Hexavalent Chromium (Chromium-6)

• Frequently asked questions (FAQ) | Preguntas frequentes
• 2023-24 Hexavalent Chromium Rulemaking

Hexavalent chromium is a heavy metal that has been used in industrial applications and found naturally occurring throughout the environment. While chromium can exist in a nontoxic, trivalent form, the hexavalent form has been shown to be carcinogenic and toxic to the liver (OEHHA, 2011). Hexavalent chromium is among the chemicals known to the state to cause cancer [Title 27, California Code of Regulations, Section 27001], pursuant to California's Safe Drinking Water and Toxic Enforcement Act of 1986 ("Proposition 65").

The hexavalent chromium MCL is 0.010 mg/L or 10 µg/L (the rest of this page will use µg/L). The State Water Board is required to set MCLs “as close as feasible to the corresponding public health goal [PHG] placing primary emphasis on the protection of public health,” to the extent that it is technologically and economically feasible [Health & Safety Code § 116365(a)]. The PHG for hexavalent chromium (0.02 μg/L) was established in 2011. The rulemaking to establish the hexavalent chromium MCL is effective on October 1, 2024.

Readers interested in the levels of hexavalent chromium in their drinking water may refer to the water systems' annual Consumer Confidence Reports (CCRs). Many CCRs are available from DDW's Drinking Water Watch website, which also includes other information about drinking water quality.

Table showing hexavalent chromium average drinking water source concentration (2012 - 2022)

Average Source Concentration (μg/L)	No. of Sources	% of Detections
≥ 1 and ≤ 5	6,850	88%
> 5 and ≤ 10	603	7.8%
> 10 and ≤ 20	263	3.4%
> 20 and ≤ 30	45	0.6%
> 30 and ≤ 40	13	0.2%
> 41 and ≤ 50	3	0.0%
> 50	3	0.0%
TOTAL	7,780	--

NOTES:

1. Data are extracted from community water system monitoring results from 2012 through February, 2022 (Excel).
2. "Sources" are active, standby, and pending sources reporting more than a single detection of hexavalent chromium. Data may include both raw and treated sources, distribution systems, blending reservoirs, and other sampled entities. This table does not include inactive sources, abandoned or destroyed wells, agricultural wells, monitoring wells, or more than one representation of the same source (e.g., a source with both raw and treated entries is counted a single source).

Average source concentrations of hexavalent chromium from the data above were reported in the greatest numbers in the following counties:

• Concentrations ≥ 1 and ≤ 5 μg/L: 6,850 sources in 58 counties, including San Bernardino (650 sources), Los Angeles (697), Fresno (448), Sacramento (195), Riverside (386), Kern (363), Monterey (302), Sonoma (245), and Tulare (311)
• Concentrations > 5 and ≤ 10 μg/L: 603 sources in 38 counties, including Los Angeles (111), Monterey (35), Sacramento (55), San Bernardino (74, Riverside (67), San Joaquin (40), Stanislaus (42), and Kern (31)
• Concentrations > 10 and ≤ 20 μg/L: 263 sources in 25 counties, including Riverside (73), Los Angeles (35), San Bernardino (22), Yolo (15), Sacramento (13), and Santa Cruz (16), Solano (10)
• Concentrations > 20 and ≤ 30 μg/L: 45 sources in 15 counties, including Yolo (5), Los Angeles (1), San Bernardino (4), Monterey (7), Merced (5), Solano (4), and Riverside (5)
• Concentrations > 30 and ≤ 40 μg/L: 13 sources in 6 counties: Merced (7), Los Angeles (1), Santa Barbara (1), San Bernardino (1), and Santa Cruz (2)
• Concentrations > 41 and ≤ 50 μg/L: 3 sources in 2 counties: Riverside (1) and Yolo (1)
• Concentrations > 50 μg/L: 3 sources in 2 counties: Los Angeles (2) and Ventura (1)

Below are significant historical events associated with the development of drinking water regulations for hexavalent chromium:

1999

• As part of its activities associated with the development of Public Health Goals (PHGs), OEHHA evaluated total chromium and established a 2.5-μg/L PHG for total chromium (PDF), reflecting a view that hexavalent chromium, a component of total chromium, poses a cancer risk when ingested.
• Following OEHHA's PHG for total chromium, the California Department of Health Services (CDHS, predecessor to the California Department of Public Health, CDPH) identified chromium as a contaminant for possible MCL review. CDHS also announced it would include hexavalent chromium among the unregulated chemicals requiring monitoring.

2000

• The Governor signed SB 2127 (Schiff) into law. It required CDHS to determine the levels of hexavalent chromium in drinking water supplied by public water systems in the San Fernando Basin aquifer, and, in consultation with OEHHA, assess the associated exposures and risks to the public.

2001

• With adoption of a regulation identifying hexavalent chromium as an unregulated chemical requiring monitoring, CDHS began receiving sampling results.
• The University of California (UC) convened an expert panel at Cal/EPA’s request to address the carcinogenicity of ingested hexavalent chromium.
• CDHS requested OEHHA to prepare a PHG for hexavalent chromium (a PHG was needed for the development of an MCL specific to hexavalent chromium).
• The National Toxicology Program (NTP) announced it would conduct long-term rodent bioassays to evaluate the potential carcinogenicity of ingested hexavalent chromium (updates of protocols and results of preliminary studies are available at the NTP website).
• The Governor signed SB 351 (Ortiz) (Health and Safety Code Section 116365.5, Chapter 602, Statutes of 2001) into law. It required CDHS to adopt a hexavalent chromium MCL by January 1, 2004.
• OEHHA announced its withdrawal of the total chromium PHG for the purpose of developing a PHG specific to hexavalent chromium.

2003

• At a legislative hearing in Sacramento on April 2, Cal/EPA announced it would not use the expert panel's report in the hexavalent chromium PHG—citing concerns about panelists' possible conflicts of interest.

2005

• OEHHA released comments of peer reviewers (PDF) of a "pre-release" draft PHG for hexavalent chromium.

2007

• NTP's reports on studies on the carcinogenesis of hexavalent chromium (dichromate dihydrate) in drinking water—which found there to be sufficient evidence of carcinogenicity in rodents—were reviewed and approved by the Board of Scientific Counselors Technical Reports Review Subcommittee.

2009

• OEHHA released a draft PHG for hexavalent chromium.

2010

• OEHHA released comments of peer reviewers of the August 2009 draft PHG.
• U.S. EPA's IRIS released its Toxicological Review of Hexavalent Chromium (External Review Draft) - now archived.
• OEHHA released a revised draft PHG for hexavalent chromium.

2011

• U.S. EPA released its recommendations for enhanced hexavalent chromium monitoring for public water systems.
• OEHHA released the final PHG for hexavalent chromium along with a PHG fact sheet.

2013

• CDPH proposed an MCL for hexavalent chromium.

2014

• The MCL for hexavalent chromium was approved by the Office of Administrative law and became effective.

2016

• OEHHA initiated a PHG review for hexavalent chromium with a data call-in for information that could assist in updating the risk assessment. Based on the review of the information from the data call-in and authoritative groups, OEHHA concluded that there was not enough evidence to warrant a change in OEHHA’s approach for determining hexavalent chromium’s cancer potency and that an updated PHG would not vary significantly from the 2011 value.

2017

• Superior Court of Sacramento County invalidated the hexavalent chromium MCL and ordered the State Water Board to adopt a new MCL (California Manufacturers and Technology Association, et al. v. California Department of Public Health, et al. (Super. Ct. Sacramento County, 2017. No. 34-2014-80001850).
  • In particular, the court determined that the regulation "failed to properly consider the economic feasibility of complying with the MCL." The court did not make any finding about whether the MCL adequately protected public health, nor did it reach a conclusion about whether the MCL was too low or too high. The court also did "not decide whether the MCL is economically feasible." Rather, the court found that the regulation did not adequately document why the MCL was economically feasible.

2020

• State Water Board published the White Paper Discussion on Economic Feasibility Analysis in Consideration of a Hexavalent Chromium Maximum Level.
  • Revised Notice
  • Notice
• State Water Board published preliminary information and held public workshops on the cost estimates.
  • Notice
  • Occurrence Data
  • Preliminary Treatment Costs
    • Cost Estimates Notice
    • Methodology and Assumptions
    • Treatment Costs Data
    • Treatment Costs Equations
    • Sources, Service Connections, and Population
    • Community Water Systems Costs
    • NTNC Water Systems Costs
    • Health Effects
    • Treatment Costs Figures

2021

• State Water Board published Notice of Preparation of a Draft Environmental Impact Report for the hexavalent chromium MCL and holds a CEQA scoping meeting.
  • Copies of comment letters received during the meeting are available upon request at ddw-hexavalentchromium@waterboards.ca.gov.

2022

• State Water Board published Notice of Public Workshop and Opportunity for Public Comment on Administrative Draft.
  • Notice | Aviso
  • Draft Regulation Text
  • Staff Report
  • Attachment to Staff Report (Tables)
• Office of Environmental Health Hazard Assessment (OEHHA) Memorandum for Hexavalent Chromium Five-Year Review

2023

• State Water Board started the formal rulemaking process for establishing an MCL of 10 µg/L with the publication of the Notice of Proposed Rulemaking.

2024

• State Water Board adopted the Hexavalent Chromium MCL Regulation with an effective date of October 1, 2024.

Prior to October 1, 2024 (the effective date of 2023-24 Hexavalent Chromium MCL Regulation), hexavalent chromium had been regulated under the total chromium MCL of 50 µg/L. California's total chromium MCL was established in 1977 with the adoption of a "National Interim Drinking Water Standard" for chromium to address exposures to hexavalent chromium, the more toxic form of chromium. Trivalent chromium (chromium-3) is a required nutrient.

The U.S. EPA adopted the same 50 µg/L MCL for total chromium, but in 1991 raised that federal MCL to 100 µg/L. California did not follow U.S. EPA's change and still has a total chromium MCL of 50 µg/L.

The total chromium MCL will continue to exist as an enforceable standard.