2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

coliform, E. Coli, or HPC, and notification to the state. SPU’s Coliform Monitoring Plan lists all
sample locations, schedules, test methods used, follow-up sampling requirements, and
notification requirements.
Surface Water Treatment Rule (40 CFR 141.70-75 and WAC 246-290 Part 6)
The Surface Water Treatment Rule (SWTR) requires a significant amount of monitoring for
SPU’s filtered surface water supply, the South Fork Tolt River. This includes raw water, treated
water, and distribution system water monitoring as follows.
Raw Water Monitoring – Continuous monitoring of turbidity at the inlet to the Tolt Water
Treatment Facility occurs as required by the SWTR. Samples analyzed for fecal coliform
density are collected at the inlet to the Tolt Water Treatment Facility daily, for at least 19 days a
month.
Treated Water Monitoring – Treated water monitoring for the SWTR consists of monitoring
required to determine the effectiveness of the disinfection process. This includes monitoring to
determine log reduction of Giardia cysts and viruses. To determine the log reduction for virus,
the pH, chlorine residual, temperature, clearwell volume, and peak hourly flow rate must be
recorded. For the Tolt system, this monitoring is continuous, but is reported once a day at peak
hourly flow. To determine the log reduction for Giardia, the pH, ozone residual at multiple
locations along the contact chamber, temperature, and peak hourly flow are recorded. CT is
calculated for each section of the ozone contact chamber. Ct is reported to the state for both the
peak hourly flow and at minimum daily CT.
In addition, continuous chlorine residual monitoring for water entering the distribution system
occurs at the outlet of the Tolt Water Treatment Facility. Turbidity is also monitored
continuously at each individual filter unit and from the combined filter effluent.
Additional monitoring is conducted at the treatment plant to meet the requirements of the Service
Agreement with the DBO contractor. This monitoring is summarized in Table 3.
Distribution System Monitoring – Residual disinfectant concentration is measured at the same
time and location that a routine or repeat coliform sample is collected within the distribution
system.
Limited Alternative to Filtration (WAC 246-290-691)
Beginning in November 2004, the Cedar water supply system was designated a Limited
Alternative to Filtration status. As such, the source and treated water monitoring requirements
are slightly different than an unfiltered surface water source subject to the SWTR. This includes
raw water, treated water, and distribution system water monitoring as follows.
Raw Water Monitoring – Continuous turbidity monitoring occurs at the Cedar Water Treatment
Facility for the raw water coming from Lake Youngs (or Landsburg during by-pass operations).
Comprehensive Water Quality Monitoring Plan Page 3 of 12