Contaminant Guide

Hexavalent Chromium in Well Water

Hexavalent Chromium in private well water: where it comes from, what the limits are, how to test for it, and which treatment methods actually remove it.

Where hexavalent chromium comes from

  • natural weathering of chromite ore and ultramafic rock (primarily Western US)
  • industrial discharge from electroplating, leather tanning, and chrome finishing
  • coal ash impoundments and leaching into groundwater
  • chromium-6 used as corrosion inhibitor in industrial cooling water (historical discharge)

Health considerations

  • gastrointestinal and systemic cancer — IARC Group 1 carcinogen via inhalation; drinking water evidence from high-exposure studies in China showed elevated stomach cancer. EPA proposed MCLG of 0.02 μg/L (0.02 ppb) in 2023 based on cancer risk assessment.
  • kidney and liver damage — Chronic exposure in animal studies shows nephrotoxicity and hepatotoxicity. Hexavalent chromium is more bioavailable and toxic than trivalent chromium (Cr-III), which is an essential nutrient at trace levels.

No federal primary MCL for hexavalent chromium specifically. The total chromium MCL is 100 μg/L (100 ppb). EPA proposed an MCLG of 0.02 μg/L for Cr-VI in 2023. California’s state MCL is 10 μg/L. The federal total chromium MCL is considered inadequate for Cr-VI given its separate cancer risk profile.

Who is most at risk

  • residents near natural chromite deposits (California Coast Ranges, ultramafic belts)
  • residents near industrial facilities with chromium discharge
  • people with reduced stomach acid (hexavalent chromium more readily absorbed)
  • California well owners (state MCL of 10 μg/L for Cr-VI since 2014)

Testing

EPA Method 218.6 (hexavalent chromium specifically) or 7196A; must specifically request Cr-VI — total chromium testing (EPA 200.8) does NOT distinguish between hexavalent and trivalent forms; certified lab required; samples must be preserved and analyzed within 24 hours

Find a certified lab and learn how to collect a sample

Treatment

  • reverse osmosis — most effective for Cr-VI removal
  • strong-base anion exchange resin — effective, regenerable
  • reduction to Cr(III) with ferrous sulfate + coagulation/filtration (whole-house)
  • standard carbon filters are NOT effective for hexavalent chromium

Compare hexavalent chromium treatment systems

Regulatory framework

No federal MCL · MCLG: 0 µg/L

No federal primary MCL for hexavalent chromium specifically. The total chromium MCL is 100 μg/L (100 ppb). EPA proposed an MCLG of 0.02 μg/L for Cr-VI in 2023. California’s state MCL is 10 μg/L. The federal total chromium MCL is considered inadequate for Cr-VI given its separate cancer risk profile.

Detection

EPA Method 218.6 (hexavalent chromium specifically) or 7196A; must specifically request Cr-VI — total chromium testing (EPA 200.8) does NOT distinguish between hexavalent and trivalent forms; certified lab required; samples must be preserved and analyzed within 24 hours

Occurrence

Most commonly reported in: California, New Mexico, Arizona, Texas, Michigan, Ohio, Pennsylvania, North Carolina.

  • serpentinite and ultramafic rock (natural occurrence)
  • any near industrial sites or coal ash ponds
  • alluvial near electroplating or tanning facilities

Data access

Access our data API and methodology

References

  1. Costa, M., & Klein, C.B. (2006). Toxicity and carcinogenicity of chromium compounds in humans. Critical Reviews in Toxicology, 36(2), 155-163. https://doi.org/10.1080/10408440500534032
  2. Zhitkovich, A. (2011). Chromium in drinking water: sources, metabolism, and cancer risks. Chemical Research in Toxicology, 24(10), 1617-1629. https://doi.org/10.1021/tx200251t