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Water: Mercury

Method 1631: Measurement of Mercury in Water; Revision C

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Fact Sheet; June 2001

EPA announces a final rule approving the use of EPA Method 1631, Revision C for the determination of mercury in EPA's wastewater program (40 CFR part 136). This method is a corrected version of a previously approved method and uses procedures and technologies identical to those in the previously approved EPA Method 1631, Revision B. This rule updates 40 CFR part 136 to reflect approval of the corrected method.


The U.S. Environmental Protection Agency (EPA) publishes analytical testing methods that are used by industrial and municipal facilities to analyze ambient water and wastewater for the purpose of data gathering and compliance monitoring under the Clean Water Act.

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Changes in Method 1631, Revision C
  • Section revised to clarify reporting requirements for samples associated with contaminated multiple field blanks
  • Section 12.4.2 revised to clarify that, if requested or required, field blank or reagent blank subtraction may be applied

Method 1631, Revision C

Method 1631 allows determination of mercury at a minimum level (ML) of 0.5 ppt (parts-per-trillion), and supports measurements at the ambient water quality criteria for mercury published in the National Toxics Rule (40 CFR 131.36) and in the Final Water Quality Guidance for the Great Lakes System (60 FR 15366).

On June 8, 1999 (64 FR 30417), EPA promulgated Method 1631, Revision B for use in determination of mercury at ppt levels in water. Following promulgation, EPA received requests for clarification of the use of field blanks in the method. EPA is publishing a final rule that approves Method 1631, Revision C in order to address this request. This rulemaking replaces Method 1631, Revision B with Method 1631, Revision C.

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More Information

For additional information, you may contact the U.S. Environmental Protection Agency, Office of Water, Engineering and Analysis Division, Mail Code 4303T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.

The Federal Register notice contains instructions on how to obtain additional information and how to review the public record for this rulemaking. The complete text of the Federal Register notice (June 08, 1999) is available.

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