Hexavalent Chromium in Well Water: California's Chromium-6 Guide

Hexavalent chromium became a household name thanks to Erin Brockovich's fight against Pacific Gas & Electric in Hinkley, California. But this cancer-causing contaminant isn't just a movie plot—it's found in drinking water across California, affecting millions of people, including many private well owners.

Also known as chromium-6 or Cr(VI), hexavalent chromium presents unique challenges for California well owners. It occurs both naturally in certain geological formations and from industrial contamination. Understanding your exposure risk and treatment options is essential for protecting your family's health.

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The Hinkley Case: A Brief History

In the 1990s, residents of Hinkley, California discovered that PG&E had contaminated their groundwater with hexavalent chromium from cooling towers. The resulting lawsuit, made famous by the 2000 film "Erin Brockovich," resulted in a $333 million settlement. Today, Hinkley is largely a ghost town, and chromium-6 contamination remains a concern across California.

Understanding Hexavalent Chromium

Chromium exists in several forms in the environment. Understanding the difference is important for evaluating your water quality:

Chromium-3 vs. Chromium-6

Trivalent chromium (chromium-3 or Cr(III)) is actually an essential nutrient. It's found naturally in many foods and is used in dietary supplements. Your body needs small amounts of chromium-3 for normal insulin function and metabolism. It's generally considered non-toxic and is poorly absorbed by the body.

Hexavalent chromium (chromium-6 or Cr(VI)) is the toxic form. It's highly soluble in water, easily absorbed by the body, and is a known carcinogen. Unlike chromium-3, hexavalent chromium can cross cell membranes and cause genetic damage.

Key Differences: Chromium-3 vs Chromium-6

Property	Chromium-3	Chromium-6
Toxicity	Low (essential nutrient)	High (carcinogen)
Absorption	Poor (1-2%)	Good (2-10%)
Solubility	Low	High
Common form in water	Less common	More common

Sources of Hexavalent Chromium

Hexavalent chromium in groundwater comes from both natural and human sources:

Natural Sources

Serpentine rock formations: Common in California's Coast Ranges and Sierra Nevada foothills
Ultramafic rocks: Naturally high in chromium, which can oxidize to hexavalent form
Manganese-rich soils: Manganese can oxidize chromium-3 to chromium-6
Arid conditions: Dry climates promote oxidation of chromium to the hexavalent form

Industrial Sources

Chrome plating operations: Electroplating uses chromic acid containing chromium-6
Cooling towers: Historically used chromate additives (like in Hinkley)
Stainless steel production: Welding and cutting can release chromium-6
Leather tanning: Some processes use chromium compounds
Wood treatment: Chromated copper arsenate (CCA) preservatives
Aerospace and defense: Chrome coatings and anti-corrosion treatments

California's Regulatory Landscape

California's approach to hexavalent chromium regulation has been complex and contentious:

The Regulatory Timeline

2011: California set a Public Health Goal (PHG) of 0.02 ppb for hexavalent chromium
2014: California established the nation's first MCL for chromium-6 at 10 ppb
2017: A court struck down the MCL due to inadequate economic analysis
Current: Total chromium MCL of 50 ppb applies; new chromium-6 standard in development

Current Status: As of 2026, California regulates total chromium at 50 ppb but has no enforceable limit specifically for hexavalent chromium. The state is developing a new chromium-6 standard that must include proper cost-benefit analysis. The Public Health Goal remains at 0.02 ppb—2,500 times lower than the total chromium MCL.

Federal Standards

The EPA sets a total chromium standard of 100 ppb but has no specific standard for hexavalent chromium. The EPA has been reviewing chromium regulations but has not established a separate chromium-6 limit. This means private well owners in California must rely on the state's total chromium standard while being aware that hexavalent chromium may pose risks at much lower levels.

Health Effects of Chromium-6 Exposure

The health risks of hexavalent chromium are well-documented for inhalation exposure and increasingly clear for ingestion through drinking water:

Cancer Risks

Hexavalent chromium is classified as a known human carcinogen (Group 1) by the International Agency for Research on Cancer. While most human studies involve occupational inhalation exposure, animal studies and emerging research link drinking water exposure to:

Stomach cancer: The primary concern for ingestion exposure
Oral cavity tumors: Documented in animal studies
Small intestine tumors: Observed in laboratory animals

The National Toxicology Program found "clear evidence of carcinogenic activity" for hexavalent chromium in drinking water studies with laboratory animals. California's Office of Environmental Health Hazard Assessment concluded that chromium-6 in drinking water poses cancer risks to humans.

Non-Cancer Health Effects

Beyond cancer, hexavalent chromium exposure may cause:

Liver damage: The liver processes and attempts to reduce chromium-6
Kidney effects: Chromium is excreted through kidneys, potentially causing damage
Reproductive effects: Some studies suggest impacts on fertility and development
Immune system effects: May affect immune function
Gastrointestinal irritation: Including stomach upset and ulcers at high exposures

Where Chromium-6 Is Found in California

Environmental Working Group (EWG) analysis has found detectable hexavalent chromium in drinking water supplies serving about 200 million Americans, with particularly high levels in several California regions:

High-Risk Areas in California

San Fernando Valley: Industrial contamination from aerospace and manufacturing
San Gabriel Valley: Multiple Superfund sites with chromium contamination
Inland Empire: Industrial sources and natural occurrence
Central Valley: Both natural and agricultural/industrial sources
Mojave Desert region: Natural occurrence from geological sources
Bay Area: Industrial contamination in some areas

For private well owners, risk depends on both geological conditions and proximity to historical or current industrial operations. Wells near chrome plating facilities, aerospace operations, or in areas with serpentine geology may be at elevated risk.

Testing Your Well for Hexavalent Chromium

Standard Testing vs. Chromium-6 Specific Testing

Most routine water tests measure only total chromium, which doesn't distinguish between the less harmful chromium-3 and the carcinogenic chromium-6. If your water tests positive for any chromium, or if you're in a high-risk area, request specific hexavalent chromium testing.

Testing Considerations

Specify chromium-6: Tell the lab you want hexavalent chromium, not just total chromium
Sample handling matters: Chromium can convert between forms; follow lab instructions exactly
Detection limits: Ensure the lab can detect low levels (ideally below 1 ppb)
Cost: Expect $50-100 for chromium-6 testing vs. $25-40 for total chromium

Interpreting Results

Because there's currently no enforceable chromium-6 standard, interpreting results requires judgment:

Below 0.02 ppb: Below California's Public Health Goal; lowest concern
0.02 - 1 ppb: Exceeds PHG but relatively low; consider treatment if vulnerable individuals present
1 - 10 ppb: Exceeds the former California MCL; treatment recommended
Above 10 ppb: Significantly elevated; treatment strongly recommended
Above 50 ppb: Exceeds total chromium MCL; treatment essential

Treatment Options for Chromium-6

Removing hexavalent chromium from water requires specific treatment technologies. Standard carbon filters are NOT effective.

Reverse Osmosis

Reverse osmosis is effective for chromium-6 removal in residential applications:

Effectiveness: 90-97% removal of hexavalent chromium
Type: Point-of-use systems (under sink) most common for residential use
Cost: $300-700 for quality under-sink systems
Maintenance: Filter replacement every 6-12 months; membrane every 2-5 years
Pros: Highly effective, also removes other contaminants
Cons: Produces wastewater, limited to drinking/cooking water

Strong Base Anion Exchange

Specialized ion exchange resins can effectively remove chromium-6:

Effectiveness: 80-95% removal
Type: Whole-house systems available
Cost: $1,500-4,000+ for whole-house systems
Note: Requires specific "strong base" anion exchange resin, not standard softener resin
Maintenance: Resin regeneration or replacement required

Reduction-Coagulation-Filtration (RCF)

This treatment approach converts chromium-6 to chromium-3, then removes it:

How it works: Chemical reduction (often with ferrous iron) converts Cr(VI) to Cr(III), which is then removed by filtration
Effectiveness: Can achieve very low levels when properly designed
Best for: Higher contamination levels or whole-house treatment
Considerations: Requires professional system design based on water chemistry

What Doesn't Work

Standard carbon filters: Not effective for chromium-6
Boiling: Does not remove chromium; may concentrate it
Standard water softeners: Not designed for chromium removal
UV treatment: Effective for bacteria, not metals

Frequently Asked Questions

What is hexavalent chromium and why is it dangerous?

Hexavalent chromium (chromium-6 or Cr(VI)) is a toxic form of the element chromium. It's a known human carcinogen when inhaled, and research increasingly links it to cancer when consumed in drinking water. It can occur naturally from geological sources or from industrial contamination including chrome plating, stainless steel production, leather tanning, and wood treatment. The Erin Brockovich case brought national attention to this contaminant after it was linked to cancer clusters in Hinkley, California.

What is California's standard for hexavalent chromium in water?

California had set the first-in-nation standard for hexavalent chromium at 10 parts per billion (ppb), but this was withdrawn after legal challenges. Currently, California enforces the total chromium MCL of 50 ppb (which includes all forms of chromium). The state is working on a new hexavalent chromium standard, with a Public Health Goal of 0.02 ppb. The EPA has no specific federal standard for hexavalent chromium, only total chromium at 100 ppb.

How do I test my well water for hexavalent chromium?

Hexavalent chromium testing requires specialized laboratory analysis that can distinguish between chromium-6 and other forms of chromium. Standard water tests typically measure only total chromium. Request hexavalent chromium testing specifically from a certified laboratory. Testing costs $50-100 for chromium-6 alone. Some comprehensive panels include it, but many don't, so verify before ordering. Sample handling is important—follow lab instructions carefully as chromium can change forms over time.

What are the health effects of chromium-6 in drinking water?

Long-term exposure to hexavalent chromium in drinking water is associated with increased cancer risk, particularly stomach and gastrointestinal cancers. Animal studies show it can cause tumors of the oral cavity and small intestine. Beyond cancer, chromium-6 may affect the liver, kidneys, and reproductive system. The developing fetus and children may be particularly vulnerable. Even low levels may pose health risks with chronic exposure, which is why California's Public Health Goal is set at just 0.02 ppb.

How do you remove hexavalent chromium from well water?

Effective treatment options for hexavalent chromium include strong base anion exchange resins (80-95% removal), reverse osmosis systems (90-97% removal), and reduction-coagulation-filtration systems that convert chromium-6 to the less toxic chromium-3 form before removal. Standard activated carbon filters are NOT effective for chromium-6. Point-of-use reverse osmosis systems for drinking water cost $300-700. Whole-house treatment is more complex and expensive, often requiring professional design based on your specific water chemistry.

Concerned About Chromium-6 in Your Well?

Southern California Well Service can help coordinate specialized water testing and connect you with treatment solutions. We serve San Diego and Riverside Counties with expert well services.

Call (760) 463-0493 for Expert Advice

Hexavalent Chromium in Well Water