NEVADA TEST SITE, Nev. — A planned 700-ton test explosion scheduled for Friday in the desert 90 miles northwest of Las Vegas was put on hold by the federal government last week.

While the test has not been cancelled, anti-nuclear activists claimed victory in stopping the ammonium nitrate and fuel oil blast expected to create a 10,000-foot mushroom cloud that could be viewed from the city. By comparison, the explosion was projected to be 280 times larger than the 1995 Oklahoma City bombing, or about one-twenty-fifth the power of the atomic bomb that leveled Hiroshima.

During a tour of the site last week, an official assured The Daily that the test would be safe. But many environmental officials and local Native American tribe leaders were unsatisfied with the environmental impact data provided by the Defense Threat Reduction Agency (DTRA). They worried that the large blast would kick up radioactive dust from extensive nuclear testing conducted near the site from the 1950s through the early 1990s.

The National Nuclear Security Administration (NNSA) explained its actions as “being taken to clarify and provide further information regarding background levels of radiation from global fallout in the vicinity of the Divine Strake experiment,” according to a statement released last Friday, following a U.S. District Court hearing in Reno, Nevada .

Before the announcement, site and federal officials had firmly defended the safety of the test, saying there was “no radioactively contaminated soil in the vicinity of the detonation site.”

According to John Spahn, a Bechtel contractor and former manger of the HazMat center program at the Nevada Test Site, “The test will take place about two miles from the nearest underground [nuclear] test and four miles away from ground zero for the closest above-ground test.”

The government withdrew this finding with last week’s announcement.

The Western Shoshone Indians had filed a lawsuit seeking an injunction, claiming that the test would irreversibly harm tribal lands.

“They say that government hasn’t provided the needed assurance [that] nearby tribal lands would [not] be threatened.” said David Cherry, the communications director for Rep. Shelley Berkley, (D-Las Vegas). He expressed support for the lawsuit, saying that the Shoshones’ claims had “good documentation.”

Bob Hager, the attorney representing the Shoshones, told The Las Vegas Review-Journal over the weekend that the government had cancelled a June 8 federal court hearing regarding the project. According to Hager, the government delayed the experiment because it cannot provide evidence demonstrating the test’s safety. Originally scheduled for June 2, the testing had already been rescheduled for June 23 before its indefinite postponement.

Sen. Harry Reid (D-Nev.), welcomed the delay in an official statement. This represents a change of heart from last week, when a Reid spokeswoman told The Daily that the Senate minority leader supported the test after being given assurances in a classified briefing.

“They showed us the test will be absolutely non-nuclear and conventional in nature,” said that spokeswoman, Sharyn Stein. “At the end of the meeting, he said he would not object because he feels they have taken the proper steps to do the test safely.”

The NNSA had said that the $23 million test would allow defense planners to understand the structural integrity of deep, underground tunnels when targeted with massive firepower. Since no plane can hold 700 tons of explosives, a hole dug at ground level would be filled with the explosives, and scientists would measure their impact on an existing tunnel 1,100 feet under the surface.

The ability to destroy underground tunnels has become a military priority as fears about bunkers deep in Iran and North Korea have intensified. Some worried the operation would foreshadow the return of nuclear testing ended by the 1992 Comprehensive Test Ban Treaty.

“The real concern is that this is in some ways a precursor to new nuclear testing and development,” Cherry said. “There are some things that don’t square up. All along, we’ve always said, ‘why do they need to test something with 700 tons of explosive?’”

Controversy ensued after several news outlets reported on the magnitude of the planned blast.

“I don’t want to sound glib here but it is the first time in Nevada that you’ll see a mushroom cloud over Las Vegas since we stopped testing nuclear weapons,” said James Tegnelia, head of the Defense Threat Reduction Agency, in May.

The State of Nevada had expressed some initial concerns about the project but seemed to accept federal government assurances that the test would not threaten the health of those downwind.

“The governor mostly deferred to NSA on this one,” said Bob Loux, director of the Nevada Agency for Nuclear Projects. “We’ll see what happens but it’s not a huge issue for us.”

Based on state support and federal assurances, other members of the Nevada congressional delegation were not opposed to the test.

“In November of 2005, my office received a report on the plan to test the explosive charge in Nevada,” said U. S. Rep. Jon Porter (R-Nev.). “This report, along with the state’s subsequent approval of the planned test, addressed my initial concerns about Nevadan’s safety.”

Nevadans weren’t the only ones alarmed. Since Utah has the dubious distinction of being downwind from Nevada, its political leaders are even more concerned about the test. Clusters of cancer patients match the dispersal patterns of radiation from after nuclear testing conducted at the site decades ago. Its congressional delegation issued some of strongest rebukes.

“After reading comments about mushroom clouds and low yield nuclear weapons, I was greatly concerned, and expressed as much to the director of DTRA,” Rep. Jim Matheson (D-Ut.) said. “I advised them to put all the health and safety data out on the table so that people’s fears about being once again exposed to radioactive contamination could be addressed. I am very pleased to see that these agencies have acted on my advice.”

A Divine Strake Coalition of 41 organizations formed to oppose the test. On Sunday, about 300 protesters gathered at the entrance to the site to celebrate the postponement.

On a tour of the site that included the location of the Divine Strake tests, visitors largely supported the test.

“I’m not a proponent of nuclear weapons or anything, but it’s something necessary to do in order to protect the state,” said Tom Harrington, a retired math teacher from Chicago. “We need to learn how to react if something happens. That’s what survival is all about.”

The project name, Divine Strake, refers nautically to a continuous line of plating from the stem to stern of a ship. In bomb manufacturing, the term ‘strake’ refers to the rail that attaches the bomb to the launch platform.