2006 Water Comprehensive Plan - City of Bellevue

surface waters, establishing requirements for Giardia lamblia, viruses, Legionella, heterotrophicbacteria, and turbidity levels of treated water.After treatment, the SWTR requires a minimum disinfectant residual of 0.2 mg/L at the point ofentry to the distribution system at all times. Additionally, a detectable disinfectant residual mustbe present in at least 95% of all distribution system samples collected at the same location andfrequency as samples collected for compliance with the Total Coliform Rule. Alternatively,samples may be analyzed for heterotrophic bacteria using the plate count method (HPC). AnHPC level of 500 colony forming units per mL (cfu/mL) or less is considered equivalent to adetectable disinfectant residual.Bellevue StatusBellevue samples chlorine residual 84 times each month at 23 sites throughout the distributionsystem. Between 1998 and 2004, chlorine residual was always detectable in at least 95% ofsamples collected at total coliform sampling stands. In addition, between 2000 and 2004,Bellevue collected 410 HPC samples throughout the distribution system. Of these, the maximumHPC result was 49 cfu/mL and nearly 88% of the collected samples contained 0 cfu/mL.Total Coliform RuleRegulatory RequirementsThe Total Coliform Rule (TCR) requires systems to monitor their distribution system forcoliforms, which are bacteria used to indicate the presence of potentially harmful bacteria suchas E. coli. Under this rule, there are two types of violations: acute and non-acute. An acuteMCL violation for coliform is the presence of fecal coliform or E. coli in a repeat sample, orcoliform presence in a repeat sample collected as a follow-up to a sample indicating the presenceof fecal coliform or E. coli. A non-acute MCL violation for coliform occurs when a system thatcollects 40 or more coliform samples per month has more than 5.0% of the routine samples takenin one month test positive for the presence of total coliform.Bellevue StatusBellevue is one of approximately 27 water systems and districts that receive water from sourcestreated and operated by SPU. SPU and its wholesale customers have been part of a regional,DOH-approved, coliform monitoring program since 1972. As part of the regional program,wholesale customers are responsible for installing and maintaining designated coliformmonitoring sample stands, while SPU collects the monthly samples. Under this agreement, SPUand its purveyors sample at a rate of 70% of samples required by the Total Coliform Rule.Bellevue currently supplies water to a population of approximately 134,000, therefore, theminimum number of routine samples collected within Bellevue’s distribution system is 84 permonth (70% of the 120 samples required for systems serving 130,001 to 220,000 customers).According to the regional monitoring plan, SPU collects routine samples. Bellevue is10-6