For a disinfection profile, annual distribution levels for TTHM and HAA5 at 0.64 mg/L and 0.40 mg/L respectively require daily log inactivation of which organism?

• A. Giardia lamblia
• B. Cryptosporidium
• C. Bacteria
• D. Virus

Answer: (A)

Disinfection profile calculations focus on how much disinfectant action is needed on a daily basis to keep disinfection effective while keeping disinfection byproduct levels (TTHM and HAA5) within limits. For this purpose, Giardia lamblia is used as the reference organism because it represents the chlorine resistance of protozoa and serves as the standard surrogate in these calculations. When the referenced DBP limits are given, the profile translates them into a required daily log inactivation for Giardia lamblia to ensure adequate protection of the distribution system without exceeding DBP limits. Cryptosporidium is more resistant to chlorine and would imply a different, typically higher, log inactivation target; bacteria and viruses are handled differently and do not set the primary DP target in this context.