EPA Releases Final UCMR 4 Dataset

On February 18, EPA posted the final set of sample results and a national data summary from the Fourth Unregulated Monitoring Rule (UCMR 4). UCMR 4 required all large public water systems (PWSs) and a representative subset of small PWSs to monitor for 30 different contaminants, which included metals, cyanotoxins, pesticides, brominated disinfection byproducts, alcohols, and semi-volatile organic chemicals. The sampling took place between 2018 and 2020, and the data represent sample results received as of December 31, 2021. Data are available for ~3,500-5,000 PWSs (depending on the analyte) for a total number of ~933K sample results. The dataset also includes sample results for water quality parameters, such as total organic carbon and bromide, associated with the disinfection byproducts.