UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG 140
Date Signed: July 18,2001
MEMORANDUM
SUBJECT: MIOX Monitoring Requirements under the Stage 1 DBPR
FROM: Ephraim King, Director
Standards and Risk Management Division
Office of Ground Water and Drinking Water
TO: Water Division Directors, Regions 1-10
Drinking Water Branch Chiefs, Regions 1-10
The purpose of this memorandum is to clarify monitoring requirements under the Stage 1
Disinfectants/Disinfection Byproducts Rule (DBPR)(63 FR 69390, December 16, 1998) for
systems that use a mixed oxidant (MIOX) generator as a treatment process.
In response to questions from Regional staff concerning disinfectant and disinfection
byproduct monitoring requirements for systems using MIOX generators, SRMD staff provided
verbal guidance that such systems were required to monitor for bromate, chlorine dioxide, and
chlorite, in addition to other requirements. This advice was based on manufacturer's literature
that stated that the MIOX process generated ozone and chlorine dioxide, in addition to chlorine.
The Stage 1 DBPR requires systems that use ozone to monitor for bromate and systems that use
chlorine dioxide to monitor for chlorine dioxide and chlorite.
Since that initial guidance, additional study has been conducted on the occurrence of
ozone and chlorine dioxide in MIOX generators. These studies, submitted by the manufacturer,
found that chlorine, but not ozone nor chlorine dioxide, is produced by the MIOX generator.
Therefore, I am modifying the guidance provided previously by my staff. Systems that use
MIOX generators have the same monitoring requirements as other chlorine systems. Also,
MIOX systems must determine inactivation credit under the Surface Water Treatment Rules
based on chlorine CT tables.
If you have any questions or would like copies of these recent studies, please don't
hesitate to give me a call, or have your staff contact Tom Grubbs of my staff at 202-260-7270.
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