Contaminant of the Month: EPA’s Unregulated Contaminant Monitoring Rule

Sept. 6, 2014

EPA is considering the next Unregulated Contaminant Monitoring Rule (UCMR4), including some that do not belong there.


  • The Safe Drinking Water Act (SDWA) specifies three conditions that EPA must meet to select candidates for regulation: It may have an adverse effect on the health; occurrence in public water systems with a frequency and at levels of public health concern; and regulation presents a meaningful opportunity for health risk reduction.
  • Beginning in 1999 and every five years thereafter, EPA must identify no more than 30 unregulated contaminants to be monitored by public water systems.
  • Monitoring is required by systems serving less than 10,000 people and in selected smaller systems.
  • Data becomes part of a national drinking water occurrence database.
  • EPA is about to propose a fourth UCMR.

Past UCMRs:

  • UCMR1 covered 2001-2005; UCMR2 covered 2008-2010; UCMR3 is underway.
  • Results in UCMR1 and UCMR2 were mostly non-detects.
  • UCMR2 detected nitrosodimethylamine (NDMA) at low ppt levels in approximately 25 percent of systems.
  • Metolachlor, a pesticide was found in less than one percent.
  • Most other compounds in UCMR1 and UCMR2 had fewer than three detections from more than 30,000 samples in over 4,000 systems.
  • Reporting limits were lowered to sub ppb in UCMR3 increasing the number of detections.
  • Preliminary results indicate few systems above tentative “Health Reference Levels (HRLs),” except vanadium (3.5 percent), 1,2,3 trichloropropane (1.9 percent), 1,4-dioxane (six percent) and chlorate (31 percent, inappropriate HRL).

Current UCMR4 working list of candidates:

  • The working list consists of 14 pesticides, four halogenated acetic acid disinfection byproducts (HAAs), four commercial chemicals plus formaldehyde and acetaldehyde, two algal toxins, two metals (germanium and manganese), nitrate/nitrite, butylatedhydroxyanisole (BHA), Triclosan and legionella bacteria.


  • A few pesticides have been detected at low levels in some drinking waters.
  • HAAs are appropriate candidates because they are ubiquitous.
  • Algal toxins occur during an algal bloom.
  • The commercial chemicals are in common usage.
  • Acetaldehyde and formaldehyde are common oxidation products.
  • BHA is a common food additive.
  • Germanium is used in electronics.
  • Manganese is an essential nutrient and current secondary MCL; some have suggested that it may have neurologic effects at high doses.
  • Nitrate/nitrate are regulated in drinking water.
  • Legionella proliferate in warm water plumbing.
  • Triclosan is a common antimicrobial in soaps and toothpaste.

Issues and questions:

  • Listing pesticides in the UCMRs creates a monitoring and cost burden for water suppliers and costs for the federal government, even though EPA could require registrants to produce the data for reasonable cause.
  • The commercial chemicals have low toxicity except for toluidine, an intermediate.
  • Formaldehyde and acetaldehyde are human metabolites.
  • HAAs will be detected in chlorinated systems. Data could be readily obtained by expanding reporting for the currently regulated HAAs.
  • Must monitor for algal toxins during an algal bloom.
  • Since BHA is an approved food additive, it is the province of the FDA.
  • Water suppliers already have much occurrence data on manganese.
  • Is germanium a likely candidate?
  • Nitrate/nitrate are potentially generated at low levels in distribution systems with long retention times. Significance beyond the current regulatory value seems questionable.
  • Triclosan has very low toxicity; human exposure is much greater from toothpaste where it is present at 0.3 percent.
  • Legionella are inhalation risks and predominantly present in plumbing systems where EPA may not have regulatory authority.


  • EPA seems to have difficulty identifying UCMR substances that are plausible candidates for regulation in drinking water. Most of the listed chemicals are very unlikely to be present at levels and frequencies that would meet the SDWA’s three selection criteria for regulation. Total costs for the UCMRs have far exceeded $100 million.

Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.

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