SPU began sampling and analysis to meet the USEPA Lead and Copper Rule in 1992. The Lead and Copper Rule sets action levels of 15 ug/L (0.015 mg/L) for lead and 1300 ug/L (1.3 mg/L) for copper. A system must make treatment changes or meet other requirements if the action level for either lead or copper is exceeded in more than 10% of the residential samples. Since 1992, the copper levels in almost 100 percent of the samples have been below the copper action level. However, the action level was exceeded for lead in 1992 and 1997.
The 1992 monitoring results initiated a two-year study of potential water quality and treatment changes that could reduce corrosiveness of the water and resulted in recommended treatment changes on the Tolt supply. The key treatment changes required were an increase in alkalinity and reduction of organics. Distribution system changes were recommended as well to limit pH reduction, to include covering open reservoirs and converting from gas chlorination to hypochlorination.
Seattle Public Utilities has put a tremendous amount of effort into reducing lead and copper levels from home plumbing materials. North-end reservoirs have been covered and gas chlorination has been converted to hypochlorination for distribution system reservoirs. The Tolt Treatment Facility began with pilot testing in 1995, design in 1996, initial construction in 1998, and was brought online in 2001. The facility includes ozonation, coagulation, flocculation, direct filtration, fluoridation, pH control, alkalinity adjustment, and chlorine disinfection. Additional studies for optimizing corrosion control at the Tolt Treatment Facility recommended an optimized increase in alkalinity from 13 mg/L to 19 mg/L, which was implemented in June 2003.
The reduction in lead levels is a direct result of distribution system and treatment facility improvements. Results of sampling in 2003 indicated that lead levels for 97 percent of the samples are below the action level. Monitoring results for 375 residential sites were included in the fall 2003 round. Of these, 167 were from SPU’s direct service area and 208 were from areas served by our wholesale customers. The 90th percentile values for lead and copper were 7.9 ug/L (0.0079 mg/L) and 201 ug/L (0.201 mg/L), respectively.