Guidelines Establishing Test Procedures for the Analysis of Pollutants; Measurement of Mercury in Water; Revisions to EPA Method 1631; Proposed Rule

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By this action, EPA is proposing modifications to EPA Method 1631, Revision C: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry (Method 1631C), which measures mercury in aqueous samples. The proposed modifications would require use of certain "clean techniques" and quality control requirements when using this test method. The Agency is proposing to modify EPA Method 1631C to fulfill obligations under a Settlement Agreement designed to resolve litigation challenging an earlier EPA rulemaking that standardized this test method. The proposed modifications are intended to improve performance of EPA Method 1631C by reducing opportunities for contamination during sample collection and analysis. In addition, EPA is proposing revisions to this test method based on comments received from method users following method approval.