• EPA has recently reviewed and revised the national primary drinking water regulation; 
• EPA is presently conducting an ongoing regulatory revision of the regulation; or
• For contaminants where the maximum contaminant levelmaximum contaminant levelThe highest level of a contaminant that is allowed in drinking water as delineated by the National Primary Drinking Water Regulations. These levels are based on consideration of health risks, technical feasibility of treatment, and cost-benefit analysis. (MCL) is currently set equal to the maximum contaminant level goalmaximum contaminant level goalThe maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. Maximum contaminant level goals are non-enforceable health goals. (MCLG), either:
  • EPA is performing a formal health effects assessment of the regulated contaminant and the results of the assessment are due after the cutoff date for the current cycle of the Six-Year Review; or
  • EPA completed a health effects assessment but subsequently identified new information with potential to affect the MCLG of the regulated contaminant.

Excluding such contaminants from subsequent steps in the Six-Year Review improves the efficiency and effectiveness of the review process. It prevents duplicative efforts for recent or current regulatory actions in progress to revise specific national primary drinking water regulations. It also avoids recommendations based on inadequate information for contaminants with ongoing or pending health risk assessments that already have MCLs set equal to their respective MCLGs.