United States                    Office of Water            EPA 823-F-06-011
                   Environmental Protection               4305T                     July 2006

                   EPA Publishes Draft Guidance for Implementing the
                   January 2001  Methylmercury Water Quality Criterion

EPA is publishing for public comment a draft of the Guidance for Implementing the January
2001 Methylmercury Water Quality Criteria. You can download the document from EPA's
website at http://www.epa.gov/waterscience/criteria/methylmercury. When final, this document
will help protect waters by giving state, territory, and authorized tribal water quality programs
guidance on how to adopt and implement the fish tissue-based methylmercury water quality


In January 2001, EPA published a new water quality criterion for mercury that for the first time
bases the human health criterion on fish and shellfish tissue rather than on a water column value.
This fish and shellfish tissue criterion approach for setting water quality standards creates several
challenges, such as translating the fish tissue residue value into a water concentration and
ultimately into NPDES permit limits. In a 2001 Federal Register announcement, EPA stated its
intent to develop guidance on implementing the criterion to address these issues. Subsequently,
EPA formed a workgroup of representatives from state environmental agencies, EPA Regions,
and headquarters air and water programs to develop the draft guidance.

About this Draft Guidance Document

The draft guidance, entitled the Guidance for Implementing the January 2001 Methylmercury
Water Quality Criterion, helps states implement the 2001 Methylmercury Water Quality
Criterion.  This guidance generally consolidates existing guidance on water quality standards,
TMDLs, and permits where relevant to mercury. The new aspect of the guidance is a suggested
approach for implementing the new methylmercury criterion that does not necessarily result in
all NPDES  discharges reducing the level of mercury in the discharge. Instead, for NPDES
discharges that contribute only a very small amount of the mercury to a watershed, the suggested
approach consists of holding the discharges at current levels. This suggested approach mirrors
current practice where wasteload allocations are developed for TMDLs where point sources are
only small contributors to the total loading in a watershed. This approach also does not require a
site-specific bioaccumulation factor that can be costly to develop.

How to Get Additional Information

You may download the draft document at www.epa.gov/waterscience/criteria/methylmercury.
You can also order a copy of the document from our Water Resource Center at (202) 566-2426;
email: center.water-resource@epa.gov. Further information is also available from Jim
Pendergast at  pendergast.jim@epa.gov.