AWWA JAW62301

Corrosion in a distribution system can lead to colored water caused by source water iron and manganese. In addition, corrosion problems may cause the system to fail to meet the Lead and Copper Rule (LCR) action levels. This study was undertaken to demonstrate that sodium silicate addition can achieve corrosion control for the LCR and simultaneous sequestration of iron and manganese at an LCR-classified medium water system that has multiple wells and entry points. At special study monitoring sites, an initial silicate dosage of 25-30 mg/L elevated the pH from 6.3 to 7.1 and resulted in a 55% reduction in lead levels and an 87% reduction in copper levels. A further increase to 45-55 mg/L silicate dosage increased the pH to 7.5 and produced even greater reductions in lead and copper. The treatment change reduced 90th percentile lead and copper levels by at least 95%, enabling compliance with the LCR. Study results showed that the aesthetic quality of the drinking water after treatment was equal or superior to the water's quality before the treatment. The higher pH and silicate combination was also found to be more compatible with protecting asbestos-cement and cement-lined pipes than polyphosphate treatment at a lower pH. Includes 34 references, table, figures.