AWWA WQTC64035

The response of distribution systems to changes in water treatment, e.g. replacement of chlorine with chloramines or changes in the pH of the treated water, is strongly dependent on the mineralogy of the corrosion scales attached to various parts of the system. These determinations are particularly critical for lead compounds, of which there have been many reported. Knowledge of the crystal form of these compounds is a key contribution to models of lead behavior. Therefore, it is necessary to understand both the mineralogy and the chemistry of the scales built up on the interior of lead containing materials in the distribution system and to carefully quantify the scale compositions over their thickness in order to understand distribution system lead level responses to various water quality conditions and potential water quality changes. Metallic lead (Pb) itself is quite soluble in water and it is only the formation of protective scales that brings the concentration of Pb down into reasonable ranges. For Pb, the dominant minerals found in distribution systems are simple oxides and carbonates. Phosphates are also found, and are increasingly relevant as systems turn to orthophosphate dosing to stabilize Pb scales. This array of minerals differs widely in solubility in water depending on the presence of H+, HCO₃^-, PO₄^3-, SO₄^2-, and the total charge in the solution. Because Pb can occupy three oxidation states, Pb⁰, Pb²⁺, and Pb⁴⁺, the oxidation level of the water is also critical. This parameter is usually expressed as Eh, or the potential relative to a standard hydrogen electrode. As part of AwwaRF Project #3018, "Contribution of Service Line and Plumbing Fixtures to Lead and Copper Rule Compliance Issues", several lead service line pipes, meters and faucets were obtained from participating utilities and sent to the University of Cincinnati for evaluation. Evaluation of the specimens consisted of visual and photographic observations and analysis of samples of scale removed from the interior surfaces of these specimens, as follows: digital macroscopic and microscopic images; collecting a representative scale sample(s) from the specimen for analytical analyses; X-ray diffraction (XRD); scanning electron microscopy (SEM); Laser Raman spectroscopy; and, X-ray fluorescence (XRF). Includes extended abstract only.