In 1952, Pacific Gas & Electric began using hexavalent chromium at a natural-gas compressor station on the edge of the Mojave Desert. The chemical was cheap, effective, and — as the company would later claim — not well understood as a groundwater hazard. Over the next fourteen years, wastewater laced with chromium-6 was discharged into unlined ponds in the dry soil outside Hinkley, California. It leached into the aquifer. It spread. And for decades, while the plume crept beneath homes and wells, no one in the community was told.
What followed — the illnesses, the investigation, the landmark lawsuit, the Hollywood adaptation, and the slow, grinding depopulation of the town — became the most consequential story in the history of US drinking water awareness. Understanding it in full means looking past the Oscar ceremony and into what actually happened to Hinkley after the cameras left.
The Compressor Station and the Unlined Ponds
The Hinkley compressor station sat along PG&E’s gas transmission pipeline in the high desert of San Bernardino County, about 120 miles northeast of Los Angeles. Compressor stations like this one use large engines to push natural gas through pipelines at pressure. Those engines and their associated cooling towers were prone to rust — a serious operational problem — and in 1952 PG&E introduced chromium-6 as a corrosion inhibitor. It was widely used in industrial cooling systems at the time.
The problem was what happened to the wastewater once it had done its job. Rather than being treated or hauled away, contaminated water was released into open, unlined ponds dug into the sandy desert soil. The assumption — or at least the practice — was that the desert would simply absorb it. Instead, chromium-6, which is highly water-soluble and chemically stable in oxidizing groundwater conditions, migrated steadily downward into the shallow aquifer that Hinkley’s roughly 2,000 residents depended on for drinking water. PG&E discontinued its use of chromium-6 at the Hinkley station in 1966, but the contamination was already well established in the ground.
PG&E was aware of contamination at the site by at least the late 1980s, when it conducted groundwater testing and found elevated chromium levels. The company began a quiet remediation effort without notifying local residents that their well water might be affected.
A Cluster of Illnesses and One Tenacious Clerk
Through the late 1980s and into the 1990s, Roberta Walker and her neighbors began comparing notes about health problems that seemed unusual for a small desert community: tumors, miscarriages, nosebleeds, chronic headaches. The clustering of serious illness in a geographically compact area drew attention, but without a known cause, it was easy to dismiss.
In 1991, a woman named Erin Brockovich went to work as a file clerk at Masry & Vititoe, a law firm in Thousand Oaks owned by attorney Ed Masry. Brockovich had no legal background. What she had was persistence, attention to detail, and a talent for talking to people. When she came across real estate documents related to Hinkley in the firm’s files — documents that included water test results for a property near the compressor station — she began investigating on her own initiative, driving out to the community and knocking on doors.
What she found was a pattern. Residents throughout the area around the compressor station had been experiencing serious health problems for years. Many had been approached by PG&E representatives about property transactions or had been offered to have their water tested, without being told why. Brockovich connected the medical histories to the groundwater data and to PG&E’s internal documents, which she ultimately obtained and which showed the company had known about the contamination for years before any disclosure.
Masry & Vititoe filed suit against PG&E in 1993 on behalf of the Hinkley residents.
How It Unfolded: A Timeline
| Year | Event |
|---|---|
| 1952 | PG&E begins using chromium-6 as a corrosion inhibitor at the Hinkley compressor station |
| 1966 | PG&E discontinues chromium-6 use at the station; contamination already established in aquifer |
| Late 1980s | PG&E conducts groundwater tests, detects chromium contamination; does not notify residents |
| 1991 | Erin Brockovich joins Masry & Vititoe as a file clerk; begins investigating Hinkley documents |
| 1993 | Masry & Vititoe files suit against PG&E on behalf of Hinkley residents |
| 1996 | Case settles for $333 million, paid to more than 660 Hinkley plaintiffs — the largest settlement in a direct-action lawsuit in US history at the time |
| 2000 | Film Erin Brockovich, directed by Steven Soderbergh and starring Julia Roberts, is released; Roberts wins the Academy Award for Best Actress |
| 2008 | National Toxicology Program publishes landmark study showing chromium-6 in drinking water causes cancer in rodents |
| 2011 | California OEHHA sets a public health goal of 0.02 ppb for chromium-6; plume confirmed at roughly 2 miles wide and more than 7 miles long |
| 2012–2014 | PG&E begins buying out Hinkley-area homes as plume continues to spread; California proposes a 10 ppb chromium-6 MCL |
| 2017 | California forced to withdraw proposed MCL after court finds cost-benefit analysis insufficient |
| 2016 | Hinkley’s elementary school closes; the community is largely depopulated |
| August 2024 | EPA finalizes IRIS assessment, reclassifying chromium-6 as a “likely human carcinogen” via oral ingestion |
The 1996 Settlement
The case was resolved through binding arbitration in 1996, producing a settlement of $333 million paid by PG&E to more than 660 Hinkley plaintiffs. At the time, it was the largest settlement ever reached in a direct-action lawsuit in US history — meaning a suit filed directly by plaintiffs rather than through a class action certified by a court. The distinction mattered: because it was not a class action, each plaintiff’s claim was evaluated individually, and many received substantial sums based on the nature and severity of their particular health effects.
The settlement compensated residents for property damage, medical expenses, and personal injury claims. It did not require PG&E to admit liability. And it did not stop the plume.
After the Movie
The 2000 film directed by Steven Soderbergh presented the Hinkley case as a story with an ending: the settlement is reached, Erin Brockovich gets her bonus, and the closing title cards suggest justice has been done. What the film could not show was the next two decades.
The Plume Kept Growing
Chromium-6 does not stop moving because a lawsuit is settled. The contamination in Hinkley’s aquifer continued to spread through the 2000s, driven by the naturally sloping terrain and the volume of contaminant already in the soil. By the early 2010s, environmental monitoring confirmed that the plume had migrated to approximately 2 miles wide and more than 7 miles long, running underneath the populated center of Hinkley itself — the areas that had been considered outside the original contamination zone.
PG&E was operating a remediation system — pumping and treating contaminated groundwater, then reinjecting it — but the system was not keeping pace with the plume’s migration. Independent monitoring repeatedly found the contamination boundary moving further than the company’s models had predicted. In 2013, the State Water Resources Control Board found that PG&E had underreported the extent of the plume and ordered more aggressive monitoring.
A Town That Disappeared
As the extent of the contamination became clear and the remediation dragged on, PG&E began purchasing homes from residents who wanted to leave. The buyout program accelerated in the early 2010s. Families who had lived in Hinkley for generations left. Businesses closed. By 2016, Hinkley’s elementary school — the social center of a small desert community — had shut down for lack of students.
By the mid-2010s, Hinkley had been effectively depopulated. Houses sat empty. The community that had existed there for decades was gone. Residents who had not joined the original lawsuit, or who had moved in after 1996, found themselves negotiating individually with PG&E for buyout prices that many considered inadequate, with limited regulatory leverage. The plume that began as an industrial pollution problem became, through slow regulatory failure and continued migration, the mechanism by which an entire town was erased.
The Cancer Cluster Question
One of the most important and genuinely complicated facts about Hinkley is this: a follow-up study by the California Cancer Registry found that cancer rates in the Hinkley area were not statistically elevated above the surrounding region.
This finding has been cited by PG&E’s defenders as evidence that the health claims underlying the lawsuit were overstated, and it deserves honest engagement. The California Cancer Registry study used the best available methodology for cancer cluster investigation, and its conclusion was real. But there are limits to what that finding can and cannot establish.
Cancer cluster epidemiology in small populations faces a fundamental statistical problem: even a genuine doubling of cancer risk in a community of a few thousand people may not produce enough excess cases to register as statistically significant. The Hinkley area had a relatively small population, many residents had moved away before or during the investigation period, and the latency period between chromium-6 exposure and cancer development can be 20 to 40 years — meaning cancers caused by 1960s exposures might appear in medical records scattered across multiple counties in the 1990s and 2000s, invisible to a geographically bounded cluster study.
The cancer registry study did not find a cluster. It could not establish that no harm occurred. These are different conclusions, and confusing them has been a recurring feature of public debate about the case. The scientific weight of evidence for chromium-6 carcinogenicity — established through animal studies, occupational cohort data, and mechanistic research — does not depend on the Hinkley cluster study resolving cleanly.
The 2008 NTP Study and Federal Regulatory Inaction
For most of the period following the 1996 settlement, federal regulators treated chromium-6 as a concern primarily limited to inhalation — the route of exposure for industrial workers — rather than ingestion. The existing federal Maximum Contaminant Level of 100 ppb applied to total chromium, not hexavalent chromium specifically, and was established in 1991 before the oral carcinogenicity evidence was developed.
In 2008, the National Toxicology Program published a landmark two-year rodent study examining chromium-6 administered in drinking water rather than by inhalation or injection. The results were unambiguous: rats and mice given chromium-6 in their water developed cancers of the oral cavity and small intestine at statistically significant rates. This was the first systematic animal study designed to evaluate the ingestion route specifically, and it changed the scientific consensus.
The NTP study created pressure on the EPA to revisit its regulatory framework. But the federal regulatory process for Maximum Contaminant Levels is slow under the best circumstances, and industry opposition to a chromium-6-specific standard added friction. As of 2026, the federal MCL still covers total chromium at 100 ppb. There is no federal standard specific to hexavalent chromium. A utility can be in full compliance with federal law while delivering water with chromium-6 concentrations far above any health-based guideline.
The contrast with arsenic is instructive. The federal arsenic MCL of 10 ppb, established in 2001, is itself criticized by health researchers as inadequately protective — but at least it exists as a contaminant-specific standard informed by carcinogenicity evidence. For chromium-6, that step has not yet been taken at the federal level.
What California Tried, and What Failed
California moved faster than the federal government, but its path has not been smooth.
In 2011, the California Office of Environmental Health Hazard Assessment established a public health goal of 0.02 ppb for chromium-6 — matching the level that the Environmental Working Group had identified as consistent with a one-in-a-million excess lifetime cancer risk. Public health goals are not enforceable standards; they are targets that guide subsequent rulemaking.
In 2014, the California Division of Drinking Water proposed an enforceable Maximum Contaminant Level for chromium-6 of 10 ppb — 500 times the public health goal, but still the first chromium-6-specific enforceable limit in the country. Utilities and water industry groups challenged the rule, arguing that the cost-benefit analysis required under California law had not been adequately conducted. A court agreed. California was required to withdraw the proposed MCL in 2017.
The revised rulemaking process has moved slowly since. As of early 2026, California does not have a finalized, enforceable chromium-6 MCL. The state remains in the position of monitoring for a contaminant it has declared hazardous but has not successfully regulated in drinking water.
August 2024: The EPA Reclassification
In August 2024, the EPA finalized its Integrated Risk Information System (IRIS) assessment of chromium-6 — the agency’s most comprehensive scientific evaluation of the contaminant. The assessment formally reclassified chromium-6 as a “likely human carcinogen” via oral ingestion, updating language that had been more equivocal about that specific exposure route. The IRIS review incorporated the full body of evidence developed since the NTP study: mechanistic data on how chromium-6 causes DNA damage inside gastrointestinal cells, epidemiological studies from occupational and community cohorts, and the growing dataset from UCMR monitoring.
The IRIS classification does not itself create a new drinking water standard. It establishes the scientific foundation on which EPA rulemaking must be built. The regulatory path forward — a new or revised MCL for chromium-6 specifically — requires economic feasibility analysis, public comment periods, and formal agency rulemaking that typically takes several years. But the August 2024 assessment closed the scientific debate that had been used to delay action since 2008. The burden of argument has shifted.
A Regulatory Gap That Persists
| Standard | Level | Status |
|---|---|---|
| US EPA MCL (total chromium) | 100 ppb | Enforceable; covers all chromium forms; no Cr(VI)-specific limit |
| California proposed MCL (Cr(VI)) | 10 ppb | Withdrawn 2017; revised rulemaking ongoing as of 2026 |
| California public health goal (Cr(VI)) | 0.02 ppb | Non-enforceable; established 2011 |
| EWG health guideline (Cr(VI)) | 0.02 ppb | Non-enforceable; based on 1-in-1,000,000 lifetime cancer risk |
| EPA IRIS classification (2024) | Likely human carcinogen via oral ingestion | Scientific basis for future MCL; no MCL proposed as of 2026 |
The gap between the enforceable federal standard and the health-based guideline is a factor of 5,000. A water system can report chromium at 99 ppb — just under the MCL — and be in full legal compliance. At 99 ppb, a person drinking that water is consuming chromium-6 at a level nearly 5,000 times higher than the EWG guideline derived from cancer risk models. That gap is the direct legacy of a regulatory framework built before the oral carcinogenicity evidence existed and not yet updated to reflect it.
The story of Hinkley is, in part, a story about what happens when that gap is not an abstraction but a physical reality flowing through someone’s kitchen tap.
Why This Story Still Matters
Hinkley was not an anomaly in terms of the chemistry involved. Industrial use of chromium-6 as a corrosion inhibitor in cooling systems was widespread across the US for decades. Coal ash disposal introduced chromium-6 into groundwater at hundreds of sites. Natural geology contributes background levels across large swaths of the American West. UCMR 3 monitoring between 2013 and 2015 found chromium-6 detectable in more than 75% of sampled water systems.
The Hinkley case made chromium-6 a household name in the late 1990s. What it did not do — despite the film, the settlement, the NTP study, and two decades of California regulatory effort — is produce a federal drinking water standard that addresses it. That standard does not yet exist.
The physical town of Hinkley is largely gone. The regulatory failure it exposed is still very much present.
What This Means for You
The easiest takeaway from the Hinkley story is that chromium-6 contamination is a California desert problem from the 1990s, now resolved. That reading is wrong on multiple counts. The contamination in Hinkley is not resolved. And chromium-6 is national in scope.
If your water comes from a public utility, your Consumer Confidence Report may list total chromium data, but most utilities do not test specifically for the hexavalent form. Search your city on WaterVerge to review your system’s chromium data, any historical violations, and how reported levels compare to both the federal MCL and health-based benchmarks. If you want to know your actual chromium-6 level, accredited labs offer specific testing for around $30 to $75 — see our guide on how to test your tap water for what to look for when choosing a lab.
If testing reveals elevated chromium-6, standard activated carbon filters will not protect you. Reverse osmosis is the most accessible household option, removing 90 to 97% of chromium-6 at the point of use. Our guide to best reverse osmosis systems covers certified models and what to look for in NSF/ANSI 58 documentation.
For the full scientific and regulatory picture of this contaminant — how it behaves in groundwater, what health effects are established, and where federal and state standards currently stand — see the chromium-6 contaminant profile.
Hinkley’s residents were not warned until a file clerk started asking questions. The underlying conditions that made that possible — an unregulated contaminant, industrial discharge into an aquifer, a community dependent on wells with no systematic monitoring — have not been fully eliminated anywhere in the country.