Which statement reflects typical EPA drinking water MCLs for microbial and chemical contaminants?

• A. Microbial limits require presence of coliform; chemical limits exclude arsenic.
• B. MCLs specify arsenic 100 µg/L, lead 150 µg/L, nitrate as N 100 mg/L.
• C. Microbial limits include absence of coliform/E. coli; chemical limits include arsenic 10 µg/L, lead 15 µg/L, nitrate as N 10 mg/L.
• D. MCLs only apply to physical contaminants, not microbial or chemical.

Answer: (C)

The key idea is that EPA drinking water MCLs set enforceable limits for substances in water, addressing both microbial and chemical hazards. Microbial limits are based on safety indicators, requiring the absence of indicator organisms such as total coliforms and E. coli, because their presence signals potential pathogen contamination and immediate health risk. For chemicals, MCLs establish very low concentration thresholds to protect against long-term health effects; a typical set includes arsenic at 10 µg/L, lead at 15 µg/L, and nitrate as nitrogen at 10 mg/L. This combination—no coliforms/E. coli for microbial safety and specific low chemical limits for contaminants—matches the EPA standards.

The other statements don’t fit because they either imply the presence of coliforms (instead of absence), list much higher or nonstandard contaminant limits (arsenic, lead, or nitrate values not used by current EPA MCLs), or claim MCLs apply only to physical contaminants, which ignores the microbial and chemical components of drinking-water standards.