AWWA ACE65572

The City of Ottawa supplies high quality drinking water to a population of 780,000 through the operation of two surface water treatment plants and a large distribution system some of which dates back to 1874. Since the source water (Ottawa River) tends to be aggressive owing to its low hardness and alkalinity, corrosion control has been practiced for 75 years, primarily through pH adjustment. In recent years, the corrosion control strategy has been reviewed and updated to provide better protection of the distribution system. In 2002, a localized area of the distribution system experienced elevated lead levels in residential water samples that exceeded the drinking water standard for flowing lead concentrations at the point of consumption (10.0 µg/L). The situation was resolved through quick adjustment of the corrosion control strategy. Recent initiatives have been undertaken to monitor corrosion in several pipe loop systems and determine optimum pH conditions to minimize lead and iron dissolution. In addition, a residential testing program has been carried out to determine typical lead exposures due to piping and plumbing materials and to assess the impact of lead service line replacement. The testing has evaluated lead arising from both transitory and stagnation contributions to lead in the tap water. The sampling program makes use of sampling methods described in Health Canada's proposed Guideline Corrosion Control in Drinking Water Distribution Systems as well as random exposure testing to assess typical exposure through domestic water use. Includes figures.