A Deep Dive into Manganese Data from UCMR4

Drinking Water
Oral Presentation

Prepared by A. Eaton
Eaton Environmental Water Quality Consulting, LLC, 1204 Milan Avenue, South Pasadena, CA, 91030, United States

Contact Information: [email protected]; 626-437-1286


Monitoring for UCMR4 occurred from 2018-2020. Data have been uploaded to the National Contaminant Occurrence Database (NCOD) on a quarterly basis, and at this point more than 90% of expected results have been reported. Most of the results from UCMR4 monitoring are relatively uninteresting in terms of occurrence and the likelihood of potential regulation. The big exception to this is manganese, where nearly 13% (628) of public water supplies had samples exceeding the current 50 ppb secondary maximum contaminant level (SMCL), and nearly 300 systems (6%) exceed the Canadian Guideline of 120 ppb. There has been extensive discussion in the literature about guidelines as low as 20 ppb for aesthetic reasons, and at that level nearly 25% of systems have exceedances. This presentation will review the manganese data in detail, including comparisons between small and large systems and the impact of the number of sample rounds in a given system.