The California State Water Resources Control Board has announced a proposed maximum contaminant level (MCL) for hexavalent chromium that prioritizes protecting public health while considering the varying abilities of the state’s 7,000 public water systems, large and small, to invest in water treatment technologies to meet the new standard.
The proposal is an administrative draft only—the MCL will be considered for final adoption by the board after an extended public comment period and once recommended changes are considered. The proposal is a major milestone toward developing a new MCL for hexavalent chromium after the prior MCL was invalidated by a court that ruled the state did not adequately document if it was economically feasible for water systems to implement.
“We restarted the MCL analysis process from scratch, using updated data, and conducted a rigorous economic feasibility analysis, paying special attention to the range of possible impacts on water systems,” said Darrin Polhemus, Deputy Director of the State Water Board’s Division of Drinking Water. “Ultimately, a standard is a balancing of risks to public health and what is achievable for systems to implement successfully. The MCL for hexavalent chromium we are proposing—10 parts per billion (ppb)—is a level that improves public health while providing water systems with a reasonable target and timeline to come into compliance.”
The State Water Board’s recent analysis shows that an MCL for hexavalent chromium of 10 ppb should be achievable for systems serving 95 percent of Californians. The analysis also shows that the remaining systems, which are mostly small and sometimes in low-income communities, may struggle with the financial and technical challenges of installing new treatment technology for hexavalent chromium. To aid these systems, board staff propose giving smaller systems a longer implementation period during which they can benefit from the research and development led by larger systems that must meet the standard first. Depending on the size of the system, the implementation period ranges from two to four years.
Hexavalent chromium, commonly called chromium-6, is an odorless and tasteless heavy metal that occurs throughout the environment and may occur in groundwater naturally or as a result of industrial sites that fail to follow proper disposal methods for contaminated waste. Studies have linked long-term exposure to a risk of cancer when ingested. At an MCL of 10 ppb, it is estimated that a person who ingests it daily for 70 years could have a one-in-2,000 chance of developing cancer.
The new MCL is expected to go into effect in early 2024, if adopted by the board.
Source: California Water Boards
