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Proposed Sufficiently Sensitive Methods Rulemaking

NPDES: Use of Sufficiently Sensitive Test Methods for Permit Applications and Reporting

The EPA is proposing minor amendments to its Clean Water Act (CWA) regulations to codify that under the NPDES program, only "sufficiently sensitive" analytical test methods can be used when completing an NPDES permit application and when performing sampling and analysis pursuant to monitoring requirements in an NPDES permit.

This proposal is based on requirements in the CWA and existing EPA regulations. It also would codify existing EPA guidance from the 2007 memorandum, "Analytical Methods for Mercury in NPDES Permits (PDF) (4 pp, 39KB)," from James A. Hanlon, Director of EPA's Office of Wastewater Management, to the Regional Water Division Directors on the use of "sufficiently sensitive" analytical methods with respect to measurement of mercury and extend the approach outlined in that guidance to the NPDES program more generally. Specifically, EPA is proposing to clarify the existing NPDES application, compliance monitoring, and analytical methods regulations. The amendments in this proposed rulemaking affect only chemical-specific methods; they do not apply to the Whole Effluent Toxicity (WET) methods or their use.

EPA has generally approved multiple analytical test methods for CWA pollutants under 40 CFR 136 and 40 CFR Chapter I, Subchapters N and O. Some of the approved analytical test methods have greater sensitivities and lower minimum levels or method detection limits (MDLs) than other approved methods for the same pollutant. This situation is often due to advances having been made in instrumentation and in the analytical protocols themselves.

EPA and state permitting authorities use data from the permit application to determine whether pollutants are present in an applicant's discharge and to quantify the levels of all detected pollutants. These pollutant data enable the director of the permitting authority to make a sound reasonable potential determination and, if necessary, establish appropriate permit limits. It is critical, therefore, that applicants provide data that are measured with a precision and accuracy that will be meaningful to the decision making process. The same holds true for monitoring and reporting relative to permit limits established for regulated parameters.

The purpose of this proposal is to clarify that NPDES applicants and permittees must use analytical methods that are capable of detecting and measuring the pollutants at, or below, the respective water quality criteria or permit limits.

On June 23, 2010 EPA issued a Federal Register Notice (PDF) (9 pp, 95KB), announcing the proposed amendments to the CWA regulations, and the public will have 45 days to comment on the proposed rulemaking.

Please contact Kathryn Kelley of the State and Regional Branch, Water Permits Division, at 202-564-7004, with any questions regarding this regulatory revision.

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Last updated on June 24, 2010 1:14 PM