Yes, Hinkley, California is still contaminated. More than three decades after the groundwater crisis made famous by Erin Brockovich, a plume of hexavalent chromium remains in the aquifer beneath this Mojave Desert community. Active remediation by Pacific Gas and Electric (PG&E) is ongoing, and as of 2024, monitoring data shows the plume is not expanding, but cleanup is far from complete. The town itself has largely emptied out, described by some observers as a ghost town.
What’s in the Groundwater Now
The contaminant at the center of Hinkley’s crisis is hexavalent chromium, a toxic form of chromium that PG&E used as a rust inhibitor at its nearby compressor station from 1952 to 1966. Wastewater containing the chemical was dumped into unlined ponds, where it seeped into the groundwater. In the 1990s, some wells in Hinkley tested as high as 80 parts per million, an extraordinarily dangerous level.
Concentrations today are far lower, but the contamination persists. The Lahontan Regional Water Quality Control Board, which oversees the cleanup, publishes quarterly plume maps tracking the spread of hexavalent chromium underground. First quarter 2024 data indicates the plume is not migrating outward, though natural fluctuations in concentration continue as remediation progresses. In some areas, remediation activities have actually caused temporary expansion of contamination. During 2022, increased underground treatment injections pushed the plume outward along Summerset Road, prompting regulators to expand the allowed boundary of plume movement by 1,000 feet to the east.
The Cleanup Target
Defining “clean” in Hinkley has been a complicated question. California adopted its first drinking water standard specifically for hexavalent chromium in 2014, and a revised regulation took effect on October 1, 2024, setting the maximum contaminant level at 10 parts per billion (ppb). Before that date, hexavalent chromium had been regulated only under the broader total chromium standard of 50 ppb, a much looser threshold.
But the cleanup goal in Hinkley is even stricter than the state drinking water standard. A background study calculated the naturally occurring level of hexavalent chromium in the local aquifer at 3.09 ppb. That figure, called the 95% upper tolerance limit, represents the highest concentration you’d expect to find in groundwater that was never contaminated. The Water Board uses this as the benchmark PG&E must ultimately meet. The regulatory order now limits the concentration allowed to migrate to the eastern edge of the plume to 3.1 ppb, essentially matching natural background.
How the Cleanup Works
PG&E uses several approaches to treat the contaminated groundwater in place. The primary method involves in-situ remediation zones, where materials are injected underground to chemically convert hexavalent chromium into trivalent chromium, a far less toxic and less mobile form that binds to soil particles rather than traveling with groundwater. The process essentially locks the chromium in place so it can no longer spread.
Regulators also monitor hydraulic capture, which tracks the direction groundwater flows to ensure contaminated water isn’t escaping the treatment area. This is assessed by comparing water pressure readings from networks of monitoring wells positioned around the plume’s boundaries.
Between 2015 and 2016, PG&E tested a bioreactor system that used phosphoric acid to feed microbes capable of breaking down hexavalent chromium. That pilot program has largely wound down, with only one monitoring well still being tracked from the experiment. As of early 2025, the Water Board is requiring PG&E to conduct a new feasibility study to reassess cleanup timelines, evaluate whether new technologies could speed up the process, update computer models with current site data, and perform a cost analysis. This signals that regulators are not satisfied with the pace of progress.
No Clear End Date
There is no publicly stated completion date for the Hinkley cleanup. The 2025 feasibility study requirement exists in part because regulators want better projections of how long remediation will take. Previous models need updating to reflect current conditions, and the Water Board has indicated it wants enforceable milestones rather than open-ended treatment. For now, the cleanup continues without a defined finish line, more than 70 years after the contamination began.
What Happened to the Town
Hinkley was never large, but the contamination hollowed it out. PG&E bought up properties in the affected area over the years, and many residents left. The community that Erin Brockovich encountered in the early 1990s, a small desert settlement of homes relying on private wells, has largely disappeared. Residents who remain or live nearby depend on monitoring programs that test domestic wells. The Water Board requires monthly sampling of private wells along the plume’s expansion boundary to ensure drinking water stays below dangerous levels.
Why Hexavalent Chromium Matters
Hexavalent chromium is not just an irritant. Inhaling it causes lung cancer in humans, a relationship well established in occupational studies. When ingested through drinking water, animal studies by the National Toxicology Program found it causes malignant tumors in the oral cavity of rats and tumors in the small intestine of mice, with cancer rates increasing at higher doses. In humans, exposure has been linked to kidney and liver damage, nasal and sinus cancers, and skin ulceration.
The concentrations currently found in Hinkley’s groundwater are orders of magnitude lower than the levels detected in the 1990s. But the science behind California’s 10 ppb drinking water standard reflects the understanding that even low-level, long-term exposure to hexavalent chromium through drinking water carries health risks, particularly cancer risk that accumulates over years. That’s why the cleanup target in Hinkley isn’t simply “below the legal limit” but rather a return to the natural background level of about 3 ppb.