Chromium-6 Drinking Water MCL


November 2023

The State Water Board released documents for a 15-Day Comment Period

August 2023

The State Water Board held a hearing under the Administrative Procedure Act (APA) on August 2nd on the proposed maximum contaminant level (MCL) for hexavalent chromium in drinking water.

June 2023

The State Water Board released the Notice of Proposed Rulemaking for the Hexavalent Chromium MCL and associated Draft Environmental Impact Report.

Rulemaking and CEQA documents are available on the Hexavalent Chromium Rulemaking Page.

Additional questions may be answered by the Hexavalent Chromium MCL FAQ.

July 2022

Office of Environmental Health Hazard Assessment (OEHHA) Memorandum for Hexavalent Chromium Five-Year Review

March 2022

The State Water Board released a Notice of Public Workshop and Opportunity for Public Comment on Hexavalent Chromium MCL Administrative Draft.

November 2021

CEQA Scoping Meeting

December 2020

Public Workshop on Cost Estimates

Fall 2020

Occurrence Data Released
Preliminary Treatment Costs Released

April 2020

White Paper Discussion on Economic Feasibility Analysis in Consideration of a Hexavalent Chromium Maximum Contaminant Level


In 1999, as part of the process of reviewing MCLs in response to public health goals (PHGs), The California Department of Public Health's (CDPH's) precursor, the California Department of Health Services (CDHS), identified the total chromium MCL (see below) as one for review (CDPH’s Drinking Water Program is now the State Water Board's Division of Drinking Water (DDW)).

In particular, DDW sought to determine whether or not an MCL that is specific for the hexavalent form of chromium—also known as chromium-6—would be appropriate. Subsequently, concerns about hexavalent chromium's potential carcinogenicity when ingested resulted in a state law that requires CDPH to adopt a hexavalent chromium-specific MCL (see hexavalent chromium timeline).

California's Health and Safety Code guides the development of an MCL for hexavalent chromium: §116365.5 requires the adoption of an MCL for hexavalent chromium by January 1, 2004. In addition, Health and Safety Code §116365(a) required CDPH to establish an MCL at a level as close as is technically and economically feasible to the contaminant's PHG, which is the concentration of a contaminant in drinking water that does not pose a significant risk to health. PHGs are developed by Cal/EPA's Office of Environmental Health Hazard Assessment (OEHHA).

In July 2011 OEHHA established a PHG for hexavalent chromium of 0.02 micrograms per liter (μg/L). The PHG represents a de minimis lifetime cancer risk from exposure to hexavalent chromium in drinking water, based on studies in laboratory animals. OEHHA also prepared a PHG fact sheet. The availability of the hexavalent chromium PHG enabled CDPH to proceed with setting a primary drinking water standard.

OEHHA reviews each PHG once every five years unless there has not been a detection of the corresponding contaminant in the preceding five years. In 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.

As part of the rulemaking process, in August 2013 CDPH proposed an MCL for hexavalent chromium of 0.010 milligram per liter (equivalent to 10 μg/L) and announced the availability of the proposed MCL for public comment. The public comment period closed in October 2013. CDPH reviewed the comments submitted by interested parties and responded to them in the final statement of reasons, which is part of the final hexavalent MCL regulations package. Documents from the regulation package can be found here.

On April 15, 2014, CDPH submitted the hexavalent chromium MCL regulations package to the Office of Administrative Law (OAL) for its review for compliance with the Administrative Procedure Act. On May 28, OAL approved the regulations, which were effective on July 1, 2014.

On May 31, 2017, the Superior Court of Sacramento County issued a judgment invalidating the hexavalent chromium maximum contaminant level (MCL) for drinking water. The court ordered the State Water Resources Control Board (State Water Board or Board) to take the necessary actions to delete the hexavalent chromium MCL from the California Code of Regulations and to file with the court by August 15 proof that it has done so (California Manufacturers and Technology Association, et al. v. California Department of Public Health, et al. (Super. Ct. Sacramento County, 2017. No. 34-2014-80001850).

The change became effective with the Office of Administrative Law filing the change with the Secretary of State, on September 11, 2017. Thus, as of September 11, 2017, the maximum contaminant level for hexavalent chromium is no longer in effect.  However, the MCL for total chromium of 50 parts per billion will remain in place.

The court's primary reason for finding the MCL invalid is that the California Department of Public Health (which was responsible for the drinking water program before it was transferred to the State Water Board) failed to comply with one of the requirements in the Safe Drinking Water Act for adopting an MCL. In particular, the department "failed to properly consider the economic feasibility of complying with the MCL." The court did "not decide whether the MCL is economically feasible." 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 merely found that the department did not adequately document why the MCL was economically feasible.

The court also ordered the State Water Board to adopt a new MCL for hexavalent chromium.

Readers interested in the levels of hexavalent chromium in their drinking water should 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.

Historical Timeline

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

MCL for Total Chromium

Hexavalent chromium has been regulated under the 50-µg/L primary drinking water standard (MCL) for total chromium. California's MCL for total chromium was established in 1977, when we adopted what was then a "National Interim Drinking Water Standard" for chromium. The total chromium MCL was established to address exposures to hexavalent chromium, the more toxic form of chromium. Chromium-3 (trivalent chromium) is a required nutrient.

The US Environmental Protection Agency (EPA) adopted the same 50-µg/L standard tor total chromium, but in 1991 raised the federal MCL to 100 µg/L. California did not follow US EPA's change and stayed with its 50-µg/L standard.