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How Recycled Wastewater Could Pump New Life Into Tucson

The Santa Cruz River, once the city's lifeblood, has been bone-dry for the past 70 years. But if all goes according to plan, the ancient waterway could be back in action by as early as next year.

Ranchers ride horses on the outskirts of the arid Tucson
Ranchers ride horses on the outskirts of the arid Tucson
Matt Weiser

TUCSON — Recycled wastewater is gaining wider acceptance as a way to boost drinking water supply across America's arid West. But in bone-dry Tucson, Arizona, planners have another use in mind: recycled effluent as decoration.

The idea, more specifically, is to use a portion of the metro area's treated wastewater to bring the long-defunct Santa Cruz River back to life — to make it flow, in other words, for the first time in 70 years — and thus revive what was once one of the city's most endearing features.

Once upon a time, the river meandered through this Sonoran Desert town year-round . But it has been reduced to a dusty flood-control channel by more than a century of groundwater pumping and development. By bringing the river back, people involved with the Santa Cruz River Heritage Project want to restore the historical riparian habitat and aquatic character that once made Tucson a haven among desert cities.

Much of the wastewater used for the river's flowing will also be absorbed into the aquifer below to augment groundwater.

"We're using it as ornamental. We want it to attract people," says Maya Teyechea, a hydrologist with Tucson Water, the city's water utility. "We're not necessarily trying to get people to buy into drinking it at this point."

The project awaits a permit from the state of Arizona, which must approve such uses of recycled wastewater. After that, making the river run again will actually be quite simple. Pipes carrying recycled wastewater — currently used for landscape irrigation — already flow near the river at strategic points. The city merely has to tap those pipes and build a small treatment facility near the waterway to extract chlorine from the wastewater, which could be harmful to aquatic life.

No difficulty is expected in obtaining the state permit, says Teyechea. And there has been no community resistance to the project. Quite the opposite, in fact, says Fletcher McCusker, chairman of Rio Nuevo, a nonprofit working to restore and develop historic areas of the Tucson riverfront.

"The factions that would normally argue about this have seemed to come together on the value of the project," he says. "So I have a pretty good feeling it's going to happen."

One of the major selling points, McCusker explains, is that much of the wastewater used for the river's flowing will also be absorbed into the aquifer below to augment groundwater. This will help the city of 530,000 people survive future droughts, so no one can claim the water is being "wasted," he says.

Brief flowing of the Santa Cruz River after heavy rains in 1978 — Photo: Gene Spesard/Flickr

Year-round flows in the river once supported one of the largest mesquite forests in the world. Shade from those trees and the cooling effect of the river made the Tucson region a lush home for the O'odham people — for thousands of years — and later a vibrant commercial center for Spanish settlers.

"This town thrived and was built on the banks of that flowing river," McCusker explains. "It's our own damn fault that it's not running, because we just over-abused the river and the water table. To have a chance to restore it is a great idea. I'm a big fan, whether it's a trickle or bank-to-bank."

The original hub of life

The city proposes to discharge as much as 3.5 million gallons per day of treated wastewater into the Santa Cruz River. The water would first be discharged at Silverlake Road. From there, it would flow north towards downtown.

The water comes from Pima County's Agua Nueva Water Reclamation Facility, which was completed in 2014 to create treated effluent that meets the state's "B+" standard. It is safe for direct application to irrigate parks, golf courses and the like, and is free of nitrates and other contaminants that could taint groundwater.

Teyechea says the city expects to get a 50% "recharge credit" from the state for every gallon it releases to the river. This means it would be allowed to withdraw half of what it releases to the river, at a later date, from the groundwater aquifer to use in its drinking water system. The 50% figure accounts for losses to evaporation and vegetation.

The city expects to have water flowing in the river again by the start of next summer, in May 2019.

"We don't have to do this," she says. "We could be putting it into our recharge basin where we get 100% credit. But the intent is to have nice areas where people can enjoy the river — hopefully a nice riparian area."

City officials don't know how rapidly the water will infiltrate into the riverbed. They don't yet know, therefore, how far the river will flow once it gets water back, which is why a second phase of the project is planned to release more recycled water into the river further downstream, at Cushing Street in the heart of downtown, just a few blocks from the Tucson Convention Center. This would ensure river flow all the way through the city's urban core.

Once it's flowing again, the river is expected to help grow back some of the mesquite forest that once provided so much shade in Tucson. It should also attract legions of birds, amphibians and other wildlife. And, of course, it's likely to draw people back to the Santa Cruz River, the original hub of life in Tucson.

"There's a lot of interest now in restoring this as Tucson's place of origin," McCusker said. "So hopefully this is part of the spark. And it has kind of energized the whole community to not only restore the river, but to restore its ancient origins as a park. We're all trying to work in that direction."

The city expects to have water flowing in the river again by the start of next summer, in May 2019.

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In Argentina, A Visit To World's Highest Solar Energy Park

With loans and solar panels from China, the massive solar park has been opened a year and is already powering the surrounding areas. Now the Chinese supplier is pushing for an expansion.

960,000 solar panels have been installed at the Cauchari park

Silvia Naishtat

CAUCHARI — Driving across the border with Chile into the northwest Argentine department of Susques, you may spot what looks like a black mass in the distance. Arriving at a 4,000-meter altitude in the municipality of Cauchari, what comes into view instead is an assembly of 960,000 solar panels. It is the world's highest photovoltaic (PV) park, which is also the second biggest solar energy facility in Latin America, after Mexico's Aguascalientes plant.

Spread over 800 hectares in an arid landscape, the Cauchari park has been operating for a year, and has so far turned sunshine into 315 megawatts of electricity, enough to power the local provincial capital of Jujuy through the national grid.

It has also generated some $50 million for the province, which Governor Gerardo Morales has allocated to building 239 schools.

Abundant sunshine, low temperatures

The physicist Martín Albornoz says Cauchari, which means "link to the sun," is exposed to the best solar radiation anywhere. The area has 260 days of sunshine, with no smog and relatively low temperatures, which helps keep the panels in optimal conditions.

Its construction began with a loan of more than $331 million from China's Eximbank, which allowed the purchase of panels made in Shanghai. They arrived in Buenos Aires in 2,500 containers and were later trucked a considerable distance to the site in Cauchari . This was a titanic project that required 1,200 builders and 10-ton cranes, but will save some 780,000 tons of CO2 emissions a year.

It is now run by 60 technicians. Its panels, with a 25-year guarantee, follow the sun's path and are cleaned twice a year. The plant is expected to have a service life of 40 years. Its choice of location was based on power lines traced in the 1990s to export power to Chile, now fed by the park.

Chinese engineers working in an office at the Cauchari park


Chinese want to expand

The plant belongs to the public-sector firm Jemse (Jujuy Energía y Minería), created in 2011 by the province's then governor Eduardo Fellner. Jemse's president, Felipe Albornoz, says that once Chinese credits are repaid in 20 years, Cauchari will earn the province $600 million.

The Argentine Energy ministry must now decide on the park's proposed expansion. The Chinese would pay in $200 million, which will help install 400,000 additional panels and generate enough power for the entire province of Jujuy.

The park's CEO, Guillermo Hoerth, observes that state policies are key to turning Jujuy into a green province. "We must change the production model. The world is rapidly cutting fossil fuel emissions. This is a great opportunity," Hoerth says.

The province's energy chief, Mario Pizarro, says in turn that Susques and three other provincial districts are already self-sufficient with clean energy, and three other districts would soon follow.

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