This story was co-published with The Weather Channel as part of Collateral, a series on climate, data and science.

Melissa Hays never would have remembered the day of her humdrum outing at Harp's, a neighborhood grocery store in her hometown of Mayflower, Arkansas, had she not suddenly been overwhelmed by the noxious, chemical smell of oil.

It was March 29, 2013. Few in Mayflower will ever forget it. As Hays ran her errands, ExxonMobil's Pegasus pipeline, which ran beneath this small town, burst without warning along a defective 22-foot seam, spewing 210,000 gallons of heavy Canadian crude oil diluted with large quantities of harmful solvents onto quiet residential streets.

Hundreds of people in this working class community of about 2,000 near Little Rock reported being sickened by an odor that was almost thick enough to feel. Residents soon began to complain about grinding headaches, diarrhea, swollen eyes, dry heaves and burning lungs.

Crews clean up oil in Mayflower, Arkansas, after Exxon's Pegasus pipeline burst along a 22-foot seam and sent heavy crude oil spilling into a subdivision on March 29, 2013. It was the beginning of a long ordeal for residents. Credit: EPA

"I started feeling kind of sick," Hays said later in a deposition as one of the lead plaintiffs in a class action lawsuit against Exxon alleging negligence in its maintenance of the 69-year-old oil artery. "And I just couldn't tolerate the smell."

The smell got into her house, she said, and for a year she couldn't shake a malaise triggered by coughing, congestion and migraines. "I was just constantly sick," she said.

Hays is among more than two dozen Mayflower residents who described their symptoms and their anxiety in depositions that were sealed as part of a 2017 settlement with Exxon but obtained by InsideClimate News.

The depositions, along with other court documents, provide the most complete account to date of the health impacts of the oil spill, which in some respects has remained shrouded in secrecy because the federal agency in charge of pipeline oversight restricted the public's access to the information, and because of the confidentiality agreements Exxon demanded in exchange for the settlements.

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An environmental consultant hired by the plaintiffs' lawyers, whose report is part of the court file, concluded that those nearby residents faced "significant risks" after being exposed to a cocktail of chemicals, including benzene, a known carcinogen; cyclohexane; naphthalene; and toluene. His findings have not previously been reported.

The chemicals he cited had been used to dilute the heavy crude extracted from the tar sands fields of Alberta that leaked from the ruptured Pegasus pipeline, according to court documents. The consultant faulted Exxon for limited air sampling after the spill and for using the wrong health risk standard for assessing potential damage.

Despite the confidentiality agreements, several plaintiffs said that compensation ranged from $2,000 to $15,000, depending on the proximity of the residents to the oil spill.

Crude oil from the broken Pegasus pipeline spilled across yards and streets and into a creek in Mayflower. Residents began to complain of headaches, congestion, swollen eyes and burning lungs. Credit: EPA

Michael Barnes, one of the attorneys representing Exxon, declined to comment and referred questions to the company's media relations arm. Exxon spokesman Jeremy Eikenberry did not address specific questions regarding the settlements, saying only that "all civil cases have been settled or otherwise resolved."

Exxon's extensive holdings of crude extracted from the Alberta tar sands are at the center of a trial that began Tuesday in which the New York Attorney General has alleged that the company misled investors by minimizing the costs and risks associated with its tar sands projects, among the most expensive and carbon-polluting sources of oil on the planet.

Public access to both the sealed depositions and to the more extensive health record from the Pegasus spill in Mayflower are critical as tar sands oil becomes more prevalent among the U.S. energy mix, including in the fuels sold by Exxon. The oil flows from Canada to the U.S. through the Keystone XL, Trans Mountain and the Enbridge pipeline system, among others, which have the capacity to carry hundreds of thousands of gallons annually. All told, there are more than 200,000 miles of oil pipelines crisscrossing the United States, including aging conduits, like Pegasus, that have been in the ground for more than 50 years and account for nearly half of the pipelines in operation.

In the Arkansas civil action stemming from the Pegasus spill—three separate actions were merged into a single class-action lawsuit—plaintiffs alleged that Exxon failed to properly maintain the pipeline and that residents were exposed to toxic chemicals in the tar sand oil that were known to cause severe health problems.

"The hazardous and toxic nature of the heavy Canadian crude oil and liquid hydrocarbons diluting the tar sands resulted in direct air quality contamination after the oil spill, personal and real property and water contamination," according to the 2014 lawsuit filed in the Faulkner County Circuit Court in Arkansas.

Exxon denied that it failed to properly maintain the pipeline and contended the oil that spilled was nothing more than "conventional" heavy crude oil, saying the term tar sands is a colloquial definition open to "varying understandings."

"ExxonMobil is not liable for the plaintiffs alleged injuries or damages because the applicable entities acted in conformity with generally recognized, state-of-the-art standards in the industry," Exxon's response said.

'No Going Up Against Exxon'

While the spill in Mayflower was subject to extensive media coverage at the time, the full extent of both the plaintiffs' health issues and a five-year battle to obtain records related to the spill from the federal Pipeline and Hazardous Materials Safety Administration (PHMSA), have only come fully into focus now. The regulatory agency formally closed the Pegasus case in August after Exxon had paid a $1 million fine two years earlier for failing to adequately maintain the pipeline.

The Pipeline Safety Trust, a non-profit watchdog group, began the five-year fight for information in 2014 about the Pegasus pipeline spill after PHMSA denied a reporter from InsideClimate News access to disciplinary hearings on the incident. The trust ultimately obtained a transcript of the hearing and some regulatory documents, but it was denied many others on grounds that they involved Exxon trade secrets and were not subject to release.

"The lack of transparency creates distrust in the system on the part of the public," the trust's Rebecca Craven said in an interview, "whether that distrust is warranted or not."

Paul Byrd, one of the attorneys who represented the Mayflower families, is now prohibited by a protective order from discussing any aspect of the case or settlement, which he compared, for some billion dollar companies, to buying a cup of coffee. "Do the math," he said, explaining that his clients were the ones who decided to settle in the end.

As in virtually all cases in which plaintiffs claim to have suffered adverse health effects from pollution, causality is extremely difficult to prove. "Exxon would say you can't prove anything," he said. "But that misses the point. Your spill caused that worry, a worry they didn't have before the spill. It's what these people were living with, and will continue to live with."

Kimla Greene said the settlement was forced on her and other plaintiffs and tilted in Exxon's favor because of the company's threat to drag out litigation until the resources of the residents and their attorneys were exhausted, a hardball tactic she said was part of Exxon's legal strategy.

"Exxon took advantage of hard working, everyday people who wanted to have a home," said Green, who said her settlement was in the neighborhood of $10,000. "'Here's your offer. Take it or leave it and if you don't we'll tie you up in litigation for the rest of your lives.' There was no going up against Exxon."

"I'm still living life captive to this spill," she said.

Marsha Cochran is done with the whole ugly thing. Although she declined to say exactly how much she received as part of the settlement, she said that it fell short of compensating for the misery and worry caused by the spill.

"They (Exxon) got off easy," she said in a telephone interview. "Let's say it was the least they could get away with."

Cochran moved away from the neighborhood within a year of the spill.

"I left it all behind," she said. "It's done and over with."

Sealed Depositions Describe Depth of Health Concerns

In hundreds of pages of depositions now sealed as part of the settlement with Exxon, more than two dozen Mayflower residents describe what they considered serious physical and mental harm suffered as a result of the oil spill.

Sitting around conference tables in pristine legal offices, miles from their sullied neighborhood, residents told of tossing out furniture and ripping up carpets that had become hopelessly steeped with the stench of oil. They told of the unexplained death of pets. They said they became afraid to even take walks through their neighborhood.

Melissa Hays, the woman overwhelmed by the smell of oil as she shopped in her neighborhood grocery store, said she threw up immediately after the spill and experienced nausea, dizziness, migraines, depression and anxiety. Asked during her deposition whether she still felt she was suffering from the spill, Hayes, now 39, replied: "I'm still dealing with migraines and it's just not going away at all. ... Because I started getting them after this oil spill and it hadn't gone away."

Hays, who has struggled with anxiety since high school, said she her mental and emotional health has suffered dramatically since the spill. "I just feel more depressed since this happened," she said. "I can't handle the pressure."

The spill ruined the character of her neighborhood, she said, assailing what once was her domestic comfort zone.

"It's not like—the same like it used to be," she said.

Christian Alexander, a 49-year-old immigrant from Nigeria, complained in his deposition of frequent nose bleeds. He'd never, in his life, had one before the spill. "But I've been having a lot of nose bleeds," he said.

Kenneth Hobby, 33, said he and his wife had blinding migraines after the spill and worried enough about the possible health effects to consult a fertility specialist a couple of years after the spill.

Tyler Bates said he and his pregnant wife and their two kids all experienced headaches, nausea and diarrhea after the spill—and Bates himself went to the emergency room at one point for a panic attack.

Connie West reported the smell was "really bad" and said she became immediately queasy and nauseous, and suffered headaches for months. Years after the spill she told Exxon lawyers she remained fearful.

"They are chemicals," she said during a deposition. "You breathe it in. You don't know what the long-term effects (are) going to be. You worry about cancer."

Wilma Subra, an environmental consultant who specializes in working with communities impacted by oil spills, said in an interview with InsideClimate News that the physical disorders experienced by Mayflower residents are typical in people who have been exposed to the kinds of chemicals in the oil that spilled.

"As soon as you are exposed you are start developing these symptoms," Subra said. "It's not unusual that you hear these kinds of complaints."

In some cases the conditions can linger "for a long time" and can become chronic even after a person is no longer exposed, she said.

There is also the worry that exposure to these chemicals can lead to cancer and some organ damage, Subra said.

"It's just not healthy to have exposure to these chemicals," she said.

Exxon Never Fully Assessed Magnitude of Environmental Hazard

The tar sands oil that flowed down the streets of Mayflower is also called bitumen. To get it through pipelines, the chemical solvents thin it into what's known as dilbit, short for diluted bitumen.

The environmental consultant hired by the plaintiff's lawyers, Frank M. Parker, a Texas-based industrial hygiene expert, assessed the potential harm posed by numerous chemicals to the residents of Mayflower on the day of the spill and in the weeks that followed, as workmen did their best to contain the oil and remove as much of it as possible. In all, 26 volatile and semi-volatile chemicals were detected.

"Their exposures were to a mixture of chemicals, which when combined most likely exceeded the threshold concentration necessary to put them at significant risk of developing at least some of the acute symptoms," Parker concluded.

The exposure didn't stop with the spill. It likely continued for some time and spread even further during the clean-up, Parker said in a 2017 report prepared for attorneys representing the residents.

"Workers and equipment also most likely generated vapors, aerosols and/or contaminated particulate matter wherever the 'crude' oil was disturbed," according to the report. "Aerosols and particulates are of special concern as they will travel long distances from their [point of origin]."

In his report, Parker also faulted Exxon for its limited air sampling in the neighborhood—testing that focused almost exclusively on benzene with the exclusion of other chemicals that may have been responsible for many of the symptoms reported by residents.

In addition to sampling for the wrong chemicals, Exxon applied the wrong health risk standards, Parker wrote.

Exxon compared sample results to permissible exposure limits established by the federal Occupational Safety and Health Administration (OSHA).

"These are occupational exposure standards and are not applicable to the general public," the report said. "These standards assume that only healthy adult workers will be exposed to these hazardous materials at these concentrations. They do not take into consideration the young, the old, the sensitized and/or, the infirm which are commonly found in the general population most likely here by plaintiffs and their families."

The OSHA standards also account for eight-hour exposure times coinciding with working hours and not the round-the-clock exposure Mayflower residents experienced.

Parker told attorneys that it would have been more accurate to employ an exposure matrix designed for the general public that was developed by the U.S. Department of Health and Human Services Agency's Toxic Substances and Disease Registry.

Applying those guidelines instead of the OSHA standards suggest Mayflower residents were at "significant risk."

"When you add the fact that the plaintiffs were most likely exposed to a mixture of ... chemicals, aerosols, and contaminated particulates the risks are increased even more," according to Parker's report.

Parker also faulted Exxon for its misleading public statements made in newsletters published by the company that did not accurately reflect the danger faced by residents because of the inadequate monitoring and risk assessments.

"The ExxonMobil Newsletters consistently report that air monitoring in the Mayflower community 'show levels that are non-detect or that are below any necessary action levels,'" the report said.

The reality is Exxon had no idea what cumulative effect of all the chemicals had on the residents of Mayflower, Parker said in an interview with InsideClimate News.

Air sampling by Exxon's paid environmental consultants showed levels of individual chemicals were below the federal safety standards. But that is parsing the results in Exxon's favor, Parker said in an interview.

"Not taking into account the cumulative effect of all the chemicals is a big problem," he said. "That's the real world of what these folks were exposed to.

"When you consider the risk criteria for each chemical alone, the bottom line is you are under estimating the risk that comes from the cumulative effects of exposure to all these chemicals."

Jason Thompson didn't know the danger posed by the toxic crude at the time, and Exxon never told him or his fiancée or his neighbors.

"They looked at Mayflower as some Podunk town," he said in an interview with InsideClimate News. "They saw us as dispensable."

"They lied to my face. The residents needed to know the truth. If there are chemicals in the air tell us so we can get the hell away from it," he said.

He moved away seven months after the spill, but the legal fight with Exxon went on for another four years. His cut of the settlement was $4,000, a sum arrived at because no oil touched his property.

"I got my settlement and they think I'm done," he said. "But as far as I'm concerned, I'll never be done with it."

Aspects of This Spill Will Never Be Known

The Pegasus spill spawned a five-year fight for disclosure and transparency by the Pipeline Safety Trust, a non-profit, non-partisan watchdog group.

The genesis for the trust's interest came about when a reporter from InsideClimate News was denied access to PHMSA disciplinary hearings in 2014 on allegations that the company delayed crucial inspections and ignored warning signs before the pipeline burst.

That prompted the trust to file an extensive Federal Freedom of Information Act request with PHMSA in 2014 for records associated with the federal agency's investigation of the spill. The trust sought records related to the agency's investigation of Exxon and those shedding light on the closed door disciplinary hearing. In essence, it wanted a transparent accounting of how Exxon explained the spill, what PHMSA concluded happened and how the federal agency reached its final disciplinary decision.

A worker conducts air monitoring at the site of Exxon's oil spill in Mayflower. An environmental consultant hired by the plaintiff’s lawyers later argued that Exxon under-reported the risks: “Not taking into account the cumulative effect of all the chemicals is a big problem,” he said. Credit: EPA

In 2015, two years after the spill, Exxon was hit with a $2.6 million fine and was harshly criticized by the Pipeline and Hazardous Materials Administration (PHMSA) for inadequately maintaining the Pegasus pipeline. Federal regulators also faulted the company for its failure to spot warning signs that the aging pipeline had structural defects that led to the rupture.

Among the nine safety violations cited by regulators was Exxon's failure to assess the integrity of the pipeline even though the company knew of risks that included cracking along its lengthwise seams. The company also did not meet deadlines to conduct required regular safety tests and failed to prioritize testing the section of pipeline that ruptured, according to the order.

Exxon appealed the findings. And in 2017, a federal court overturned the violations and dismissed $1.6 million of the fine after the company argued there was no proof its conduct contributed to the spill. The court agreed, saying the company met its legal obligation when it "conducted a lengthy, repeated and in-depth analysis" of the pipeline and its risks.

Beyond settling with the Mayflower residents, Exxon has also reached settlements to resolve environmental damage. Exxon agreed to pay $3.19 million in federal civil penalties for Clean Water Act violations, $1 million in state civil penalties for state water and pollution violations, $600,000 for a project to improve water quality at Lake Conway and $280,000 to the Arkansas Attorney General's Office for litigation costs.

The oil spill reached waterways, including the "cove" area of Lake Conway, and led to fines for environmental damage. Credit: EPA.

Still, secrecy prevailed around numerous aspects of the Pegasus spill, as the Pipeline Safety Trust engaged in what it saw as a highly frustrating battle with PHMSA and Exxon.

During the five-year effort to pry open the box of secrecy surrounding the Pegasus spill, the trust's Rebecca Craven encountered multiple denials for records by PHMSA, coordination between the federal agency and Exxon on whether certain records should be released, and unsatisfactory explanations for the secrecy.

The public should know what happens in enforcement hearings and what information is exchanged between PHMSA and the pipeline operator, along with legal arguments being made by the operators and PHMSA's attorneys, Craven said.

"Without access to the hearings and documents, the public can't know why the agency may dismiss certain violations or lower penalties or what safety information the operator may have provided," she said.

The most enlightening information wrenched from PHMSA was a transcript of the closed enforcement hearing, Craven said.

"I think the release of the transcript makes clear that in a lot of cases, if not all of them, there's no reason the hearings shouldn't be open and subject to public notice," she said.

More than 200,000 miles of oil pipelines crisscross the United States, including aging conduits, like Pegasus, that have been in the ground for more than 50 years and account for nearly half of the pipelines in operation. Credit: U.S. EPA

PHMSA spokesman Darius Kirkwood explained a number of caveats that restrict public access, including closing portions of hearings when a pipeline operator objects that public disclosure of information would mean revealing trade secrets.

After being notified of the Pipeline Safety Trust's request for records, Exxon responded by asserting the records should remain confidential because of the trade secrets exemption and because the company was still embroiled in litigation related to the spill, citing an exemption based on the premise that the company could be deprived of a fair and impartial adjudication of the pending legal action if the records were made public.

"The response is clearly an attempt to prevent disclosure of any records at all relating to the Pegasus pipeline, its failure and the enforcement action brought by PHMSA," Craven told federal regulators.

The struggle for transparency ended earlier this year with a curt statement from an agency FOIA officer that PHMSA had concluded its response, citing the release of 708 pages of documents along with a slew of final denials.

Top photo illustration based on an EPA photo from the oil spill in Mayflower, Arkansas.

Clarification: An earlier version of a graphic in this article incorrectly described synthetic crude as being the same as diluted bitumen. Both are crude oil blends produced from the oil sands, but have different densities and other properties.