Big Central Aquifer Rises 25 Feet: Use of CAP is Credited, but Groundwater Levels Continue to Decline in Outlying Areas
By Rob O’Dell, The Arizona Daily Star, Tucson
Jun. 25–Tucson got its best regional water supply news in years last week as Tucson Water confirmed the aquifer lying directly below the city rose for the first time in memory.
The central well field — which supplies Tucson Water with half of its supply — has been on a historic decline for decades, falling 250 feet since 1940, said Tucson Water spokesman Mitch Basefsky.
While the bounce-back in the central wellfield doesn’t make up for those decades of losses — at its highest point it rose 25 feet — the key is that, for a change, the level is up, not down, Basefsky said.
“It’s a huge deal,” he said, noting that a declining water table not only reduces Tucson’s supply but can also lead to native plants dying out in riparian areas and even land subsidence, where ground compacts and ultimately collapses due to groundwater pumping that outpaces recharge.
Basefsky said much of the rise can be attributed to the shutting down of many wells in the central part of the city, and replacing that supply with Colorado River water from the Central Arizona Project, which is recharged in wells in Avra Valley.
Pumping creates a cone of depression that lowers the water table where it is being pulled out, he said. By stopping pumping, Basefsky said, that pressure has been released, allowing the water to rise. Some of the rise could also be attributed to last year’s rainfall, Basefsky said.
But the news is not universally positive, as the water is not rising everywhere in the metropolitan Tucson area. It’s only rising in a small area centered near North Swan Road between East Broadway and East Speedway, where the increase was 25 feet. The increases are smaller moving outward from there, or at least there was no decline.
But outside the core, bounded roughly by East Fort Lowell Road, Campbell Avenue, East 22nd Street and Kolb Road, the level continued to fall. What’s worse, the area where the level is still falling is larger than where it’s rising, Basefsky said.
“We’re still pumping more groundwater than nature is replenishing,” he said. “We’re still seeing groundwater declines outside that area.”
The worst declines are the Northwest, where the level has dropped 4 feet, Basefsky said. In addition, the water level also fell in the Tanque Verde Valley, where some native plants have died out because of the disappearing of groundwater.
Daniel Patterson, a city planning commissioner who is also an ecologist, said the rise in the center was a positive sign, but the outlying declines are still an issue.
“It’s good that it has come up,” Patterson said. “Tucson still has a big water concern. It could be a temporary rise.”
Patterson said he believes the change is attributable to the city limiting pumping in the center of the well field. But he said until local governments get serious about limiting growth, the rise “will be temporary.”
“Unless we get a value of what growth this valley can maintain, we’re going to have a water crisis,” he said.
Beyond turning off wells in the central city, Councilwoman Carol West said people are beginning to conserve more water, which is reflected in the drop in water sales from Tucson Water and the increased interest in residents wanting to use “gray water” or even effluent to water their lawns.
Gray-water systems use household wastewater from showers and washing machines for plant watering rather than sending it down the drain.
She said the extra water means “we’re conserving for the future.”
Councilwoman Nina Trasoff also said the rise was positive but highlighted the need to stay vigilant over the long term.
“What it may indicate is that we’re moving in the right direction,” Trasoff said, but added “it also highlights the concerns we have — too many straws in the aquifer.”
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