California Water Commission Seminar on Chromium 6 Contamination Levels

From April 5-7, 2022, the State Water Control Board (Board) will host a public workshop to provide information and solicit public comments on the proposed administrative draft on the maximum contaminant level (MCL) for hexavalent chromium (chromium-6) . MCL is a drinking water standard that public water systems must comply with. The workshop and the MCL’s administrative draft will help inform the board’s formal rulemaking, which is expected to begin later this year. If passed, the MCL will become the nation’s first hexavalent chromium drinking water standard. [1]


Section 116365(a) of the California Health and Safety Code (HSC) requires the Commission to establish an MCL at a level that is as close to the Public Health Goal (PHG) as is technically and economically feasible. PHGs are concentrations of contaminants in drinking water that are not expected to cause or contribute to adverse health effects.

In 2011, the Office of Environmental Health Hazard Assessment (OEHHA) determined hexavalent chromium PHG to be 0.02 parts per billion (ppb) based on cancer risk. In 2014, the California Department of Public Health established an MCL for 10 ppb (0.010 mg/L) chromium 6. [2] In 2017, the California Superior Court invalidated the MCL, found the state failed to consider the economic viability of compliance, and directed the state to revoke the MCL and create a new one.


The board’s new chromium-6 MCL draft proposal provides:

  • The recommended MCL for hexavalent chromium is 10 ppb.

  • The recommended detection limit for hexavalent chromium for reporting purposes (DLR) is 0.05 ppb. [3]

  • The proposed compliance plan based on the size of the water system is as follows:

    • Systems with 10,000 or more service connections will have a two-year compliance timeline;

    • Systems with 1,000 to 10,000 service connections will have a three-year compliance timeline; and

    • Systems with fewer than 1,000 service connections will have a four-year compliance timeline.

Primary drinking water standards must be set at levels that are technically and economically feasible. HSC 116365(a). The committee recommends the following three processing technologies as “best available technologies” to meet the proposed MCL of 10 ug/L:

  • Reduction Coagulation Filtration (RCF): Reduction of hexavalent chromium to trivalent chromium. The solubility of trivalent chromium is extremely low, and precipitates are formed, which can be removed by filtration, so that the concentration of hexavalent chromium in the finished water is less than 5 μg/L;

  • Ion exchange: using a strong base resin that can adsorb hexavalent chromium anions to reduce the hexavalent chromium concentration in finished water to below 1 μg/L; and

  • Reverse Osmosis: Can filter hexavalent chromium through membranes to less than 1 μg/L.

In its Economic Feasibility Analysis, the Board estimated the following Chromium-6 MCL compliance costs: [4]

  • Average annual total cost per system: $82,711 to $15,865,599, depending on system type and size [5]

  • Average annual cost per person: Again, $34 to $2,657, depending on the type and size of the system.

EPA Scientific Symposium

While California is moving forward with a draft chromium-6 MCL, the EPA may be heading in the same direction. Currently, the EPA (like California) only regulates total chromium in drinking water.To inform its ongoing IRIS assessment of Chromium-6, EPA convened a panel of experts representing scientific areas related to reduction and absorption of Chromium-6 at a two-day workshop in September 2021 [6] For more information on the workshop, click here.

Next step

Oral comments on the board’s proposed chromium-6 MCL are available via Zoom link at either of the two workshops on April 5 or 7, 2022. The board will accept written comments until 12:00 noon (PT) on Friday, April 29, 2022. The board will accept additional comment once formal rulemaking begins later this year. For more information on the board’s chromium-6 MCL proposal, click here.

EPA has not announced any follow-up to the September 2021 scientific symposium.


[1] As described below, EPA held a scientific workshop in September 2021 as part of the agency’s work to develop an updated IRIS hexavalent chromium assessment.

[2] The Department of Public Health’s drinking water program was handed over to the State Water Authority in 2014.

[3] The DLR is the specified minimum level at or above which any monitoring analysis of contaminants in drinking water must be reported to the Commission.

[4] The cost estimates for the board are based on strong base anion exchange technology, as this is expected to be the most common treatment method for hexavalent chromium.

[5] Systems include systems with fewer than 100 connections and systems with more than 10,000 connections, including community water systems (CWS), non-temporary non-community water systems (NTNCWS), temporary non-community water systems (TNCWS), and wholesalers. Cost estimates are available here.

[6] IRIS is the “Integrated Risk Information System”. An IRIS assessment includes the first two steps of the risk assessment process: hazard identification and dose response assessment. IRIS assessments can inform EPA’s regulatory decisions.

Copyright © 2022, Hunton Andrews Kurth LLP. all rights reserved.National Law Review, Vol. XII, No. 89

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