Septic sewage is typically characterized by which combination of features?

• A. Low pH, rotten egg odor, dark gray-black color
• B. High pH, sweet odor, clear color
• C. Neutral pH, no odor, clear
• D. Low pH, no odor, yellow color

Answer: (A)

The main idea is that septic sewage under anaerobic decay tends to become acidic, develop foul sulfurous gases, and darken in color due to sulfide formation. The best match is the option that describes low pH, a rotten egg odor, and a dark gray‑black color. Hydrogen sulfide produced during decomposition gives the characteristic rotten egg smell, while acids from anaerobic processes drive the pH down. The dark coloration comes from sulfide reactions and the presence of decomposed organic matter under low-oxygen conditions. Other options don’t fit because septic conditions are not typically high in pH with a sweet odor and clear color, nor neutral with no odor and clarity, nor low pH with no odor and a yellow tint.