City of Tumwater

- Coliform Updates -

In October, 2004, City staff detected small amounts of coliform bacteria in the water system. Coliform is an indicator bacteria that suggests conditions exist that could support the development of harmful bacteria, such as fecal coliform and E.coli.  Because these conditions existed, the City of Tumwater worked with the WA State Department of Health (DOH) to identify and resolve the issue, instituting a temporary disinfection program until upgrades to the system could be completed.

By November of 2004, the City had installed the necessary equipment and began the disinfection program.  The levels of chlorine added to the system were lower than that of most systems required to chlorinate on a permanent basis.  Over the next eighteen months, the City continued to disinfect the system while plans were implemented with the expectation that upgrades to the storage facilities would alleviate the problem, allowing the City to end the temporary disinfection program.  During this time, staff continued to evaluate the system in hopes of determining a definitive source of the coliform bacteria. 

Despite diligent efforts, no “smoking gun” was ever identified, and the City continued with the temporary chlorination program until the retrofits on the reservoir system was complete.  These retrofits were designed to facilitate more uniform temperatures in the reservoirs during periods of low use, and by extension, reducing the temperatures at which coliform bacteria thrive.

In April of 2006, the City had completed the upgrades and was ready to end the disinfection program.  Over the next few months, staff carefully monitored the system to ensure the retrofits were working as planned.  While temperatures remained constant in the storage facilities, staff continued to detect coliform at various monitoring sites throughout the system.

That summer, staff reviewed additional measures that could be taken to improve infrastructure and eliminate coliform detections.  In July, staff replaced all aging water quality monitoring stations, as the older stations were identified as a potential source for coliform bacteria entering the distribution system.

After all the equipment upgrades and retrofits, coliform detections still occurred.  By late August 2006, the City reached the point where a tough decision had to be made.  Staff discussed alternatives to a disinfection program, but none could ensure the safety of our customer’s health or reduce the possibility of future coliform detections.  By September, the City made the decision to implement a permanent disinfection program voluntarily – a tough, but necessary, choice.

Since the disinfection program has been underway, no detection of coliforms has occurred.  Over the next year, the City will evaluate alternative viable methods of disinfection.  While chlorine disinfection is a proven and safe technology, the City hopes to look at alternative methods of disinfection to ensure our customers continue receiving the highest quality of water possible.

Below are a series of links to provide you with more information.  This site will be updated as necessary, so please check back often for the most current information.

WA State Dept. of Health - Drinking Water
Coliform Fact Sheet
Frequently Asked Questions - Coliform
Frequently Asked Questions - Chlorine Disinfection
US EPA - Office of Drinking Water
Notice to Our Customers - 2/15/2004

Updated: March 4, 2008