Tucson Water recently shut down a treatment plant after discovering it was sending water contaminated with chemical compounds to thousands of residents of downtown and the city’s west and north sides.
Shortly after making that discovery, utility officials also learned that they had mistakenly thought for some time that uncontaminated water was coming out of the plant, which has long treated south-side water pollution.
The utility had been sampling the water at a point its officials thought was connected to the south-side treatment plant, but which actually was getting water from other sources, administrators said last week.
It turned out that water coming out of the treatment plant was now tainted with what’s known as perfluorinated chemicals, also known as PFAS compounds.
The plant’s water is served to a large V-shaped area, population about 60,000, stretching north from East 29th Street through downtown and flanking Interstate 10.
Because the utility hadn’t sampled points in the treatment plant’s water-delivery area until this year, Tucson Water officials say they don’t know how long the contaminated water had been served to customers there.
That’s also because the utility had repeatedly found none of the compounds when it sampled for them at a water main lying less than 2 miles north of the Santa Cruz Lane Reservoir where the TARP water is stored for delivery.
Since 2009, the utility had been sampling its well system and other points in its water-delivery network for the PFAS compounds.
Looking at old maps of its water system and visiting the area, utility officials discovered that the sampling spigot was actually connected to another main across the street from the water main where most of the TARP water was going, Biggs said.
Then, it took samples both at the treatment plant and in the distribution system, and found no PFAS compounds.