ORGAN PIPE CACTUS NATIONAL MONUMENT — A large water tanker parked under an elevated yellow tank was storing thousands of gallons of water.

It took just minutes to fill the truck's tank, and just a few more before it began making its rounds again.

The truck drove along the worn dirt road, spraying the water, momentarily drenching the ground before sun and earth soaked it up in one of the desert's driest areas.

Other drops clung a little longer to the rusted metal poles and grates of the wire-mesh fencing that delineates the United States-Mexico border, before they, too, soaked into the ground or evaporated into the hot air.

In the coming weeks, construction crews will remove the 15-foot fence panels now standing around the Lukeville port of entry, about 150 miles southwest of Phoenix.

Workers will dig holes 7 feet deep into the softened, sandy soil and fill them up with wet, sticky concrete. Panels of steel bollards with a solid metal plate at the top, measuring 30 feet in height, will complete the new border fence design.

Similar active construction scenes are playing out throughout the U.S.-Mexico border. But this latest effort is shaping up at the Organ Pipe Cactus National Monument, one of the toughest, most remote and well-preserved stretches of the Sonoran Desert.

Since 2001, at least 233 migrants have perished within the monument as they trekked through hundreds of miles of protected desert wilderness because there wasn't enough water. This year, the U.S. government began to prosecute humanitarian-aid volunteers for dropping off gallons of water for them along this busy corridor.

As construction workers broke ground Aug. 22, the contractor hired to replace the first 5 miles of aging fencing near Lukeville turned to the only source of water in this arid desert environment: underground.

The Department of Homeland Security cleared the way for the construction company to pump water from wells along the U.S.-Mexico border. In May, it waived more than 30 environmental and public health laws to expedite construction.

The move, allowed under a 2005 law, has raised questions about the federal government's transparency, as well as the practices in place, to monitor and regulate the extraction and use of one of the most precious resources in the desert.

The pumping of groundwater drew criticism from environmental groups that are concerned about the depletion of aquifers, as well as its potential impact on existing sources of water and the wildlife that depend on them.

"U.S. Customs and Border Protection, the U.S. Army Corps. of Engineers, and the barrier construction contractor have been coordinating the construction process and use of groundwater with the park," a statement from Customs and Border Protection to The Arizona Republic read.

Pristine Sonoran Desert wilderness

Construction to replace 5 miles of wire-mesh fencing with 5 miles of new bollards around the Lukeville port of entry will take about a month and a half. In October, work is expected to expand to an additional 38 miles along protected desert wilderness areas.

The $646 million project was paid for using funds diverted from the U.S. Department of Defense, using a provision that allows the Pentagon to build barriers along known drug-trafficking corridors at the border.

The U.S. Army Corps of Engineers awarded the multimillion-dollar contract to Southwest Valley Constructors of Albuquerque, New Mexico. The contract also includes the construction of nearly 20 miles of bollards in nearby Cochise County.

Once they are done replacing the wire mesh fencing, in October, construction crews will begin to replace the vehicle barriers the federal government installed in 2003. They are intended to stop cars but allow people and wildlife to walk under with ease.

Once completed by November 2020, the new bollards will stretch about 11 miles east of the port of entry, close to the eastern boundary of Organ Pipe with the Tohono O'Odham Nation. The bollards also will stretch west for about 32 miles into the Cabeza Prieta National Wildlife Refuge, until it reaches the Yuma County line.

The area on the U.S. side is sparsely populated. The small town of Ajo, with a population of 3,300, is the nearest community and is about 40 miles north of the border. The surrounding area is vast, protected desert wilderness.

On the Mexican side, the border city of Sonoyta, with a population of 13,000, is the only major community for dozens of miles around. It's also flanked by protected lands, forming a binational preserve of Sonoran Desert wilderness.

More pumping — and potentially more wells

Due to its remoteness, and the few populated centers in proximity, transporting water to the construction site from outside the park likely would be a time-consuming, costly effort. But it's been done before.

Customs and Border Protection — the agency responsible for border security — confirmed it is working with other federal agencies and the contractor to pump groundwater from wells located within Organ Pipe Cactus National Monument and using it for construction. Officials said they haven't drilled any new wells.

"The park has identified existing groundwater wells that may be used by the construction contractor," the agency said in a statement.

According to the Arizona Water Resources Department, all existing and proposed new wells must be registered with the department, regardless if they are on state, private or federal land.

A search through the Water Resources Department's well registry online identified several wells within Organ Pipe where officials had measured the water levels as recently as October 2018, according to the registry.

In a statement, the Water Resources Department said that "if an existing registered well is put into production, no notification to the Department is required unless the ownership of the well needs to be updated."

In past construction efforts along the Arizona border, the contractor negotiated water access and use directly with landowners close to where the project was taking place. But the area directly surrounding construction near Lukeville is public, federal land.

Southwest Valley Constructors deferred any comments about border-fence construction to Customs and Border Protection. The federal agencies that manage the public lands on the U.S. side also referred to CBP for questions.

Customs and Border Protection told The Republic that the contractor estimated they would need 84,000 gallons of water per day for the project.

The replacement of the first two miles of fencing east of the Lukeville port of entry will take 45 days. That means that Southwest Valley Constructors will use 3.7 million gallons of groundwater on that two-mile stretch, CBP said.

Using those same metrics — roughly 1.85 million gallons per mile of new fencing — the construction of the 43 miles of bollard fencing through similar terrain and location could require a total of 79.56 million gallons of groundwater.

In a written statement, Customs and Border Protection said that based on an agreement with the U.S. Department of Interior, the contractor may monitor water levels at the existing wells, if they're equipped with to do so, to ensure there is enough water to pump.

"The construction contractor will ultimately determine how much water they will need for daily construction activities and may use water from one or more wells depending on proximity to construction activities," the statement read.

In its 2008 assessment, Customs and Border Protection said it planned on trucking in water from wells near Ajo, which forms part of a separate groundwater basin from Lukeville. The idea was not to disrupt water levels at places like Quitobaquito Springs, an oasis 13 miles west of the port of entry.

But with the latest construction projects along Organ Pipe monument land and the Cabeza Prieta, Customs and Border Protection has not ruled out drilling new wells closer to the border, on land it owns and manages.

"The construction contractor has proposed the installation of additional groundwater wells within the Roosevelt Reservation (i.e. the portion of land that occurs from the international border to 60 feet north) and various locations of the project to support the water needs of the project," the CBP statement read.

Although it declined comment on construction, the National Park Service, which operates Organ Pipe, said that because of its location on the border, the park "is challenged with managing impacts stemming from various cross-border illegal activities. As such, the National Park Service works closely with the Department of Homeland Security to provide for life safety and to protect monument resources."

The agency added that, as construction of the new bollards began Aug. 22, it restricted public access to the road that runs parallel to the border fence east of the port of entry to the Santa Rosa Mountains, at the monument's eastern boundary. The move was made to protect the public from construction activities, the Park Service said.

Quitobaquito: Desert oasis at risk?

A big concern environmental groups have with the continued pumping of groundwater is the potential impact it could have to perennial water sources such as Quitobaquito Springs.

The spring is on the western portion of Organ Pipe but near the path of wall construction. It's also the only natural, permanent source of surface water for wildlife for hundreds of miles around, a literal oasis in the desert.

Pumping water within the park to build border barriers "will only contribute to the lowering of the groundwater table, and it could cause a precious desert oasis like this one to run dry," said Laiken Jordhal, the borderlands campaigner for the Center for Biological Diversity.

The Tucson-based group has sued, challenging the Trump administration's ability to waive environmental laws to expedite construction of new barriers on the border. The lawsuit is making its way through federal court in Washington, D.C., and the presiding judge has yet to rule.

Court records that Customs and Border Protection filed in response to that lawsuit show that the agency agreed to not drill wells within 5 miles of Quitobaquito Springs, to minimize the impact on water levels. Officials also said they would have "biological monitors" during construction near the site to measure water levels and assess impacts on wildlife in the springs and the surrounding land.

On a recent visit, a National Park Service employee worked to clear the springs of debris left behind by brief but intense summer monsoon storms.

The intensity of the rainfall had stirred the waters of the man-made holding pond into a murky brown, hiding from view the Quitobaquito pupfish, an endemic fish found nowhere else in the world and listed as an endangered species.

The springs' proximity to the border, about a quarter-mile from vehicle barriers, adds other concerns for environmentalists.

They worry that if construction is allowed to proceed, the 30-foot barriers and the permanent road and floodlights that come as part of the "border wall system" will permanently disrupt the ecosystem.

The springs also support other species found nowhere else in the United States, such as the Sonoyta mud turtle and the miniature Quitobaquito spring snail. Environmentalists also argue the bollards would keep out migratory species such as the endangered Sonoran pronghorn.

As the only natural source of surface water in the area, the National Park Service also recognizes the cultural significance of Quitobaquito Springs. Artifacts dating as far back as 16,000 years have been discovered on-site, the Park Service said.

The springs have helped sustain people for centuries, including the Tohono O'Odham, who have used the area as a stop along their sacred salt pilgrimage across the border from Arizona to Sonora.

In a resolution passed on June 16, the Tohono O'Odham Nation formally opposed Customs and Border Protection plans to build the 43 miles of bollard fencing through traditional O'Odham lands, including Quitobaquito.

"Building a border wall through Organ Pipe Cactus National Monument and Cabeza Prieta National Wildlife Refuge would cut across the route of a ceremonial salt pilgrimage and damage Quitobaquito springs, a sacred desert oasis used during the pilgrimage. The plans to build this wall would make it impossible to carry out the salt ceremony and threaten to end this sacred tradition forever," the resolution said.

Waivers of typical impact laws

The construction of bollard fencing in public lands such as Organ Pipe Cactus National Monument normally would require assessments on the potential environmental and cultural impacts on these areas, as required by a number of federal laws.

But in May, the Department of Homeland Security waived those laws, citing the Real ID Act of 2005. Congress granted then-President George W. Bush's administration the ability to bypass them in order to expedite construction of barriers along the U.S.-Mexico border.

In its place, Customs and Border Protection conducts its own environmental assessments, or EA's, on construction projects. Examples include the agency's installation of 5 miles of wire-mesh fencing near Lukeville in 2008 and most recently the completion of 20 miles of new bollard fencing in Santa Teresa, New Mexico, in 2018.

In May, CBP issued a request for public comment on the 63 miles of vehicle fencing the agency intends to replace with 30-foot bollards in Pima and Cochise counties. The period for the public and other government and non-government groups to submit comments closed on July 5.

However, Customs and Border Protection has yet to publish its environmental assessments on the replacement projects, even though construction began on the first 5-mile stretch Aug. 22.

Jordhal, with the Center for Biological Diversity, spoke out against the perceived lack of transparency and chided Customs and Border Protection for awarding the $646 million contract to Southwest Valley Constructors before the center could submit its public comments.

"They asked for our comments, and just a week later they issued a construction contract for this project, which obviously shows that they have no intention of changing their course of action or taking any of our comments seriously," he said.

Customs and Border Protection officials described a number of steps they are taking to mitigate impacts on the environment, in documents submitted to the D.C. federal court in response to the lawsuit against the agency.

In a sworn declaration, Paul Enriquez, Border Patrol's Acquisition, Real Estate and Environmental director, told the court that CBP sought input from numerous individuals, groups and federal agencies on the construction of the 63 miles of bollards.

He described Customs and Border Protection as being "responsive to concerns and input" submitted to it for proposed projects.

"CBP will provide these federal land managers and resource agencies the opportunity to review both the alignment and design of the (wall projects) and to propose design changes that could minimize potential environmental impacts," his declaration read.

Aid volunteers protest

The decision by Customs and Border Protection to pump groundwater to build new bollard fencing in one of the deadliest corridors for U.S.-bound migrants also raised eyebrows among some humanitarian-aid volunteers.

Aid groups and government officials have recovered at least 3,100 bodies of migrants in the Arizona desert since 2001, according to a map maintained by the humanitarian organization Humane Borders, using information from the Pima County Office of the Medical Examiner.

That includes about 233 remains found during that time within the boundaries of Organ Pipe and 167 bodies found at Cabeza Prieta. It's unclear how many more migrant bodies remain undiscovered in these areas.

"What we're doing with water is totally immoral by taking it from the environment, and taking it from the people who need it, and instead just dumping it into concrete," Dan Millis said.

Millis is the borderlands campaign coordinator for the environmental group Sierra Club. In 2008, a federal judge in Tucson convicted Millis, as a volunteer with humanitarian-aid group No More Deaths, for dropping off plastic water gallons for thirsty migrants crossing through the Buenos Aires National Wildlife Refuge, west of Nogales.

Two years later, the 9th U.S. Circuit Court of Appeals overturned his conviction. And though it previously was rare, the U.S. government's prosecution of humanitarian-aid volunteers has picked up under the Trump administration.

Earlier this year, the same Tucson judge who convicted Millis also convicted four other volunteers with No More Deaths for dropping off water at Cabeza Prieta. Another four pleaded guilty to civil infractions and agreed to pay fines.

In the most high-profile case in a decade, a felony trial against No More Deaths volunteer Scott Warren ended in a hung jury in June.

The next month, U.S. prosecutors announced they would seek a retrial on two counts of harboring an undocumented immigrant. Warren's trial is scheduled to start Nov. 12.

Millis pointed out the irony of the federal government trying to deprive migrants of lifesaving water crossing through the Arizona desert while at the same time taking the water underneath it to build barriers to keep those migrants out.

"They're taking water from thirsty people and feeding it to the wall," he said. "And that really shows the sickness of our border policies and what a terrible point we've come to as a country where our priorities are backwards, and we put things over people, we put politics over people."

Have any news tips or story ideas about the U.S.-Mexico border? Reach the reporter at rafael.carranza@arizonarepublic.com, or follow him on Twitter at @RafaelCarranza.