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Division of Drinking Water proposes lower manganese advisory thresholds tied to existing secondary standard
Summary
The Division of Drinking Water proposed Oct. 7 to set the manganese non‑regulatory notification level equal to California’s existing secondary MCL (0.05 mg/L) and to set a single‑sample response level at 0.20 mg/L to prompt rapid confirmation and action.
Sacramento — The Division of Drinking Water (DDW) proposed revisions to the state’s non‑regulatory manganese notification and response levels at a State Water Resources Control Board briefing on Oct. 7. The division proposed aligning the lower “notification level” with California’s enforceable secondary maximum contaminant level (MCL) for manganese (0.05 mg/L) and setting the response level — the single‑sample level that triggers immediate action — at 0.20 mg/L.
Officials said the aim is clearer, health‑oriented messaging and faster follow‑up where manganese presents a risk to infants and other vulnerable groups. DDW staff noted that young children retain and absorb more manganese and that health guidance differs between infants and adults.
Key points - Proposed thresholds: DDW proposes the notification level be the running annual average of 0.05 mg/L (the existing secondary MCL for community water systems); staff propose a response level of 0.20 mg/L (0.202 rounded to two significant figures) based on a single confirmed sample to trigger expedited confirmation sampling and actions such as taking a source offline, providing treatment or direct customer notification. - Rationale and process: DDW said the change responds to comments received after a 2023 informational discussion and seeks to align non‑regulatory advisory behavior with the existing secondary MCL and bottled‑water regulatory levels. DDW follows Health and Safety Code authority for issuing notification/response advisories and will follow outreach and the department’s internal processes before issuing final advisory levels. - Monitoring and timing: Because manganese sample hold times can be long for some analytical methods, DDW recommended systems request quicker laboratory turnaround and proposed that confirmation sampling occur within 48 hours when a result exceeds the response level. DDW said community water systems are already required to comply with the secondary MCL; non‑community systems (for example some schools) may not be required to comply and might need monitoring orders. - Estimated scale: Using single‑sample data as a conservative estimate, DDW stated roughly 1,000 public water systems have reported at least one manganese result above 0.05 mg/L, about half of which have readings above the proposed response level. DDW estimated roughly 300 community water systems may need detailed compliance review; about 30 systems currently operate under waivers and may require new sources or treatment to comply.
Public‑health messaging and action: DDW said revised public notice templates and clearer, timely laboratory reporting are essential to avoid confusing or inactionable notices to consumers. DDW reported outreach to school and child‑care agencies and said it would ask OEHHA to develop a public‑health goal for manganese as a longer‑term step.
Board response and next steps: Board members welcomed the move, asked for continued analysis of distribution‑system dynamics (manganese can accumulate in pipes) and requested further equity‑focused analysis of community impacts. DDW said it will review comments from this meeting, revise public‑notice language, issue final notification/response levels, and pursue monitoring orders and OEHHA consultation.
Ending: The proposal is an interim, health‑oriented step intended to make advisories actionable while DDW and OEHHA continue science and rulemaking work that would be needed for a primary (health‑based) MCL.
