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UCMR 4 requires Public Water Systems (PWSs) to monitor for up to 30 contaminants:

  • PWSs that serve >10,000 people and selected small systems that use surface water (SW) or groundwater under the direct influence of surface water (GWUDI) as source water must do sampling for: 10 Cyanotoxins and 20 chemicals, as well several indicator parameters. Monitoring must be done in a schedule set by EPA during an 8-month period from March 2018 through November 2020. In addition, EPA is selecting 800 representative PWSs serving 10,000 or fewer people for monitoring at EPA’s cost.
  • PWSs that serve >10,000 people and selected small systems that use groundwater (GW) as source water must do sampling for: 20 chemicals, as well several indicator parameters. Monitoring must be done in a schedule set by EPA during an 8-month period from March 2018 through November 2020. In addition, EPA is selecting 800 representative PWSs serving 10,000 or fewer people for monitoring at EPA’s cost.