Lead contamination of potable water in new buildings on the University of North Carolina at Chapel Hill campus was traced to corrosion of inline brass plumbing devices. Commissioning procedures to remove lead sediment and hasten brass passivation were developed. Forensic evaluation of a water fountain dispensing > 100 μg/L lead in flushed water after commissioning led to the discovery of ball valves containing brass with > 8% lead by weight on exterior surfaces and > 18% on surfaces contacting the water. Removing these ball valves resolved the lead problems, bench‐testing verified that the valves had a high lead‐leaching propensity, and subsequent surveying of ball valves in three buildings found 22% contained exterior surface lead > 8%. Significant lead‐leaching problems can occur when: (1) the water is at least moderately corrosive to brass, (2) brass with a high lead content is present, and (3) premise plumbing lines have relatively low water demand.

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Conventional coagulation and sedimentation processes can be significantly disrupted by gas bubbles, attaching to, and then floating coagulant floc. This study sought to understand the fundamental factors that lead to bubble formation and corresponding floating floc during coagulation and sedimentation. Gas bubbles ͑causing the floating floc͒ can form whenever the total dissolved gas pressure exceeds the local solution pressure, which can occur at localized minimum pressures during rapid mixing at high fluid velocities. Very high rate rapid mixers can cause bubble formation and floating floc even in waters undersaturated with dissolved gas. The formation and stability of floating floc are dependent on the local solution pressure, amount and type of dissolved gas supersaturation, temperature, length of rapid mixing, surface chemistry of the mixing paddle, floc, and attachment forces.

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