Guidelines Establishing Test Procedures for the Analysis of Pollutants, Measurement of Mercury in Water, Revisions to EPA Method 1631
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.
EPA Regions, as well as States, Territories and Tribes authorized to implement the National Pollutant Discharge Elimination System (NPDES) program, issue permits that comply with the technology-based and water quality-based requirements of the Clean Water Act. In doing so, NPDES permitting authorities, including authorized States, Territories, and Tribes, make a number of discretionary choices associated with permit writing, including the selection of pollutants to be measured and, in many cases, limited in permits. If EPA has "approved" (i.e., promulgated through rulemaking) standardized testing procedures for a given pollutant, the NPDES permitting authority must specify one of the approved testing procedures or an approved alternate test procedure for the measurements required under the permit. In addition, when a State, Territory, or authorized Tribe provides certification of Federal licenses under Clean Water Act section 401, States, Territories and Tribes are directed to use the approved testing procedures.
This rulemaking proposes to modify EPA Method 1631 to require the use of certain clean techniques and quality control (QC) provisions in accordance with clause 4 of the Settlement Agreement. These changes are in response to the petitioners' concerns that results produced by laboratories using EPA Method 1631 would not be reliable unless the optional clean techniques and QC provisions are required. These revisions are discussed in Section IV of this proposal and are included in draft Method 1631, Revision D (Method 1631D).
Today's notice also proposes improvements and clarifications to EPA Method 1631 to make this test method more consistent with other approved methods and current practices, and easier to use. These proposed revisions are based on comments received from method users since promulgation of Method 1631. The proposed revisions are discussed in Section V and are included in draft Method 1631D.