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NHDES Proposing Enforceable Limits for Manganese

Date: May 25, 2021

This is a very challenging time for public water systems, which are facing a new, more protective limit for arsenic, new standards for PFAS (per- and polyfluorinated alkyl substances), a more stringent Lead and Copper Rule, and the COVID pandemic, in addition to the challenges of aging infrastructure that existed before 2020. One more issue is entering the mix: a new, enforceable standard for manganese. Because many systems are already considering the investments they need to make to comply with the arsenic and PFAS standards, now is the time to include manganese in those plans, rather than dealing with arsenic and PFAS now and manganese a year from now.

Manganese has long been an aesthetic concern for public water system customers, system operators, and users of private wells, although there is no federal or state primary (health-based) maximum contaminant level (MCL) for the metal. Because it causes aesthetic concerns at levels below which it is a health concern, most water systems have already brought manganese down to levels at which it is not a health concern.

Unfortunately, despite many years of urging and technical assistance from NHDES, not all water systems consistently remove manganese to safe levels. NHDES estimates that 28 sources for community systems and 30 sources for non-transient systems exceed 0.3 mg/L, and three to four times as many may exceed 0.1 mg/L.

NHDES is in the process of establishing an enforceable standard of 0.3 mg/L for manganese in drinking water. State statute (RSA 485-C:6,I.) requires NHDES to adopt a groundwater standard in line with EPA’s 2004 health advisory limit of 0.3 mg/L, and NHDES rules (Env-Dw 707.02) make the state’s groundwater standard an enforceable drinking water standard. The effective date for NHDES’ 0.3 mg/L drinking water standard would be July 1, 2022.

In addition to the enforceable standard (similar to an MCL), NHDES is proposing a mandatory notification level of 0.1 mg/L, since even short-term exposure to levels as low as 0.1 mg/L are a health concern for infants.

In February 2020, we began notifying systems that use sources with elevated Mn levels, providing them with materials that explain the health concerns and asking them to confirm whether those sources are still in regular use, as opposed to being back-up or emergency sources. We are encouraging systems to take voluntary measures including educating customers, using alternate sources, changing treatment, or blending to manage Mn levels.

NHDES has also reached out to water systems and other stakeholders, asking for input on the details of the proposed new standard, addressing issues such as the effective date, monitoring frequency, language to be included in the required notification when 0.1 mg/L is exceeded, analytical methods and reporting limits, and whether Mn should be treated as an acute or chronic contaminant. 

The State of New Hampshire has numerous grant and loan programs to assist water systems in reducing the public’s exposure to contaminants in drinking water. These programs can fund projects to connect small water systems to nearby larger systems or install treatment systems. NHDES also will continue to provide technical assistance to water systems addressing contaminants in their drinking water. Working together, NHDES and water systems will find effective solutions to ensure water systems have an adequate quantity of safe drinking water.

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