumbing tap water (<3 to 1600 ppb), and concentrations in tap water varied erratically. Lead 206/207 isotope ratios of tap water samples with elevated lead concentrations matched plumbing components, particularly brass. Ratios associated with lower lead concentrations in well and tap water are more similar to lead in galena (PbS) from the mineralized zone. The variable lead concentrations in tap water are consistent with the intermittent release of corroded pipe products or a lead-bearing scale such as cerussite (PbCO 3 ). Cerussite scale has since been identified in a brass valve from the local elementary school by using x-ray diffraction.