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Update: May 2004

Current Massachusetts Regulatory Limit
MMCL = Treatment Technique. (Refer to 310 CMR 22.20.) ORS has adopted the MCL published by the U.S. EPA.

Federal Regulatory Limit
The MCL for Legionella is a Treatment Technique. Under U.S. EPA's Surface Water Treatment Rule, systems using surface water or groundwater under the direct influence of surface water must control Legionella (U.S. EPA, 2002). Although there is no limit for Legionella, U.S. EPA believes that if Giardia and viruses are removed/inactivated, Legionella will also be controlled. The MCLG for Legionella is zero.

Basis for Criteria
The MCL for Legionella is based on a Treatment Technique as described above.

Critical Effects
Legionella is a naturally occurring genus of bacteria. Some species of Legionella have been known to multiply in heating systems and cause Legionnaire’s Disease, a type of pneumonia (U.S. EPA, 2002).

Cancer Assessment: 

Biological Pathogen

Analytical Information
: See 310 CMR 22.20 

Analytical Methods
See 310 CMR 22.20

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at

Federal Register. January 14, 2002. Environmental Protection Agency. Parts 9, 141 and 142. National Primary Drinking Water Regulations: Long Term 1 Enhanced Surface Water Treatment Rule. Final Rule. (67 FR 1811).

U.S. Environmental Protection Agency (U.S. EPA). July 2002. List of Contaminants and Their MCLs. EPA 816-F-02-013.