AWWA JAW62060

With the implementation of groundwater conservation measures, many utilities with a historical reliance on groundwater sources have been obligated to consider alternative sources to augment their supplies or eliminate their groundwater dependence. Switching from traditional source water, however, can bring about unacceptable changes in water quality resulting from destabilization and release of chemical and biological films from the interior surfaces of the existing distribution systems. For example, red water release in distribution systems is caused by the release of corrosion products from unlined- and galvanized-iron pipes. In this two-year study, the effect of changing water quality on red water release in distribution systems was evaluated under a wide range of conditions to simulate blending of different source waters (groundwater, surface water, and desalinated water). First, investigators identified alkalinity, chlorides, sulfates, sodium, dissolved oxygen, temperature, and hydraulic retention time (HRT) as significant water quality parameters. Next, a predictive nonlinear model was developed to estimate the corrosivity of blends based on water quality. The results of the statistical analysis indicate that alkalinity, chlorides, sulfates, sodium, and dissolved oxygen of the source water or blend of source waters have a significant effect on release of corrosion byproducts in the form of red water. Alkalinity has a strong negative correlation to increase in color, but chlorides, sulfates, sodium, dissolved oxygen, temperature, and HRT showed a positive correlation to increase in color. Temperature and HRT were the significant physical and operational parameters identified. This work resulted in a valuable tool for evaluating release problems resulting from different blends of water. Includes 13 references, tables, figures.