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TO: Chuck Ziegmont, Division of Water Facilities
FROM: Silky S. Labie, Administrator
Quality Assurance Section
DATE: November 2, 1999
SUBJECT: Method of Standard Additions for Residual Chlorine – "Monitoring Chlorine and Sulfur Dioxide at Wastewater Treatment Plant, Mike Birch, USEPA, Athens
The referenced method can be used for monitoring residual chlorine at low levels, however, the author, Mike Birch emphasized the following:
- The method application is to determine absence of any residual chlorine – it is not intended to quantitate a permit compliance value.
- The analysis must be within the 15 minute holding time, prescribed by the method;
- No additional waste streams can enter the system between the point at which the chlorinated sampled is collected and the point of compliance (dechlorinated) sample.
- Equal portions of the sample must be mixed without turbulence (see method) so that the residual chlorine is not volatilized.
- The analytical instrument must be sensitive enough to distinguish 0.02 to 0.05 mg/L chlorine. To achieve this kind of sensitivity, the laboratory must demonstrate a method detection limit in the same range. This means that an MDL study must have been performed, and the detection limit verified with each use.
- In order to be valid, the mixed effluent sample must contain exactly half (± 10%) of the residual chlorine in the chlorinated sample. The method also outlines corrective actions if the mixed sample value is less than the expected concentration range. If the value is greater than the expected range, the value may be reported as "estimated" (J qualifier), but immediate measures must be taken to adjust the amount of dechlorination agent so that the value of the mixed effluent sample falls within the proper range.
All the above factors must be taken into consideration if the facility decides to use this method for residual chlorine monitoring. In addition to documenting the meter calibration and the value of the chlorinated effluent, the facility must maintain adequate records so that each of the above points is documented.
If you have any questions, please feel free to call me (SC 278-2796) or e-mail me at (silky.labie@dep.state.fl.us).
SSL/tb
cc: District Chemists
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