Santa Susana Field Laboratory, one of the country's most toxic sites, is just 40 miles from LA.

It’s only a 45-minute drive from downtown Los Angeles to reach one of the most toxic hills in the country - a vivid case study of the chaos that ensues when scientific hubris meets corporate carelessness.

Just take the 101 north into Ventura County, take exit 29 and turn left on a winding road that traces the edges of the Simi Hills, a brown, rocky terrain veined with low shrubs.

The road leads past a mobile home park and a few tony housing developments, past a sign that says “No jogging” and to guarded gate - the entrance to the former Santa Susana Field Laboratory. In an ironic nod to past wrongs, a retro-style sign affixed to the gate reads, “Safety does it.”

At the entrance, I met Mary Aycock, a safety specialist with the Environmental Protection Agency. She’s an energetic woman with wide eyes and a loud voice with a Southern lilt.

She quickly ushered me to her car so we could go “see some cool stuff.”

In the 1950s, this 2600-acre mountaintop roared with nuclear reactors, bombarding uranium-238 to make plutonium, a powerful radioactive fuel.

The site’s sodium reactor experiment was the first to generate electricity, briefly, for the nearby city of Moorpark. It was also home to the SNAP-10, the first nuclear reactor to be launched into space.

Back then, the U.S. government pursued nuclear development with few holds barred, anxious to keep pace with the Soviet Union’s nuclear power programs. “This was gonna save the day,” said Christina Walsh, a resident who lives in West Hills at the base of Santa Susana’s mountain. “This was gonna beat the Russians.”

Unfortunately, Santa Susana never beat anyone but itself. In 1959, the sodium reactor became America’s first partial nuclear meltdown when eager engineers pushed it beyond its power limits. The reactor’s damaged fuel rods spewed radioactive gasses into the atmosphere - hundreds of times more than at Pennsylvania’s Three Mile Island, by some estimates.

In the decades to come, at least three other reactors malfunctioned. Making matters worse, rocket tests that were conducted on another part of the site contaminated the land with millions of gallons of the toxic chemical trichloroethylene, an engine degreaser otherwise known as TCE.

“This place provokes fear in peoples' hearts,” Aycock explained. “Most people don't understand radioactivity. The don't know what the levels mean, and they don't know what's still out here."

Fear is an understandable reaction to Santa Susana, because after decades of radioactive and chemical spills, nobody knows how deadly the mountain really is. And worse yet, nobody is sure if it’s what is causing cancer in local residents.

Years of cover-ups, shoddy safety practices and changes of ownership between Atomics International, Rocketdyne and Boeing have made it virtually impossible to know for sure just how many harmful chemicals and radioactive elements remain in the soil and just how severely they affect the health of surrounding communities.

Although activists secured the promise of a decontamination in 2007, the cleanup process has turned out to be just as messy as the nuclear operations themselves. Today even the most ardent environmentalists disagree about the best way to return the area to its rightful state.

In September, two of the site’s current owners, NASA and the Department of Energy, reached an agreement to remove all of the contaminated soil. To begin that process, they charged the EPA with finding out exactly how high the radiation levels are.

Each day, EPA staff members sweep the area using forklifts that hold detectors - four-by-four steel boxes containing sodium iodide crystals that glow when they’re struck by radioactive energy. Soon the EPA’s staff will be sucking out chunks of soil to be tested for radioactive elements, also called radionuclides, and for chemical contamination left over from the rocket tests.

“Oh, this is really nice,” Aycock said, walking up to a brand-new yellow agricultural forklift. “These are the kinds of things that get us excited.” The new, smaller forklifts have a better turning radius, which comes in handy as they comb the steep mountainside, searching for signs of gamma radiation, a footprint of decaying radioactive elements.

In areas where the terrain is inhospitable for forklifts, the EPA sends in one of their two mules, Sarah and Kate, to walk the ground with detectors strapped to their saddles.

At the EPA’s administrative headquarters at the site - a drab building reminiscent of a military bunker - workers pore over maps of the field lab. Occasionally, they meet in a conference room, which is wallpapered in more maps showing areas that have been scanned, areas that still need to be scanned and what elements might still be in the soil.

One map shows all the radiation levels, and so far, it doesn’t look like there’s very much. The map was mostly green, meaning that the levels of radiation were “background,” or the same level you might find anywhere else in the world - a combination of natural elements and residue from past nuclear weapons tests. A few splotches were yellow, which meant the area was slightly above background levels.

“But,” Aycock assured me, “there's a difference between things that are above background and things that are dangerous to your health."

Red, on the other hand, means high levels of radiation; one fat red stripe glares from the map’s center. Aycock attributes it to naturally-occurring thorium and uranium in rocks that had been used to construct a building, but some who have studied the site think the red might be from radioactive waste in the soil beneath the rocks.

The EPA hasn’t scanned some parts of the area yet - most notably, the remnants of the ill-fated sodium reactor. In 1959, the reactor’s coolant channels became blocked and its blazing-hot fuel rods overheated, melting and leaking radioactive elements into the environment.

Although the site’s current owners maintain that no radioactivity was released, uncertainty persists because no one measured the release at the time of the accident. Atomics International, who operated the reactor, originally said that no radiation escaped the reactor’s walls during the 1959 accident. But in memos to the Atomics Energy Commission years later, the company admitted that gasses were, in fact, released.

The biggest potential cancer culprit would be releases of radioactive iodine, which would have been transferred into milk supplies from cows in the area. But Atomics International never tested for iodine.

As further evidence, workers spent “considerable time decontaminating the building where the reactor was contained [after the accident],” said Gregg Dempsey, a physicist with the EPA. “Noble gases shouldn't have caused lasting contamination, so I suspect there was more than noble gases released.”

Years later, other scientists found radioactive elements scattered around the site and in the groundwater, possibly remnants from the sodium reactor or other accidents. Former employees have also said that the reactor gasses were allowed to “vent” into the atmosphere.

“It's a big mess,” said Jan Beyea, a nuclear reactor researcher and former professor at Princeton. “When you hide the data, when you're not straight with everybody, when there's no public body investigating it, there's no way anybody can be sure what happened.”

Today, the sodium reactor’s foundation lies covered by a black felt tarp to prevent the escape of any potential remaining radiation. When the sodium reactor and other reactors at the site were decommissioned, much of the land was excavated and trucked off to waste facilities in the ‘80s and ‘90s. Then in 2007, the Santa Susana cleanup law, Senate Bill 990, was passed, mandating the removal of any remaining contaminated soil so as to achieve the lowest levels of radiation possible and make the land suitable for agriculture again.

The law’s purpose is to allay the anxieties of people, like me, who fear what still might be lurking beneath Santa Susana.

“So, is it safe for us to be right here?” I asked as we stood next to the edge of the former sodium reactor’s tarp. A hokey brown sign next to us announced, “SODIUM REACTOR,” as though it were a tourist attraction, and a worker wearing only a sun hat for protection casually strolled by.

“No! We’re all gonna drop dead!” Aycock said. She let out a riotous laugh. “No, of course it’s safe.” I laughed, too, and shuffled nervously toward the car.

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Dan Hirsch, a nuclear policy lecturer at the University of California at Santa Cruz, describes the operations at Santa Susana in the ‘50s as the cavalier actions of “nuclear cowboys.” Descriptions of the site’s operations read like an apocalyptic movie script: Toxic waste was burned in open, unprotected pits. Sometimes, workers shot barrels of chemicals with rifles in order to burn them, releasing deadly fumes into the air.

“There was a certain laissez-faire attitude towards safety,” Dempsey said. “After all, it was the Cold War.”

In cleaning up the sodium reactor accident, workers crawled stomach-first along the contaminated floor, fishing for partially-melted fuel rods. Multiple workers told local activists that books, furniture and clothing from inside the contaminated buildings were heaped outside in piles to decay. Occasionally, the workers used Kotex sanitary pads to scrub down the reactor because their brooms and sponges would become contaminated with radiation too quickly.

Boeing, which owns part of the land, has challenged SB 990 in court because it says the agricultural cleanup standard is stricter than that expected of other comparable sites. The company said they plan to use the land as a park, which would mean the radiation levels could be left at above-background levels because people wouldn’t be receiving a constant radiation dose from living there.

According to Boeing, the waste-management practices were standard for their time. “In the '50s and '60s, the atmosphere was different,” said Kamara Sams, a Boeing spokeswoman.

She said burning potentially hazardous waste in open pits was standard operating procedure, and not just at Santa Susana. “We were in a race with the Soviets. There were certain practices, like burn pits, that were standard, and [waste] disposal sometimes meant land-filling on site.”

The dubious practices at Santa Susana went largely unmonitored until the late 1980s. That’s when Chernobyl showed the world what happens when nuclear energy goes horribly wrong, and the Department of Energy launched a campaign to inspect nuclear reactors across the U.S. The review of Santa Susana found poor safety practices and profound contamination, and in 1989 Gregg Dempsey surveyed the land and confirmed those suspicions.

Dempsey also found that Rocketdyne was dishonest in monitoring radiation levels. Rocketdyne workers washed vegetation samples and filtered water samples prior to testing them. “If you didn’t want to find radiation, [washing and filtering] was a good way to do it," Dempsey said. 

Photo by Christina Walsh.

The body naturally repairs damage from small amounts of radiation, but large amounts can mutate cells, causing cancer years later. We absorb low amounts of radiation from space when we ride in airplanes or climb on top of mountains. We get even smaller doses from eating bananas or brazil nuts, because both have trace amounts of radioactive elements in them.

Humans absorb about .24 rems of radiation per year, but limits for workers in nuclear power plants are higher, about 5 rem per year.

Workers at Santa Susana may have absorbed much more than that, but there’s no telling exactly how much because entire boxes of the workers’ dosimeters, devices that measure radiation, were lost or hidden. In the 1990s, researchers from UCLA found that the more Rocketdyne workers were exposed to both radiation and chemicals at the site, the more likely they were to die from cancer.

Local residents also say they’ve been sickened by the site. Former worker James Dodge, who lives in Simi Valley, said he knows of roughly 30 cases of cancer within 500 feet of his house. Though Dodge is healthy, his son was diagnosed with testicular cancer in 2008.

“Did he get it from the hill?” Dodge said. “Shoot, I don’t know.”

But epidemiologists who’ve studied potential cancers in the local community say it’s hard to say how many cases were caused by the activities at Santa Susana. Most of the gasses from the sodium reactor dispersed about 60 miles away - and that’s where many of the cancers in residents were found.

But that’s also where the population is denser, and therefore one would expect more cases of cancer in any event. Jan Beyea, the nuclear reactor researcher, found an average of 50 cancers in the community related to the sodium reactor accident alone.

But he doesn’t know if that figure is accurate because “we're not sure about the size of the release,” he said.

But even if they find no radiation at Santa Susana, cleanup officials would still be left with the site’s underground stew of chemical toxins. Throughout the 1980s, Rocketdyne employees would pour the leftover chemical TCE onto the ground in the course of testing jet engines.

“The TCE would soften up the asphalt,” said Dodge. “So I always put mine in a bread pan.”

Today, thousands of gallons of TCE and other chemicals remain in the site’s soil and groundwater. TCE causes everything from liver cancer to leukemia. Another chemical used in the engine tests called perchlorate disrupts thyroid function in even tiny concentrations, and it’s been found in multiple wells near the site.

Knowing what’s up there, residents are worried about what’s coming down.

“This stuff is on a mountaintop,” Hirsch said. “Gravity being what it is, the contamination that’s on that plateau wants to move on to the people below.”

In response, the people below formed something of a cleanup militia. Led by Hirsch, they pressured lawmakers for over 15 years to restore the site to its original state - tranquil farmland. With the passage of Senate Bill 990, they finally secured the promise of a cleanup in 2007, but it took three years of legal wrangling between Boeing, the DOE and NASA before the EPA was finally able to begin soil testing in October.

Now, they wait to see what the EPA digs up.

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"If you look out that window, you can see it," said Christina Walsh, a thin, blond-haired woman with a booming voice and big smile. She points out her back window to her yard, which looks out onto a peaceful valley and then, a few miles away, to Santa Susana itself. If there is, in fact, any toxic goo coming off the mountain, she is at ground zero.

Soon after she moved into her house in the West Hills in 2001, she saw a flier at her karate studio asking, "Did you know there was a nuclear meltdown here in 1959?"

Recently, one of her neighbors told her that there’s cancer in half the houses on her street. Walsh, who is healthy, wonders if it's only a matter of time.

"I'm a ticking time bomb," she said.

Walsh gesticulates wildly, even with a bandaged hand (kitchen accident) and a busted shoulder (horse-riding accident). She’s the sort of person who goes to great lengths for a cause, like hopping a fence at Santa Susana, taking 30,000 pictures of contamination and showing them to the EPA. Over the years she has pored over thousands of pages of documents to find out how the spill might have affected her community.

Since 2001, she’s run a group called CleanUpRocketydyne.org, which lobbied with Dan Hirsch’s organization, the Committee to Bridge the Gap, for the passage of SB 990.

Hirsch convinced the state to use California’s standards for the cleanup, which are even stricter than the EPA’s standards for the so-called “superfund” sites - the most polluted areas of the nation. In effect, the cleanup - which involves removing any soil above background levels of chemical or radioactive substances - should effectively eliminate any cancer risk for residents by 2017.

Carting away all of the contaminated soil would be the only way to get rid of the longer-lasting radioactive elements, if they’re found.

“Some radionuclides are very short-lived, but some take a quarter billion years to break down,” said David Lochbaum, a nuclear specialist with the Union of Concerned Scientists.

Cesium, for example, has a 28-year half-life, or the time it takes for half of its atoms to die off. But uranium or plutonium will continue being radioactive for tens of thousands of years.

But excavation is also a difficult and dirty task. The levels of contamination would add up to an estimated 1.6 million cubic yards of soil, or 100,000 dump-truck loads, which would mean a soil-toting dump truck would chug past the Simi Hills’ homes every hour for months.

There’s also no clear destination for the soil that gets scooped out. Chemical waste can go to lower-level landfills, but only a few dumps in America accept radioactive materials. Transporting soil there is expensive and dangerous.

“There's no way to resolve this ever if we have nowhere to put it,” Walsh said.

As the cleanup has dragged on, the activists have broken into splinter factions, debating about the best way to de-toxify the mountain. Walsh is grateful to Hirsch for helping pass a cleanup law, but she thinks the bill might be going too far with its plan for total removal of any contaminated soil.

She, along with a few others, have called the intensive soil removal “revenge science,” meaning that they think the aim is to get revenge on Boeing for polluting the land in the first place. Instead, she and some of the others in her group would like to see a cleanup that purifies the soil while removing less of it - a strategy known as “in situ” remediation.

It would mean planting various types of flora, like mustard plants and willow trees, that have been shown to eventually break down chemical compounds. One scientist who studied Santa Susana said certain kinds of bacteria can be used to metabolize TCE, the engine degreaser, by eating up its chlorine until only the benign gas ethelyne remains.

Other experts agree that the current radiation levels at the site may prove to be too low to merit soil excavation. According to the EPA’s figures, the site gives off about half a rem of radiation per year. Cleaning the soil up to background may not be worthwhile, some argue, because the term “background” has a lot of statistical variation and might be too broad.

“You’re going to be cleaning everything, and some of it might be natural,” said Abe Weitzberg, an engineer who once worked at the site and has been close to the debate for years. Like Walsh, he thinks the site should be made clean enough to be park land, where people could visit occasionally, but not live.

And, since most of the health risk fell on the site’s former employees and, in some cases, the people who lived near the site at the time of the SRE incident, some say its not worth it to meticulously tear apart the mountain if there are only traces of radiation left in the present-day.

“They should contribute to cancer research or something that will end up reducing cancer deaths in the future instead,” Beyea said. “I don't think someone should cart away soil for revenge. You can make things worse if you do things like this.”

The problem? Less excavation is exactly what’s favored by Boeing. But Boeing and their predecessors have lost credibility in the community, according to some activists, because of Santa Susana scientists' past secrecy. And now, total excavation might be the only way to reassure worried residents that they aren’t getting cancer from the mountain next door.

Even after the EPA finishes soil testing in the middle of next year, there still won’t be much certainty about the best way forward for Santa Susana, or about what it has done to public health as its toxins have laid simmering for 50 years.

Every nuclear disaster leaves a different type of footprint on the land, and all are notoriously difficult to undo.

“It’s a hell of a lot easier to spill stuff than it is to clean it up,” Hirsch said.

Of the 100 similar nuclear facilities in the country, Santa Susana is in the middle range as far as environmental damage. Savannah River in South Carolina, Rocky Flats in Denver and Hanford in Washington state are all far worse, according to Hirsch.

But there’s one key difference between those sites and Santa Susana: the latter is in the middle of a major metropolitan area. The site’s groundwater flows under Simi Valley homes, and it feeds directly into the L.A. River.

That means the unsafe practices at Santa Susana didn’t just sicken its workers, they landed Santa Susana’s ominous refuse squarely in Los Angeles’ backyard.

To reach Olga Khazan click here. Follow her on Twitter.