Washington Water Service Company

Boil Water Advisory Lifted for Pressure Zone 2
Minterbrook Water System (Pierce County)

April 15, 2015

We are pleased to report that all of the bacteriological samples collected by our staff on Monday, April 13th, and Tuesday, April 14th, were absent of any coliform bacteria (including those of fecal origin, such as E. coli). We have consulted with the Washington State Department of Health and we are hereby advising that:

It is no longer necessary for you to boil your water. Your water is safe to drink without boiling!

As stated in the boil water notices delivered on Saturday evening, April 11th, the E. coli bacteria was detected – and confirmed – only in Pressure Zone 2. All follow up samples collected on Friday afternoon from all other pressure zones of the Minterbrook water system, all wells and all storage tanks were absent of any coliform bacteria. This included a sample collected from Well #6. But because Well #6 serves only this pressure zone, it was removed from service as a possible source, pending further investigation and additional sampling at this and other locations. Well #6 has not been positively identified as the source of contamination and we continue to diligently check the system closely looking for any possible causes of these failures.

Temporary chlorination equipment was set up at the Zone 2 East Booster Pump Station on Saturday evening. This continuously disinfected the mains serving the affected homes overnight, ridding the water of any bacteria. Customers were asked in the notice to use this chlorinated water in the home so that household plumbing was disinfected, also. The chlorinator was turned off early Sunday afternoon and our crews performed an intensive flush of the zone with water from unchlorinated water from neighboring Zone 1 to get the chlorine out of the system so follow up samples could be collected. The water must be absent of any chlorine because it can kill/mask coliform bacteria that may be present, resulting in false-negative results.

The first set of 5 routine samples required on two different days was collected within Zone 2 on Sunday. Additional samples were also collected from neighboring zones to confirm they were still satisfactory (they were). One of the 5 samples collected in Zone 2 was E. coli positive (the other four were absent of any coliforms), and this was a third and different home than the two previous E. coli positive samples. All three positives have been on 91st Ave NW only. A second set of 9 samples from the same locations was collected the following morning and all 9 samples were satisfactory this time around. As all 18 sample locations except for one were satisfactory after disinfection of the system, an intensive flushing of Zone 2 with unchlorinated water was performed on Tuesday, with emphasis on the house hose bib sample locations that have been unsatisfactory. It is possible that the one sample that was unsatisfactory after disinfection was due to the hose bib sample conditions, and not representative of water quality in the distribution mains as a whole. Another round of 11 total samples was collected on Tuesday and all of these samples were satisfactory. We are confident that the system is now absent of coliform bacteria. You no longer need to boil your water. The temporary chlorination that was restarted on Tuesday, April 14th will remain in service through Friday, April 17th.

Washington Water Service Company sincerely appreciates your patience and understanding during this water quality investigation. Safe drinking water is our number one priority and we apologize for the inconvenience of having to boil your water. We will continue to monitor the system as we routinely do each month, advising you any time there are any additional confirmed unsatisfactory samples.

If you have any remaining unanswered questions or concerns, please call our Customer Service Department toll free at (877) 408-4060 or email us at: customerservice@wawater.com.

Customer notice

DOH fact sheet

Additional information