The Process for Adoption of a Maximum Contaminant Level

Health and Safety Code §116365(a) requires the State Water Resources Control Board (SWRCB), while placing primary emphasis on the protection of public health, to establish a contaminant's maximum contaminant level (MCL) at a level as close as is technically and economically feasible to its public health goal (PHG).

The PHG—established by the Office of Environmental Health Hazard Assessment (OEHHA)—is the contaminant's concentration in drinking water that does not pose any significant risk to health, derived from a human health risk assessment.

As part of the MCL process, SWRCB's Division of Drinking Water (DDW) evaluates the technical and economic feasibility of regulating a chemical contaminant. Technical feasibility includes an evaluation of commercial laboratories' ability to analyze for and detect the chemical in drinking water, the costs of monitoring, and the costs of treatment required to remove it. Costs are required by law to be considered whenever MCLs are adopted.

To determine technical and economic feasibility, SWRCB goes through the following steps:

  1. Receives the PHG from OEHHA
  2. Selects possible draft MCL concentration or concentrations for evaluation
  3. Evaluates the occurrence data
  4. Evaluates available analytical methods and estimate monitoring costs at a draft MCL concentration or various draft MCL concentrations
  5. Estimates population exposures at the draft MCL concentration or various draft MCL concentrations of the chemical
  6. Identifies best available technologies for treatment
  7. Estimates treatment costs at the draft MCL concentration or the possible draft MCL concentrations
  8. Reviews the costs and associated health benefits (health risk reductions) that result from treatment at the draft MCL concentration or the possible draft MCL concentrations
  9. Proposes the draft MCL concentration or selects an MCL for proposal from the possible draft MCL concentrations considered above

Then the proposed MCL moves through the remainder of the regulatory process.


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State Water Resources Control Board
Division of Drinking Water
Regulatory Development Unit

Mailing Address:
P.O. Box 100
Sacramento, CA 95812-0100

Street Address:
1001 I Street
Sacramento, CA 95814

E-mail us at DDWRegUnit@waterboards.ca.gov.