25 
cha pter in 
Application of Chesapeake Bay 
Water Quality Criteria 
Assessment Procedures 
BACKGROUND 
Beginning in the late 1990s and continuing through 2003, the Chesapeake Bay 
Program partners developed new Chesapeake Bay water quality criteria designed 
specifically to protect the ecological health of the Bay (U.S. EPA 2003a). Delaware, 
Maryland, and Virginia, along with the District of Columbia, then adopted these 
criteria and new tidal water designated uses into their water quality standards regu¬ 
lations. The states’ new Chesapeake Bay water quality standards were applied for the 
first time in each state’s 2006 Clean Water Act 303(d) listing cycle. 
The four jurisdictions also adopted criteria assessment methods — published by EPA 
in 2003 and in a 2004 addendum — into state water quality standards regulations (U.S. 
EPA 2003a, 2004a). The methods characterize the spatial and temporal variability of 
the appropriate water quality parameters, while providing a clear basis for determining 
whether a portion of the Bay’s tidal waters reached attainment of the applicable desig¬ 
nated use. Despite the methods’ detail, technical limitations remained for their 
complete application. This chapter and those that follow address many of the prior 
technical limitations. Continued efforts to develop further refinements to the criteria 
assessment methodology in specific areas, however, will likely remain. 
In addition to the technical limitations, obstacles related to the states’ transition from 
an old set of water quality standards to the newer, more detailed Chesapeake Bay 
water quality standards also existed. Differences occurred in the spatial extent of past 
listing/delisting decisions. New water quality criteria components also exist that 
have never been previously assessed. Furthermore, the mechanisms and processes 
used to report listings in the past required updating to allow reporting based on the 
states’ new Chesapeake Bay water quality standards regulations. As with the tech¬ 
nical limitations referenced above, an ongoing effort to refine and update the 
methodology for making future listing decisions based on the new Chesapeake Bay 
water quality standards will also be required (see Chapter 8 for further details). 
chapter iii 
Application of Chesapeake Bay Water Quality Criteria Assessment Procedures 
