What does Maximum Contaminant Level (MCL) mean?

  • The MCL is an enforceable standard for public water systems regulated under the Safe Drinking Water Act. Private wells are unregulated and owners are responsible for managing the safety of their own drinking water; therefore, this standard only serves as a guideline value. Private well users must decide for themselves what concentration of arsenic in their drinking water is acceptable.
  • The Federal MCL for arsenic is 10 μg/L, chosen in 2001 by the Environmental Protection Agency (EPA) using discretionary authority to consider the costs of treating publicly supplied water to meet this standard. The State of New Jersey has adopted a lower MCL of 5 μg/L, the most protective in the nation. However, arsenic is a known carcinogen; therefore the EPA also set an MCL-Goal for arsenic of 0 μg/L, meaning there is no level of arsenic in drinking water that can be considered safe.
  • The risks from drinking water with arsenic at the federal MCL of 10 μg/L are significantly higher than for other carcinogenic drinking water contaminants at their MCL.