Tucson and Southern Arizona have ample supplies of water into the future, according to a new report from the University of Arizona’s Water Research Center, provided there is effective management. Not addressed in the report, though, was the growing concern over arsenic and other contaminants.

The Flowing Wells Irrigation District on Tucson’s near northwest side is completing an arsenic removal system. In Nogales, Friday (Aug. 4) is the deadline to submit bids on a new water filtration plant.

Barbara Johnson, project manager for the City of Nogales, said the bids are part of the final process to meeting tougher requirements set by the U.S. Environmental Protection Agency (EPA). Nogales has already ordered $915,000 of filtration equipment and done $90,000 in engineering work.

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The EPA has lowered acceptable arsenic levels from 50 to 10 parts per billion, which has put a number of water systems in violation of the law. The new limits have also served to highlight what is a recurring problem in the desert Southwest, where deep wells bring water up, along with whatever minerals have been leached along the way.

Thanks to mineral leaching, especially through the area’s abundant copper deposits, three of the nine wells providing water to Nogales are slightly over the limit, Johnson said.

“We’ll have to pass a test by the end of 2007 to show we’re in compliance with the new level,” she said.

Using an iron-based adsorption system, Nogales will leach the arsenic back out of the water to make it legal to use again, Johnson said. But that won’t be the end for the border city.

Although there’s no sign that as the aquifer goes down, the amount of arsenic goes up, Johnson said some level of contamination is inevitable. As an example, she said, “Because the Coronado No. 1 well is one of those wells to be treated, we expect that Coronado No. 2 will also need arsenic remediation once it’s ready for use.” There will be others, too.

“We expect that this type of contamination is something we’re going to anticipate, any time we drill a well.”

The Flowing Wells Irrigation District is anticipating the same ongoing need to consider metal contaminants, even if the district stays with 10 wells.

Jim Cavanaugh, assistant superintendent, said the district is spending about $1 million to remove arsenic from two wells that didn’t meet the EPA’s new standard. One of the wells didn’t have any arsenic contamination until it was deepened to avoid possible nitrate contamination.

“We happened to hit a pocket of rock with higher concentrations of arsenic,” he said.

Arsenic, lead and a variety of other exotic metals can show up at any time. In fact, the deeper the wells go, the more likely they’ll hit contamination.

“They’re found within volcanic rock, which is what we’re drilling into,” Cavanaugh said.

This emphasizes the need to prevent a drop in groundwater levels. The Flowing Wells district is fine for now, he said, “because we’re pumping the same amount as previous years” but “our aquifer is the same as everyone’s in this area.” More growth and more pumping, even in Vail or Sahuarita, could change the situation for everyone, he said.

What happens to that aquifer is crucially important to Tucson Water, which had less than 10 of its 100 wells affected by the new EPA arsenic standard, but still looks at mineral contamination as an ongoing cause for concern.

“We’re being very vigilant today,” said Mitch Basefsky, Tucson Water’s public information officer. “We’re watching for more than just arsenic. There’s fluoride and nitrate, too.”

Basefsky said all the Tucson Water wells are limited by state law to no deeper than 1,000 feet, but as they pump deeper, they know the water is warmer and leaches a variety of naturally occurring minerals, including heavy metals and even radioactive substances.

“We’re also looking for things we don’t consider problems, now, but we still want to know if they’re there and why,” he said.

Already, Basefsky said, they know locations closer to the Tucson Mountains are more likely to have metals, “but whenever we consider a site, we check with other users in the area, including private wells, before drilling to make sure the water we get meets our standards.”

As demand continues to increase, so does the risk. The further down they go, the more likely they are “to find layers in the aquifer that have compounds we don’t want in our water,” Basefsky said. “So, this will definitely become an issue.”

For the future, he said, “we’re going to have to consider our options, because it’s not just quantity we need, but quality as well.”

E-mail comments for publication to editor@azbiz.com. Contact Philip S. Moore by e-mail at pmoore@azbiz.com or call (520) 295-4238.

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