Tucson Water plans to start discharging water containing low levels of PFAS compounds from its south-side water treatment plant into the Santa Cruz River in early October — if it gets a state permit for the discharge by then.
The utility is building a pipeline to take the water from that treatment plant near Interstate 10 and Irvington Road to the river near Irvington.
It also has submitted a permit application for the discharge to the Arizona Department of Environmental Quality. It will post a public notice advertising the permit application before deciding on it, ADEQ Director Misael Cabrera said.
Utility officials hope to transfer those discharges into their reclaimed water system sometime next spring, after they've built a second pipeline to take the water to its reclaimed water system. Tucson Water already has designed and installed some sections of that pipeline.
The south-side pipeline is supposed to be temporary while the one to take the water to the reclaimed system will be permanent, the utility says. ADEQ gave the city $2 million for construction of the pipeline to the Santa Cruz.
Construction of the pipelines will let the utility reopen its shuttered, south-side Tucson Airport Remediation Project treatment plant.
The utility closed it in late June because PFAS levels in south-side groundwater being treated at the plant were increasing rapidly. Utility officials said the PFAS was threatening to overwhelm the treatment plant's ability to clean the potentially cancer causing compounds from water.
The TARP plant, built in 1994, wasn't designed to treat PFAS compounds but the utility had over time installed granular activated carbon filtering material in the plant to remove PFAS.
The treatment plant was getting PFAS at average concentrations of 95 parts per trillion and treating the water to where PFAS levels were so low the utility's equipment couldn't detect it.
The utility wants to be able to keep TARP open and treating the PFAS in its water until it can get money to build a new treatment plant specifically designed to remove PFAS.
That could be years away, although a new federal infrastructure bill that has passed the U.S. Senate would give Arizona about $72 million a year for five years for PFAS cleanups in Arizona, U.S. Sen. Mark Kelly's office said last week.
In discharging TARP water into the Santa Cruz, the utility says it plans to keep PFAS levels below 18 parts per trillion. That's the limit the city sets for drinking water it serves to customers.
ADEQ will set a limit of 70 parts per trillion for the city's water discharges into the Santa Cruz. That matches the Environmental Protection Agency's recommended health advisory limit for a person's lifetime exposure to PFAS compounds in drinking water. There's no federal regulatory limit for PFAS concentrations in drinking water or surface water.
Tucson Water officials have said they have no plans to send water with that high a concentration into the river. They've also said their discharge plans will take into account the fact that PFAS is already found in that portion of the Santa Cruz, in some areas at levels at or above 70 parts per trillion.
PFAS is an abbreviation for a group of commonly used, human-made chemicals known as perfluorinated and polyfluorinated alkyl substances that are very persistent in the environment and the human body, meaning they don’t break down easily.
Last week, the Pima County Board of Supervisors passed a resolution asking the city to reduce PFAS concentrations as much as possible before discharging treated water into the river. The resolution didn't specify a limit.
Yolanda Herrera, a clean water advocate on Tucson's south side, has raised concerns about the plan to discharge TARP water into the Santa Cruz. In late June, she told the Star she's concerned that even at lower concentrations, PFAS compounds in that water could seep into the aquifer.
“You are throwing in that water where it may sink down back into our aquifer. What are we solving?” asked Herrera, Sunnyside Neighborhood Association president and community co-chair of the Unified Community Advisory Board that has overseen the south-side groundwater cleanup.
This week, she warned that as the Santa Cruz is running right now during a supercharged monsoon season, "the river will carry it down to Marana," where PFAS has already contaminated groundwater in parts of the town's water service area.
But Bill Ellett, a retired ADEQ hydrologist, has said he thinks the risk to the aquifer from putting the TARP-cleaned water into the river is outweighed by the risks of leaving the contaminated water in the aquifer under and near the plant, and letting the compounds continue building to higher concentrations and moving downhill toward the rest of the city.
An ADEQ spokeswoman said that the discharges to the Santa Cruz River from TARP will provide a net benefit to the groundwater quality. Because this plan will allow TARP to reopen, south side groundwater that currently exceeds recommended limits for trichloroethylene, 1,4-Dioxane and PFAS will be treated by TARP, said ADEQ spokeswoman Caroline Oppleman.
It will meet regulatory standards for the first two compounds and Environmental Protection Agency's recommended health advisory level for PFAS before being discharged to the Santa Cruz and infiltrating back into the aquifer, she said.
In an Aug. 5 memo, Pima County Department of Environmental Quality Director Ursula Nelson essentially agreed with Ellett. She also recommended the treatment plant water be cleaned to no more than 18 parts per trillion total for two commonly found PFAS compounds, PFOA and PFOS.
Nelson told the Star that she supports the city’s plan to discharge treated water into the river.
While putting water of that quality into the river poses some risks, they're not as great as for leaving untreated groundwater in the south-side's aquifer, she said.
Her memo acknowledged that treated water entering the normally dry riverbed "will infiltrate into the sands and percolate into a porous portion of the aquifer, carrying potential contaminants."
The added water will have the potential for flowing laterally into a nearby well, within 1,000 feet of where the TARP water will be flowing, that now contains PFAS concentrations exceeding 70 parts per trillion, she wrote.
But while movement of pollutants in the aquifer should be discouraged, the impact from the new discharge is expected to be less damaging than leaving PFAS-tainted water in the south side's aquifer, she said — along with two other toxic compounds in the aquifer, TCE and 1,4-dioxane.
As the PFAS in that aquifer moves toward the TARP plant, "concentrations are expected to increase and great care needs to be expended to protect the aquifer," Nelson wrote.
