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Tempe's water in compliance with safe drinking water requirements

Tempe back in compliance for safe drinking water

Post Date:08/10/2017 12:34 PM

Results of quarterly compliance sampling for TTHMs conducted on Tuesday, August 8 establish the City’s return to compliance with all Safe Drinking Water requirements.

On Wednesday, June 12, Tempe published notification that the annual average for total trihalomethanes (TTHMs) in Tempe’s drinking water exceeded the maximum contaminant level at one of eight locations sampled quarterly to assess TTHM compliance.  This exceedance occurred at sample site A-10, located at the corner of Baseline Road and 48th Street, just inside the city’s western boundary. Compliance with the drinking water standard of 80 parts per billion (ppb) for TTHMs is determined based on an average of quarterly samples collected for the last year, and is calculated every quarter for the four most recent quarters. 

TTHM is a carcinogen and considered by the EPA to have health effects based on long-term consumption. The Safe Water standard is calculated to protect consumers from the potential health effects of drinking two liters of water per day for 70 years. TTHMs have been associated with negative health effects such as cancer when water is consumed for that time period at concentrations above the standard.

Beginning within 48 hours of verifying the May sampling result and the annual average, Public Works - Water Utilities took immediate and ongoing action to ensure that TTHMs return to target levels. Measures included:

·       Using wells to blend groundwater with surface water throughout the entire system

·       System flushing at strategic locations within our water system to reduce water age

·       Strategic management of reservoir storage volumes to reduce water age

·       Chemical adjustments at water treatment plants

Collectively, these strategies quickly reduced TTHMs at A-10 and system-wide to levels that would ensure Tempe’s return to compliance after August 8th sampling.  On August 8, the result of sampling at site A-10 was 58ppb, resulting in an average of 76ppb at A-10 for the four most recent quarters.

Having returned to compliance, Water Utilities’ strategic team is implementing a plan to ensure that the City meets its goal of 100 percent compliance with Safe Drinking Water requirements in perpetuity, as it had since promulgation of the Safe Drinking Water Act until May’s sampling event.  This plan will begin with the isolation and assessment of individual strategies (e.g., flushing, treatment changes, storage, and blending), to better determine their individual contributions to meeting goals throughout the distribution system.  These measurements will provide a menu of compliance strategies that will allow system operators to deploy the best recipe for compliance based on changing source water and system conditions on an ongoing basis.

Tempe’s Public Works Department, Water Utilities Division, collects over 2,000 drinking water samples annually, from which its laboratory produces roughly 8,500 analytical results, to assess compliance with federal drinking water standards for 96 individual contaminants or groups of contaminants.  Tempe monitors samples at two drinking water treatment plants, 15 active drinking water wells, and 60 locations within its drinking water distribution.

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