USEPA Method 415.3, Measurement of Total Organic Carbon, Dissolved Organic Carbon and Specific UV Absorbance at 254 nm in Source Water and Drinking Water, is a method published by the United States Environmental Protection Agency for quantifying organic carbon in water supplies. It permits either high-temperature combustion or UV-promoted persulfate oxidation to convert organic carbon to CO2, which is then measured by non-dispersive infrared (NDIR) detection, and it specifies the NPOC approach as the standard measurement mode.
Download EPA Method 415.3 (PDF)
Method 415.3 was developed for US drinking water utilities monitoring TOC and DOC as part of the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules, where organic carbon load is used to assess the risk of trihalomethane and haloacetic acid formation during chlorination. It covers sample collection and preservation, instrument calibration, and the acidification-and-sparge step that defines NPOC measurement, alongside the specific UV absorbance (SUVA) calculation used to characterise the reactivity of the organic matter present.
Although it is a US method, Australian NATA-accredited laboratories reference Method 415.3 alongside Standard Methods 5310C and ISO 8245 when validating TOC and NPOC procedures, because the underlying chemistry, acidification, sparging, oxidation and NDIR detection, is the same regardless of jurisdiction. A method document search is common for lab staff setting up or auditing a TOC procedure, which is why it is referenced directly from the Aurora 1030W buyer's guide on this site rather than only described in summary.
Method 415.3 does not mandate a specific instrument or oxidation technology. It accepts both combustion-based and persulfate-UV/heated-persulfate analysers, provided the instrument meets the method's calibration, detection limit and quality-control requirements. This is why the choice between a combustion TOC analyser and a heated-persulfate analyser like the Aurora 1030W is a lab operating decision, not something the method itself dictates.
Key Points
- USEPA method for TOC, DOC and SUVA254 in source water and drinking water
- Permits combustion or UV/heated-persulfate oxidation, both with NDIR detection
- Specifies NPOC (acidify and sparge) as the standard measurement approach
- Developed for US Disinfectants and Disinfection Byproducts Rule compliance
- Referenced by Australian NATA-accredited labs alongside Standard Methods 5310C and ISO 8245, not used as a standalone AU regulatory requirement
Relevant Standards
- USEPA 415.3 (TOC, DOC and SUVA254 in source water and drinking water)
- Standard Methods 5310C (persulfate-UV or heated-persulfate oxidation method, NPOC mode)
- ISO 8245 (water quality: guidelines for the determination of TOC and DOC)
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Frequently Asked Questions
Is EPA Method 415.3 used in Australia?
It is not a mandated Australian regulatory method, but Australian NATA-accredited laboratories commonly reference it alongside Standard Methods 5310C and ISO 8245 when setting up or validating TOC and NPOC procedures, because the measurement chemistry it describes, acidification, sparging, oxidation and NDIR detection, is the same approach used under those standards.
What is the difference between combustion and persulfate oxidation under Method 415.3?
Both convert organic carbon to CO2 for NDIR detection. Combustion analysers use high temperature alone or with a catalyst. UV/heated-persulfate analysers, including the Aurora 1030W, use a persulfate oxidant activated by UV light or heat at a lower temperature. Method 415.3 accepts either approach provided the instrument meets its calibration and detection-limit requirements.
Does Method 415.3 require NPOC measurement specifically?
It specifies NPOC, acidifying the sample and sparging with inert gas to remove inorganic carbon and volatile organics before oxidation, as the standard approach. This matches the default operating mode of most benchtop TOC analysers used in Australian environmental and drinking water labs.