Using a GIS and GIS-Assisted Water Quality Model to Analyze the Deterministic Factors for Lead and Copper Corrosion in Drinking Water Distribution Systems

Abstract

Various physical and chemical characteristics of a water distribution system can provide favorable conditions for lead or copper leaching. This study applied geographic information systems (GIS) and a hydraulic model of distribution systems to test the influences of pipe material, pipe age, water age, and other water quality parameters on lead/copper leaching. This study was based on a study performed at North Carolina State University (NCSU) using spatial analysis and geostatistics analysis to test for lead leaching based on water age and the influence of other water quality parameters. Results of the study indicate that higher levels of first-draw lead concentrations most likely occur in buildings constructed between 1970 and 1986 with copper plumbing systems. A long water age to the building and high water temperature also likely contribute to lead leaching into the drinking water. Switching the disinfectant to free chlorine during the “burn out” period then back to chloramines appear not to accelerate lead leaching; however, lead leaching and chloramine decay appear to be correlated. The study is expected to provide utilities with an overview of using a spatial and temporal methodology to test the influences of hydraulic and water quality parameters on lead leaching in water distribution systems. With the methodology, utilities will be able to have a better understanding of the causative factors behind lead leaching in distribution systems and use their scarce resources to focus on high-probability areas for lead leaching. During this special study of lead and copper corrosion in the water distribution system, an assessment of water quality was performed based on the water treatment operation records and water chemistry at the same period when the lead and copper compliance data and the special lead and copper sampling took place. The study was to identify the relationship between water chemistry in the water treatment plant (WTP), and especially, the lead corrosion in the water distribution system. Although no strong correlation was found between raw water/finished water quality at the WTP and lead level in the water distribution system, the results implied that the dominant factors for the lead corrosion lay outside of the water treatment plant, such as from local plumbing materials and stagnant time in the plumbing system.