AWWA WQTC58969

A pipe loop system comprised of new ductile iron and lead pipes was operated for 13 months to investigate the effects of corrosion inhibitors on lead release and bacterial regrowth. Four pipe loops were treated with a corrosion inhibitor (orthophosphate, polyphosphate, orthophosphate/polyphosphate blend, and SnCl₂) and one served as an untreated control. The pipe loop system received treated surface water from a full-scale lime softening plant and was monitored for total lead, dissolved lead, heterotrophic plate count (HPC), and coliform concentrations. Total lead concentrations in each of the treated loops were significantly lower (95% confidence level) than in the untreated control, and orthophosphate (1 mg/L as P) consistently yielded the lowest lead concentrations of all of the inhibitors tested. Nevertheless, none of the corrosion inhibitors was able to consistently maintain total lead concentrations below the 15 mg/L maximum contaminant level for the 8-hour stagnation time sample in the new lead pipes used for this study. In addition, all of the phosphate-containing chemicals caused HPC concentrations to exceed those in the untreated control loop during the warm summer months, raising concerns about regrowth and the potential for increased coliform detections. Conversely, HPC levels in the SnCl₂ loop were significantly lower than in the control during the same period. The microbiological results suggest that water utilities need to exercise caution when adding corrosion inhibitors, so that reduced corrosion is not achieved at the expense of other water quality indicators. Includes 12 references, tables, figures.