Drinking water

Tucson Water is installing new carbon filtering materials at its south-side treatment plant to remove more PFAS contaminants from drinking water.

The pollutants have become the subject of local and national concern this year as they’ve been discovered in drinking wells around the country, including in Tucson and Marana.

Formerly used in a wide range of products, including firefighting foam and nonstick containers, PFAS (perfluoroalkyl) compounds are known to be highly persistent in the environment and are suspected of causing cancer in humans over lifetime exposure.

Over the next nine weeks, Tucson Water will replace 56 tons of granular activated carbon in use at its Tucson Airport Remediation Project (TARP) treatment plant with carbon that’s more effective at removing the PFAS compounds.

The job is costing about $600,000 for buying and installing the new carbon materials, Tucson Water Director Timothy Thomure said in an email to the Star.

This is an interim measure toward grappling with the PFAS. City officials hope it will cut levels of the long-lasting compounds in drinking water to below the levels that can be detected by today’s technology.

Recent tests show the water contains PFAS concentrations well below the city’s goals, and much farther below those recommended by the Environmental Protection Agency. But the city would like to get them even lower.

The action comes nearly four months after Tucson Water discovered that the plant was sending drinking water with higher-than-desirable levels of the PFAS compounds to customers in a V-shaped area covering downtown and parts of the city’s west, northwest and north sides.

In all, about 60,000 people drink water from the TARP plant, although not all got water with PFAS compounds at what officials decided were unacceptably high levels.

The levels found in three monitoring wells at the southern end of that area were at or just below 30 parts per trillion PFAS. That’s less than the EPA’s recommended health advisory level of 70 parts per trillion, but significantly more than what’s been recommended by the Agency for Toxic Substances Disease Registry, part of the Centers for Disease Control and Prevention.

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That agency has recommended no more than a combined 18 parts per trillion for the two most commonly found PFAS compounds, known as PFOA and PFOS. That’s the goal Tucson Water has also adopted for its supplies.

In the fall, the city cut off the three south-side wells with high PFAS levels from having their water delivered to the treatment plant. It also added some Colorado River water that doesn’t have PFAS to the treatment plant’s water. Those steps pushed the contamination levels in the TARP water served to customers to 8 to 8.3 parts per trillion.

There have been warnings from some scientists and the Environmental Working Group that PFAS can be harmful even at levels below what’s in the treatment plant’s water today, or at worst, that there is no safe level.

Eventually, the utility wants to replace the treatment plant, now nearly 25 years old, with a more modern plant.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987