December 2003

In June 2003, a groundwater well pump failure released a small amount of mercury into the drinking water supply for two neighborhoods and several individual homes on Tucson's east side served by that groundwater well. Approximately 50 homes were impacted. Tucson Water immediately shut down the water main supplying that area and switched the residences to an alternate water supply. Bottled water was delivered to all affected residences until testing could confirm that their tap water did not have measurable levels of mercury contamination. Extensive water system testing confirmed that the mercury did not reach any other customers.

The affected neighborhoods are shown in the photo below.

By the end of June, an aggressive water system and private plumbing flushing program had reduced the level of mercury in the tap water at the majority of the affected homes below the minimum quantifiable limit of 0.5 parts per billion. Those residents were contacted and told that they could resume their use of tap water for all purposes.

However, several homes in the 9400 block of East Calle Cascada continued to show the presence of mercury at their taps at levels just above the limit of measurable detection. Although mercury at these levels presents no health risk and is far below the limit allowed under federal drinking water standards, Tucson Water and the residents agreed that until mercury was no longer detected in all ten homes, the utility would continue to provide bottled water service to all ten homes.

In late December 2003, repeated water quality tests confirmed that mercury was no longer detectable in the Calle Cascada homes. Once the water quality test results were confirmed, the last of the homes to show detectable levels of mercury were released from any restrictions on the use of tap water.

Tucson Water is continuing to clean up mercury still present in the groundwater well that provided water to these neighborhoods. Once the clean-up has been completed, Tucson Water will evaluate whether the well can be returned to service or will be sealed. The well will not return to service without direct evidence that the water will have no measurable mercury.

For additional information on this event, click here.