Environmentalists say the U.S. Army Corps of Engineers failed to comprehensively assess the impacts the massive Benson development will have on groundwater supplies.

For the second time in three years, a critical permit for the controversial Villages at Vigneto development in Benson has been suspended.

The U.S. Army Corps of Engineers last week suspended the 28,000-home project’s Clean Water Act permit. The move comes less than two weeks after environmentalists filed a lawsuit alleging the Army Corps’ November decision to approve the permit violated the Endangered Species Act and National Environmental Policy Act.

The lawsuit alleged Phoenix-based developer El Dorado Holdings used a dubious argument to persuade the Army Corps to dramatically limit its scope of analysis when evaluating Vigneto’s potential environmental impacts. The agency’s narrow analysis avoided any exploration of potential effects of the project’s groundwater pumping for 70,000 anticipated new residents, said Stu Gillespie, attorney for Earthjustice, the environmental law firm representing the six plaintiffs in the Vigneto lawsuit. The plaintiffs are the Lower San Pedro Watershed Alliance, Sierra Club, Center for Biological Diversity, Tucson Audubon Society, Maricopa Audubon Society and Cascabel Conservation Association.

“It’s hard not to come away from this (permit suspension) with the impression they have understood there are legal flaws in their permit that we identified in our lawsuit,” Gillespie said.

El Dorado Holdings spokesman Mike Reinbold did not respond to the Star’s request for comment.

In a Feb. 15 letter to Reinbold, Army Corps regulatory division chief David Castanon said the permit suspension is effective immediately, and the developer must stop any activities previously authorized under the permit. El Dorado had intended to break ground on Vigneto in the first quarter of 2019.

“The Corps has determined that it is in the public interest to suspend the permit while the Corps considers corrections and clarifications to the October 2018 Memorandum for the Record (and any related materials) that I relied upon in deciding to reinstate the modified permit and whether any additional modifications to the permit are warranted prior to making a new permit decision,” Castanon wrote. Castanon was referring to the October environmental assessment that paved the way for the permit approval.

Army Corps spokesman Dave Palmer said the agency cannot comment on the permit suspension due to pending litigation.

This is the second lawsuit to beset the project, which secured Benson City Council approval in July 2016. The approval came two months after six environmental groups filed their first lawsuit involving Vigneto, alleging the Army Corps failed to engage in required consultation with the U.S. Fish and Wildlife Service about the project’s impacts on protected species and their habitats.

Within days of the City Council approval, the Army Corps suspended the Clean Water Act permit pending interagency consultation on the project’s impacts. The parties ultimately settled the lawsuit after the consultation occurred.

Robin Silver, co-founder of the Center for Biological Diversity, cited two studies that show Vigneto will likely deplete water in the St. David Cienega, the only marshland left in the San Pedro River’s federally protected conservation area. The Bureau of Land Management calls 57,000-acre San Pedro Riparian National Conservation Area one of the most important riparian areas in the country.

One study, commissioned by the Center for Biological Diversity for about $4,000, found that in three of five tested scenarios, well pumping at Vigneto would lower the water table beneath the cienega by between 0.8 feet to 1.5 feet within 100 years.

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The study was a scaled-down version of a $1 million U.S. Geological Survey study that was canceled in 2010 amid budget cuts. It would have been the last in a series of three studies funded by the USGS and Arizona Department of Water Resources exploring how groundwater pumping could affect the San Pedro River.

Silver questioned why Bureau of Land Management officials have not weighed in on a project that affects waters under their management in the San Pedro Riparian National Conservation Area.

“We can’t replace these places,” he said. “BLM has been silent, even though it’s their water that’s going to be stolen.”

BLM’s Arizona director Ray Suazo could not be reached for comment Wednesday.

In a Feb. 18 email to Gillespie, the U.S. Department of Justice attorney representing the Army Corps said the agency may be able to make a decision on the suspended permit — whether to reissue, further modify or revoke it — before it must file a response to the environmentalists’ lawsuit in April.

Gillespie said that email, which he shared with the Star, makes him suspect the Corps may seek a swift reinstatement of the permit, rather than engage in a thorough analysis before reevaluating the permit.

“They could actually go through the full NEPA (National Environmental Policy Act) process and do an environmental impact statement to really grapple with the hydrological studies and take a comprehensive look at the entire development,” he said. “That would be a multiyear process.”

Contact reporter Emily Bregel at ebregel@tucson.com or 573-4233. On Twitter: @EmilyBregel