2006 Water Comprehensive Plan - City of Bellevue

equired by state or federal regulations to conduct DBP monitoring, Bellevue has beenmonitoring those DBPs regulated by the Stage 1 D/DBP Rule since the first quarter of 2004.Prior to this, SPU performed DBP monitoring in Bellevue’s system. This monitoring has beenconducted in anticipation for the upcoming Stage 2 DBP Rule, which will apply to Bellevue, andto ensure public health protection. DBP monitoring has been conducted quarterly at locationsanticipated to be consistent with upcoming IDSE and Stage 2 requirements. The DBP levels inthe voluntary samples are all below the MCLs established in the Stage 1 D/DBP.Bellevue’s compliance with these regulations during the last six years is detailed below.Disinfection By-Product MonitoringRegulatory RequirementsSome disinfection by-products (DBPs), such as trihalomethanes, have been shown to causecancer and negative reproductive health effects. Until 2002, Bellevue was required to samplequarterly for Total Trihalomethanes (TTHMs). The Maximum Contaminant Level (MCL) forTTHMs was 100 µg/L. In 2002, the federal Stage 1 Disinfectant/Disinfection By-Product Rulebecame effective for surface water supplied systems with more than 10,000 customers, makingthe previous TTHM requirements no longer applicable. The TTHM MCL was reduced from 100to 80 µg/L and an MCL was added for the total of five haloacetic acids (HAA5) at 60 µg/L. Asadopted in the WAC 246-290, the Stage 1 DBP requirements were not enforced for systems thatpurchase all of their water and do not apply any disinfectant.Bellevue StatusBellevue participated in SPU’s TTHM Regional Monitoring Plan, which resulted in reducedmonitoring. TTHM monitoring was conducted by SPU quarterly at two locations in Bellevue’sdistribution system, one served by the Tolt supply and the other served by the Cedar supply.Annual average TTHMs from 1998 through 2003 are shown in Table 10-2. Between 1999 and2002, Bellevue collected 12 HAA5 samples per DOH requirements at location BE-S15, thataveraged to 37 µg/L. The monitoring sites were changed in 2001, and the Tolt River supplybecame filtered, reducing DBP precursor levels entering Bellevue’s distribution system.Bellevue has been in compliance with the DBP MCLs throughout this period.10-4