Assessment of Manganese Occurrence in Drinking Water in the United States
Andrew Eaton
Abstract
The United States Environmental Protection Agency (USEPA) Unregulated Contaminant Monitoring Rule (UCMR) requires the nationwide monitoring of drinking water for specific unregulated contaminants. In the recent (2018–2020) fourth round (UCMR 4), more than 37 000 samples from over 5000 water systems (4200 large and 800 small) were analyzed for manganese. USEPA developed (2004) a 300 μg/L health advisory limit, but both Health Canada (2020) and the World Health Organization (2021) have recently re-evaluated the levels of health concern. UCMR 4 data indicates that over 20% of US systems (32% groundwater and 15% surface water) have entry point manganese that may exceed the recommended Health Canada and Water Research Foundation 20 μg/L aesthetic threshold and that nearly 5% (9% groundwater and 1.8% surface water) may exceed the Health Canada 120 μg/L Health Guideline. Multiple rounds of samples increase the likelihood that a given manganese level will be exceeded. Systems with high levels of manganese are widely distributed across the US, and a potential regulation could impact numerous water supplies. USEPA could sample from a smaller subset of the approximately 4000 large systems and still have a good assessment of nationwide occurrence frequencies, while the 800 small systems are inadequate to characterize the small system universe. Including manganese in the UCMR 5 program for systems serving 3001-10000 would likely greatly improve estimates of nationwide occurrence data.