Effect of Installation Practices on Galvanic Corrosion in Service Lines, Low Flow Rate Sampling for Detecting Water-Lead Hazards, and Trace Metals on Drinking Water Pipeline Corrosion: Lessons in Unintended Consequences
Clark, Brandi Nicole
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Corrosion of drinking water distribution systems can cost water utilities and homeowners tens of billions of dollars each year in infrastructure damage, adversely impacting public health and causing water loss through leaks. Often, seemingly innocuous choices made by utilities, plumbers, and consumers can have a dramatic impacts on corrosion and pipeline longevity. This work demonstrated that brass pipe connectors used in partial lead service line replacements (PLSLR) can significantly influence galvanic corrosion between lead and copper pipes. Galvanic crevice corrosion was implicated in a fourfold increase in lead compared to a traditional direct connection, which was previously assumed to be a worst-case connection method. In field sampling conducted in two cities, a new sampling method designed to detect particulate lead risks demonstrated that the choice of flow rate has a substantial impact on lead-in-water hazards. On average, lead concentrations detected in water at high flow without stagnation were at least 3X-4X higher than in traditional regulatory samples with stagnation, demonstrating a new 'worst case' lead release scenario due to detachment of lead particulates. Although galvanized steel was previously considered a minor lead source, it can contain up to 2% lead on the surface, and elevated lead-in-water samples from several cities were traced to galvanized pipe, including the home of a child with elevated blood lead. Furthermore, if both galvanized and copper pipe are present, as occurs in large buildings, deposition corrosion is possible, leading to both increased lead exposure and pipe failures in as little as two years. Systematic laboratory studies of deposition corrosion identified key factors that increase or decrease its likelihood; soluble copper concentration and flow pattern were identified as controlling factors. Because of the high copper concentrations and continuous flow associated with mixed-metal hot water recirculating systems, these systems were identified as a worst-case scenario for galvanic corrosion. Deposition corrosion was also confirmed as a contributing mechanism to increased lead release, if copper pipe is placed before a lead pipe as occurs in partial service line replacements. Dump-and-fill tests confirmed copper solubility as a key factor in deposition corrosion impacts, and a detailed analysis of lead pipes from both laboratory studies and field tests was consistent with pure metallic copper deposits on the pipe surface, especially near the galvanic junction with copper. Finally, preliminary experiments were conducted to determine whether nanoparticles from novel water treatment techniques could have a negative impact on downstream drinking water pipeline infrastructure. Although increases in the corrosion of iron, copper, and stainless steel pipes in the presence of silver and carbon nanomaterials were generally small or non-existent, in one case the presence of silver nanoparticles increased iron release from stainless steel by more than 30X via a localized corrosion mechanism, with pitting rates as high as 1.2 mm/y, implying serious corrosion consequences are possible for stainless steel pipes if nanoparticles are present.
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